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Effect of field establishment methods on root-knot nematode (Meloidogyne spp.) infection and growth of Sesbania sesban in western Kenya
Crop Protection 20 (2001) 31}41
E!ect of "eld establishment methods on root-knot nematode (Meloidogyne spp.) infection and growth of Sesbania sesban in western Kenya J. Desaeger, M.R. Rao* International Centre for Research in Agroforestry (ICRAF), P.O. Box 30677, Nairobi, Kenya Received 16 December 1999; received in revised form 8 February 2000; accepted 11 April 2000
Abstract Pot studies indicated that root-knot nematode (Meloidogyne javanica) infection reduces sesbania (Sesbania sesban) growth and planting methods modify the nematode damage, but their e!ects on sesbania biomass production at the "eld scale are not known. A "eld study was conducted in western Kenya for 2 yr, comparing direct seeding of sesbania with transplanting of bare-rooted seedlings in pure stands, with and without nematicide application in the "eld and in the nursery. In moist conditions, neither planting method nor nematicide had any in#uence on seedling survival and early growth. When early season rainfall was low and erratic, transplanted seedlings survived and grew better than seedlings from direct sowing, and nematicide application in the "eld and/or nursery improved seedling survival. Direct seeded sesbania had signi"cantly less nematode galling and smaller nematode populations in the roots than transplanted sesbania. Both the establishment methods produced similar quantities of biomass, but direct seeded sesbania produced signi"cantly greater biomass than the transplanted crop, if seedlings were already infected with nematodes in the nursery. Nematode infection on average reduced total sesbania biomass by 19%. Where sesbania cover crops have to be established by transplanting for socio-economic reasons, it is essential to use healthy seedlings free from nematodes for a good plant stand and early growth. Nematode-free seedlings can be produced on farms by at least one month of solarization of seedbeds. Neither "eld establishment method, nor nematicide application altered the soil nematode populations over a 12-month period. This means that the potential threat of increased Meloidogyne populations to nematode-susceptible crops following sesbania cover crops remains the same irrespective of how sesbania is established. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Agroforestry; Cover crop; Meloidogyne javanica; Tree fallow; Root-knot nematode; Soil fertility; Soil solarization
1. Introduction Nutrient depletion is one of the major causes of low crop yields in smallholders' farms in sub-Saharan Africa (Smaling et al., 1997). As small-scale farmers cannot afford to use chemical fertilizers, research in recent years has focused on developing technologies that would replenish soil fertility through agroforestry and organic inputs. Short-duration leguminous trees or shrubs have been found to increase soil fertility and subsequent crop yields in N-depleted soils (Szott et al., 1999). Sesbania (Sesbania sesban), an N -"xing and deep rooting shrub with good-quality foliage is one of the most promising
* Corresponding address: 11, ICRISAT colony (Phase 1), Akbar Road, Secunderabad-500 009, Andhra Pradesh, India. E-mail address: [email protected] (M.R. Rao).
species for short-duration cover cropping (Buresh and Tian, 1997). Sesbania cover crops have been found to increase N supply in the soil through biological nitrogen "xation and recycling of leached N at depth, and increase the availability of nutrients to crops grown in rotation. The residual e!ect of sesbania on subsequent maize was highly dependent on biomass produced by sesbania (Szott et al., 1999). Whereas 0.5-yr (one season) sesbania cover cropping is appropriate for the small farms in highly populated, western Kenya (Niang et al., 1996), 2-yr cover cropping is appropriate for the relatively larger farms in the less populated, eastern Zambia (Kwesiga et al., 1999). Sesbania cover crops, also referred to as &improved fallows' or &planted tree fallows', are being widely tested on farms and disseminated in both these regions (Rao et al., 1998). Root-knot nematodes (Meloidogyne incognita and M. javanica) may be a potential constraint for the use of
0261-2194/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 1 - 2 1 9 4 ( 0 0 ) 0 0 0 4 9 - 1
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J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
sesbania cover crops (Karachi, 1995) and increase the nematode populations in the soil (Desaeger and Rao, 1999). This implies that sesbania growth may be reduced in nematode-infested soils and nematode-susceptible crops may risk yield loss following sesbania. High seedling mortality and growth reduction of sesbania were observed with increased inoculum of M. javanica, particularly in lighter-textured soils (Desaeger and Rao, 2000a). While direct seeded sesbania was found to have greater nematode infection than transplanted sesbania in pots (Desaeger and Rao, 1999), the reverse was the case in "eld studies (SteinmuK ller, 1995). In eastern Zambia, sesbania is established as a pure crop using 4}6-week-old bare-rooted seedlings (Kwesiga and Beniest, 1998), but in western Kenya it is established by both direct seeding and transplanting as an intercrop with maize (A. Niang, pers. comm.). Quantitative information is lacking on how Meloidogyne infection a!ects sesbania growth under "eld conditions. Production of healthy seedlings plays an important role in minimizing the impact of soil-borne pathogens in the case of transplanted crops. Seedbed solarization has shown good potential for controlling nematodes and many other soil-borne pests and diseases in some tropical countries (Gaur and Dhingra, 1991; Kamra and Gaur, 1998). If this practice controls the local soil-borne pathogens, even the poor farmers in Africa can adopt it to produce seedlings of sesbania as well as other transplanted crops that they grow such as tomato (Lycopersicon esculentum Mill.), cabbage (Brassica oleracea v. capitata L.) and kale (Brassica oleracea v. acephala). However, the e$cacy of solarization depends on climatic factors (e.g. solar radiation, temperature, air humidity and wind) and soil characteristics (absorption of solar radiation, heat capacity and thermal di!usion). The objectives of the present studies were to determine (1) the e!ect of Meloidogyne infection on sesbania growth and biomass production, (2) the e!ect of the method of
establishing sesbania on nematode infection and biomass production, and (3) whether nematode-free sesbania seedlings can be produced through soil solarization on farms.
2. Materials and methods 2.1. Study 1 2.1.1. Experimental sites and treatments The study was conducted on farms in Maseno (Vihiga District) and Lela (Kisumu District) villages in western Kenya (altitude 1500 m, latitude 03 06 N, and longitude 343 34 E) from March 1997 to March 1999. The soil at both sites was clay loam, deep, well drained and of moderate fertility, except for low extractable phosphorus (Table 1). The Maseno farm was previously under sesbania for 18 months and the Lela farm under natural fallow for 36 months. The region has a bimodal rainfall, with about 1000 mm during the &long rains' (March} August) and 800 mm during the &short rains' (September}February). The mean monthly temperature ranges from 18 to 273C. The study involved six factorial treatments of two "eld establishment methods (direct seeding and transplanting of seedlings) with and without nematode control in the "eld for both methods and for seedlings in the nursery. Nematode control in the "eld was attempted by nematicide application. Plots were 5 m wide by 10 m long and were separated by 1 or 2 m paths on all sides. At Maseno, plots were grouped into replications on the basis of initial root-knot nematode populations, which were large and varied considerably between plots. Nematode populations were determined in soil samples taken from the top 30-cm soil layer at six locations in each plot. At Lela, the initial soil nematode populations were small and relatively more uniform, so replications were made on the basis of proximity and vegetation gradient. The treatments at
Table 1 Site characteristics of farms in the two studies Study/village
Study 1 Maseno Lela Study 2 Lela Yala Maseno farm Maseno centre
Particle distribution (%)
Organic C (%)
Extractable P (mg kg\)
CEC (Ca#Mg#K) (cmol kg\)
pH
Sand
Silt
Clay
27 31
28 26
45 43
1.54 1.43
3.3 2.0
3.69 8.33
4.4 5.2
41 37 29 83
24 22 30 11
35 41 41 6
1.48 1.53 1.58 0.63
3.5 5.7 3.4 7.8
4.74 6.30 5.08 2.89
5.1 5.1 5.2 6.4
Period of solarization. Period of seedling growth.
Rainfall in speci"ed period (mm) March}August
September} February
629 661 January}February 0 200 120 163
1467 263 March}April 189 219 463 574
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
each site were replicated "ve times in a randomized complete block design. 2.1.2. Nursery and xeld management Sesbania (provenance: Kakamega, Kenya) seedlings were raised with and without controlling of nematodes in the nursery at the Maseno Regional Research Centre. In 1998, nematode control was attempted with 5% carbofuran at 20 g m\, but in 1999, nematode control was attempted by heating the top 20-cm soil layer in a drum for 4 h at over 903C. The seedbed soil was loamy sand and the beds were used previously to raise a variety of tree seedlings. The plants were carefully lifted after 6 weeks and transplanted as bare-rooted seedlings in the "eld. Direct seeding of sesbania was done simultaneously with transplanting of seedlings in the "eld, using seeds soaked overnight in hot water (503C) and placing four to "ve seeds at each planting hole. Plant spacing was 1 m;1 m at both farms. Seedlings were thinned to one plant per spot 4 weeks after emergence. Nematicide was applied in the "eld at planting and subsequently at 2-month intervals. At Maseno, Nemacur (a.i. 5% fenamiphos) was used at 150 kg ha\ (7.5 kg a.i. ha\) per application. At Lela, di!erent nematicides were used at each application hoping that such a strategy may control the nematode better than continuous application of one chemical. The chemicals used were Furadan (a.i. 5% carbofuran) at planting at 2 g per hill (1 kg a.i. ha\), and subsequently Vydate (a.i. 24% oxamyl) at 40 l ha\ (9.6 l a.i.), Nemacur at 150 kg ha\ (7.5 kg a.i.) and Mocap (a.i.10% ethoprophos) at 150 kg ha\ (15 kg a.i.) in rotation at 2-month intervals. The chemicals, except Furadan and Vydate, were uniformly spread and incorporated into the soil by hand hoes. Vydate was sprayed diluted in 400 l per ha on the soil surface. Nematode contamination across plots through lateral spread of sesbania roots was avoided by di!erent methods. At Maseno (1997}1998), trenches 0.3 m wide and 0.5 m deep were dug surrounding the plots, sesbania roots were severed and trenches re"lled with soil at 4 and 9 months after planting. At Lela (1998}1999), galvanized iron sheets were installed to 0.5 m depth around the plots before planting. No fertilizer was applied to sesbania at either farm. Any gaps in the stand were "lled in with seeds or seedlings as per treatments in the "rst 2 weeks after planting. The plots were hand weeded twice in the "rst 3 months to remove weed competition to the slow growing sesbania seedlings in the early stages. If sesbania seedlings were infested by leaf eating beetles (Mesoplatys ochroptera), the beetles were removed manually as they can cause severe damage in the early stages, but no control measures were taken after 3 months. 2.1.3. Data collection and analyses At the time of transplanting sesbania in the "eld, 20 randomly selected seedlings were measured for height
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and assessed for gall index (GI) on a 0}10 scale (Zeck, 1971). At 3 months after planting (or sowing) in the "eld, nematode populations in the roots were determined at Maseno by uprooting four seedlings per plot, but not at Lela because of a poor initial stand establishment. Nematode populations in the soil and the roots were determined at 7 and 12 months by taking six core samples in each plot from 0 to 30 cm soil layer using a 10 cm diameter pipe at 25 and 50 cm from trees. The samples were taken with reference to three trees spread over the net plot area at similar positions in all plots. The soil was bulked, and, after separating roots from soil, nematodes were extracted from 100 cm soil according to the modi"ed Baermann method (Southey, 1986). Roots were washed and rated on 0}10 scale, chopped into 1 cm pieces, mixed in a kitchen blender for 3 s, and a 10 g fresh root sample was used for extracting nematodes following the modi"ed Baermann method. Meloidogyne eggs were extracted from the same sample using the bleach method (Southey, 1986). A 1.0 g subsample of roots was stained with phloxine B for counting egg masses, and nematode fecundity assessed using the bleach method only at Maseno. At 7 months, sesbania growth was assessed by measuring plant height and stem diameter at 5 cm above the ground of 24 trees in the middle three rows of each plot. At 12 months, above-ground biomass of sesbania was determined by harvesting trees at ground level from a 24 m area, leaving a 1 m border on all sides of the plots. Foliage (leaves and twigs (5 mm diameter) was separated from wood ('5 cm diameter) and dry weights were estimated based on fresh weights and the percent dry matter determined on sub-samples dried at 703C for a constant weight. A severe drought in the 1998 short rains had caused considerable litterfall at Lela. Leaf litter was collected from three 1-m quadrats in each plot and added to the foliar biomass. Nodule numbers and weights were determined at harvest on three randomly selected plants uprooted from the net area of each plot. Nematode populations in the roots and the soil at each observation and growth and biomass measurements of sesbania were subjected to analysis of variance (ANOVA). As the site ; treatment interaction was signi"cant for a number of parameters, results from each site were analysed separately. Nematode populations were (natural) log transformed to ensure that the data had a normal distribution before ANOVA and the signi"cance of treatment di!erences was judged on the transformed data. 2.2. Study 2 This study was conducted from January to May 1999 on three farms, one each in Maseno (Vihiga District), Lela (Kisumu District), and Yala (Siaya District) villages, and at the Maseno Regional Agroforestry Research Centre, to study the potential of solarization to produce
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J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
nematode-free sesbania seedlings. The experimental sites were previously covered with sesbania at Maseno, Guizotia scabra and Gutenbergia cordifolia (both the weeds are good hosts of Meloidogyne spp. (Desaeger and Rao, 2000b)) at Lela, and tomato (Lycopersicon esculentum) at Yala; the site at the Maseno Centre was under bare fallow. The treatments tested were (1) 1-month soil solarization, (2) 2-month soil solarization, (3) bare fallow, (4) bare fallow#nematicide, and (5) bare fallow#plastic overlaid with a 30 cm soil layer. At each site the treatments were replicated four times in a randomized complete block design. For solarization, the plots were covered with a transparent plastic sheet with its edges buried into the soil. The plots were wetted thoroughly before applying the plastic sheet. In treatment 5, the seedbed was covered with black plastic to prevent rain water percolating into soil and stimulating nematode eggs to hatch and a 30-cm thick layer of soil placed over the plastic to insulate the seedbed soil from solarization. The 2-month solarization treatment was started in early January 1999, and the 1-month treatment in early February 1999, so that both treatments ended at the same time in early March, coinciding with the start of the long rains. Before commencing 1-month solarization, the respective seedbeds were protected from the in#uence of external factors as explained for treatment 5. The plots were 1.0 m and separated from each other by 0.5}1.0 m paths. Sesbania seeds (provenance: Kakamega, Kenya) soaked overnight in hot water (503C) were sown about 1 week after solarization, allowing the soil to aerate. For the nematicide treatment, Vydate (a.i. oxamyl) was applied at 40 l ha\ mixed in 400 l of water per ha before sowing sesbania seeds. The potential for nematode infection at the four sites was assessed by a bioassay for which sesbania was grown in eight 2.5 l pots per site, "lled with soil from the respective test sites. The seedlings were uprooted 6 weeks after sowing, and roots scored for root galls and stained for counting egg masses using phloxine B (Southey, 1986). Soil temperature was measured at 0, 5, 10, 15, 20, and 30 cm depths at the end of solarization. At 1 or 2 months after sowing, 10 randomly selected seedlings were measured for plant height and biomass, and the same seedlings were uprooted carefully and assessed for nematode galls. Meloidogyne infection was assessed by staining the roots of two plants with lactoglycerol (Southey, 1986) and counting all stages of the nematode. Weeds in each plot were counted, removed and weighed at Lela, Yala, and Maseno Centre. The data were analysed following the ANOVA procedures.
3. Results The root-knot nematode in the nursery seedbeds and at all the "eld sites was Meloidogyne javanica. Carbofuran
Table 2 Meloidogyne javanica infestation and growth of 6-week-old Sesbania sesban seedlings, produced at Maseno Centre with and without nematode control treatments in the nursery for study 1 in two years Year
Nematode control
Gall index (0}10)
1997
Yes No
0.1 1.5 0.22 (0.01 0.4 4.3 0.26 0.01
SED t-Test 1998 SED t-Test
Yes No
Seedling height (cm) 28.6 18.7 1.05 (0.01 21.7 11.1 1.26 (0.01
In 1997, nematode control was attempted with 5% carbofuran at 20 g m\, but in 1998, it was with heat sterilization of the top 20-cm soil layer. SED"standard error of di!erence of means.
treatment in 1997 and heat sterilization of soil in 1998 gave good protection to sesbania seedlings against Meloidogyne infection in the nursery (Table 2). The seedlings grown with either of the treatments showed low nematode infection (GI"0.1}0.4) and were 65}100% taller than those produced without any nematode control. The seedlings produced in the unprotected plots in 1998 for Lela farm had three times greater root galling (GI"4.3) than those produced in 1997 for Maseno farm (GI"1.5). Obviously, the nursery beds used in 1998 were more heavily infected by the root-knot nematode than those in 1997. 3.1. Sesbania seedling mortality The initial soil Meloidogyne juvenile (J ) populations at Maseno were high with an average of 368 (SE$107) J per 100 cm soil compared with (10 J per 100 cm soil at Lela. At Maseno, 98}99% of the seedlings survived from direct seeding and transplanting with healthy seedlings, whether or not a nematicide was used in the "eld. Survival of seedlings produced without nematicide in the nursery was also high at 87% irrespective of nematicide application in the "eld. Seedling mortality at Lela was much greater than at Maseno. At 3 months, 95% of the transplanted seedlings produced with nematode control in the nursery survived compared with 70% of those produced without protection. Nematicide use in the "eld did not increase the stand of transplanted seedlings. Direct seeding with nematicide application gave 80% survival compared with 67% survival without a nematicide. At harvest, the stand of direct seeded sesbania in both nematicide treated and untreated plots remained the same as at 3 months. Similarly, transplanted seedlings free from nematodes did not experience any further stand mortality and their survival at harvest was 94%.
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
However, transplanting with nematode-infected seedlings experienced an additional 12% mortality resulting in a "nal stand of only 58% at harvest. 3.2. Nematode infection of sesbania At Maseno, treatment di!erences were negligible for nematode infection of roots and GI at 3 months after planting in the "eld. Transplanted sesbania without nematicide in the nursery and/or "eld had an average GI of 3.5 compared with 2.2 for direct seeded sesbania. Nematode populations generally varied from 200 to 530 juveniles and eggs per gram root. At 7 months after planting, root nematode populations were large and varied from 480 to 3700 juveniles and eggs per gram root. Transplanted sesbania had 115% greater GI and 152%
35
greater nematode root populations than the direct seeded sesbania (p(0.01) (Table 3). Nematicide application in the nursery and/or "eld for both planting methods did not reduce nematode infection. Gall indices increased with age of plants by 45}160%. At 12 months, transplanted sesbania averaged a GI of 5.4 compared with 3.7 by direct seeded sesbania (p( 0.01). However, nematode infection was similar across all treatments, irrespective of "eld establishment methods and nematicide application. Neither planting method, nor nematicide application affected the soil nematode populations at 7 and 12 months after planting (Table 4). Soil nematode populations at harvest were slightly greater than or comparable with those at the start of the study. At Lela, in spite of fewer galls (GI"0}2) at 3 months after planting in both the establishment methods,
Table 3 Meloidgyne javanica infestation of Sesbania, established by two planting methods with and without nematode control treatments in nursery and "eld, at two growth stages on farms in western Kenya Method of planting
Nematicide application
At 7 months
Nursery
Field
Gall index
No Yes No Yes No Yes
1.7 1.5 3.5 2.7 4.0 3.6 0.6
482 1372 1894 2372 3701 2883 *
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
0.01 0.67 0.10 0.16 0.61
(0.01 0.32 0.12 0.53 0.23
Lela (1998}1999) Seed n.a. Seed n.a. Seedling No Seedling No Seedling Yes Seedling Yes SED
0.9 1.1 0.9 1.2 1.8 1.4 0.48
Maseno (1997}1998) Seed n.a. Seed n.a. Seedling No Seedling No Seedling Yes Seedling Yes SED
No Yes No Yes No Yes
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
0.28 0.68 0.12 0.88 0.42
At 12 months Eggs#J per g fresh root
152 35 87 113 164 424 *
0.03 0.40 0.37 0.86 0.24
Root dry weight (mg cm\ soil in 0}30 cm depth)
1.22 1.32 1.86 1.89 2.14 1.88 0.25
Gall index
4.4 3.1 5.0 5.0 5.8 5.9 0.7
(0.01 0.67 0.45 0.52 0.41
(0.01 0.08 0.10 0.92 0.91
0.90 0.94 0.63 0.53 0.88 1.07 0.19
1.6 1.1 1.7 1.9 2.6 1.9 0.47
0.23 0.85 (0.01 0.71 0.32
0.02 0.30 0.19 0.46 0.32
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. F probability was based on the ANOVA of log transformed data. n.a."not applicable. SED"standard error of di!erence of means.
Eggs#J per g fresh root
Root dry weight (mg cm\ soil in 0}30 cm depth)
1793 2020 2875 2699 2634 1182 *
2.34 2.24 1.61 2.09 1.70 2.74 0.55
0.15 0.75 0.10 0.21 0.13
21 18 72 29 55 35 *
0.38 0.90 0.61 0.23 0.57
0.46 0.86 0.35 0.07 0.30
1.67 1.45 1.80 1.44 1.24 1.48 0.41
0.77 0.59 0.39 0.84 0.34
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Table 4 Meloidogyne javanica populations in the soil at 7 and 12 months and Rhizobium nodulation at 12 months of Sesbania sesban fallows, established by two planting methods with and without nematode control treatments in nursery and "eld, on two farms at Maseno (1997}1998) and Lela (1998}1999) in western Kenya Method of planting
Seed Seed Seedling Seedling Seedling Seedling SED
Nematicide application
Nursery
Field
n.a. n.a. No No Yes Yes
No Yes No Yes No Yes
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
Soil population (J per 100 cm soil)
Nodule fresh weight (g plant\) in 0}30 cm
Maseno
Maseno
Lela At 12 months
At 7 months 70 43 271 101 253 150 67
(0.01 0.71 0.76 0.01 0.57
Lela At 12 months
At 7 months
At 12 months
At 12 months
326 333 394 312 402 482 *
18 8 14 12 24 16 10
16 9 14 8 37 4 9
1.84 1.93 3.01 3.38 2.22 3.36 1.33
3.41 9.09 2.01 9.50 2.16 9.27 2.41
0.19 0.95 0.67 0.43 0.73
0.73 0.03 0.98 (0.01 0.92
0.34 0.25 0.39 0.36 0.52
0.58 0.32 0.33 0.47 0.72
0.57 0.45 0.16 0.01 0.09
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. Initial soil nematode population at the establishment of sesbania averaged 368$107 J per 100 cm soil at Maseno and (10 J per 100 cm soil at Lela. n.a."not applicable. F probability based on natural log transformed data. SED"standard error of di!erence of means.
nematode control in nursery and "eld improved seedling growth in the early stages (data not presented). Soil and root nematode populations were small throughout the study period. At 7 months, while the root populations varied from 35 to 424 eggs#J per gram fresh root (Table 3), the soil populations varied from 8 to 24 J per 100 cm soil. Nematode populations at 12 months were even smaller than at 7 months. Direct seeded sesbania had signi"cantly smaller M. javanica (J #egg) root populations at 7 months and fewer root galls at 12 months than transplanted sesbania. Neither planting method, nor nematicide application in nursery and/or "eld in#uenced root galling and nematode populations in roots and soils, except that nematicide application in the "eld signi"cantly reduced the soil nematode populations at harvest (Table 4). Between the two farms, root and soil nematode populations, and degree of root galling was greater at Maseno than at Lela (p(0.01) (Tables 3 and 4). Nematicide use in the "eld signi"cantly increased rhizobium nodulation of both direct seeded and transplanted sesbania only at Lela (Table 4). 3.3. Sesbania growth and biomass production At 7 months, transplanted sesbania grew signi"cantly better with taller and thicker stems than direct seeded
sesbania at Maseno, but the di!erence between the two planting methods was signi"cant only for height at Lela (Table 5). While nematode control in the nursery improved sesbania growth up to 7 months after "eld planting at both sites, nematicide application in the "eld signi"cantly improved the growth of direct seeded sesbania only at the highly nematode-infested site Maseno. Treatment di!erences became smaller over time and "eld establishment methods did not di!er signi"cantly by harvest at this site. Sesbania transplanted with nematode-free seedlings averaged 11.7 t ha\ of wood compared with 9.8 t ha\ by the crop planted with nematode-infected seedlings (p(0.01). Nematicide application both in the nursery and "eld increased the total biomass of transplanted crop (12.9 t ha\) by 19% over the yield of the untreated crop (p(0.01). Direct seeded sesbania with nematicide produced 11.1 t ha\ of foliar and twig biomass which was 36% greater than the biomass of the crop without nematicide. At Lela, direct seeded sesbania produced 8.4 t ha\ wood and 7.3 t ha\ twig and foliar biomass. The total biomass of direct seeded sesbania was 20% greater than that of transplanted sesbania (p(0.01). Direct seeding was superior to transplanting particularly when seedlings were not protected from nematodes in the nursery (p(0.01). Sesbania transplanted with healthy seedlings produced 20% more wood and 33% more twigs and foliage, resulting
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
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Table 5 Biomass production of 12-month-old Sesbania fallows, established by direct seeding and transplanting with and without nematode control treatments in nursery and "eld, on farms at Maseno and Lela in western Kenya Method of planting
Nematicide application
Nursery
Maseno (1997}1998)
Field
Lela (1998}1999)
Growth at 7 months
Biomass at 12 months (t ha\)
Growth at 7 months
Biomass at 12 months (t ha\)
Height (m)
Wood (t ha\)
Height (m)
Bd (cm)
Wood
Leaves and twigs
Seed n.a. No 2.84 Seed n.a. Yes 3.28 Seedling No No 3.50 Seedling No Yes 3.73 Seedling Yes No 3.84 Seedling Yes Yes 3.86 SED 0.22 F probability of contrasts Seed vs. seedling (0.01 Nematicide vs. none in "eld (seed) 0.05 Nematicide vs. none in nursery 0.14 Nematicide vs. none in "eld (seedlings) 0.41 Nematicide in nursery;"eld 0.43 (seedlings)
Bd (cm)
Leaves and twigs (t ha\)
2.58 2.76 3.03 3.31 3.33 3.70 0.22
9.43 10.85 9.64 9.93 10.67 12.73 1.28
8.16 11.06 11.83 10.14 8.46 12.93 1.42
2.72 3.02 2.17 2.44 2.88 3.07 0.19
2.67 2.84 2.31 2.46 2.86 2.95 0.20
7.83 8.97 5.88 6.10 7.28 7.07 0.97
6.87 7.75 4.73 6.40 7.30 7.59 0.66
(0.01 0.05 0.04 0.41 0.77
0.45 0.28 0.05 0.21 0.34
0.17 0.05 0.77 0.18 (0.01
0.05 0.11 (0.01 0.10 0.75
0.38 0.41 0.01 0.39 0.87
0.01 0.25 0.10 0.99 0.74
0.26 0.44 0.03 0.24 0.44
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. Bd"basal stem diameter. n.a."not applicable. SED"standard error of di!erence of means.
overall in 26% greater quantity of total biomass compared with sesbania planted with nematode-infected seedlings (p)0.01). Nematicide use in the "eld did not bene"t sesbania established by either method. Total biomass production of sesbania at Maseno was 50% more than at Lela. 3.4. Ewect of solarization on Meloidogyne infection and growth of sesbania In the bioassay study, sesbania seedlings grown in soils taken from Lela, Yala and Maseno farms had high gall indices (3.5}4.4) and egg masses (29}112 per plant), and poor growth, which indicate high potential for nematode infestation at these sites (Table 6). Sesbania grown in the soil from Maseno Centre had low GI (1.8) and egg masses (20 per plant), and the seedlings grew better (average height 12 cm) than in soils of other sites (average height 5.4 cm), re#ecting lower potential for nematode infection of this site. One- and two-month solarization signi"cantly increased the soil temperature at all depths compared with bare soil plot controls. The temperature increase averaged 153C near the soil surface, 103C at 10 cm depth, and 53C at 20}30 cm depth (Fig. 1A). Soil temperature under plastic reached almost 603C near the surface and decreased gradually to 30}403C at 30-cm depth. Temperature in the insulated bare plot was not signi"cantly di!erent from that of the normal bare plot. Considerable
Table 6 Meloidogyne javanica infection potential of four farms selected for the solarization study, determined by the nematode infection and growth of 6-week-old Sesbania grown in pots with soil from the test sites Farm site
Gall index
Egg masses per plant
Fresh root weight (g plant\)
Height (cm)
Lela Yala Maseno farm Maseno Centre SED F probability
4.4 3.5 4.2 1.8 0.91 0.08
29 74 112 20 22 0.01
0.10 0.39 0.27 0.96 0.10 (0.01
3.4 7.5 5.3 12.3 1.6 (0.01
di!erences were observed among sites, with the greatest surface temperature under solarization (673C) being at Yala and the lowest (423C) at Maseno Centre (Fig. 1B). Di!erences among sites increased for soil temperature with depth, for example from around 33% for nearsurface temperature to about 44% for the temperature at 30-cm depth. Sesbania in nurseries at Lela and Yala experienced greater nematode infection than at the two Maseno sites, as evident from greater GI and nematode populations in the roots of seedlings grown in the bare plot controls (Table 7). Seedlings grown in the solarized plots at all farms had signi"cantly fewer root galls and Meloidogyne
38
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
Fig. 1. Soil temperature at di!erent depths following implementation of di!erent seedbed treatments. (A) Soil temperature in di!erent treatments averaged over sites. (B) Soil temperature with solarization at di!erent sites.
Table 7 E!ect of soil solarization compared with and without nematicide treatments on Meloidogyne javanica infestation of 2-month-old Sesbania seedlings at four farms in western Kenya Treatment
Solarization (1 m) Solarization (2 m) Bare bed#nematicide Bare bed Bare bed (insulated) SED F probability
Lela
Yala
Gall index
Nematodes per plant
Gall index
1.2 1.1 1.7 3.0 3.1 0.44 (0.01
5.0 (0.39) 1.2 5.2 (0.47) 0.6 7.0 (0.07) 2.8 25.0 (0.06) 3.0 33.0 (0.10) 2.5 6.5 (0.08) 0.45 (0.01((0.01) (0.01
Maseno farm
Maseno Centre
Nematodes per plant
Gall index
Nematodes per plant
Gall index
Nematodes per plant
5.7 (0.17) 4.2 (0.69) 9.3 (0.04) 17.0 (0.04) 9.3 (0.03) 3.8 (016) 0.04 ((0.01)
1.2 1.1 0.7 2.3 1.8 0.36 (0.01
2.2 (0.07) 1.8 (0.08) 1.8 (0.05) 8.3 (0.05) 18.3 (0.01) 4.7 (0.01) 0.02 ((0.01)
1.0 0.9 0.8 1.3 1.3 0.21 0.13
2.3 (0.13) 1.8 (0.12) 1.5 (0.13) 0.3 (0.12) 7.0 (0.11) 1.8 (0.03) 0.03 (0.95)
Includes all stages of the nematode from J to J and adults; values in parentheses are fresh root weight in grams per plant. SED"standard error of di!erence of means.
populations than those in the bare plots. At Lela and Yala, solarization was particularly e!ective where it resulted in signi"cantly lower GI and nematode populations compared with bare plot controls and nematicide treatment. Di!erences in root populations were more striking if nematodes were expressed per g root, as root weights in untreated beds ranged between 0.01 and 0.1 g per plant compared with 0.07}0.69 g per plant in the solarized beds (Table 7). Seedlings in the solarized beds grew 3}4.5 times taller and accumulated 10}20 times
more biomass than in the unsolarized beds (Table 8). Although 1- and 2-months solarization treatments did not di!er signi"cantly in nematode infection, 2-month solarization signi"cantly improved seedling growth compared with 1-month solarization. At Lela and Yala, nematicide treatment did not bene"t the seedling growth compared with bare plot controls. At both sites in Maseno, the e!ect of solarization was comparable to that of nematicide treatment and both nematicide and solarization increased sesbania height growth by over 60% and
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
39
Table 8 E!ect of soil solarization compared with and without nematicide treatments on the growth of 2-month-old Sesbania seedlings at four farms infested with Meloidogyne javanica in western Kenya Treatment
Lela Height (cm)
Solarization (1 m) Solarization (2 m) Bare bed#nematicide Bare bed Bare bed (insulated) SED F probability
15.4 13.6 3.4 3.2 3.8 1.9 (0.01
Yala Dry weight (g plant\) 4.1 4.1 0.3 0.4 0.5 0.7 (0.01
Height (cm)
10.9 24.6 4.4 3.5 5.3 4.7 (0.01
Maseno farm
Maseno Centre
Dry weight (g plant\)
Height (cm)
Dry weight (g plant})
Height (cm)
Dry weight (g plant\)
4.5 13.5 0.4 0.4 0.3 2.6 (0.01
5.9 6.9 5.7 4.1 2.6 1.3 0.04
1.2 1.8 1.4 0.7 0.4 0.4 0.05
11.7 9.5 12.0 6.0 9.3 1.6 0.02
1.2 0.7 1.2 0.4 0.8 0.2 0.01
SED"Standard error of di!erence of means.
biomass by over 100%. An additional bene"t of solarization at all sites was a signi"cant reduction of weed populations in seedbeds.
4. Discussion Better growth of sesbania seedlings due to nematode control in the nursery con"rms the previous reports of the detrimental e!ect of Meloidogyne on sesbania in its early stages of growth (Desaeger and Rao, 2000a). The degree of nematode infection in the nursery largely determines the survival and growth of seedlings in the "eld. Poor growth of seedlings in the nursery means that transplanting may be delayed in the "eld. Nematode control in the nursery was particularly bene"cial when the seedbed soil was heavily infested with the nematode. At Lela, the survival and growth of nematode-infected seedlings was poor in the "eld, even though the nematode infestation was low. In contrast, the results at Maseno suggest that healthy seedlings survive and grow better in the early stages even if nematode infestations in the "eld are large. Large nematode populations in the nematicide treatments indicate that the chosen nematicides were probably ine!ective against the root-knot nematode. The results further suggest that (1) controlling of the endoparasitic Meloidogyne in a deep-rooted perennial such as sesbania is di$cult and (2) nematicide application has limited bene"cial e!ect on sesbania growth. Lower biomass production by sesbania at Lela (1998}1999) than at Maseno (1997}1998) was because of the drought in the 1998 short rains, which probably aggravated the nematode damage, particularly in the crop planted with nematode-infected seedlings. Drought was probably also responsible for the failure of nematode infestations to increase between 7 and 12 months at Lela. In contrast, fast growth and a large biomass at Maseno, despite high
nematode populations, was associated with greater and well-distributed rainfall. It appears that tolerance of sesbania to nematodes increases with age of the plant and nematode infection has a relatively limited impact on the crop under good growing conditions. High biomass production of sesbania even in the highly infested "eld at Maseno con"rms the previous observations that grown up sesbania is highly tolerant to Meloidogyne (Desaeger and Rao, 2000b). High biomass with (50% of the stand in some treatments at Lela indicates the high plasticity of sesbania to plant population, but it is doubtful whether relay-planted sesbania in standing cereal crops would show similar response to that of sole-planted crop over a 12-month growing period. Less nematode infection of direct seeded sesbania compared with transplanted sesbania in this study contradicts the results of our earlier pot studies (Desaeger and Rao, 1999) but con"rms the "eld results in Ethiopia (SteinmuK ller, 1995). Greater nematode density in relation to the smaller root system of direct seeded sesbania might be responsible for greater nematode infection of direct seeded sesbania than transplanted sesbania in the short-term pot studies. Greater nematode infection of transplanted sesbania in Ethiopia was attributed to nematode infection of the seedlings in the nursery (SteinmuK ller, 1995). However, no speci"c reason could be ascribed to less nematode infection of direct seeded sesbania compared to transplanted sesbania with healthy seedlings in this study. Some possible explanations include (1) decrease of nematode populations in the soil due to mortality of juveniles hatched from eggs following wet and dry spells before sesbania was sown (Maas, 1987), (2) reduction of nematode infection potential due to time lag from sowing to the development of a reasonable root system for nematode reproduction to occur, and (3) thinning of excess seedlings at 4 weeks served the purpose of a &trap crop' and reduced the nematode pressure.
40
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
The method by which sesbania is established depends on the cropping system, relative planting time of sesbania to the crop(s) in intercropping, and land and labour constraints. If sesbania is to be grown as a pure crop with timely weed control under good rainfall, direct seeding appears to be better than transplanting, as production of seedlings incurs additional labour and bears the risk of nematode infection in the nursery. Timely weeding of sesbania is often not possible for most small-scale farmers because of competing labour demands from food and cash crops at the beginning of the season. As 4}6-weekold sesbania seedlings withstand weed competition better and allow weeding to be delayed to a later time, farmers may prefer to establish sesbania by transplanting. If sesbania is planted together with crops, it gets weeded along with crops. If both sesbania and crop are to be planted simultaneously at the start of the season, direct seeding of sesbania may be better than transplanting, as seedlings may reduce crop yields because of competition (Niang et al., 1996). However, transplanting may have an advantage over direct sowing if sesbania is to be relay-planted later in the season, as seedlings generally establish better in a standing crop. The extra growth period for seedlings in the nursery is advantageous when the growth period for tree in the "eld is short as in western Kenya. Sesbania relay-sown using seeds in standing maize crops often produced less biomass than sesbania relay-transplanted with seedlings due to poor plant stand and suppression of seedling growth by the competitive maize (Niang et al., 1996). Where sesbania establishment by transplanting is preferred over direct seeding, then production of healthy seedlings free from nematode infection is important to improve seedling survival and early growth. Soil solarization seems to o!er an e!ective and economical means of producing nematode-free seedlings to small-scale African farmers. The e!ectiveness of solarization di!ered among sites because of rainfall during solarization, di!erences in soil characteristics and interference from shade at some sites. The soil temperature increase achieved by solarization at Lela and Yala is within the range for e!ective control of Meloidogyne and most other soil-borne pathogens (Maas, 1987). Solarization had a limited e!ect at Maseno Centre due to low heat retention capacity of coarse sand in the upper 30 cm, shade from big trees surrounding the seedbeds and rainfall during solarization. This technique was also less e!ective at Maseno farm probably because of a 3-day interruption to solarization due to theft of plastic. The soil temperature at this site following solarization was probably not lethal to all plant-parasitic nematodes, although similar temperature increments gave good results earlier (Kamra and Gaur, 1998; Gaur and Dhingra, 1991). Similar levels of soil nematode populations in both the planting methods at harvest of sesbania point out that none of the "eld establishment methods can reduce the
risk of root-knot nematodes a!ecting the nematodesusceptible crops following sesbania cover crops. As nematicide use cannot be justi"ed for cover crops such as sesbania and arable crops, e!orts have to be made to identify nematode-resistant sesbania germplasm. Acknowledgements The senior author was seconded to ICRAF by the Flemish O$ce for Development Cooperation and Technical Assistance (VVOB), Belgium and the Swedish International Development Cooperation Agency (Sida) has provided funds for the research reported here. We sincerely thank Dr. John Bridge, Senior Nematologist, CABI Bioscience, UK, for providing helpful comments on the draft of this paper. References Buresh, R.J., Tian, G., 1997. Soil improvement by trees in sub-Saharan Africa. Agroforest. Systems 38, 51}76. Desaeger, J., Rao, M.R., 1999. The root-knot nematode (Meloidogyne spp.) problem in sesbania fallows and scope for managing it in western Kenya. Agroforest. Systems 47, 273}288. Desaeger, J., Rao, M.R., 2000a. Infection and damage potential of Meloidogyne javanica on Sesbania sesban in di!erent soil types. Nematology 2, 169}178. Desaeger, J., Rao, M.R., 2000b. Parasitic nematode populations in natural and improved cover crops and their e!ects on subsequent crops in Kenya. Field Crops Res. 65, 41}56. Gaur, H.S., Dhingra, A., 1991. Management of Meloidogyne incognita and Rotylenchulus reniformis in nursery-beds by soil solarization and organic soil amendment. Rev. NeH matol. 14, 185}195. Kamra, A., Gaur, H.S., 1998. Control of nematodes, fungi and weeds in nursery beds by soil solarization. Int. J. Nematol. 8, 46}52. Karachi, M., 1995. Sesbania species as potential hosts to root-knot nematode (Meloidogyne javanica) in Tanzania. Agroforest. Systems 32, 119}125. Kwesiga, F.R., Beniest, J., 1998. Sesbania improved fallows for eastern Zambia: an extension guideline. International Centre for Research in Agroforestry, Nairobi, 56 pp. Kwesiga, F.R., Franzel, S., Place, F.M., Phiri, D., Simwanza, C.P., 1999. Sesbania sesban improved fallows in eastern Zambia: their inception, development and farmer enthusiasm. Agroforest. Systems 47, 49}66. Maas, P.W.Th., 1987. Physical methods and quarantine. In: Brown, R.H., Kerry, B.R. (Eds.), Principles and Practice of Nematode Control in Crops. Academic Press, Sidney, pp. 265}293. Niang, A., Gathumbi, S., Amadalo, B., 1996. The potential of shortduration improved fallows for crop productivity enhancement in the highlands of western Kenya. In: Mugah, J.O. (Ed.), People and Institutional Participation in Agroforestry for Sustainable Development. Kenya Forestry Research Institute, Kenya, Muguga, Nairobi, pp. 218}230. Rao, M.R., Niang, A., Kwesiga, F., Duguma, B., Franzel, S., Jama, B., Buresh, R., 1998. Soil fertility replenishment in sub-Saharan Africa: new techniques and the spread of their use on farms. Agroforest. Today 10 (2), 3}8. Smaling, E.M.A., Nandwa, S.M., Janssen, B.H., 1997. Soil fertility in Africa at stake. In: Buresh, R.J., Sanchez, P.A., Calhoun, F. (Eds.), Replenishing Soil Fertility in Africa. SSSA Special Publication No. 51, Madison, WI, USA, pp. 47}62.
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41 Southey, J.F. (Ed.), 1986. Laboratory Methods for Work with Plant and Soil Nematodes. Reference Book 402, Ministry of Agriculture, Fisheries and Food, 202 pp. SteinmuK ller, N., 1995. Agronomy of the N -"xing fodder trees Sesbania sesban (L.) Merr. and Sesbania goetzii harms in the Ethiopian highlands. Dissertation UniversitaK t Hohenheim, Institut fur P#anzenproduktion in den Tropen und Subtropen, Verlaug Ulrich E. Grauer, Stuttgart, Germany, 230 pp.
41
Szott, L.T., Palm, C.A., Buresh, R.J., 1999. Ecosystem fertility and fallow function in the humid and subhumid tropics. Agroforest. Systems 47, 163}196. Zeck, W.M., 1971. A rating scheme for "eld evaluation of root-knot nematode infestations. P#anzenschutz Nachr. Bayer AG 24, 141}144.
E!ect of "eld establishment methods on root-knot nematode (Meloidogyne spp.) infection and growth of Sesbania sesban in western Kenya J. Desaeger, M.R. Rao* International Centre for Research in Agroforestry (ICRAF), P.O. Box 30677, Nairobi, Kenya Received 16 December 1999; received in revised form 8 February 2000; accepted 11 April 2000
Abstract Pot studies indicated that root-knot nematode (Meloidogyne javanica) infection reduces sesbania (Sesbania sesban) growth and planting methods modify the nematode damage, but their e!ects on sesbania biomass production at the "eld scale are not known. A "eld study was conducted in western Kenya for 2 yr, comparing direct seeding of sesbania with transplanting of bare-rooted seedlings in pure stands, with and without nematicide application in the "eld and in the nursery. In moist conditions, neither planting method nor nematicide had any in#uence on seedling survival and early growth. When early season rainfall was low and erratic, transplanted seedlings survived and grew better than seedlings from direct sowing, and nematicide application in the "eld and/or nursery improved seedling survival. Direct seeded sesbania had signi"cantly less nematode galling and smaller nematode populations in the roots than transplanted sesbania. Both the establishment methods produced similar quantities of biomass, but direct seeded sesbania produced signi"cantly greater biomass than the transplanted crop, if seedlings were already infected with nematodes in the nursery. Nematode infection on average reduced total sesbania biomass by 19%. Where sesbania cover crops have to be established by transplanting for socio-economic reasons, it is essential to use healthy seedlings free from nematodes for a good plant stand and early growth. Nematode-free seedlings can be produced on farms by at least one month of solarization of seedbeds. Neither "eld establishment method, nor nematicide application altered the soil nematode populations over a 12-month period. This means that the potential threat of increased Meloidogyne populations to nematode-susceptible crops following sesbania cover crops remains the same irrespective of how sesbania is established. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Agroforestry; Cover crop; Meloidogyne javanica; Tree fallow; Root-knot nematode; Soil fertility; Soil solarization
1. Introduction Nutrient depletion is one of the major causes of low crop yields in smallholders' farms in sub-Saharan Africa (Smaling et al., 1997). As small-scale farmers cannot afford to use chemical fertilizers, research in recent years has focused on developing technologies that would replenish soil fertility through agroforestry and organic inputs. Short-duration leguminous trees or shrubs have been found to increase soil fertility and subsequent crop yields in N-depleted soils (Szott et al., 1999). Sesbania (Sesbania sesban), an N -"xing and deep rooting shrub with good-quality foliage is one of the most promising
* Corresponding address: 11, ICRISAT colony (Phase 1), Akbar Road, Secunderabad-500 009, Andhra Pradesh, India. E-mail address: [email protected] (M.R. Rao).
species for short-duration cover cropping (Buresh and Tian, 1997). Sesbania cover crops have been found to increase N supply in the soil through biological nitrogen "xation and recycling of leached N at depth, and increase the availability of nutrients to crops grown in rotation. The residual e!ect of sesbania on subsequent maize was highly dependent on biomass produced by sesbania (Szott et al., 1999). Whereas 0.5-yr (one season) sesbania cover cropping is appropriate for the small farms in highly populated, western Kenya (Niang et al., 1996), 2-yr cover cropping is appropriate for the relatively larger farms in the less populated, eastern Zambia (Kwesiga et al., 1999). Sesbania cover crops, also referred to as &improved fallows' or &planted tree fallows', are being widely tested on farms and disseminated in both these regions (Rao et al., 1998). Root-knot nematodes (Meloidogyne incognita and M. javanica) may be a potential constraint for the use of
0261-2194/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 1 - 2 1 9 4 ( 0 0 ) 0 0 0 4 9 - 1
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J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
sesbania cover crops (Karachi, 1995) and increase the nematode populations in the soil (Desaeger and Rao, 1999). This implies that sesbania growth may be reduced in nematode-infested soils and nematode-susceptible crops may risk yield loss following sesbania. High seedling mortality and growth reduction of sesbania were observed with increased inoculum of M. javanica, particularly in lighter-textured soils (Desaeger and Rao, 2000a). While direct seeded sesbania was found to have greater nematode infection than transplanted sesbania in pots (Desaeger and Rao, 1999), the reverse was the case in "eld studies (SteinmuK ller, 1995). In eastern Zambia, sesbania is established as a pure crop using 4}6-week-old bare-rooted seedlings (Kwesiga and Beniest, 1998), but in western Kenya it is established by both direct seeding and transplanting as an intercrop with maize (A. Niang, pers. comm.). Quantitative information is lacking on how Meloidogyne infection a!ects sesbania growth under "eld conditions. Production of healthy seedlings plays an important role in minimizing the impact of soil-borne pathogens in the case of transplanted crops. Seedbed solarization has shown good potential for controlling nematodes and many other soil-borne pests and diseases in some tropical countries (Gaur and Dhingra, 1991; Kamra and Gaur, 1998). If this practice controls the local soil-borne pathogens, even the poor farmers in Africa can adopt it to produce seedlings of sesbania as well as other transplanted crops that they grow such as tomato (Lycopersicon esculentum Mill.), cabbage (Brassica oleracea v. capitata L.) and kale (Brassica oleracea v. acephala). However, the e$cacy of solarization depends on climatic factors (e.g. solar radiation, temperature, air humidity and wind) and soil characteristics (absorption of solar radiation, heat capacity and thermal di!usion). The objectives of the present studies were to determine (1) the e!ect of Meloidogyne infection on sesbania growth and biomass production, (2) the e!ect of the method of
establishing sesbania on nematode infection and biomass production, and (3) whether nematode-free sesbania seedlings can be produced through soil solarization on farms.
2. Materials and methods 2.1. Study 1 2.1.1. Experimental sites and treatments The study was conducted on farms in Maseno (Vihiga District) and Lela (Kisumu District) villages in western Kenya (altitude 1500 m, latitude 03 06 N, and longitude 343 34 E) from March 1997 to March 1999. The soil at both sites was clay loam, deep, well drained and of moderate fertility, except for low extractable phosphorus (Table 1). The Maseno farm was previously under sesbania for 18 months and the Lela farm under natural fallow for 36 months. The region has a bimodal rainfall, with about 1000 mm during the &long rains' (March} August) and 800 mm during the &short rains' (September}February). The mean monthly temperature ranges from 18 to 273C. The study involved six factorial treatments of two "eld establishment methods (direct seeding and transplanting of seedlings) with and without nematode control in the "eld for both methods and for seedlings in the nursery. Nematode control in the "eld was attempted by nematicide application. Plots were 5 m wide by 10 m long and were separated by 1 or 2 m paths on all sides. At Maseno, plots were grouped into replications on the basis of initial root-knot nematode populations, which were large and varied considerably between plots. Nematode populations were determined in soil samples taken from the top 30-cm soil layer at six locations in each plot. At Lela, the initial soil nematode populations were small and relatively more uniform, so replications were made on the basis of proximity and vegetation gradient. The treatments at
Table 1 Site characteristics of farms in the two studies Study/village
Study 1 Maseno Lela Study 2 Lela Yala Maseno farm Maseno centre
Particle distribution (%)
Organic C (%)
Extractable P (mg kg\)
CEC (Ca#Mg#K) (cmol kg\)
pH
Sand
Silt
Clay
27 31
28 26
45 43
1.54 1.43
3.3 2.0
3.69 8.33
4.4 5.2
41 37 29 83
24 22 30 11
35 41 41 6
1.48 1.53 1.58 0.63
3.5 5.7 3.4 7.8
4.74 6.30 5.08 2.89
5.1 5.1 5.2 6.4
Period of solarization. Period of seedling growth.
Rainfall in speci"ed period (mm) March}August
September} February
629 661 January}February 0 200 120 163
1467 263 March}April 189 219 463 574
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
each site were replicated "ve times in a randomized complete block design. 2.1.2. Nursery and xeld management Sesbania (provenance: Kakamega, Kenya) seedlings were raised with and without controlling of nematodes in the nursery at the Maseno Regional Research Centre. In 1998, nematode control was attempted with 5% carbofuran at 20 g m\, but in 1999, nematode control was attempted by heating the top 20-cm soil layer in a drum for 4 h at over 903C. The seedbed soil was loamy sand and the beds were used previously to raise a variety of tree seedlings. The plants were carefully lifted after 6 weeks and transplanted as bare-rooted seedlings in the "eld. Direct seeding of sesbania was done simultaneously with transplanting of seedlings in the "eld, using seeds soaked overnight in hot water (503C) and placing four to "ve seeds at each planting hole. Plant spacing was 1 m;1 m at both farms. Seedlings were thinned to one plant per spot 4 weeks after emergence. Nematicide was applied in the "eld at planting and subsequently at 2-month intervals. At Maseno, Nemacur (a.i. 5% fenamiphos) was used at 150 kg ha\ (7.5 kg a.i. ha\) per application. At Lela, di!erent nematicides were used at each application hoping that such a strategy may control the nematode better than continuous application of one chemical. The chemicals used were Furadan (a.i. 5% carbofuran) at planting at 2 g per hill (1 kg a.i. ha\), and subsequently Vydate (a.i. 24% oxamyl) at 40 l ha\ (9.6 l a.i.), Nemacur at 150 kg ha\ (7.5 kg a.i.) and Mocap (a.i.10% ethoprophos) at 150 kg ha\ (15 kg a.i.) in rotation at 2-month intervals. The chemicals, except Furadan and Vydate, were uniformly spread and incorporated into the soil by hand hoes. Vydate was sprayed diluted in 400 l per ha on the soil surface. Nematode contamination across plots through lateral spread of sesbania roots was avoided by di!erent methods. At Maseno (1997}1998), trenches 0.3 m wide and 0.5 m deep were dug surrounding the plots, sesbania roots were severed and trenches re"lled with soil at 4 and 9 months after planting. At Lela (1998}1999), galvanized iron sheets were installed to 0.5 m depth around the plots before planting. No fertilizer was applied to sesbania at either farm. Any gaps in the stand were "lled in with seeds or seedlings as per treatments in the "rst 2 weeks after planting. The plots were hand weeded twice in the "rst 3 months to remove weed competition to the slow growing sesbania seedlings in the early stages. If sesbania seedlings were infested by leaf eating beetles (Mesoplatys ochroptera), the beetles were removed manually as they can cause severe damage in the early stages, but no control measures were taken after 3 months. 2.1.3. Data collection and analyses At the time of transplanting sesbania in the "eld, 20 randomly selected seedlings were measured for height
33
and assessed for gall index (GI) on a 0}10 scale (Zeck, 1971). At 3 months after planting (or sowing) in the "eld, nematode populations in the roots were determined at Maseno by uprooting four seedlings per plot, but not at Lela because of a poor initial stand establishment. Nematode populations in the soil and the roots were determined at 7 and 12 months by taking six core samples in each plot from 0 to 30 cm soil layer using a 10 cm diameter pipe at 25 and 50 cm from trees. The samples were taken with reference to three trees spread over the net plot area at similar positions in all plots. The soil was bulked, and, after separating roots from soil, nematodes were extracted from 100 cm soil according to the modi"ed Baermann method (Southey, 1986). Roots were washed and rated on 0}10 scale, chopped into 1 cm pieces, mixed in a kitchen blender for 3 s, and a 10 g fresh root sample was used for extracting nematodes following the modi"ed Baermann method. Meloidogyne eggs were extracted from the same sample using the bleach method (Southey, 1986). A 1.0 g subsample of roots was stained with phloxine B for counting egg masses, and nematode fecundity assessed using the bleach method only at Maseno. At 7 months, sesbania growth was assessed by measuring plant height and stem diameter at 5 cm above the ground of 24 trees in the middle three rows of each plot. At 12 months, above-ground biomass of sesbania was determined by harvesting trees at ground level from a 24 m area, leaving a 1 m border on all sides of the plots. Foliage (leaves and twigs (5 mm diameter) was separated from wood ('5 cm diameter) and dry weights were estimated based on fresh weights and the percent dry matter determined on sub-samples dried at 703C for a constant weight. A severe drought in the 1998 short rains had caused considerable litterfall at Lela. Leaf litter was collected from three 1-m quadrats in each plot and added to the foliar biomass. Nodule numbers and weights were determined at harvest on three randomly selected plants uprooted from the net area of each plot. Nematode populations in the roots and the soil at each observation and growth and biomass measurements of sesbania were subjected to analysis of variance (ANOVA). As the site ; treatment interaction was signi"cant for a number of parameters, results from each site were analysed separately. Nematode populations were (natural) log transformed to ensure that the data had a normal distribution before ANOVA and the signi"cance of treatment di!erences was judged on the transformed data. 2.2. Study 2 This study was conducted from January to May 1999 on three farms, one each in Maseno (Vihiga District), Lela (Kisumu District), and Yala (Siaya District) villages, and at the Maseno Regional Agroforestry Research Centre, to study the potential of solarization to produce
34
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nematode-free sesbania seedlings. The experimental sites were previously covered with sesbania at Maseno, Guizotia scabra and Gutenbergia cordifolia (both the weeds are good hosts of Meloidogyne spp. (Desaeger and Rao, 2000b)) at Lela, and tomato (Lycopersicon esculentum) at Yala; the site at the Maseno Centre was under bare fallow. The treatments tested were (1) 1-month soil solarization, (2) 2-month soil solarization, (3) bare fallow, (4) bare fallow#nematicide, and (5) bare fallow#plastic overlaid with a 30 cm soil layer. At each site the treatments were replicated four times in a randomized complete block design. For solarization, the plots were covered with a transparent plastic sheet with its edges buried into the soil. The plots were wetted thoroughly before applying the plastic sheet. In treatment 5, the seedbed was covered with black plastic to prevent rain water percolating into soil and stimulating nematode eggs to hatch and a 30-cm thick layer of soil placed over the plastic to insulate the seedbed soil from solarization. The 2-month solarization treatment was started in early January 1999, and the 1-month treatment in early February 1999, so that both treatments ended at the same time in early March, coinciding with the start of the long rains. Before commencing 1-month solarization, the respective seedbeds were protected from the in#uence of external factors as explained for treatment 5. The plots were 1.0 m and separated from each other by 0.5}1.0 m paths. Sesbania seeds (provenance: Kakamega, Kenya) soaked overnight in hot water (503C) were sown about 1 week after solarization, allowing the soil to aerate. For the nematicide treatment, Vydate (a.i. oxamyl) was applied at 40 l ha\ mixed in 400 l of water per ha before sowing sesbania seeds. The potential for nematode infection at the four sites was assessed by a bioassay for which sesbania was grown in eight 2.5 l pots per site, "lled with soil from the respective test sites. The seedlings were uprooted 6 weeks after sowing, and roots scored for root galls and stained for counting egg masses using phloxine B (Southey, 1986). Soil temperature was measured at 0, 5, 10, 15, 20, and 30 cm depths at the end of solarization. At 1 or 2 months after sowing, 10 randomly selected seedlings were measured for plant height and biomass, and the same seedlings were uprooted carefully and assessed for nematode galls. Meloidogyne infection was assessed by staining the roots of two plants with lactoglycerol (Southey, 1986) and counting all stages of the nematode. Weeds in each plot were counted, removed and weighed at Lela, Yala, and Maseno Centre. The data were analysed following the ANOVA procedures.
3. Results The root-knot nematode in the nursery seedbeds and at all the "eld sites was Meloidogyne javanica. Carbofuran
Table 2 Meloidogyne javanica infestation and growth of 6-week-old Sesbania sesban seedlings, produced at Maseno Centre with and without nematode control treatments in the nursery for study 1 in two years Year
Nematode control
Gall index (0}10)
1997
Yes No
0.1 1.5 0.22 (0.01 0.4 4.3 0.26 0.01
SED t-Test 1998 SED t-Test
Yes No
Seedling height (cm) 28.6 18.7 1.05 (0.01 21.7 11.1 1.26 (0.01
In 1997, nematode control was attempted with 5% carbofuran at 20 g m\, but in 1998, it was with heat sterilization of the top 20-cm soil layer. SED"standard error of di!erence of means.
treatment in 1997 and heat sterilization of soil in 1998 gave good protection to sesbania seedlings against Meloidogyne infection in the nursery (Table 2). The seedlings grown with either of the treatments showed low nematode infection (GI"0.1}0.4) and were 65}100% taller than those produced without any nematode control. The seedlings produced in the unprotected plots in 1998 for Lela farm had three times greater root galling (GI"4.3) than those produced in 1997 for Maseno farm (GI"1.5). Obviously, the nursery beds used in 1998 were more heavily infected by the root-knot nematode than those in 1997. 3.1. Sesbania seedling mortality The initial soil Meloidogyne juvenile (J ) populations at Maseno were high with an average of 368 (SE$107) J per 100 cm soil compared with (10 J per 100 cm soil at Lela. At Maseno, 98}99% of the seedlings survived from direct seeding and transplanting with healthy seedlings, whether or not a nematicide was used in the "eld. Survival of seedlings produced without nematicide in the nursery was also high at 87% irrespective of nematicide application in the "eld. Seedling mortality at Lela was much greater than at Maseno. At 3 months, 95% of the transplanted seedlings produced with nematode control in the nursery survived compared with 70% of those produced without protection. Nematicide use in the "eld did not increase the stand of transplanted seedlings. Direct seeding with nematicide application gave 80% survival compared with 67% survival without a nematicide. At harvest, the stand of direct seeded sesbania in both nematicide treated and untreated plots remained the same as at 3 months. Similarly, transplanted seedlings free from nematodes did not experience any further stand mortality and their survival at harvest was 94%.
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
However, transplanting with nematode-infected seedlings experienced an additional 12% mortality resulting in a "nal stand of only 58% at harvest. 3.2. Nematode infection of sesbania At Maseno, treatment di!erences were negligible for nematode infection of roots and GI at 3 months after planting in the "eld. Transplanted sesbania without nematicide in the nursery and/or "eld had an average GI of 3.5 compared with 2.2 for direct seeded sesbania. Nematode populations generally varied from 200 to 530 juveniles and eggs per gram root. At 7 months after planting, root nematode populations were large and varied from 480 to 3700 juveniles and eggs per gram root. Transplanted sesbania had 115% greater GI and 152%
35
greater nematode root populations than the direct seeded sesbania (p(0.01) (Table 3). Nematicide application in the nursery and/or "eld for both planting methods did not reduce nematode infection. Gall indices increased with age of plants by 45}160%. At 12 months, transplanted sesbania averaged a GI of 5.4 compared with 3.7 by direct seeded sesbania (p( 0.01). However, nematode infection was similar across all treatments, irrespective of "eld establishment methods and nematicide application. Neither planting method, nor nematicide application affected the soil nematode populations at 7 and 12 months after planting (Table 4). Soil nematode populations at harvest were slightly greater than or comparable with those at the start of the study. At Lela, in spite of fewer galls (GI"0}2) at 3 months after planting in both the establishment methods,
Table 3 Meloidgyne javanica infestation of Sesbania, established by two planting methods with and without nematode control treatments in nursery and "eld, at two growth stages on farms in western Kenya Method of planting
Nematicide application
At 7 months
Nursery
Field
Gall index
No Yes No Yes No Yes
1.7 1.5 3.5 2.7 4.0 3.6 0.6
482 1372 1894 2372 3701 2883 *
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
0.01 0.67 0.10 0.16 0.61
(0.01 0.32 0.12 0.53 0.23
Lela (1998}1999) Seed n.a. Seed n.a. Seedling No Seedling No Seedling Yes Seedling Yes SED
0.9 1.1 0.9 1.2 1.8 1.4 0.48
Maseno (1997}1998) Seed n.a. Seed n.a. Seedling No Seedling No Seedling Yes Seedling Yes SED
No Yes No Yes No Yes
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
0.28 0.68 0.12 0.88 0.42
At 12 months Eggs#J per g fresh root
152 35 87 113 164 424 *
0.03 0.40 0.37 0.86 0.24
Root dry weight (mg cm\ soil in 0}30 cm depth)
1.22 1.32 1.86 1.89 2.14 1.88 0.25
Gall index
4.4 3.1 5.0 5.0 5.8 5.9 0.7
(0.01 0.67 0.45 0.52 0.41
(0.01 0.08 0.10 0.92 0.91
0.90 0.94 0.63 0.53 0.88 1.07 0.19
1.6 1.1 1.7 1.9 2.6 1.9 0.47
0.23 0.85 (0.01 0.71 0.32
0.02 0.30 0.19 0.46 0.32
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. F probability was based on the ANOVA of log transformed data. n.a."not applicable. SED"standard error of di!erence of means.
Eggs#J per g fresh root
Root dry weight (mg cm\ soil in 0}30 cm depth)
1793 2020 2875 2699 2634 1182 *
2.34 2.24 1.61 2.09 1.70 2.74 0.55
0.15 0.75 0.10 0.21 0.13
21 18 72 29 55 35 *
0.38 0.90 0.61 0.23 0.57
0.46 0.86 0.35 0.07 0.30
1.67 1.45 1.80 1.44 1.24 1.48 0.41
0.77 0.59 0.39 0.84 0.34
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J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
Table 4 Meloidogyne javanica populations in the soil at 7 and 12 months and Rhizobium nodulation at 12 months of Sesbania sesban fallows, established by two planting methods with and without nematode control treatments in nursery and "eld, on two farms at Maseno (1997}1998) and Lela (1998}1999) in western Kenya Method of planting
Seed Seed Seedling Seedling Seedling Seedling SED
Nematicide application
Nursery
Field
n.a. n.a. No No Yes Yes
No Yes No Yes No Yes
F probability of contrasts Seed vs. seedling Nematicide vs. none in "eld (seed) Nematicide vs. none in nursery Nematicide vs. none in "eld (seedlings) Nematicide in nursery;"eld (seedlings)
Soil population (J per 100 cm soil)
Nodule fresh weight (g plant\) in 0}30 cm
Maseno
Maseno
Lela At 12 months
At 7 months 70 43 271 101 253 150 67
(0.01 0.71 0.76 0.01 0.57
Lela At 12 months
At 7 months
At 12 months
At 12 months
326 333 394 312 402 482 *
18 8 14 12 24 16 10
16 9 14 8 37 4 9
1.84 1.93 3.01 3.38 2.22 3.36 1.33
3.41 9.09 2.01 9.50 2.16 9.27 2.41
0.19 0.95 0.67 0.43 0.73
0.73 0.03 0.98 (0.01 0.92
0.34 0.25 0.39 0.36 0.52
0.58 0.32 0.33 0.47 0.72
0.57 0.45 0.16 0.01 0.09
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. Initial soil nematode population at the establishment of sesbania averaged 368$107 J per 100 cm soil at Maseno and (10 J per 100 cm soil at Lela. n.a."not applicable. F probability based on natural log transformed data. SED"standard error of di!erence of means.
nematode control in nursery and "eld improved seedling growth in the early stages (data not presented). Soil and root nematode populations were small throughout the study period. At 7 months, while the root populations varied from 35 to 424 eggs#J per gram fresh root (Table 3), the soil populations varied from 8 to 24 J per 100 cm soil. Nematode populations at 12 months were even smaller than at 7 months. Direct seeded sesbania had signi"cantly smaller M. javanica (J #egg) root populations at 7 months and fewer root galls at 12 months than transplanted sesbania. Neither planting method, nor nematicide application in nursery and/or "eld in#uenced root galling and nematode populations in roots and soils, except that nematicide application in the "eld signi"cantly reduced the soil nematode populations at harvest (Table 4). Between the two farms, root and soil nematode populations, and degree of root galling was greater at Maseno than at Lela (p(0.01) (Tables 3 and 4). Nematicide use in the "eld signi"cantly increased rhizobium nodulation of both direct seeded and transplanted sesbania only at Lela (Table 4). 3.3. Sesbania growth and biomass production At 7 months, transplanted sesbania grew signi"cantly better with taller and thicker stems than direct seeded
sesbania at Maseno, but the di!erence between the two planting methods was signi"cant only for height at Lela (Table 5). While nematode control in the nursery improved sesbania growth up to 7 months after "eld planting at both sites, nematicide application in the "eld signi"cantly improved the growth of direct seeded sesbania only at the highly nematode-infested site Maseno. Treatment di!erences became smaller over time and "eld establishment methods did not di!er signi"cantly by harvest at this site. Sesbania transplanted with nematode-free seedlings averaged 11.7 t ha\ of wood compared with 9.8 t ha\ by the crop planted with nematode-infected seedlings (p(0.01). Nematicide application both in the nursery and "eld increased the total biomass of transplanted crop (12.9 t ha\) by 19% over the yield of the untreated crop (p(0.01). Direct seeded sesbania with nematicide produced 11.1 t ha\ of foliar and twig biomass which was 36% greater than the biomass of the crop without nematicide. At Lela, direct seeded sesbania produced 8.4 t ha\ wood and 7.3 t ha\ twig and foliar biomass. The total biomass of direct seeded sesbania was 20% greater than that of transplanted sesbania (p(0.01). Direct seeding was superior to transplanting particularly when seedlings were not protected from nematodes in the nursery (p(0.01). Sesbania transplanted with healthy seedlings produced 20% more wood and 33% more twigs and foliage, resulting
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
37
Table 5 Biomass production of 12-month-old Sesbania fallows, established by direct seeding and transplanting with and without nematode control treatments in nursery and "eld, on farms at Maseno and Lela in western Kenya Method of planting
Nematicide application
Nursery
Maseno (1997}1998)
Field
Lela (1998}1999)
Growth at 7 months
Biomass at 12 months (t ha\)
Growth at 7 months
Biomass at 12 months (t ha\)
Height (m)
Wood (t ha\)
Height (m)
Bd (cm)
Wood
Leaves and twigs
Seed n.a. No 2.84 Seed n.a. Yes 3.28 Seedling No No 3.50 Seedling No Yes 3.73 Seedling Yes No 3.84 Seedling Yes Yes 3.86 SED 0.22 F probability of contrasts Seed vs. seedling (0.01 Nematicide vs. none in "eld (seed) 0.05 Nematicide vs. none in nursery 0.14 Nematicide vs. none in "eld (seedlings) 0.41 Nematicide in nursery;"eld 0.43 (seedlings)
Bd (cm)
Leaves and twigs (t ha\)
2.58 2.76 3.03 3.31 3.33 3.70 0.22
9.43 10.85 9.64 9.93 10.67 12.73 1.28
8.16 11.06 11.83 10.14 8.46 12.93 1.42
2.72 3.02 2.17 2.44 2.88 3.07 0.19
2.67 2.84 2.31 2.46 2.86 2.95 0.20
7.83 8.97 5.88 6.10 7.28 7.07 0.97
6.87 7.75 4.73 6.40 7.30 7.59 0.66
(0.01 0.05 0.04 0.41 0.77
0.45 0.28 0.05 0.21 0.34
0.17 0.05 0.77 0.18 (0.01
0.05 0.11 (0.01 0.10 0.75
0.38 0.41 0.01 0.39 0.87
0.01 0.25 0.10 0.99 0.74
0.26 0.44 0.03 0.24 0.44
For the study at Lela (1998}1999), nematode control in nursery was attempted by soil sterilization. Bd"basal stem diameter. n.a."not applicable. SED"standard error of di!erence of means.
overall in 26% greater quantity of total biomass compared with sesbania planted with nematode-infected seedlings (p)0.01). Nematicide use in the "eld did not bene"t sesbania established by either method. Total biomass production of sesbania at Maseno was 50% more than at Lela. 3.4. Ewect of solarization on Meloidogyne infection and growth of sesbania In the bioassay study, sesbania seedlings grown in soils taken from Lela, Yala and Maseno farms had high gall indices (3.5}4.4) and egg masses (29}112 per plant), and poor growth, which indicate high potential for nematode infestation at these sites (Table 6). Sesbania grown in the soil from Maseno Centre had low GI (1.8) and egg masses (20 per plant), and the seedlings grew better (average height 12 cm) than in soils of other sites (average height 5.4 cm), re#ecting lower potential for nematode infection of this site. One- and two-month solarization signi"cantly increased the soil temperature at all depths compared with bare soil plot controls. The temperature increase averaged 153C near the soil surface, 103C at 10 cm depth, and 53C at 20}30 cm depth (Fig. 1A). Soil temperature under plastic reached almost 603C near the surface and decreased gradually to 30}403C at 30-cm depth. Temperature in the insulated bare plot was not signi"cantly di!erent from that of the normal bare plot. Considerable
Table 6 Meloidogyne javanica infection potential of four farms selected for the solarization study, determined by the nematode infection and growth of 6-week-old Sesbania grown in pots with soil from the test sites Farm site
Gall index
Egg masses per plant
Fresh root weight (g plant\)
Height (cm)
Lela Yala Maseno farm Maseno Centre SED F probability
4.4 3.5 4.2 1.8 0.91 0.08
29 74 112 20 22 0.01
0.10 0.39 0.27 0.96 0.10 (0.01
3.4 7.5 5.3 12.3 1.6 (0.01
di!erences were observed among sites, with the greatest surface temperature under solarization (673C) being at Yala and the lowest (423C) at Maseno Centre (Fig. 1B). Di!erences among sites increased for soil temperature with depth, for example from around 33% for nearsurface temperature to about 44% for the temperature at 30-cm depth. Sesbania in nurseries at Lela and Yala experienced greater nematode infection than at the two Maseno sites, as evident from greater GI and nematode populations in the roots of seedlings grown in the bare plot controls (Table 7). Seedlings grown in the solarized plots at all farms had signi"cantly fewer root galls and Meloidogyne
38
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
Fig. 1. Soil temperature at di!erent depths following implementation of di!erent seedbed treatments. (A) Soil temperature in di!erent treatments averaged over sites. (B) Soil temperature with solarization at di!erent sites.
Table 7 E!ect of soil solarization compared with and without nematicide treatments on Meloidogyne javanica infestation of 2-month-old Sesbania seedlings at four farms in western Kenya Treatment
Solarization (1 m) Solarization (2 m) Bare bed#nematicide Bare bed Bare bed (insulated) SED F probability
Lela
Yala
Gall index
Nematodes per plant
Gall index
1.2 1.1 1.7 3.0 3.1 0.44 (0.01
5.0 (0.39) 1.2 5.2 (0.47) 0.6 7.0 (0.07) 2.8 25.0 (0.06) 3.0 33.0 (0.10) 2.5 6.5 (0.08) 0.45 (0.01((0.01) (0.01
Maseno farm
Maseno Centre
Nematodes per plant
Gall index
Nematodes per plant
Gall index
Nematodes per plant
5.7 (0.17) 4.2 (0.69) 9.3 (0.04) 17.0 (0.04) 9.3 (0.03) 3.8 (016) 0.04 ((0.01)
1.2 1.1 0.7 2.3 1.8 0.36 (0.01
2.2 (0.07) 1.8 (0.08) 1.8 (0.05) 8.3 (0.05) 18.3 (0.01) 4.7 (0.01) 0.02 ((0.01)
1.0 0.9 0.8 1.3 1.3 0.21 0.13
2.3 (0.13) 1.8 (0.12) 1.5 (0.13) 0.3 (0.12) 7.0 (0.11) 1.8 (0.03) 0.03 (0.95)
Includes all stages of the nematode from J to J and adults; values in parentheses are fresh root weight in grams per plant. SED"standard error of di!erence of means.
populations than those in the bare plots. At Lela and Yala, solarization was particularly e!ective where it resulted in signi"cantly lower GI and nematode populations compared with bare plot controls and nematicide treatment. Di!erences in root populations were more striking if nematodes were expressed per g root, as root weights in untreated beds ranged between 0.01 and 0.1 g per plant compared with 0.07}0.69 g per plant in the solarized beds (Table 7). Seedlings in the solarized beds grew 3}4.5 times taller and accumulated 10}20 times
more biomass than in the unsolarized beds (Table 8). Although 1- and 2-months solarization treatments did not di!er signi"cantly in nematode infection, 2-month solarization signi"cantly improved seedling growth compared with 1-month solarization. At Lela and Yala, nematicide treatment did not bene"t the seedling growth compared with bare plot controls. At both sites in Maseno, the e!ect of solarization was comparable to that of nematicide treatment and both nematicide and solarization increased sesbania height growth by over 60% and
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
39
Table 8 E!ect of soil solarization compared with and without nematicide treatments on the growth of 2-month-old Sesbania seedlings at four farms infested with Meloidogyne javanica in western Kenya Treatment
Lela Height (cm)
Solarization (1 m) Solarization (2 m) Bare bed#nematicide Bare bed Bare bed (insulated) SED F probability
15.4 13.6 3.4 3.2 3.8 1.9 (0.01
Yala Dry weight (g plant\) 4.1 4.1 0.3 0.4 0.5 0.7 (0.01
Height (cm)
10.9 24.6 4.4 3.5 5.3 4.7 (0.01
Maseno farm
Maseno Centre
Dry weight (g plant\)
Height (cm)
Dry weight (g plant})
Height (cm)
Dry weight (g plant\)
4.5 13.5 0.4 0.4 0.3 2.6 (0.01
5.9 6.9 5.7 4.1 2.6 1.3 0.04
1.2 1.8 1.4 0.7 0.4 0.4 0.05
11.7 9.5 12.0 6.0 9.3 1.6 0.02
1.2 0.7 1.2 0.4 0.8 0.2 0.01
SED"Standard error of di!erence of means.
biomass by over 100%. An additional bene"t of solarization at all sites was a signi"cant reduction of weed populations in seedbeds.
4. Discussion Better growth of sesbania seedlings due to nematode control in the nursery con"rms the previous reports of the detrimental e!ect of Meloidogyne on sesbania in its early stages of growth (Desaeger and Rao, 2000a). The degree of nematode infection in the nursery largely determines the survival and growth of seedlings in the "eld. Poor growth of seedlings in the nursery means that transplanting may be delayed in the "eld. Nematode control in the nursery was particularly bene"cial when the seedbed soil was heavily infested with the nematode. At Lela, the survival and growth of nematode-infected seedlings was poor in the "eld, even though the nematode infestation was low. In contrast, the results at Maseno suggest that healthy seedlings survive and grow better in the early stages even if nematode infestations in the "eld are large. Large nematode populations in the nematicide treatments indicate that the chosen nematicides were probably ine!ective against the root-knot nematode. The results further suggest that (1) controlling of the endoparasitic Meloidogyne in a deep-rooted perennial such as sesbania is di$cult and (2) nematicide application has limited bene"cial e!ect on sesbania growth. Lower biomass production by sesbania at Lela (1998}1999) than at Maseno (1997}1998) was because of the drought in the 1998 short rains, which probably aggravated the nematode damage, particularly in the crop planted with nematode-infected seedlings. Drought was probably also responsible for the failure of nematode infestations to increase between 7 and 12 months at Lela. In contrast, fast growth and a large biomass at Maseno, despite high
nematode populations, was associated with greater and well-distributed rainfall. It appears that tolerance of sesbania to nematodes increases with age of the plant and nematode infection has a relatively limited impact on the crop under good growing conditions. High biomass production of sesbania even in the highly infested "eld at Maseno con"rms the previous observations that grown up sesbania is highly tolerant to Meloidogyne (Desaeger and Rao, 2000b). High biomass with (50% of the stand in some treatments at Lela indicates the high plasticity of sesbania to plant population, but it is doubtful whether relay-planted sesbania in standing cereal crops would show similar response to that of sole-planted crop over a 12-month growing period. Less nematode infection of direct seeded sesbania compared with transplanted sesbania in this study contradicts the results of our earlier pot studies (Desaeger and Rao, 1999) but con"rms the "eld results in Ethiopia (SteinmuK ller, 1995). Greater nematode density in relation to the smaller root system of direct seeded sesbania might be responsible for greater nematode infection of direct seeded sesbania than transplanted sesbania in the short-term pot studies. Greater nematode infection of transplanted sesbania in Ethiopia was attributed to nematode infection of the seedlings in the nursery (SteinmuK ller, 1995). However, no speci"c reason could be ascribed to less nematode infection of direct seeded sesbania compared to transplanted sesbania with healthy seedlings in this study. Some possible explanations include (1) decrease of nematode populations in the soil due to mortality of juveniles hatched from eggs following wet and dry spells before sesbania was sown (Maas, 1987), (2) reduction of nematode infection potential due to time lag from sowing to the development of a reasonable root system for nematode reproduction to occur, and (3) thinning of excess seedlings at 4 weeks served the purpose of a &trap crop' and reduced the nematode pressure.
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J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41
The method by which sesbania is established depends on the cropping system, relative planting time of sesbania to the crop(s) in intercropping, and land and labour constraints. If sesbania is to be grown as a pure crop with timely weed control under good rainfall, direct seeding appears to be better than transplanting, as production of seedlings incurs additional labour and bears the risk of nematode infection in the nursery. Timely weeding of sesbania is often not possible for most small-scale farmers because of competing labour demands from food and cash crops at the beginning of the season. As 4}6-weekold sesbania seedlings withstand weed competition better and allow weeding to be delayed to a later time, farmers may prefer to establish sesbania by transplanting. If sesbania is planted together with crops, it gets weeded along with crops. If both sesbania and crop are to be planted simultaneously at the start of the season, direct seeding of sesbania may be better than transplanting, as seedlings may reduce crop yields because of competition (Niang et al., 1996). However, transplanting may have an advantage over direct sowing if sesbania is to be relay-planted later in the season, as seedlings generally establish better in a standing crop. The extra growth period for seedlings in the nursery is advantageous when the growth period for tree in the "eld is short as in western Kenya. Sesbania relay-sown using seeds in standing maize crops often produced less biomass than sesbania relay-transplanted with seedlings due to poor plant stand and suppression of seedling growth by the competitive maize (Niang et al., 1996). Where sesbania establishment by transplanting is preferred over direct seeding, then production of healthy seedlings free from nematode infection is important to improve seedling survival and early growth. Soil solarization seems to o!er an e!ective and economical means of producing nematode-free seedlings to small-scale African farmers. The e!ectiveness of solarization di!ered among sites because of rainfall during solarization, di!erences in soil characteristics and interference from shade at some sites. The soil temperature increase achieved by solarization at Lela and Yala is within the range for e!ective control of Meloidogyne and most other soil-borne pathogens (Maas, 1987). Solarization had a limited e!ect at Maseno Centre due to low heat retention capacity of coarse sand in the upper 30 cm, shade from big trees surrounding the seedbeds and rainfall during solarization. This technique was also less e!ective at Maseno farm probably because of a 3-day interruption to solarization due to theft of plastic. The soil temperature at this site following solarization was probably not lethal to all plant-parasitic nematodes, although similar temperature increments gave good results earlier (Kamra and Gaur, 1998; Gaur and Dhingra, 1991). Similar levels of soil nematode populations in both the planting methods at harvest of sesbania point out that none of the "eld establishment methods can reduce the
risk of root-knot nematodes a!ecting the nematodesusceptible crops following sesbania cover crops. As nematicide use cannot be justi"ed for cover crops such as sesbania and arable crops, e!orts have to be made to identify nematode-resistant sesbania germplasm. Acknowledgements The senior author was seconded to ICRAF by the Flemish O$ce for Development Cooperation and Technical Assistance (VVOB), Belgium and the Swedish International Development Cooperation Agency (Sida) has provided funds for the research reported here. We sincerely thank Dr. John Bridge, Senior Nematologist, CABI Bioscience, UK, for providing helpful comments on the draft of this paper. References Buresh, R.J., Tian, G., 1997. Soil improvement by trees in sub-Saharan Africa. Agroforest. Systems 38, 51}76. Desaeger, J., Rao, M.R., 1999. The root-knot nematode (Meloidogyne spp.) problem in sesbania fallows and scope for managing it in western Kenya. Agroforest. Systems 47, 273}288. Desaeger, J., Rao, M.R., 2000a. Infection and damage potential of Meloidogyne javanica on Sesbania sesban in di!erent soil types. Nematology 2, 169}178. Desaeger, J., Rao, M.R., 2000b. Parasitic nematode populations in natural and improved cover crops and their e!ects on subsequent crops in Kenya. Field Crops Res. 65, 41}56. Gaur, H.S., Dhingra, A., 1991. Management of Meloidogyne incognita and Rotylenchulus reniformis in nursery-beds by soil solarization and organic soil amendment. Rev. NeH matol. 14, 185}195. Kamra, A., Gaur, H.S., 1998. Control of nematodes, fungi and weeds in nursery beds by soil solarization. Int. J. Nematol. 8, 46}52. Karachi, M., 1995. Sesbania species as potential hosts to root-knot nematode (Meloidogyne javanica) in Tanzania. Agroforest. Systems 32, 119}125. Kwesiga, F.R., Beniest, J., 1998. Sesbania improved fallows for eastern Zambia: an extension guideline. International Centre for Research in Agroforestry, Nairobi, 56 pp. Kwesiga, F.R., Franzel, S., Place, F.M., Phiri, D., Simwanza, C.P., 1999. Sesbania sesban improved fallows in eastern Zambia: their inception, development and farmer enthusiasm. Agroforest. Systems 47, 49}66. Maas, P.W.Th., 1987. Physical methods and quarantine. In: Brown, R.H., Kerry, B.R. (Eds.), Principles and Practice of Nematode Control in Crops. Academic Press, Sidney, pp. 265}293. Niang, A., Gathumbi, S., Amadalo, B., 1996. The potential of shortduration improved fallows for crop productivity enhancement in the highlands of western Kenya. In: Mugah, J.O. (Ed.), People and Institutional Participation in Agroforestry for Sustainable Development. Kenya Forestry Research Institute, Kenya, Muguga, Nairobi, pp. 218}230. Rao, M.R., Niang, A., Kwesiga, F., Duguma, B., Franzel, S., Jama, B., Buresh, R., 1998. Soil fertility replenishment in sub-Saharan Africa: new techniques and the spread of their use on farms. Agroforest. Today 10 (2), 3}8. Smaling, E.M.A., Nandwa, S.M., Janssen, B.H., 1997. Soil fertility in Africa at stake. In: Buresh, R.J., Sanchez, P.A., Calhoun, F. (Eds.), Replenishing Soil Fertility in Africa. SSSA Special Publication No. 51, Madison, WI, USA, pp. 47}62.
J. Desaeger, M.R. Rao / Crop Protection 20 (2001) 31}41 Southey, J.F. (Ed.), 1986. Laboratory Methods for Work with Plant and Soil Nematodes. Reference Book 402, Ministry of Agriculture, Fisheries and Food, 202 pp. SteinmuK ller, N., 1995. Agronomy of the N -"xing fodder trees Sesbania sesban (L.) Merr. and Sesbania goetzii harms in the Ethiopian highlands. Dissertation UniversitaK t Hohenheim, Institut fur P#anzenproduktion in den Tropen und Subtropen, Verlaug Ulrich E. Grauer, Stuttgart, Germany, 230 pp.
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Szott, L.T., Palm, C.A., Buresh, R.J., 1999. Ecosystem fertility and fallow function in the humid and subhumid tropics. Agroforest. Systems 47, 163}196. Zeck, W.M., 1971. A rating scheme for "eld evaluation of root-knot nematode infestations. P#anzenschutz Nachr. Bayer AG 24, 141}144.