Effects of 6 years of continuous no-till or puddling systems on soil properties and rice (Oryza sativa) yield of a loamy soil

Soil & Tillage Research, 8 (1986) 181--200

181

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

EFFECTS OF 6 YEARS OF CONTINUOUS NO-TILL OR PUDDLING SYSTEMS ON SOIL PROPERTIES AND RICE (ORYZA SATIVA) YIELD OF A LOAMY SOIL

R. LAL

International Institute of Tropical Agriculture, Oyo Road, PMB 5320, Ibadan (Nigeria) (Accepted for publication 11 December 1985)

ABSTRACT Lal, R., 1986. Effects of 6 years of continuous no-till or puddling systems on soil properties and rice (Oryza sativa) yield of a loamy soil. Soil Tillage Res., 8: 181--200. Rice response to no-till and puddling methods of seedbed preparation were evaluated for four levels of N application: 0, 50, 100 and 150 kg ha -L N. Growing 11 consecutive crops of rice on an Aeric Tropaquent in southwestern Nigeria produced mean grain yields of 3.5 and 5.5 t ha -~ with no-till and 3.9 and 5.6 t ha -1 with puddling systems at 0 and 150 kg ha -1 N per crop, respectively. In general, puddled treatments yielded more at a low level of N than no-till plots and the rice grain yields were lower for the second than the first growing seasons. The mean organic carbon content measured after 6 years in the 0--5-cm layer was 2.2 and 1.7% (w/w), respectively, for the no-till and the puddled seedbeds. In the 5--10-cm layers, however, the no-tilled soil contained less organic carbon than the puddled, viz. 1.1 and 1.7% (w/w), respectively. The mean bulk densities of notill and puddled soils were 0.96 and 1.24 Mg m -3 for the 0--1-cm layer and 0.91 and 1.07 Mg m -3 for the 1--2-cm layer. The clay content of the 0--1-cm layer was higher in the puddled (36.6%, w/w) than in the no-till treatment (34.0%, w/w). The surface 0--1- and 1--2-cm layers of the no-till system retained significantly more water at water potentials from 3 kPa to 1.5 MPa than the puddled soil, viz. 66.5 vs. 51.1% (w/w) for the 0--1-cm depth and 51.1 vs. 49.5% (w/w) for the 1--2-cm depth at 3 kPa and 24.7 vs. 21.5% (w/w) for the 0--1-cm depth and 20.5 vs. 20.2% (w/w) for the 1--2-cm depth at 1.5 MPa, respectively. The differences in soil moisture retention in favor of no-till were more pronounced at high than at low soil moisture potentials.

INTRODUCTION T h e r e are t w o p r e d o m i n a n t a r a b l e l a n d u s e s y s t e m s i n s o u t h w e s t N i g e r i a . T h e u p l a n d s , p r e d o m i n a n t l y c o m p r i s i n g easily c o m p a c t e d a n d e r o d e d A l f i s o l s , are t r a d i t i o n a l l y u s e d a c c o r d i n g t o s h i f t i n g c u l t i v a t i o n a n d r e l a t e d b u s h f a l l o w s y s t e m s f o r soil f e r t i l i t y r e s t o r a t i o n i n a n e x t e n s i v e l a n d u s e system. In contrast, the wetlands comprise Inceptisols of relatively high f e r t i l i t y a n d w i t h f a v o r a b l e soil m o i s t u r e r e g i m e , b u t h i t h e r t o u n d e r u t i l i z e d or unutilized because of health hazards and lack of appropriate technologies.

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182 However, if appropriate technologies were available, the problems associated with introducing continuous cultivation on tropical wetlands may not be as severe as those for uplands because there is no soil erosion hazard and because of the relatively small importance of soil structure. In fact, soil structure is deliberately destroyed by puddling or wet tillage to decrease percolation losses and facilitate water ponding. However, puddling is an energy-intensive process and the need for it differs among soils. Tillage requirements for irrigated rice (Oryza sativa) vary among soils of varying percolation rates and textural and structural properties. For the same soil, rice response to tillage methods depends on exogenous factors, e.g., microclimate, supplemental irrigation, crop residue management and fertilizer rate and m e t h o d of application. For a heavy-textured and well-structured soil containing high-activity clay near Los Bafios (Philippines), Mabbayad and Buencosa ( 1 9 6 7 ) r e p o r t e d that economic yields were obtained without puddling (wet tillage), provided weeds were effectively controlled. For Mahas clay at the experimental farm of the International Rice Research Institute (IRRI), also at Los Bafios, Bradfield (1970) proposed a rice-based multiple cropping system, recommending that rice be grown on the seedbed with a ridge--furrow system in an unpuddled soil. In a follow-up study, Sanchez (1973) also observed little differences in either grain yield or nutrient uptake, although puddling reduced percolation losses. However, in contrast, De Datta and Karim (1974) reported 2.5 times more nitrogen use efficiency in puddled than in unpuddled soil. It seems that poorly structured soils of heavy texture and softs that are easily dispersed on wetting do not respond to puddling. Croon (1978) studied the effects of three tillage methods on the yield of irrigated rice on a Vertisol in Kenya and observed no differences in yield on puddled and unpuddled treatments. Bogging down of the tractor in flooded land, however, was a major hazard in conducting wet tillage operations. Therefore, providing adequate drainage is an important consideration for poorly drained flood-plain soils of low permeability. In Surinam, Ten Have (1967) and Scheltema (1974) observed no benefits of puddling; in fact, grain yield was improved by dry tillage. An objective of tillage operations in highly permeable coarse-textured softs in relation to rice is the reduction of percolation and leaching losses. Experiments conducted in western Nigeria on such soils indicated equivalent or lower rice yield on unpuddled soil depending on the crop residue management (Lal, 1983). Curfs (1976) observed 10--20% yield reduction on unpuddled compared with puddled soil. The adverse effects of no-till, probably due to anaerobic decomposition of rice straw, are usually not observed in the first one or two crops (Maurya and Lal, 1979; Rodriguez and Lal, 1985). Reduction in percolation can be better achieved by mechanical compaction than by wet tillage (Ogunremi et al., 1985). Little research data exist regarding the long-term effects of methods of

183

seedbed preparation on rice yield and soil properties. The objective of this investigation, therefore, was to study the effects of tillage methods and different rates of N application on rice grown in a hydromorphic soil for 6 consecutive years. MATERIALS AND METHODS

A series of experiments was c o n d u c t e d from 1979 to 1983 at the International Institute of Tropical Agriculture (IITA), near Ibadan, Nigeria. The mean annual rainfall of this region ranges from 900 to 1300 mm and is received over t w o distinct growing seasons -- the first from March to July and the second from August to November. There was a gap of approximately 4 weeks between harvesting of the first-season and planting of the second-season crops. This experiment was conducted on a hydromorphic valley-bottom soft. The soil is a poorly structured, medium textured loamy, mixed isohyperthermic Aeric Tropaquent. These experiments were established in 1978 and the first-year results have been reported by Rodriguez and Lal (1985). A factorial experiment o f 2 tillage systems and 4 nitrogen levels was arranged in a split-plot design with 6 replications. Tillage systems, as the main plots, included no-till and conventional puddling methods. In the notill system, there was no pre-planting mechanical seedbed preparation. Weeds were controlled with two sprayings of paraquat at 0.5 kg ha -1 a.i. On all no-till plots, the rice straw from the previous crop was chopped and retained on the soil surface. The puddling treatments consisted of both dry and wet tillage. These tillage operations were performed with a rotovator m o u n t e d on a Landmaster power tiller (Fig. 1). On puddled plots, the rice straw from the previous crop was removed from the field before tilling. There were 4 nitrogen levels: 0 (No), 50 (N1), 100 (N2) and 150 (N3) kg ha -1 N. The nitrogen was applied in equal applications at transplanting and at 30 and 60 days after. All plots received a uniform application of 35 kg ha -1 P as superphosphate and 50 kg ha -1 K as muriate of potash at transplanting. The plot size was 25.8 m 2 (6 X 4.3 m). Each plot had an independent drainage/irrigation channel. Four-week-old rice seedlings of cultivar ITA 212 were transplanted in mid-March and mid-August for the first- and second-season crops, respectively. To control stem borer, the insecticide Furadan 10 G was applied 3 times: 1, 4 and 8 weeks after transplanting at rates of 1, 2 and 3 kg ha -' a.i., respectively. Weekly counts were made of the number of tillers in 8 hills per plot and plant height was measured. Grain and straw yields were measured at maturity. Leaf samples from the 1980 crop were dried, milled and passed through a 0.5-mm sieve. Total N was analysed by the Kjeldahl method. P and K were determined by the metavandate and flame p h o t o m e t e r

184

Fig. 1. Dry (above) and wet (below) tillage in IITA's rice paddies (Photographs courtesy of Mr. E. Oro and Mr. N. Navasero). m eth o d , respectively. All ot her nut r i e nt elements were analysed spectrophotometrically. At the end of the 1980 second season, soil samples were obtained for 0--1-, 1--2-, 2--5- and 5--10-cm depths for determination o f soil physical and chemical properties. Soil bulk density and p e n e t r o m e t e r resistance

185 were monitored in the field. Saturated hydraulic conductivity was determined on 100-cm 3 cores using a constant head permeameter. Soil moisture retention was obtained on disturbed (unsieved) samples using tension table and pressure plate extractors. Soil chemical properties, organic C (by dichromate oxidation), total N (by Kjeldahl digestion), Bray-1 P, 1N ammonium acetate-extractable Ca, Mg, K, Na and Mn were analyzed. RESULTS AND DISCUSSION

Soil chemical properties The effects of tillage and nitrogen treatments on soil chemical properties for the 0--5-, 5--10- and 10--20-cm depths are shown in Tables I, II and III. In the 0 - - 5 ~ m layer, soil organic carbon content was higher in no-till than in puddled plots for all levels of N application (Table I). The mean organic carbon c o n t e n t was 2.2 and 1.7% for the no-till and puddled plots, respectively. Total nitrogen content was significantly higher in the no-till than in the puddled treatment, being 0.26 and 0.20% (w/w), respectively. The available P content of the soil was low, b u t slightly higher in the no-till plots. Exchangeable calcium and magnesium contents were 8.5 and 2.5 meq per 100 g for no-till in comparison with 7.3 and 2.1 meq per 100 g for the puddled treatments. The exchangeable K and Na contents were significantly higher in the no-till plots. The Mn contents and total acidity were n o t significantly different among treatments. In contrast to the 0--5-cm layer, the organic carbon content (1.1 vs. 1.7%, w/w) and total nitrogen (0.14 vs. 0.18%, w/w) of the 5--10-cm depth were lower in the no-till plots (Table II). Once again, the available P content was low. There was no significant effect of tillage methods on exchangeable calcium, magnesium, potassium, sodium, manganese and total acidity. In the 10--20-cm layer, the organic carbon c o n t e n t was n o t significantly different between tillage treatments (Table III). The mean organic carbon c o n t e n t was 1.0% (w/w) for the no-till and 1.2% (w/w) for the puddling treatment. However, total nitrogen content was higher in the puddled soil (0.17 vs. 0.12%, w/w). There was no effect of tillage methods or nitrogen levels on other variables presented in Table III.

Soil physical properties Compaction The bulk density of the 0--1- and 1--2-cm layers of the no-till plots was lower than that of the puddled treatments (Table IV). The mean bulk density for the no-till and puddled soils was 0.96 and 1.24 Mg m -3 for the 0--1-cm layer and 0.91 and 1.07 Mg m -3 for the 1--2-cm layer, respectively. In contrast, the bulk density of the 2--5- and 5--10-cm layers was higher for no-till. The mean bulk density for these layers was 1.1 and 0.95 Mg

No No N1 N, N2 N2 N~ N~

NT CT NT CT NT CT NT CT 0.45 0.46 0.64

2.3 1.9 2.5 1.5 1.8 1.7 2.2 1.7

Organic carbon (%, w/w)

0.023 0.040 0.057

0.27 0.21 0.28 0.19 0.25 0.18 0.27 0.22

Total nitrogen (%, w/w)

~NT = no-till; CT = conventional puddling.

LSD (0.05) Tillage (T) Nitrogen (N) T × N

Nitrogen

Tillage

Treatments ~

2.6 1.6 2.3

2.4 1.0 1.9 1,2 1.7 1.7 4,1 0.7

Bray-1 P (ug g-~)

1.1 0.9 1.2

8.9 7.8 9.1 7.1 7.7 7.3 8,4 7.2

Ca

0.3 0.3 0.4

2.6 2.3 2.6 1.9 2.4 2.2 2.5 2.1

Mg

0.04 0.04 0.06

0.19 0.17 0.17 0.13 0.18 0.13 0.16 0.12

K

0.2 0.2 0.3

1.4 0.7 0.7 0.5 0.8 0.5 0.5 0.5

Na

0.03 0.02 0.02

0.32 0.35 0.34 0.35 0.36 0.34 0.33 0.36

Mn

Exchangeable cations (meq per 100 g)

Effects of tillage methods and nitrogen application on soil chemical properties of the 0--5-cm layer

TABLE I

0.06 0.06 0.09

0.09 0.09 0.11 0.11 0.21 0.10 0.14 0.09

Total acidity (meq per 100 g)

b.a O0 O~

No No N1 N, N2 N2 N3 N3

NT CT NT CT NT CT NT CT 0.66 0.54 0.77

0.9 1.9 1.0 1.6 1.4 1.4 1.1 1.8

Organic carbon (%, w/w)

0.011 0.27 0.038

0.14 0.18 0.15 0.17 0.14 0.19 0.12 0.19

Total nitrogen (%, w/w)

~NT = no-till; CT = conventional puddling.

LSD (0.05) Tillage (T) Nitrogen (N) T × N

Nitrogen

Tillage

Treatments'

1.6 1.3 1.8

2.3 1.0 1.0 0.9 0.7 0.6 2.4 0.7

Bray-1 P (~g g - ' )

0.9 0.9 1.2

7.4 8.5 7.4 7.4 8.1 7.8 7.6 7.7

Ca

2.7 2.8 4.0

2.3 2.4 2.3 5.3 4.8 2.3 2.3 2.0

Mg

0.04 0.02 0.03

0.14 0.14 0.11 0.14 0.12 0.11 0.11 0.11

K

0.4 0.3 0.4

0.9 0.9 0.8 0.9 0.8 0.8 0.5 0.7

Na

0.05 0.02 0.03

0.34 0.32 0.34 0.36 0.35 0.34 0.32 0.36

Mn

Exchangeable cations (meq per 100 g)

Effects of tillage methods and nitrogen application on soil chemical properties of the 5--10-cm layer

TABLE II

0.12 0.13 0.18

0.10 0.12 0.10 0.13 0.25 0.10 0.09 0.10

Total acidity (meq per 100 g)

No No N1 N~ N: N~ N3 N3

NT CT NT CT NT CT NT CT 0.32 0.40 0.57

1.0 1.4 1.2 1.0 1.0 1.3 0.9 1.0

Organic carbon (%, w / w )

' N T = no-till; CT = c o n v e n t i o n a l puddling.

LSD (0.05) Tillage (T) Nitrogen (N) T × N

Nitrogen

Tillage

Treatments ~

0.039 0.040 0.057

0.12 0.17 0.10 0.18 0.12 0.17 0.14 0.14

Total nitrogen (%, w / w )

0.7 0.4 0.6

1.3 1.1 0.9 1.0 1.0 0.5 1.5 0.7

Bray-1 P (ug g-' )

0.4 0.9 1.3

7.4 7.8 7.4 7.0 8.1 7.5 7.5 7.4

Ca

1.7 1.9 2.7

2.3 2.9 2.3 2.3 2.5 2.4 2.4 2.3

Mg

0.01 0.01 0.02

0.12 0.13 0.10 0.12 0.11 0.11 0.10 0.11

K

0.2 0.2 0.3

0.8 0.8 0.7 0.7 0.8 0.8 0.6 0.6

Na

0.06 0.02 0.03

0.31 0.34 0.30 0.35 0.31 0.35 0.30 0.35

Mn

Exchangeable cations ( m e q per 100 g)

Effects of tillage m e t h o d s and nitrogen application on soil chemical properties o f the 1 0 - - 2 0 - c m layer

T A B L E III

0.02 0.03 0.04

0.07 0.12 0.08 0.09 0.08 0.14 0.10 0.09

T o t a l acidity ( m e q per 100 g)

b-a 00 O0

0.23 0.26 0.36

20 34 20

10.1 41.3 17.1 11.9 9.4 16.2 5.1 10.7 0.25 0.20 0.28

0.89 1.08 0.84 1.05 0.94 1.16 0.97 1.00

Db

21.1 11.6 16.4

9.2 36.7 8.1 13.7 7.6 15.9 6.7 13.0

PR

1--2 c m

0.20 0.24 0.35

1.11 1.00 1.01 0.91 1.01 0.96 1.27 0.92

Db

23.8 8.0 11.2

15.9 17.9 9.7 12.2 11.7 13.4 15.7 9.1

PR

2--5 c m

0.18 0.18 0.26

1.59 1.15 1.51 1.21 1.44 1.17 1.57 1.11

Db

17.3 10.1 14.3

27.7 7.1 27.7 5.1 36.7 6.4 37.8 4.2

Pit

5--10 cm

0.13 0.17 0.23

1.29 1.40 1.40 1.22 1.22 1.08 1.31 1.26

Db

]4.9 15.2 21.4

34.3 39.7 26.5 30.0 43.2 28.2 42.8 31.5

Pit

10--20 cm

6.6 9.6 13.6

< 0.001 8.8 11.5 5.1 3.1 4.7 6.2 1.7

0--5 c m

11.7 11.1 19.6

< 0.001 1.1 13.8 0.1 16.6 2.7 1.0 0.3

5--10 cm

Saturated hydraulic c o n d u c t i v i t y ( c m h TM )

aD b -- d r y b u l k d e n s i t y (Mg m 3); PR = p e n e t r o m e t e r r e s i s t a n c e ( k P a ) ; N T = no-till; C T = c o n v e n t i o n a l p u d d l i n g .

LSD ( 0 . 0 5 ) Tillage ( T ) Nitrogen (NT) T × N

NO No N, N~ N2 N2 N3 N3

NT CT NT CT NT CT NT CT

0.98 1.20 0.75 1.23 1.05 1.36 1.04 1.16

Db

Nitrogen

Tillage

PR

0--1 c m

Treatments

Effects o f tillage m e t h o d s a n d n i t r o g e n a p p l i c a t i o n o n p h y s i c a l p r o p e r t i e s o f d i f f e r e n t soil layers a

T A B L E IV

Oo ¢O

190 m -3 for the 2--5-cm depth and 1.53 and 1.16 Mg m -3 for the 5--10-cm depth for no-till and puddling treatments, respectively. Although there were no consistent trends, bulk density of the 10--20-cm layers was generally higher in no-till treatments (1.24 vs. 1.30 Mg m-3). The penetrometer resistance followed a trend similar to that of soil bulk density (Fig. 2). In the surface 0--1- and 1--2-cm layers, the penetrometer resistance was lower in no-till than in puddled treatments. However, below 3.5-cm depth, the penetrometer resistance of no-till plots was higher. There was no consistent trend in the saturated hydraulic conductivity in relation to tillage or nitrogen treatment (Table IV). The saturated hydraulic conductivity, though variable, was generally high. This variation is to be expected when measurements are made on small cores where cracks next to the cylinder walls can create major differences in water flux. Texture The data in Table V show the percentage of sand, silt and clay in the 0--1-, 1--2- and 2--5-cm layers of plots subjected to different treatments. The clay content of the 0--1-cm layer was significantly higher in puddled than in no-till plots (36.6 vs. 34.0%, w/w). In no-till plots there was more sand (31.1 vs. 29.9%, w/w) and silt (34.9 vs. 33.5%, w/w), but the differences were not statistically significant. In the 1--2-cm layer, the no-till treatments had more silt (34.1 vs. 32.4%, w/w) and less sand (29.4 vs. 31.2%, w/w). The particle size distribution of the 2.5-cm layer was not affected by the tillage treatments. Moisture retention The effects of tillage methods and nitrogen levels on the soil moisture retention of the 0--1-, 1--2- and 2--5-cm layers are shown in Tables VI, VII and VIII. Nitrogen application had no effect on moisture characteristics. Soil moisture retention for the 0--1- and 1--2-cm layers was influenced by tillage methods, while that of the 2--5-cm layer was n o t (Fig. 3). In the 0--1-cm depth, the soil from no-till plots retained more water than puddled treatments at all suctions. The differences in moisture retention were more apparent at low than high suctions. The effects of tillage methods on differences in moisture retention in the 1--2-cm layer were similar, but less pronounced than in the 0--1-cm depth. In the 2--5-cm layer there were slight or no effects of tillage methods on moisture retention (Table VIII). Generally, the response of moisture retention properties to tillage methods was partly attributed to differences in soil organic matter content. The surface layers of no-till plots had more soil organic carbon content than the puddled soil. Tillage-induced differences in soil texture may also have influenced soil moisture retention properties.

191 TABLE V Effects of tillage methods and nitrogen application on soil texture (%, w / w ) o f different layers Treatments 1

0--1 cm

1--2 cm

2--5 cm

Tillage

Nitrogen Sand

Silt

Clay

Sand

Silt

Clay

Sand

Silt

Clay

NT CT NT CT NT CT NT CT

No No N, N, N2 N2 N3 N3

30.6 29.7 29.5 29.3 31.6 27.7 32.5 32.9

35.6 32.4 36.8 34.9 32.9 33.9 34.1 32.9

33.8 37.9 33.7 35.8 35.5 38.4 33.4 34.2

28.8 31.2 27.9 31.6 30.3 28.1 30.6 33.9

34.0 33.2 34.9 31.4 32.5 34.2 34.9 30.9

37.2 35.6 37.2 37.0 37.2 37.7 34.5 35.2

29.9 30.5 29.9 30.3 31.3 30.1 31.9 32.1

33.5 31.9 33.5 34.2 31.8 32.9 31.9 31.9

36.5 37.6 36.6 35.5 36.9 37.0 36.2 36.0

3.2 4.8 7.6

1.9 2.8 4.4

2.3 3.4 5.4

2.9 4.1 5.9

1.5 2.3 3.7

2.4 3.6 5.7

3.8 4.1 5.8

1.4 1.7 2.4

3.7 3.0 4.2

LSD (0.05) Tillage (T) Nitrogen (N) T × N

~NT = no-till; CT = conventional puddling.

BULK DENSITY (Mgm-3)

09 0

Ji0

IjI

Ij2

IL3

PENETROMETER RESISTANCE (k Pa)

li4

,o

15

20

2

/ \

/P

It

sp

60

\

\ \ \

12

40

~NT

\

JO

3o_

\ \ \

i /

\

\

%

J

Fig. 2. Soil penetrometer resistance and bulk density measured during the dry season of 1980--1981, about 6 weeks after harvesting the previous season crop. P = puddling; NT = no-till.

192 TABLE VI Effects of tillage methods and nitrogen application on water retention characteristics of the 0--1-cm layer Treatments

Soil moisture retention (%, w/w) at different suctions (MPa)

Tillage'

Nitrogen

0

0.003

0.01

0.05

0.1

0.5

1.5

NT CT NT CT NT CT NT CT

No No Nl N, N: N2 N3 N3

82.1 67.8 103.3 68.8 71.8 66.1 78.1 61.3

60.8 52.4 82.1 50.7 57.6 53.2 65.6 48.0

56.9 44.9 63.9 45.7 51.5 43.8 59.1 42.3

40.2 29.7 42.9 32.6 35.7 32.0 40.1 29.7

31.9 27.5 36.8 24.3 30.5 27.6 32.0 25.5

22.6 21.7 29.1 21.2 25.4 23.9 25.6 18.3

24.7 22.1 26.2 21.2 23.8 23.9 24.1 18.6

3.6 5.3 8.5

2.4 3.6 5.7

3.0 4.4 7.0

2.2 3.3 5.2

2.4 3.6 5.8

2.6 3.8 6.1

2.3 3.4 5.4

LSD (0.05) Tillage (T) Nitrogen (N) T × N

'CT = conventional puddling; NT = no-till.

TABLE VII Effects of tillage methods and nitrogen application on water retention characteristics of the 1--2-cm layer Treatments

Soil moisture retention (%, w/w) at different suctions (MPa)

Tillage'

Nitrogen

0

0.003

0.01

0.05

0.1

0.5

1.5

NT CT NT CT NT CT NT CT

No No N, N, N~ N2 N3 N3

68.4 64.5 76.1 60.4 63.5 64.8 57.3 60.9

51.0 50.7 58.4 47.5 49.2 51.1 45.7 48.8

44.2 41.7 47.8 43.3 43.5 41.0 46.1 39.6

32.1 29.0 34.0 29.4 29.9 29.8 31.9 28.1

26.8 24.9 28.1 24.6 26.8 26.5 26.6 26.6

21.9 21.7 22.5 20.1 19.6 21.8 17.9 18.1

20.6 21.3 21.9 19.0 19.8 21.6 19.6 18.8

3.1 4.6 7.3

1.8 2.7 4.2

2.9 4.4 6.9

1.8 2.6 4.2

1.5 2.2 3.1

1.9 2.8 4.5

1.2 1.8 2.9

LSD (0.05) Tillage (T) Nitrogen (N) T × N

~CT = conventional puddling; NT = no-till.

193 TABLE VIII E f f e c t s of tillage m e t h o d s a n d n i t r o g e n a p p l i c a t i o n o n w a t e r r e t e n t i o n c h a r a c t e r i s t i c s of the 2--5-cm layer Treatments

Soil m o i s t u r e r e t e n t i o n (%, w / w ) at d i f f e r e n t s u c t i o n s (MPa)

Tillage 1

Nitrogen

0

0.003

0.01

0.05

0.1

0.5

1.5

NT CT NT CT NT CT NT CT

No No Nz N, N2 N2 N3 N3

66.2 61.8 69.0 61.5 61.6 60.6 57.8 60.9

50.9 49.9 54.1 48.0 49.9 49.0 46.8 48.8

39.2 40.5 39.3 39.7 38.7 39.6 39.6 39.6

28.4 28.8 28.6 28.4 27.6 29.2 27.6 28.7

24.4 26.0 24.4 24.2 24.0 25.5 24.4 24.9

19.6 21.4 19.6 20.9 18.9 21.4 19.5 18.9

18.9 20.9 18.6 19.2 18.9 20.3 19.3 18.3

5.1 5.1 7.2

5.2 4.4 6.2

1.3 1.7 2.5

1.5 1.8 2.5

1.5 1.7 2.4

2.4 1.7 2.4

2.3 1.3 1.9

LSD (0.05) Tillage ( T ) N i t r o g e n (N) T × N

'CT

=

conventional puddling; NT

=

no-till.

20tO"

A

O-Icm depth

I

B i-2

cm depth

o

\ \

\ \

00~

\ \ \

O( r~

~

4~

60

SOIL

MOS ITURE CONTEN(°/ To,V/V)

Fig. 3. Soil m o i s t u r e r e t e n t i o n c h a r a c t e r i s t i c s o f t h e surface layers as a f f e c t e d b y tillage m e t h o d s for soil samples o b t a i n e d d u r i n g t h e d r y s e a s o n o f 1 9 8 0 - - 1 9 8 1 . P = p u d d l i n g ; N T = no-till.

0.5 0.6 0.9

2.9 3.2 3.9 4.5 4.7 4.7 5.:[ 5.1

Y

20 12 17

86 87 109 100 107 105 121 116

T

4 4 5

106 104 112 111 115 112 117 116

H

1980 A

1.2 0.5 0.7

3.2 3.2 4.0 3.8 5.0 3.9 5.0 4.2

Y

1O 7 9

48 76 64 77 72 92 73 93

T

4 3 4

92 100 98 105 100 108 101 110

H

1980 B

0.9 0.6 0.8

2.0 3.8 2.9 4.8 3.6 4.5 4.0 5.1

Y

13 10 14

95 101 97 102 96 105 102 109

T

6 5 7

99 109 103 111 108 111 108 112

H

1981 A

1.2 0.7 0.9

4.7 4.9 5.3 5.7 5.2 5.6 5.5 5.8

Y

10 10 14

43 60 50 76 59 79 75 83

T

4 5 7

86 103 91 108 103 107 98 111

H

1982 A

0.6 0.5 0.7

2.6 4.0 2.8 4.7 3.8 4.9 4.8 5.1

Y

10 10 14

47 80 56 78 75 83 78 89

T

0.8 0.6 0.8

2.5 3.7 3.1 4.1 3.7 3.7 5.0 4.2

Y

1982 Bb

13 21 29

97 116 114 113 126 134 147 129

T

5 4 6

98 99 101 107 103 104 106 107

H

1983 A

1.2 0.7 1.0

5.9 4.9 6.1 6.0 7.2 6.2 7.4 6.4

Y

11 7 10

43 64 48 74 52 75 55 78

T

7 4 6

60 67 60 70 62 66 64 70

H

1983 B

1.4 0.6 0.8

3.1 3.8 4.1 4.6 4.8 4.9 5.5 5.0

Y

bplant height for 1982 second-season crop was not measured.

a A = first s e a s o n ; B = s e c o n d s e a s o n ; T = tillers m-2; H = p l a n t h e i g h t a t m a x i m u m tillering ( c m ) ; Y = g r a i n y i e l d (t ha - l ) N T = no-tillage; CT ffi c o n v e n tional puddling.

5 3 4

105 106 112 116 118 122 118 126

66 71 93 92 114 109 122 120

No NO N1 N, N2 N~ N3 N3

NT CT NT CT NT CT NT CT

12 9 13

H

T

Nitrogen

Tillage

L S D (O.O5) Tillage (T) N i t r o g e n (N) TXN

1979 B

Treatment

E f f e c t s of tillage m e t h o d s a n d n i t r o g e n a p p l i c a t i o n o n rice g r o w t h a n d g r a i n y i e l d a

TABLE IX

195

Rice growth and yield The data of 1978, reported by Rodriguez and Lal (1985), showed that grain yields were not significantly different under the two tillage systems (5920 for no-tillage vs. 5660 kg ha -1 for puddled treatments). However, there were significant differences between tillage systems in the root density when measured between four rice hills and in the K content at flowering. Rice in no-till plots had a lower root density and a higher K content than puddled plots. In the present study, seedling establishment and growth were generally slower in no-till than in puddled soil. The differences in tiller number and the maximum plant height were, however, less pronounced at later stages as is shown by the data of the second-season 1979 and the first-season 1980 crops (Table IX). With the continuous use of no-till, rice growth in unpuddled plots lagged behind the puddled treatments, particularly from the 1980 second-season crop onward. Puddled rice had a tendency to produce more tillers than no-till. This was particularly so in the first season of 1981, 1982 and 1983 and the second-season crops of 1980, 1982 and 1983. Tiller production also increased with increasing application of nitrogen, particularly for the no-till treatment. Within a tillage method, plant height also increased with increasing level of N application, though the differences were n o t always statistically significant between N2 and N3 levels. Both the maximum plant height at harvest and the tiller numbers per hill were lower in unpuddled than in puddled soil (Table IX). Even after 11 consecutive crops (and at least six additional crops before this tillage study was initiated) there was no indication of a decline in rice grain yield (Fig. 4). There were seasonal variations in grain yield, yield being higher in the first growing season than in the second. Better crop performance in the first season is probably due to the more favorable radiation level. The mean average yields for the 11 consecutive crops were 3.5 and 5.5 t ha -1 for no-till in comparison with 3.9 and 5.6 t ha-' for conventional puddling for zero and 150 kg ha -~ N, respectively. The effects of N application and tillage methods on rice grain yields for 8 consecutive crops are summarised in Table IX. For the first two crops, e.g., 1979 second season and 1980 first season, tillage methods had no significant effect on rice grain yield. However, the grain yield increased linearly with increasing level of N application (Figs. 5 and 6). A similar response was observed for the first-season crop in 1981 and the secondseason crop in 1983. Generally, the rice grain yields in favor of puddling were particularly conspicuous at low levels of N application. Similar results were obtained for the first-season crop in 1982 only (Fig. 5). The reverse was the case, however, for the first-season crops of 1980 and 1983 (Fig. 5). The optimum rate of N may be different for the tillage systems. There were also differences in N response during the first and second

0

I-

2-

3"

4-

2-

6-

,

1978

r

\

\

r

1979

-

f

1980

0kg'h°-IN

r

/'~f/ NT

i

..

19S(

(

1982

~

/~

{

'C

19e3

//"&

1.I

"~:K,\\ //

P-'r-.'~

kqho-t N

CROPSEQUENCE

"~\\z~./

150

L~

z

>-

_.

0

I

2-

3"

4-

5-

6-

7-

o

6

~

50

DO

I ~ . . / I El , ~

1980

N

tSO RATE

NT

.......=P

(k(Jho -i)

50

SEASON

100

1983

1982

150

P

NT

Fig. 5. (right). Rice grain y i e l d s for d i f f e r e n t rates o f N a p p l i c a t i o n for the first-season crops b e t w e e n 1 9 8 0 and 1 9 8 3 . P = puddling; NT = no-till.

Fig. 4. (left). Effects o f tillage m e t h o d s o n grain yield for 11 c o n s e c u t i v e rice crops w i t h o u t and w i t h 1 5 0 kg ha -~ nitrogen fertilizer.

(D

z

;:,,.

5 w

5

t

°

8L

t 979

SECOND

b.a Ob

197 FIRST

SEASON f982

f980

~

--.JoP

NT /

.

~

N

T

P

w )z

8-

f981

1983

NT

(9 7-

6"

-- ---.oP NT

.I J

f 4-

3"

2-

I0

~o

~o

J~ N

RATE

o

~o

~o

,~o

(kg ho-f )

Fig. 6. Rice grain yields for different rates o f N application for the s e c o n d - s e a s o n crops b e t w e e n 1 9 7 9 and 1 9 8 3 . P = puddling; N T = no-till.

seasons. For the two crops in 1983, the mean grain yield was 6.3 and 4.5 t ha -' for the first and second season, respectively. In the first season, rice grain yield increased with increase in N application for both tillage methods, with yields in unpuddled soil being higher than in puddled treatments for all levels of N application. There were also differences in incremental increase: for no-till 4, 22 and 4 kg grain k g -1 N between No and N~, N1 and N2 and N2 and N3 levels, respectively. The corresponding incremental increases for the puddled treatment were 22, 4 and 4 kg grain kg -~ N, The total yield in the no-till treatments was higher than with puddling for all levels of N application (Table IX). Yields trends were different in the second season, grain yield being generally higher for puddled treatments. The increase in rice grain yield with increase in N application for the no-till treatments was 20, 14 and 14 kg grain kg -1 N between No and N~, N1 and

198

N2 and N2 and N3 levels, respectively. In puddled treatments, the increase in yield was 16, 6 and 2 kg grain kg-' N for increasing N application between No and N1, NI and N2 and N2 and N3 treatments, respectively. G E NE R AL DISCUSSION

There were some adverse effects of crop residue on seedling establishment and rice growth in the no-till system. Some of the crop residue, no doubt, had decomposed within the 4-week interval between harvesting the previous crop and transplanting the succeeding crop. The rate of crop residue decomposition is generally high in this ecology (Jenkinson and Ayanaba, 1977). The effects may have been more severe for softs of another texture and in another ecology. Nevertheless, the crop residue should either be removed or burnt in situ to facilitate transplanting and other farm operations. Results of grain yields indicate that for these loamy soils, no-tillage with the appropriate chemical weed control produced rice grain yields comparable to those of conventional puddling. Differences in yield are particularly insignificant at fertilizer application rates of 100--150 kg ha-' N. In addition, the continuous no-till system created favourable soil physical and nutritional properties of the surface layer. The high soil organic carbon content in the surface layer of no-till plots is obviously due to retention of crop residue. High clay content of the surface 0--1-cm layer of the puddled soil is due to the settling of the clay fraction from the soil--water suspension following puddling. Within the 3--15-cm depth, the puddled soil has a lower bulk density and penetrometer resistance. This may be regarded as the direct effect of mechanical loosening. The lower bulk density and penetrometer resistance of the surface soil between 0- and 3-cm depth of the no-till plots are due to the high organic matter content and the concentration of roots within this layer (Rodriguez and Lal, 1985). More favorable soil moisture retention in the no-till plots is also due to high soil organic matter content. For softs with a relatively high clay content, there are no obvious advantages in rice yield in puddling over the no-till method of seedbed preparation. An identical rice response to different levels of N indicates similar losses of N by percolation, which may be rather low. High productivity of well managed wetlands is also evident from the grain yield data of the eight consecutive crops studied in this experiment. To obtain mean rice grain yields of 3.5--3.9 t ha-' per crop without fertilizer and 5.5--5.6 t ha-' per crop with 150 kg ha-' N, is an agronomically important consideration. These agronomic returns should be assessed in view of the relatively lower yields from uplands and severe degradation of soil resources due to accelerated soil erosion. The latter problem does not exist in well developed wetlands with adequate provisions for water management. In addition to health hazard based social taboos, land clearing, levelling

199

and water management of wetlands are challenges that deserve a high research priority. The results reported herein are particularly significant because Nigeria, similar to other countries of West Africa, is at the threshold of developing wetlands for boosting rice production towards attempts to attain self sufficiency. The knowledge of tillage and nitrogen requirements is timely for planning resource allocation to achieve the desired yields. There are obvious advantages of adopting the no-tiU strategy for rice production because it involves lower capital investment in farm machinery. The economical availability of chemicals for weed and pest control and the environmental consequences of using herbicides closer to the source of natural waters are obvious considerations for future investigations. CONCLUSIONS

(1) Equivalent rice grain yields were obtained from no-till and puddled seedbeds at a high fertilizer application rate of 150 kg ha -~ N. Generally, in unpuddled treatments without N application, lower yields were obtained. (2) Rice grain yields were generally higher in the first than in the second growing season, probably due to lower levels of radiation and build-up of pests. (3) The surface layer of unpuddled treatments had a higher soil organic matter and total nitrogen content and, at high soil water potentials, a higher water retention than puddled soil. (4) The surface layer of puddled treatments attained a higher bulk density and a lower hydraulic conductivity at harvest than the no-till plots. (5) The no-till system of producing transplanted, irrigated lowland rice is agronomically feasible for intensive use of tropical wetlands with soil of medium texture and poor structural properties.

REFERENCES Bradfield, R., 1970. Increasing food production in the tropics by multiple cropping. In: D.G. Aldrich, Jr. (Editor), Research for the World Food Crisis. Am. Assoc. Adv. Sci., Washington, DC, pp. 229--242. Croon, F.W., 1978. Zero tillage for rice on Vertisols. World Crops, 30: 12--16. Cuffs, H.P.F., 1976. Systems development in agricultural mechanization with special reference to soil tillage and weed control. H. Veenman and Zonen B.V., Wageningen, 179 pp. De Datta, S.K. and Karim, A.A.S.M.S., 1974. Water and nitrogen economy of rainfed rice as affected by soil puddling. Soil Sci. Soc. Am. Proc., 38: 515--518. Jenkinson, D.S. and Ayanaba, A., 1977. Decomposition of carbon-14 labeled plant material under tropical conditions. Soil Sci. Soc. Am. J., 41: 912--915. Lal, R., 1983. No-till Farming. IITA Monogr. Ser. 2, IITA, Ibadan, Nigeria, 64 pp. Mabbayad, B.B. and Buencosa, I.A., 1967. Tests on m i n i m u m tillage of transplanted rice. Philipp. Agric., 5: 541--555.

200 Maurya, P.R. and Lal, R., 1979. Influence o f tillage and seeding methods on flooded rice. In: R. Lal (Editor), Soil Tillage and Crop Production. IITA Proc. Set. 2, pp. 337--345. Ogunremi, L.T., Lal, R. and Babalola, O., 1986. Effects of tillage methods and water regimes on soil properties and yield of lowland rice from a sandy loam soil in southwest Nigeria. Soil Tillage Res., 6 : 223--234. Rodriguez, M.S. and Lal, R., 1985. Growth and yield of p a d d y rice as affected by tillage and nitrogen levels. Soil Tillage Res., 6: 163--178. Sanchez, P.A., 1973. Puddling tropical rice soils: I. Growth and nutritional aspects. Soil Sci., 115: 149--158. Scheltema, W., 1974. Puddling against dry plowing for lowland rice culture in Surinam. Pudoc, Wageningen, Agric. Res. Rep. 828, The Netherlands, 241 pp. Ten Have, H., 1967. Research and breeding for mechanical culture of rice in Surinam. Pudoc, Wageningen, Agric. Res. Rep., The Netherlands, 309 pp.