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cereal fodder intercropping systems in the semi-arid tropics of India
Field Crops Research 88 (2004) 227–237
Growth, yield, competition and economics of groundnut/cereal fodder intercropping systems in the semi-arid tropics of India P.K. Ghosh* National Research Centre for Groundnut, P.B. No. 5, Junagadh 362001, Gujarat, India Received 14 May 2003; received in revised form 30 November 2003; accepted 5 January 2004
Abstract Intercropping legumes with non-legume crops during the rainy season (wet season) is a common practice in the semi-arid tropics of India. Of late, the concept of intercropping has also been utilized in irrigated (dry season) situations. In a 2-year field study during the dry season (February–May), we assessed yield, competition and economics in a groundnut/cereal fodder intercropping system compared with monocropped groundnut. Maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum L.) were grown for fodder. One cutting for all and two cuttings (first at 50 days after sowing and second at 95 days after sowing) for sorghum and pearl millet were made. In intercrops one row of cereal fodder was sown between every three rows of groundnut (1:3). The green fodder yields and pod yield of groundnut were lower in intercropped than in monoculture plots. The highest green fodder yield in intercrops was recorded in pearl millet with two cuts (16.5 t ha1) followed by pearl millet with one cut (11.8 t ha1) and sorghum with two cuts (10.7 t ha1). In intercrops the growth and yield of groundnut were affected by cereal fodder and intensity of cutting. A significant (P < 0:05) reduction in leaf area index (LAI) and crop growth rate (CGR) was observed in the groundnut–pearl millet system over sole groundnut. Decrease in nodule mass at pod filling stages in groundnut ranged from 3.5 to 11.0% when intercropped with cereal fodders compared to sole groundnut crop. Groundnut yield was reduced more due to pearl millet and sorghum with two cuts. However, maize as the associated crop produced 9.0 t green fodder ha1 and affected the groundnut less with respect to pod yield (5.76% reduction), yield attributes, CGR, LAI and nodule dry mass. Of the two cutting situations under intercropping, one cut gave 9.9% higher yield of groundnut as compared to two cuts. A higher land equivalent ratio (LER) and relative crowding coefficient (RCC) value leads to a crop yield advantage. Accordingly, yield advantage was greater in case of the groundnut/maize association. The competition ratio (CR) is a better indication of performance than RCC. The CRs of pearl millet and sorghum with two cuts were greater than maize but the corresponding CRs of groundnut were less. Thus, pearl millet and sorghum were more competitive, and groundnut under these two crops was affected more. The maximum monetary advantage was also recorded for the groundnut/maize intercropping system. # 2004 Elsevier B.V. All rights reserved. Keywords: Zea mays; Sorghum bicolor; Pennisetum glaucum; Arachis hypogaea; Cereal fodder; Fodder yield; Intensity of cutting; Intercrops; Competition indices
1. Introduction * Present address: Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, Madhya Pradesh, India. Tel.: þ91-755-2730970; fax: þ91-755-2733310. E-mail address: [email protected] (P.K. Ghosh).
In recent days there is mounting interest in diversified agricultural production systems to obtain improved crop protection, increased productivity and
0378-4290/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2004.01.015
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profitability offered by many intercropping system. This may be due to some of the established and speculated advantages for intercropping systems such as higher yields, greater land-use efficiency and improvement of soil fertility through the addition of N by fixation and excretion from the component legume (Willey, 1979; Ofori and Stern, 1987). Groundnut (Arachis hypogaea L.) is traditionally intercropped with crops like pearl millet, maize and sorghum, and also with pigeon pea in groundnut-growing areas of India by marginal and sub-marginal farmers during rainy season (Reddy et al., 1980). Such legume/nonlegume mixtures probably reduce competition for nitrogen (N), since the legume depends mainly on its own N fixation while the cereal uses mineral N (Ofori and Stern, 1987; Rerkasem et al., 1988). Many studies of cereal/legume intercropping have shown that the quantity of N fixed by the legume depends on such factors as the morphology, density and competitive ability of the legume (Ofori and Stern, 1987), the effectiveness of the rhizobia symbiosis and the system of intercropping (Rerkasem and Rerkasem, 1988). India has traditionally been a livestock-rearing country. The increasing human population pressure and its ramifications resulted in a demand for more food, thus diverting the attention of farmers to food crop production and rendering forage farming a secondary priority. This neglect of forage crops led to a decline in the productivity of livestock (Mal, 1998). According to the National Commission on Agriculture, the green fodder requirement for the existing livestock in India is around 1136 Mt, whereas the availability is 695 Mt, indicating a 61% deficit in fodder supply (Singh and Roy, 1999). Further, fodder availability in the dry season is scarce and costly. Groundnut in the dry season (summer) is grown mainly in pure stands with irrigation. The crop is sown from the second fortnight of January to the first fortnight of February. Though this summer crop gives almost double the yield and profit of rainy season groundnut, recently doubts have been raised about the economic advantages of further investment by farmers in sole groundnut production due to higher labor cost and higher input requirement, particularly irrigation. Intercropping is a viable option in such situations. Of late, in irrigated situations during the dry season, intercropping of groundnut with vegetables (AICRPO,
1980; UNIAS, 1978) and with cereal fodders (Ghosh et al., 1999) has been reported. In the semi-arid tropics of central and western India, Yadav and Yadav (2001) also observed that to meet the shortage of fodder, it is a common practice to put some seed of maize/sorghum/ pearl millet in the groundnut field along with seed of groundnut where these crops are cut early for fodder and groundnut is raised as a seed crop. However, systematic study of this system in the dry season has not been done. The frequency of cutting (Spedding, 1971; Devkota and Rerkasem, 2000) and time of cutting of fodders (Brann and Juny, 1974) are known to affect the performance of legumes in mixtures but there is little information on the effects of cutting management and the economy of cereal/legume intercropping system. Therefore, the present study aims to explore the possibility of providing green fodder during the dry season from an intercropping system, and to assess the groundnut/cereal fodder intercropping system as a means of better resource management with respect to growth, productivity, competition and monetary advantage.
2. Materials and methods 2.1. Experimental site Field experiments were conducted at the research farm of the National Research Centre for Groundnut, Junagadh, Gujarat, India (708360 E longitude and 218310 N latitude at an altitude of 60 m above mean sea level) during two dry seasons (1997–1998). The experimental site is located in a semi-arid region with mean annual rainfall of 844 mm. In this region the onset of monsoon rains occurs in the third week of June but can start as late as the first week of August. The rainfall is confined to three-and-a-half months from June to September with practically negligible rainfall during winter and summer (October–May). The average maximum temperature from April to June is very high (37–44 8C) with a mean of 41 8C. In January, temperature falls to a minimum of 12 8C. It reaches a maximum of 42 8C in May. The soil is classified as Vertic Ustochrept, medium black, clayey, shallow (15–20 cm depth), highly calcareous in nature (pH 7.7). The soil is characterized by low organic carbon (0.55), available N (117–123 kg ha1) and
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available P (7.9–8.3 kg ha1), high in available K (318–328 kg ha1), high P fixation capacity (75–95%) and contains an appreciable amount of CaCO3 (Kanzariya and Patel, 1985). Groundnut, castor, wheat, cotton, pulses, sorghum and pearl millet are mainly grown on this soil. 2.2. Experimental and crop culture Cereal fodders, namely, maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum L.), sole as well as intercrops were sown simultaneously with groundnut (cv. GG 2, a Spanish bunch) in the first week of February. Initially 3–5 seeds of all cereals were planted per hill at a row spacing of 60 cm but the seedlings were thinned to one plant per hill 1 week after emergence giving a plant density of 50 103 ha1. For groundnut, row spacing of 30 cm was maintained giving a plant density of 300 103 ha1. These are very close to the optimum populations for these crops. In intercrops one row of cereal fodder was sown between every three rows of groundnut (1:3) and plant population of both the crops were adjusted as per area occupied by each crop. This way, cereal to cereal row distance in intercropping was 120 cm (Fig. 1). Sole cropping of groundnut and fodder were also maintained for comparison and for calculation of competition indices. One cutting for all and two cuttings for sorghum and pearl millet were made. The first cut was at 50 days after sowing (DAS) and second was at 95 DAS. Nine treatments comprised T1: sole groundnut, T2: sole maize, T3: sole sorghum, T4: sole pearl millet, T5: groundnut þ maize (one cut), T6: groundnut þ sorghum (one cut), T7: groundnut þ pearl millet (one cut), T8: groundnut þ sorghum (two cuts) and T9: groundnut þ pearl millet (two cuts), and were tested in a completely randomized block design. All treatments were replicated four times. Seeds were treated with appropriate fungicides for all the crops before sowing. A basal application of 50 kg P2O5, 30 kg K2O and 1/2 of the N (12.5 kg ha1) was applied to groundnut in the furrow before planting. The remainder of the N (12.5 kg ha1) was applied at 25 DAS. The cereal fodders received 60 kg N ha1, 40 kg P2O5, 30 kg K2O ha1 as basal. Twenty kilograms additional N ha1 was applied to the fodder crops after the harvest of the first cut in treatments where two cuts were planned. Urea (46.4% N), single
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superphosphate (16% P2O5) and muriate of potash (60% K2O) were used to supply N, P and K, respectively. The necessary plant protection, irrigation and other management practices were followed during crop growth. Crops were grown with irrigation. Nine irrigations were given at 10-day interval; in each irrigation 50 mm water was applied through flooding. The crop was hand-weeded once, 1 month after sowing to keep the field weed-free. No serious incidence of insects or diseases was observed. Plot sizes of 4:8 m 10 m were maintained. Crops were harvested manually by sickle from ground level and the total above-ground biomass was removed from each plot as per treatment and the fodder yield was recorded. The groundnut was uprooted manually at 105 days and pod yield was recorded. 2.3. Plant and soil sampling Groundnut plants from each plot were sampled for growth analysis at 15-day intervals between 15 DAS and harvest. The plant samples were oven-dried at 65 8C for 72 h to a constant weight and dry weight was recorded. Leaf area was estimated from area to dry mass ratio based on a sub-sample, whose area was measured on leaf area meter (LI-COR; Lincoln, NE). For comparison of growth analysis between middle rows and rows adjacent to fodder, groundnut plants were also sampled from four locations of each plot. Five plants were tagged for recording the tiller and plant height of fodder crops at each cutting. The plant height was measured from base of the plant to tip of the topmost leaf of plants. Three groundnut plants were uprooted with a ball of soil for recording nodulation. Keeping the root portion intact, the ball of soil was washed gently with clean running water followed by washing with camel hairbrush to dislodge any soil particles adhering to it. Nodules from roots were removed, counted and dry mass was measured (Vincent, 1970). Nitrogen content of shoot from a bulk sample was estimated at 30 and 60 days growth following micro-Kjeldhal method. 2.4. Growth analysis Crop growth rate (CGR), the increase in dry weight per unit ground area of crop in a unit time, was
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30 cm
230
60 cm
Sole groundnut
Sole fodder
Groundnut Fodder
30 cm
30 cm
3:1 row ratio
120 cm
Fig. 1. Planting pattern in intercropping system.
calculated as (W2 W1 )/(t2 t1 ), where W1 and W2 are dry weights at times t1 and t2, respectively, and expressed as g m2 per day. Net assimilation rate (NAR), the increase in dry weight per unit time per unit leaf area (g cm2 per day) was calculated as (W2 W1 )(ln L2 ln L1 )/(t2 t1 )(L2 L1 ), where L1 and L2 are leaf areas at t1 and t2 times. Leaf area index (LAI) was calculated as leaf area/ground area.
2.5. Competition indices and monetary advantages The yield advantage of intercropping was calculated according to Ofori and Stern (1987), Willey and Osiru (1972), and Willey and Rao (1980). The land equivalent ratio (LER) gives an accurate assessment of the greater biological efficiency of the intercropping situation and was calculated as LER ¼ ðYab =Yaa Þþ ðYba =Ybb Þ, where Yaa and Ybb are yields as sole crops
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and Yab and Yba are yields as intercrops. LER values greater than 1 are considered advantageous. LER has also been used to calculate monetary advantage. Relative crowding coefficient (RCC) is a measure of relative dominance of one component crop over the other in an intercropping system. For crop ‘a’ in association with ‘b’, Kab ¼ Yab Xba =ðYaa Yab ÞXab , where Xab is the sown proportion of ‘a’ in mixture of ‘b’ and Xba the sown proportion of ‘b’ in mixture of ‘a’. The product of two coefficients ðKab Kba Þ ¼ K; if K obtained in the system is greater than 1, there is a yield advantage, if K obtained in the system equals to 1, there is no yield advantage, if K in the system is less than 1, there is a yield disadvantage. Aggressivity is another index that represents a simple measure of how much the relative yield increase in ‘a’ crop is greater than that of ‘b’ crop in an intercropping system. It was calculated as Aab ¼ ðYab =Yaa Xab Þ ðYba =Ybb Xba Þ; if Aab ¼ 0, both crops are equally competitive, if Aab is positive, ‘a’ is dominant, if Aab is negative, ‘a’ is the dominated crop. Willey and Rao (1980) suggested the ratio of these terms, which they designated as competition ratio (CR), instead of taking the difference of two terms in aggressivity. The CR represents simply the ratio of individual LERs of the two component crops, but taking into account the proportion of the crops in which they were initially sown. CRa ¼ ðLERa =LERb ÞðXba =Xab Þ, and if CRa < 1, there is a positive benefit and the crop can be grown in association, if CRa > 1, there is negative benefit. The reverse is true for CRb. There is a large labor cost associated with growing the groundnut. Farmers are concerned mostly with total profit and the marginal benefit:cost ratio from investment in labor and inputs. The yield and economic performance of the intercropping was traced to decide whether groundnut yield and additional fodder yield are sufficient to justify farmers using this intercropping system. Moreover, none of the competition indices explains economic advantage of the intercropping system. Thus, we computed monetary advantage index (MAI) as MAI ¼ value of combined intercrops ðLER 1Þ=LER. The higher the index value, the more profitable is the cropping system. 2.6. Data analysis Data collected for various studies were subjected to the analysis of variance (ANOVA) appropriate to the
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design as given by Cochron and Cox (1958). Test of significance of the treatment difference was done on the basis of a ‘T-test’. The significant differences between treatments were compared with the critical difference at 5% level of probability.
3. Results 3.1. Fodder crops Since treatment year was not significant, pooled data of 2 years are discussed. The plant height of sorghum and pearl millet was comparatively greater than maize. In general, cereal fodder growth measured by plant height and tiller number was greater in second cut than first cut and also in monocrops than in intercrops (Table 1). On average, monocropped cereals produced 20% higher fodder yields than intercropped. The fodder yield was the highest in pearl millet with two cuts followed by pearl millet with one cut and sorghum with two cuts (Table 1), both in sole and intercropping systems. The lowest fodder yield was recorded in sorghum with one cut. The fodder yield in maize and sorghum with one and two cuts, and pearl millet with one cut were not different in intercropping systems, but were significantly different in sole cropping. 3.2. Groundnut 3.2.1. Growth The CGR of groundnut was low at initial stage, and attained its peak between 60 and 75 days (Fig. 2b). LAI followed a trend similar to CGR (Fig. 2a). The CGR and LAI of groundnut were reduced in association with fodder crops. The magnitude of reduction varied with component crops and number of cuttings. Except between 15 and 30 DAS, monocropped groundnut recorded significantly (P < 0:05) greater CGR at all stages over intercropped groundnut with all fodders and cuttings. However, up to 30–45 DAS, the CGR of groundnut with maize was significantly higher over sorghum and pearl millet with two cuts. A significant (P < 0:05) reduction in LAI (Fig. 2a) was observed in groundnut/pearl millet system over sole groundnut. However, maize/groundnut intercropping system reduced LAI the least. Fig. 2 shows that
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Table 1 Yields and growth attributes of fodders in intercrops and monoculture Plant height at first cut (cm)
Tiller number at first cut
Total green fodder yield (t ha1)
Total dry fodder yield (t ha1)
Sole cropping Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean
112.7 112.3 114.4 120.3 (143.6)a 118.5 (148.7)a 115.4
1.8 2.4 3.0 (4.6)b 3.5 (5.2)b 2.7
10.25 9.10 12.60 14.96 17.72 15.81
3.27 2.89 3.76 4.61 5.12 3.93
Intercropping Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean LSD 5%
103.3 107.6 110.3 111.3 (146.5)a 110.3 (139.2)a 108.6 NSc
1.9 2.6 2.3 (4.1)b 3.2 (4.9)b 2.5 0.54
9.00 7.98 11.81 10.80 16.50 13.7 3.04
2.64 2.19 3.55 3.16 4.83 3.27 0.76
Treatments
a
Plant height at two cuts. Tiller number at two cuts. c Not significant. b
8.0 7.0 6.0
LAI
5.0 4.0 3.0 2.0 1.0
SG
G+M
G+S (1 cut)
G+P (1 cut)
G+S (2 cut)
G+P (2 cut)
0.0
(a)
0
15
30
45
60
75
90
105
16.0 14.0 CGR (g m-2 day-1)
12.0 10.0 8.0 6.0 4.0 2.0 0.0 15-30
(b)
30-45
45-60
60-75
75-90
90-105
Days after sowing
Fig. 2. (a) Leaf area index and (b) crop growth rate of groundnut under different combinations of cereal fodder. G, M, S and P represents groundnut, maize, sorghum and pearl millet, respectively. The line above the bars indicates LSD at 5% probability.
the dry weight of groundnut expressed in terms of CGR was affected more than LAI due to shading effect of cereal fodders. There was 20.8 and 40.4% reduction in LAI and CGR in intercropped groundnut in association with pearl millet with two cuts over sole groundnut, and it was 9.5 and 30.7%, respectively, with maize. The NAR of groundnut in middle rows and in rows adjacent to cereal in intercropping system showed considerable differences. In rows adjacent to cereal, the NAR was less than the middle rows in all treatments; however, differences were significant in pearl millet with two cuts and sorghum with two cuts at all the three stages measured (Fig. 3). The NAR of groundnut between adjacent rows and middle rows in case of maize and pearl millet one cut at three stages and in sorghum one cut at 60–75 and 75–90 DAS was not different. 3.2.2. Nodulation and nitrogen content In general, nodule number and nodule mass at pod filling stage (60 DAS) were much lower in groundnut when cereals were used as intercrops as compared to sole groundnut. However, there were no marked differences in nodulation between groundnuts in sole and cereal intercropping system during initial stages of crop growth. Nodule number and nodule mass were
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(37.7 g); these were significantly (P < 0:05) reduced in association with fodders (Table 2). The magnitude of reduction in these yield attributes was more when two cuts were allowed. The lowest pod numbers (5.0), pod yield per plant (3.8 g) and 100-kernel mass (34.4 g) were recorded in association with pearl millet (two cuts). Maize as associated crop had less impact on yield attributes. The highest pod yield (2.43 t ha1) and harvest index (0.42) were recorded in sole groundnut. Pod yield of groundnut intercropped with cereals was reduced due to suppressive effect of fodder. Significant (P < 0:05) reduction in grain yield of groundnut and harvest index were recorded when two cuts of pear millet (2.01 t ha1, 0.34) and sorghum (2.04 t ha1, 0.34) were made. Two cuts of pearl millet and sorghum produced 0.18 and 0.16 t ha1, respectively, less grain yield of groundnut than their corresponding one cut (Table 2). 3.3. Yield advantages and competition indices
Fig. 3. Trend in the net assimilation rate of groundnut at three stages in the middle row and adjacent rows to cereal fodders. AR and MR represent adjacent row and middle row, while G, M, S and P represent groundnut, maize, sorghum and pearl millet, respectively. The line above the bars indicates standard error at 5% probability.
significantly higher in monocropped groundnut over its intercropped counterpart with all cereal fodders except maize. Decrease in nodule mass at pod filling stages ranged from 3.5 to 11.0% with cereal fodders compared to sole groundnut crop. There was 30% reduction in nodule mass in intercropped groundnut in association with pearl millet with two cuts compared to sole groundnut, and the reduction was 20% with maize. The N content in shoot followed the same trend to nodule number and its mass (Table 2). 3.2.3. Yield and yield attributes Sole groundnut recorded greater pod numbers (9.8), pod yield per plant (7.9 g) and 100-kernel mass
Yield advantage in terms of LER was greatest (1.68) in the groundnut/maize association. The lowest LER (1.34) was recorded in groundnut/sorghum association (Table 3). The RCC value was significantly greater (26.0) in groundnut/maize associated over all other combinations. The lowest RCC (8.7) was recorded in groundnut/pearl millet (two cuts). Table 3 reveals that the value of aggressivity of groundnut was negative and it was considered as the less-dominant crop in the system. Due to a positive value of aggressivity for associated cereals, fodder crops were the dominant crops in the present study. Among the cereal crops, pearl millet was more dominant than the others. The CR value of groundnut was less than those of the associated cereal fodders. 3.4. Monetary advantage Monetary advantage index followed the trend similar to LER (Table 3). The MAI was significantly higher in groundnut/maize association over all other treatments. The MAI due to groundnut/sorghum one cut and groundnut/pearl millet two cuts association was statistically the same. The lowest monetary benefit was recorded in groundnut/pearl millet one cut.
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Table 2 Nodulation, nitrogen content, yield, yield attributes and harvest index of groundnut under different combinations of fodder and number of cuttings Treatments
Nodule per plant
Nodule mass (mg per plant)
N content (mg per plant)
30 DASa
60 DAS
30 DAS
60 DAS
30 DAS
60 DAS
17.0 15.8 15.6 16.8 15.1 14.8 15.81 1.41
44.1 42.5 40.3 41.7 41.2 39.2 41.5 NS
186.0 179.5 171.5 165.4 172.5 169.8 177.1 13.6
165 159 155 151 148 144
353 312 282 288 260 254
Sole groundnut 10.7 Maize (one cut) 9.4 Sorghum (one cut) 9.3 Pearl millet (one cut) 8.9 Sorghum (two cuts) 9.2 Pearl millet (two cuts) 9.0 Mean 9.4 LSD 5% NS a
16.2
29.2
Hundred- Pods per kernel plant mass (g)
Pod yield Pod yield Harvest per plant (t ha1) index (g)
37.7 35.7 34.5 34.7 33.3 34.4 35.05 1.73
7.9 4.5 5.5 4.9 4.2 3.8 5.13 1.78
9.8 6.1 6.5 5.2 5.9 5.0 6.4 1.83
2.43 2.29 2.20 2.19 2.04 2.01 2.19 0.34
0.423 0.406 0.386 0.386 0.343 0.340 0.380 0.041
Days after sowing.
Table 3 Assessment of yield advantage under different competition treatments (unit price (Rs. kg1) of fodder and groundnut pods represent 1 and 15, respectively) Treatments
Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean LSD 5%
LERa
1.68 1.34 1.49 1.43 1.54 1.49 0.17
RCCb
25.98 17.35 8.74 10.67 11.7 14.88 5.34
Aggressivity
Competition ratio
Groundnut
Cereals
Groundnut
Cereals
1.93 1.69 2.03 1.99 2.32 1.99
1.93 1.69 2.03 1.99 2.32 1.99 0.54
0.38 0.40 0.32 0.34 0.29 0.34 NSd
2.64 2.45 3.06 2.92 3.42 2.28 0.78
MAIc
16543 14383 12656 13503 14699 14356 2897
a
Land equivalent ratio. Relative crowding coefficient. c Monetary advantage index. d Not significant. b
4. Discussion Monoculture production of cereal fodder or groundnut yielded higher than in the intercropped culture. This was partly the result of the higher plant population in the monocrops. In addition, the crop did not experience inter-specific competition. Superiority of green fodder yields of pearl millet over sorghum and maize was perhaps due to a higher number of tillers. Despite tiller formation, higher fodder yield obtained in maize with one cut than sorghum with one cut was possibly due to more rapid dry matter accumulation in maize. In intercrops the yield of groundnut was affected by cereal fodders and intensity of cutting. Reduction in yield of groundnut due to pearl millet and
sorghum was more than due to maize. Of the two cutting situations under intercropping, one cut gave relatively higher yield of groundnut compared to two cuts because of increased inter-specific competition between the component crops (Mandal et al., 1990). Competition for nutrients and light in intercropping systems is often interrelated, particularly for legume/ non-legume crop combinations. On low-N soils, the non-legume is often suppressed, but on high-N soils, the vigorous growth of the non-legume usually causes it to dominate over the legume by shading (Trenbath, 1976). In the present study, application of 20 kg N after first cut of sorghum and pearl millet produced more dry matter and plant height that caused adverse shading of the groundnut. This also explains why
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groundnut yield was low in case of two cuts as compared to one cut. These effects of intercropped pearl millet and sorghum were also prominent on CGR, LAI, nodule dry mass and yield attributes (pod numbers, pod yield per plant, 100-kernel mass). Nambiar et al. (1983) demonstrated that intercrops like pearl millet, maize and sorghum limited the light reaching the groundnut canopy by at least 33% thereby reducing photosynthesis. This restricted photosynthesis was further shown by lower CGR. Such a reduction in yield, growth and yield attributes in association with pearl millet and sorghum were also reported by Bandel et al. (1992), Ghosh and Dayal (1998), Willey and Reddy (1981), Reddy and Willey (1981), and Marshal and Willey (1983). The reproductive sink size and its relative strength appear to have an innate bearing on photosynthesis and consequently the pod yield. Duncan et al. (1978) observed partitioning of photosynthate to pods as the most influential physiological factor in yield determination. Comparatively less reproductive sink mass as reflected in harvest index might be the reason for lower pod yield of groundnut in treatments when two cuts of sorghum and pearl millet were planned (Table 2). The NAR of groundnut in rows adjacent to cereals was less than the middle rows (Fig. 3) in all treatments. This may be attributed to the less efficient conversion of light energy into dry matter in adjacent rows of groundnut (Reddy and Willey, 1979). Further, significant reduction in NAR between these two rows was observed only in the systems with two cuts of sorghum and pearl millet. In fact, number of tillers and plant height in second cuts are more than in the first cut, which caused effective shading to groundnut at later growth stages also in adjacent rows of pearl millet and sorghum. However, in treatments with only one cut of maize, sorghum and pearl millet stress, shading was released at 50 days in those treatments, hence the NAR between these two rows did not vary. It is apparent from the results that tall-growing cereal intercrops significantly affected nitrogen fixation traits in groundnut. Reduced light due to shading by tall-growing cereals may be the cause of poor nodulation in groundnut. This reduced light energy affects N2 fixation by restricting photosynthesis and the energy supply to roots, thereby reducing nodulation and nodule size (Nambiar et al., 1983). Low N content of groundnut shoots measured in the cereal
235
intercropping systems could be attributed mainly to lower nitrogen fixation and reduced N uptake from soil under restricted photosynthesis. Nambiar et al. (1983) observed that when lateral leaves of the sorghum crop were removed, the intercropped groundnut nodulated better and fixed more N. Similar reduction in N2 fixation of soybean by shading caused by maize was reported by Wahue and Miller (1978). Non-significant differences in the nodulation in the initial stage could be attributed to shorter height of intercrops, which apparently did not create effective shading. Further, maximum nodulation and nitrogen fixation in groundnut are known to occur at the pod filling stage (Nambiar et al., 1986). Thus any discrepancy in nodulation and nitrogen fixation is bound to contribute to differences in pod yield. Hence it is clear that pod yield of groundnut was significantly affected in the intercropping system with cereal fodders. Though cereal fodders depressed the yield of groundnut, an overall benefit was observed when yield of both the crops are considered together. The LER gives an accurate assessment of the greater biological efficiency of the intercropping situation. LER values indicated that groundnut recorded yield advantage in all intercropping systems due to crop complementarities. This corroborated the findings of several researchers (Willey, 1979; Reddy and Willey, 1981). Yield advantage in terms of LER and RCC was greater in case of the groundnut/maize association. The higher the LER and RCC value, the greater is the yield advantage. The aggressivity of groundnut is negative; thus, it is considered as the less-dominant crop in the system. Associated cereals were the dominant crops in the present study as measured by the positive value of aggressivity. The data in Table 3 show that among the cereal crop treatments, pearl millet was more dominant than others. The CR value of groundnut was less compared to the associated crops, which indicated that groundnut in the intercropping system is less competitive than the associated cereals. According to Willey and Rao (1980), CR gives a better measure of competitive ability of the crops and is also advantageous as an index over RCC and aggressivity. The data in Table 3 revealed that the CR values of pearl millet and sorghum (two cuts) were greater than maize, and the corresponding CR value of groundnut was also less. This clearly indicates that pearl millet and sorghum were more competitive, and groundnut under these
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two crops was affected more. When monetary advantage was considered, groundnut/maize association gave maximum MAI which might be due to higher LER, RCC and less CR value. 5. Conclusion The study provides information that shading created by tall-growing pearl millet, sorghum and maize on groundnut inhibited the normal nodulation and affected CGR, LAI and NAR in groundnut, resulting in decreased pod yield. However, growing maize between groundnut rows could produce additional green fodder yield in the intercropping system without jeopardizing the pod yield of groundnut and mitigate the fodder scarcity to some extent during the dry season. From this study it has also been found that although groundnut/maize fodder combination is of great economic importance, the choice depends on which cereal is preferred for food and which is better adapted to the particular environment. Crop components in a mixture have differential requirements; therefore, fertilizer use is complicated, particularly rate, time and application of fertilizers in order to obtain the highest economic effect without disturbing the biological function of legumes in nitrogen economy. Research on these aspects needs to be strengthened to obtain the greatest economic return from legume/non-legume intercropping systems. References AICRPO (All India Coordinated Research Project on Oilseeds), 1980. Annual Progress Report on Groundnut. Directorate of Oilseeds Research, Rajendranagar, Hyderabad, Andhra Pradesh, India, p. 42. Bandel, H., Purushotham, S., Shivashankar, K., 1992. Feasibility of raising fodders as intercrops in summer groundnut (Arachis hypogaea L.). J. Oilseeds Res. 9 (2), 326–327. Mal, B., 1998. Forage research in India. The post-independence scenario. Indian J. Agric. Sci. 68 (8), 439–447. Brann, D.E., Juny, G.A., 1974. Influence of cutting management and environmental variation on the yield, but activity and autumn carbohydrate reserve levels of crown vetch. Agron. J. 66, 767–773. Cochron, W.G., Cox, G.M., 1958. Experimental Designs, 2nd ed. Wiley, New York. Devkota, N.R., Rerkasem, B., 2000. Effect of cutting on the nitrogen economy and dry matter yield of lablab grown under
monoculture and intercropped with maize in northern Thailand. Exp. Agric. 36, 459–468. Duncan, W.G., Mc Cloud, O.E., Mc Grow, R.C., Boote, K.J., 1978. Physiological aspects of peanut yield improvement. Crop Sci. 18, 1015–1020. Ghosh, P.K., Dayal, D., 1998. Effect of varying levels of nitrogen in three groundnut-based intercropping systems. In: Proceeding of the International Conference on Food Security and Crop Science, CCS Haryana Agricultural University, Hissar, India, p. 133. Ghosh, P.K., Dayal, D., Bandyopadhyay, A., Singh, V., Naik, P.R., 1999. Resource-use efficiency and profitability of intercropping of summer groundnut with short duration vegetables: evaluation of a concept. Int. Arachis Newl. 19, 57–60. Kanzariya, M.V., Patel, M.S., 1985. Soils of Gujarat and their management in soil of India. FAI, New Delhi, pp. 103–129. Mandal, B.K., Dhara, M.C., Mandal, B.B., Das, S.K., Nandy, R., 1990. Rice, mungbean, soybean, peanut, ricebean and blackgram yields under different intercropping systems. Agron. J. 82, 1063–1066. Marshal, B., Willey, R.W., 1983. Radiation interception and growth in an intercrop of pearl millet/groundnut. Field Crops Res. 7, 141–160. Nambiar, P.T.C., Rao, M.R., Reddy, M.S., Floyd, C.N., Dart, P.J., Willey, R.W., 1983. Effect of inter-cropping on nodulation and N2-fixation by groundnut. Exp. Agric. 19, 1979–1986. Nambiar, P.T.C., Rupela, O.P., Kumar Rao, J.V.D.K., 1986. Nodulation and nitrogen fixation on groundnut, chickpea and pigeon pea. In: Subba Rao, N.S. (Ed.), New Trends in Biological Nitrogen Fixation. Oxford and IBH Publishers, New Delhi. Ofori, F., Stern, W.R., 1987. Cereal-legume intercropping systems. Adv. Agron. 41, 41–90. Singh, P., Roy, M.M., 1999. Agro forestry and rangeland development. In: Yadav, R.L., Singh, P., Prasad, R., Ahlawat, I.P.S. (Eds.), Fifty Years of Agronomic Research in India. Indian society of Agronomy, IARI, New Delhi, pp. 221–254. Reddy, M.S., Floyd, C.N., Willey, R.W., 1980. Groundnut in intercropping systems. In: Gibbons, R.W. (Ed.), Proceedings of the International Intercropping Workshop. ICRISAT, Andhra Pradesh, India, pp. 133–142. Reddy, M.S., Willey, R.W., 1979. A study of groundnut/groundnut inter-cropping: leaf canopy and rooting pattern. In: Proceeding of the International Intercropping Workshop. ICRISAT, India. Reddy, M.S., Willey, R.W., 1981. Growth and Resource use studies in an inter crop of pearl millet/groundnut. Field Crops Res. 4, 13–24. Rerkasem, K., Rerkasem, B., 1988. Yields and nitrogen nutrition of intercropped maize (Zea mays L.) and rice bean (Vigna umbellta (Thumb.) Ohwi and Onashi). Plant Soil 108, 151–162. Rerkasem, B., Rerkasem, K., Peoples, M.B., Herrigde, B.F., Bergersen, F.J., 1988. Measurement of N2 fixation in maize (Zea mays L.)—rice bean (Vigna umbellata (Thumb) Ohwi and Ohashi) intercrops. Plant Soil 108, 125–135. Spedding, C.R.W., 1971. Grassland Ecology. Oxford University Press, London. Trenbath, B.R., 1976. Plant interactions in mixed crop communities. In: Papendick, R.I., Sanchez, P.A., Triplett, G.B. (Eds.),
P.K. Ghosh / Field Crops Research 88 (2004) 227–237 Multiple Cropping, vol. 27. American Society of Agronomy, pp. 129–169 (special publication). UNIAS (UNI Agriculture Service), 1978. Intercropping in Groundnut. UNIAS, New Delhi, India, pp. 5, 107. Vincent, J.M., 1970. A Manual for the Practical Study of Root Nodule Bacteria, IP Handbook No. 15. Blackwell Scientific Publication, London. Wahue, T.A.T., Miller, D.A., 1978. Effect of intercropping on soybean N2 fixation and plant composition of associated sorghum soybeans. Agron. J. 70, 292–295. Willey, R.W., 1979. Intercropping its importance and research needs. Part I. Competition and yield advantage. Field Crops Abstr. 32, 1–10.
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Willey, R.W., Rao, M.R., 1980. A competitive ratio for quantifying competition between intercrops. Exp. Agric. 16, 117–125. Willey, R.W., Osiru, D.S.O., 1972. Studies on mixtures of maize and beans (Phaseolus vulgaris) with particular references to plant population. J. Agric. Sci. (Camb.) 79, 519–529. Willey, R.W., Reddy, M.S., 1981. A field technique for separating above- and below-ground interaction in intercropping: an experiment with groundnut/groundnut intercropping. Exp. Agric. 17, 257–264. Yadav, R.S., Yadav, O.P., 2001. The performance of cultivars of pearl millet and clusterbean under sole cropping and intercropping systems in arid zone conditions in India. Exp. Agric. 37, 231–240.
Growth, yield, competition and economics of groundnut/cereal fodder intercropping systems in the semi-arid tropics of India P.K. Ghosh* National Research Centre for Groundnut, P.B. No. 5, Junagadh 362001, Gujarat, India Received 14 May 2003; received in revised form 30 November 2003; accepted 5 January 2004
Abstract Intercropping legumes with non-legume crops during the rainy season (wet season) is a common practice in the semi-arid tropics of India. Of late, the concept of intercropping has also been utilized in irrigated (dry season) situations. In a 2-year field study during the dry season (February–May), we assessed yield, competition and economics in a groundnut/cereal fodder intercropping system compared with monocropped groundnut. Maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum L.) were grown for fodder. One cutting for all and two cuttings (first at 50 days after sowing and second at 95 days after sowing) for sorghum and pearl millet were made. In intercrops one row of cereal fodder was sown between every three rows of groundnut (1:3). The green fodder yields and pod yield of groundnut were lower in intercropped than in monoculture plots. The highest green fodder yield in intercrops was recorded in pearl millet with two cuts (16.5 t ha1) followed by pearl millet with one cut (11.8 t ha1) and sorghum with two cuts (10.7 t ha1). In intercrops the growth and yield of groundnut were affected by cereal fodder and intensity of cutting. A significant (P < 0:05) reduction in leaf area index (LAI) and crop growth rate (CGR) was observed in the groundnut–pearl millet system over sole groundnut. Decrease in nodule mass at pod filling stages in groundnut ranged from 3.5 to 11.0% when intercropped with cereal fodders compared to sole groundnut crop. Groundnut yield was reduced more due to pearl millet and sorghum with two cuts. However, maize as the associated crop produced 9.0 t green fodder ha1 and affected the groundnut less with respect to pod yield (5.76% reduction), yield attributes, CGR, LAI and nodule dry mass. Of the two cutting situations under intercropping, one cut gave 9.9% higher yield of groundnut as compared to two cuts. A higher land equivalent ratio (LER) and relative crowding coefficient (RCC) value leads to a crop yield advantage. Accordingly, yield advantage was greater in case of the groundnut/maize association. The competition ratio (CR) is a better indication of performance than RCC. The CRs of pearl millet and sorghum with two cuts were greater than maize but the corresponding CRs of groundnut were less. Thus, pearl millet and sorghum were more competitive, and groundnut under these two crops was affected more. The maximum monetary advantage was also recorded for the groundnut/maize intercropping system. # 2004 Elsevier B.V. All rights reserved. Keywords: Zea mays; Sorghum bicolor; Pennisetum glaucum; Arachis hypogaea; Cereal fodder; Fodder yield; Intensity of cutting; Intercrops; Competition indices
1. Introduction * Present address: Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, Madhya Pradesh, India. Tel.: þ91-755-2730970; fax: þ91-755-2733310. E-mail address: [email protected] (P.K. Ghosh).
In recent days there is mounting interest in diversified agricultural production systems to obtain improved crop protection, increased productivity and
0378-4290/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2004.01.015
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profitability offered by many intercropping system. This may be due to some of the established and speculated advantages for intercropping systems such as higher yields, greater land-use efficiency and improvement of soil fertility through the addition of N by fixation and excretion from the component legume (Willey, 1979; Ofori and Stern, 1987). Groundnut (Arachis hypogaea L.) is traditionally intercropped with crops like pearl millet, maize and sorghum, and also with pigeon pea in groundnut-growing areas of India by marginal and sub-marginal farmers during rainy season (Reddy et al., 1980). Such legume/nonlegume mixtures probably reduce competition for nitrogen (N), since the legume depends mainly on its own N fixation while the cereal uses mineral N (Ofori and Stern, 1987; Rerkasem et al., 1988). Many studies of cereal/legume intercropping have shown that the quantity of N fixed by the legume depends on such factors as the morphology, density and competitive ability of the legume (Ofori and Stern, 1987), the effectiveness of the rhizobia symbiosis and the system of intercropping (Rerkasem and Rerkasem, 1988). India has traditionally been a livestock-rearing country. The increasing human population pressure and its ramifications resulted in a demand for more food, thus diverting the attention of farmers to food crop production and rendering forage farming a secondary priority. This neglect of forage crops led to a decline in the productivity of livestock (Mal, 1998). According to the National Commission on Agriculture, the green fodder requirement for the existing livestock in India is around 1136 Mt, whereas the availability is 695 Mt, indicating a 61% deficit in fodder supply (Singh and Roy, 1999). Further, fodder availability in the dry season is scarce and costly. Groundnut in the dry season (summer) is grown mainly in pure stands with irrigation. The crop is sown from the second fortnight of January to the first fortnight of February. Though this summer crop gives almost double the yield and profit of rainy season groundnut, recently doubts have been raised about the economic advantages of further investment by farmers in sole groundnut production due to higher labor cost and higher input requirement, particularly irrigation. Intercropping is a viable option in such situations. Of late, in irrigated situations during the dry season, intercropping of groundnut with vegetables (AICRPO,
1980; UNIAS, 1978) and with cereal fodders (Ghosh et al., 1999) has been reported. In the semi-arid tropics of central and western India, Yadav and Yadav (2001) also observed that to meet the shortage of fodder, it is a common practice to put some seed of maize/sorghum/ pearl millet in the groundnut field along with seed of groundnut where these crops are cut early for fodder and groundnut is raised as a seed crop. However, systematic study of this system in the dry season has not been done. The frequency of cutting (Spedding, 1971; Devkota and Rerkasem, 2000) and time of cutting of fodders (Brann and Juny, 1974) are known to affect the performance of legumes in mixtures but there is little information on the effects of cutting management and the economy of cereal/legume intercropping system. Therefore, the present study aims to explore the possibility of providing green fodder during the dry season from an intercropping system, and to assess the groundnut/cereal fodder intercropping system as a means of better resource management with respect to growth, productivity, competition and monetary advantage.
2. Materials and methods 2.1. Experimental site Field experiments were conducted at the research farm of the National Research Centre for Groundnut, Junagadh, Gujarat, India (708360 E longitude and 218310 N latitude at an altitude of 60 m above mean sea level) during two dry seasons (1997–1998). The experimental site is located in a semi-arid region with mean annual rainfall of 844 mm. In this region the onset of monsoon rains occurs in the third week of June but can start as late as the first week of August. The rainfall is confined to three-and-a-half months from June to September with practically negligible rainfall during winter and summer (October–May). The average maximum temperature from April to June is very high (37–44 8C) with a mean of 41 8C. In January, temperature falls to a minimum of 12 8C. It reaches a maximum of 42 8C in May. The soil is classified as Vertic Ustochrept, medium black, clayey, shallow (15–20 cm depth), highly calcareous in nature (pH 7.7). The soil is characterized by low organic carbon (0.55), available N (117–123 kg ha1) and
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available P (7.9–8.3 kg ha1), high in available K (318–328 kg ha1), high P fixation capacity (75–95%) and contains an appreciable amount of CaCO3 (Kanzariya and Patel, 1985). Groundnut, castor, wheat, cotton, pulses, sorghum and pearl millet are mainly grown on this soil. 2.2. Experimental and crop culture Cereal fodders, namely, maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum L.), sole as well as intercrops were sown simultaneously with groundnut (cv. GG 2, a Spanish bunch) in the first week of February. Initially 3–5 seeds of all cereals were planted per hill at a row spacing of 60 cm but the seedlings were thinned to one plant per hill 1 week after emergence giving a plant density of 50 103 ha1. For groundnut, row spacing of 30 cm was maintained giving a plant density of 300 103 ha1. These are very close to the optimum populations for these crops. In intercrops one row of cereal fodder was sown between every three rows of groundnut (1:3) and plant population of both the crops were adjusted as per area occupied by each crop. This way, cereal to cereal row distance in intercropping was 120 cm (Fig. 1). Sole cropping of groundnut and fodder were also maintained for comparison and for calculation of competition indices. One cutting for all and two cuttings for sorghum and pearl millet were made. The first cut was at 50 days after sowing (DAS) and second was at 95 DAS. Nine treatments comprised T1: sole groundnut, T2: sole maize, T3: sole sorghum, T4: sole pearl millet, T5: groundnut þ maize (one cut), T6: groundnut þ sorghum (one cut), T7: groundnut þ pearl millet (one cut), T8: groundnut þ sorghum (two cuts) and T9: groundnut þ pearl millet (two cuts), and were tested in a completely randomized block design. All treatments were replicated four times. Seeds were treated with appropriate fungicides for all the crops before sowing. A basal application of 50 kg P2O5, 30 kg K2O and 1/2 of the N (12.5 kg ha1) was applied to groundnut in the furrow before planting. The remainder of the N (12.5 kg ha1) was applied at 25 DAS. The cereal fodders received 60 kg N ha1, 40 kg P2O5, 30 kg K2O ha1 as basal. Twenty kilograms additional N ha1 was applied to the fodder crops after the harvest of the first cut in treatments where two cuts were planned. Urea (46.4% N), single
229
superphosphate (16% P2O5) and muriate of potash (60% K2O) were used to supply N, P and K, respectively. The necessary plant protection, irrigation and other management practices were followed during crop growth. Crops were grown with irrigation. Nine irrigations were given at 10-day interval; in each irrigation 50 mm water was applied through flooding. The crop was hand-weeded once, 1 month after sowing to keep the field weed-free. No serious incidence of insects or diseases was observed. Plot sizes of 4:8 m 10 m were maintained. Crops were harvested manually by sickle from ground level and the total above-ground biomass was removed from each plot as per treatment and the fodder yield was recorded. The groundnut was uprooted manually at 105 days and pod yield was recorded. 2.3. Plant and soil sampling Groundnut plants from each plot were sampled for growth analysis at 15-day intervals between 15 DAS and harvest. The plant samples were oven-dried at 65 8C for 72 h to a constant weight and dry weight was recorded. Leaf area was estimated from area to dry mass ratio based on a sub-sample, whose area was measured on leaf area meter (LI-COR; Lincoln, NE). For comparison of growth analysis between middle rows and rows adjacent to fodder, groundnut plants were also sampled from four locations of each plot. Five plants were tagged for recording the tiller and plant height of fodder crops at each cutting. The plant height was measured from base of the plant to tip of the topmost leaf of plants. Three groundnut plants were uprooted with a ball of soil for recording nodulation. Keeping the root portion intact, the ball of soil was washed gently with clean running water followed by washing with camel hairbrush to dislodge any soil particles adhering to it. Nodules from roots were removed, counted and dry mass was measured (Vincent, 1970). Nitrogen content of shoot from a bulk sample was estimated at 30 and 60 days growth following micro-Kjeldhal method. 2.4. Growth analysis Crop growth rate (CGR), the increase in dry weight per unit ground area of crop in a unit time, was
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30 cm
230
60 cm
Sole groundnut
Sole fodder
Groundnut Fodder
30 cm
30 cm
3:1 row ratio
120 cm
Fig. 1. Planting pattern in intercropping system.
calculated as (W2 W1 )/(t2 t1 ), where W1 and W2 are dry weights at times t1 and t2, respectively, and expressed as g m2 per day. Net assimilation rate (NAR), the increase in dry weight per unit time per unit leaf area (g cm2 per day) was calculated as (W2 W1 )(ln L2 ln L1 )/(t2 t1 )(L2 L1 ), where L1 and L2 are leaf areas at t1 and t2 times. Leaf area index (LAI) was calculated as leaf area/ground area.
2.5. Competition indices and monetary advantages The yield advantage of intercropping was calculated according to Ofori and Stern (1987), Willey and Osiru (1972), and Willey and Rao (1980). The land equivalent ratio (LER) gives an accurate assessment of the greater biological efficiency of the intercropping situation and was calculated as LER ¼ ðYab =Yaa Þþ ðYba =Ybb Þ, where Yaa and Ybb are yields as sole crops
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and Yab and Yba are yields as intercrops. LER values greater than 1 are considered advantageous. LER has also been used to calculate monetary advantage. Relative crowding coefficient (RCC) is a measure of relative dominance of one component crop over the other in an intercropping system. For crop ‘a’ in association with ‘b’, Kab ¼ Yab Xba =ðYaa Yab ÞXab , where Xab is the sown proportion of ‘a’ in mixture of ‘b’ and Xba the sown proportion of ‘b’ in mixture of ‘a’. The product of two coefficients ðKab Kba Þ ¼ K; if K obtained in the system is greater than 1, there is a yield advantage, if K obtained in the system equals to 1, there is no yield advantage, if K in the system is less than 1, there is a yield disadvantage. Aggressivity is another index that represents a simple measure of how much the relative yield increase in ‘a’ crop is greater than that of ‘b’ crop in an intercropping system. It was calculated as Aab ¼ ðYab =Yaa Xab Þ ðYba =Ybb Xba Þ; if Aab ¼ 0, both crops are equally competitive, if Aab is positive, ‘a’ is dominant, if Aab is negative, ‘a’ is the dominated crop. Willey and Rao (1980) suggested the ratio of these terms, which they designated as competition ratio (CR), instead of taking the difference of two terms in aggressivity. The CR represents simply the ratio of individual LERs of the two component crops, but taking into account the proportion of the crops in which they were initially sown. CRa ¼ ðLERa =LERb ÞðXba =Xab Þ, and if CRa < 1, there is a positive benefit and the crop can be grown in association, if CRa > 1, there is negative benefit. The reverse is true for CRb. There is a large labor cost associated with growing the groundnut. Farmers are concerned mostly with total profit and the marginal benefit:cost ratio from investment in labor and inputs. The yield and economic performance of the intercropping was traced to decide whether groundnut yield and additional fodder yield are sufficient to justify farmers using this intercropping system. Moreover, none of the competition indices explains economic advantage of the intercropping system. Thus, we computed monetary advantage index (MAI) as MAI ¼ value of combined intercrops ðLER 1Þ=LER. The higher the index value, the more profitable is the cropping system. 2.6. Data analysis Data collected for various studies were subjected to the analysis of variance (ANOVA) appropriate to the
231
design as given by Cochron and Cox (1958). Test of significance of the treatment difference was done on the basis of a ‘T-test’. The significant differences between treatments were compared with the critical difference at 5% level of probability.
3. Results 3.1. Fodder crops Since treatment year was not significant, pooled data of 2 years are discussed. The plant height of sorghum and pearl millet was comparatively greater than maize. In general, cereal fodder growth measured by plant height and tiller number was greater in second cut than first cut and also in monocrops than in intercrops (Table 1). On average, monocropped cereals produced 20% higher fodder yields than intercropped. The fodder yield was the highest in pearl millet with two cuts followed by pearl millet with one cut and sorghum with two cuts (Table 1), both in sole and intercropping systems. The lowest fodder yield was recorded in sorghum with one cut. The fodder yield in maize and sorghum with one and two cuts, and pearl millet with one cut were not different in intercropping systems, but were significantly different in sole cropping. 3.2. Groundnut 3.2.1. Growth The CGR of groundnut was low at initial stage, and attained its peak between 60 and 75 days (Fig. 2b). LAI followed a trend similar to CGR (Fig. 2a). The CGR and LAI of groundnut were reduced in association with fodder crops. The magnitude of reduction varied with component crops and number of cuttings. Except between 15 and 30 DAS, monocropped groundnut recorded significantly (P < 0:05) greater CGR at all stages over intercropped groundnut with all fodders and cuttings. However, up to 30–45 DAS, the CGR of groundnut with maize was significantly higher over sorghum and pearl millet with two cuts. A significant (P < 0:05) reduction in LAI (Fig. 2a) was observed in groundnut/pearl millet system over sole groundnut. However, maize/groundnut intercropping system reduced LAI the least. Fig. 2 shows that
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Table 1 Yields and growth attributes of fodders in intercrops and monoculture Plant height at first cut (cm)
Tiller number at first cut
Total green fodder yield (t ha1)
Total dry fodder yield (t ha1)
Sole cropping Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean
112.7 112.3 114.4 120.3 (143.6)a 118.5 (148.7)a 115.4
1.8 2.4 3.0 (4.6)b 3.5 (5.2)b 2.7
10.25 9.10 12.60 14.96 17.72 15.81
3.27 2.89 3.76 4.61 5.12 3.93
Intercropping Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean LSD 5%
103.3 107.6 110.3 111.3 (146.5)a 110.3 (139.2)a 108.6 NSc
1.9 2.6 2.3 (4.1)b 3.2 (4.9)b 2.5 0.54
9.00 7.98 11.81 10.80 16.50 13.7 3.04
2.64 2.19 3.55 3.16 4.83 3.27 0.76
Treatments
a
Plant height at two cuts. Tiller number at two cuts. c Not significant. b
8.0 7.0 6.0
LAI
5.0 4.0 3.0 2.0 1.0
SG
G+M
G+S (1 cut)
G+P (1 cut)
G+S (2 cut)
G+P (2 cut)
0.0
(a)
0
15
30
45
60
75
90
105
16.0 14.0 CGR (g m-2 day-1)
12.0 10.0 8.0 6.0 4.0 2.0 0.0 15-30
(b)
30-45
45-60
60-75
75-90
90-105
Days after sowing
Fig. 2. (a) Leaf area index and (b) crop growth rate of groundnut under different combinations of cereal fodder. G, M, S and P represents groundnut, maize, sorghum and pearl millet, respectively. The line above the bars indicates LSD at 5% probability.
the dry weight of groundnut expressed in terms of CGR was affected more than LAI due to shading effect of cereal fodders. There was 20.8 and 40.4% reduction in LAI and CGR in intercropped groundnut in association with pearl millet with two cuts over sole groundnut, and it was 9.5 and 30.7%, respectively, with maize. The NAR of groundnut in middle rows and in rows adjacent to cereal in intercropping system showed considerable differences. In rows adjacent to cereal, the NAR was less than the middle rows in all treatments; however, differences were significant in pearl millet with two cuts and sorghum with two cuts at all the three stages measured (Fig. 3). The NAR of groundnut between adjacent rows and middle rows in case of maize and pearl millet one cut at three stages and in sorghum one cut at 60–75 and 75–90 DAS was not different. 3.2.2. Nodulation and nitrogen content In general, nodule number and nodule mass at pod filling stage (60 DAS) were much lower in groundnut when cereals were used as intercrops as compared to sole groundnut. However, there were no marked differences in nodulation between groundnuts in sole and cereal intercropping system during initial stages of crop growth. Nodule number and nodule mass were
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(37.7 g); these were significantly (P < 0:05) reduced in association with fodders (Table 2). The magnitude of reduction in these yield attributes was more when two cuts were allowed. The lowest pod numbers (5.0), pod yield per plant (3.8 g) and 100-kernel mass (34.4 g) were recorded in association with pearl millet (two cuts). Maize as associated crop had less impact on yield attributes. The highest pod yield (2.43 t ha1) and harvest index (0.42) were recorded in sole groundnut. Pod yield of groundnut intercropped with cereals was reduced due to suppressive effect of fodder. Significant (P < 0:05) reduction in grain yield of groundnut and harvest index were recorded when two cuts of pear millet (2.01 t ha1, 0.34) and sorghum (2.04 t ha1, 0.34) were made. Two cuts of pearl millet and sorghum produced 0.18 and 0.16 t ha1, respectively, less grain yield of groundnut than their corresponding one cut (Table 2). 3.3. Yield advantages and competition indices
Fig. 3. Trend in the net assimilation rate of groundnut at three stages in the middle row and adjacent rows to cereal fodders. AR and MR represent adjacent row and middle row, while G, M, S and P represent groundnut, maize, sorghum and pearl millet, respectively. The line above the bars indicates standard error at 5% probability.
significantly higher in monocropped groundnut over its intercropped counterpart with all cereal fodders except maize. Decrease in nodule mass at pod filling stages ranged from 3.5 to 11.0% with cereal fodders compared to sole groundnut crop. There was 30% reduction in nodule mass in intercropped groundnut in association with pearl millet with two cuts compared to sole groundnut, and the reduction was 20% with maize. The N content in shoot followed the same trend to nodule number and its mass (Table 2). 3.2.3. Yield and yield attributes Sole groundnut recorded greater pod numbers (9.8), pod yield per plant (7.9 g) and 100-kernel mass
Yield advantage in terms of LER was greatest (1.68) in the groundnut/maize association. The lowest LER (1.34) was recorded in groundnut/sorghum association (Table 3). The RCC value was significantly greater (26.0) in groundnut/maize associated over all other combinations. The lowest RCC (8.7) was recorded in groundnut/pearl millet (two cuts). Table 3 reveals that the value of aggressivity of groundnut was negative and it was considered as the less-dominant crop in the system. Due to a positive value of aggressivity for associated cereals, fodder crops were the dominant crops in the present study. Among the cereal crops, pearl millet was more dominant than the others. The CR value of groundnut was less than those of the associated cereal fodders. 3.4. Monetary advantage Monetary advantage index followed the trend similar to LER (Table 3). The MAI was significantly higher in groundnut/maize association over all other treatments. The MAI due to groundnut/sorghum one cut and groundnut/pearl millet two cuts association was statistically the same. The lowest monetary benefit was recorded in groundnut/pearl millet one cut.
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Table 2 Nodulation, nitrogen content, yield, yield attributes and harvest index of groundnut under different combinations of fodder and number of cuttings Treatments
Nodule per plant
Nodule mass (mg per plant)
N content (mg per plant)
30 DASa
60 DAS
30 DAS
60 DAS
30 DAS
60 DAS
17.0 15.8 15.6 16.8 15.1 14.8 15.81 1.41
44.1 42.5 40.3 41.7 41.2 39.2 41.5 NS
186.0 179.5 171.5 165.4 172.5 169.8 177.1 13.6
165 159 155 151 148 144
353 312 282 288 260 254
Sole groundnut 10.7 Maize (one cut) 9.4 Sorghum (one cut) 9.3 Pearl millet (one cut) 8.9 Sorghum (two cuts) 9.2 Pearl millet (two cuts) 9.0 Mean 9.4 LSD 5% NS a
16.2
29.2
Hundred- Pods per kernel plant mass (g)
Pod yield Pod yield Harvest per plant (t ha1) index (g)
37.7 35.7 34.5 34.7 33.3 34.4 35.05 1.73
7.9 4.5 5.5 4.9 4.2 3.8 5.13 1.78
9.8 6.1 6.5 5.2 5.9 5.0 6.4 1.83
2.43 2.29 2.20 2.19 2.04 2.01 2.19 0.34
0.423 0.406 0.386 0.386 0.343 0.340 0.380 0.041
Days after sowing.
Table 3 Assessment of yield advantage under different competition treatments (unit price (Rs. kg1) of fodder and groundnut pods represent 1 and 15, respectively) Treatments
Maize (one cut) Sorghum (one cut) Pearl millet (one cut) Sorghum (two cuts) Pearl millet (two cuts) Mean LSD 5%
LERa
1.68 1.34 1.49 1.43 1.54 1.49 0.17
RCCb
25.98 17.35 8.74 10.67 11.7 14.88 5.34
Aggressivity
Competition ratio
Groundnut
Cereals
Groundnut
Cereals
1.93 1.69 2.03 1.99 2.32 1.99
1.93 1.69 2.03 1.99 2.32 1.99 0.54
0.38 0.40 0.32 0.34 0.29 0.34 NSd
2.64 2.45 3.06 2.92 3.42 2.28 0.78
MAIc
16543 14383 12656 13503 14699 14356 2897
a
Land equivalent ratio. Relative crowding coefficient. c Monetary advantage index. d Not significant. b
4. Discussion Monoculture production of cereal fodder or groundnut yielded higher than in the intercropped culture. This was partly the result of the higher plant population in the monocrops. In addition, the crop did not experience inter-specific competition. Superiority of green fodder yields of pearl millet over sorghum and maize was perhaps due to a higher number of tillers. Despite tiller formation, higher fodder yield obtained in maize with one cut than sorghum with one cut was possibly due to more rapid dry matter accumulation in maize. In intercrops the yield of groundnut was affected by cereal fodders and intensity of cutting. Reduction in yield of groundnut due to pearl millet and
sorghum was more than due to maize. Of the two cutting situations under intercropping, one cut gave relatively higher yield of groundnut compared to two cuts because of increased inter-specific competition between the component crops (Mandal et al., 1990). Competition for nutrients and light in intercropping systems is often interrelated, particularly for legume/ non-legume crop combinations. On low-N soils, the non-legume is often suppressed, but on high-N soils, the vigorous growth of the non-legume usually causes it to dominate over the legume by shading (Trenbath, 1976). In the present study, application of 20 kg N after first cut of sorghum and pearl millet produced more dry matter and plant height that caused adverse shading of the groundnut. This also explains why
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groundnut yield was low in case of two cuts as compared to one cut. These effects of intercropped pearl millet and sorghum were also prominent on CGR, LAI, nodule dry mass and yield attributes (pod numbers, pod yield per plant, 100-kernel mass). Nambiar et al. (1983) demonstrated that intercrops like pearl millet, maize and sorghum limited the light reaching the groundnut canopy by at least 33% thereby reducing photosynthesis. This restricted photosynthesis was further shown by lower CGR. Such a reduction in yield, growth and yield attributes in association with pearl millet and sorghum were also reported by Bandel et al. (1992), Ghosh and Dayal (1998), Willey and Reddy (1981), Reddy and Willey (1981), and Marshal and Willey (1983). The reproductive sink size and its relative strength appear to have an innate bearing on photosynthesis and consequently the pod yield. Duncan et al. (1978) observed partitioning of photosynthate to pods as the most influential physiological factor in yield determination. Comparatively less reproductive sink mass as reflected in harvest index might be the reason for lower pod yield of groundnut in treatments when two cuts of sorghum and pearl millet were planned (Table 2). The NAR of groundnut in rows adjacent to cereals was less than the middle rows (Fig. 3) in all treatments. This may be attributed to the less efficient conversion of light energy into dry matter in adjacent rows of groundnut (Reddy and Willey, 1979). Further, significant reduction in NAR between these two rows was observed only in the systems with two cuts of sorghum and pearl millet. In fact, number of tillers and plant height in second cuts are more than in the first cut, which caused effective shading to groundnut at later growth stages also in adjacent rows of pearl millet and sorghum. However, in treatments with only one cut of maize, sorghum and pearl millet stress, shading was released at 50 days in those treatments, hence the NAR between these two rows did not vary. It is apparent from the results that tall-growing cereal intercrops significantly affected nitrogen fixation traits in groundnut. Reduced light due to shading by tall-growing cereals may be the cause of poor nodulation in groundnut. This reduced light energy affects N2 fixation by restricting photosynthesis and the energy supply to roots, thereby reducing nodulation and nodule size (Nambiar et al., 1983). Low N content of groundnut shoots measured in the cereal
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intercropping systems could be attributed mainly to lower nitrogen fixation and reduced N uptake from soil under restricted photosynthesis. Nambiar et al. (1983) observed that when lateral leaves of the sorghum crop were removed, the intercropped groundnut nodulated better and fixed more N. Similar reduction in N2 fixation of soybean by shading caused by maize was reported by Wahue and Miller (1978). Non-significant differences in the nodulation in the initial stage could be attributed to shorter height of intercrops, which apparently did not create effective shading. Further, maximum nodulation and nitrogen fixation in groundnut are known to occur at the pod filling stage (Nambiar et al., 1986). Thus any discrepancy in nodulation and nitrogen fixation is bound to contribute to differences in pod yield. Hence it is clear that pod yield of groundnut was significantly affected in the intercropping system with cereal fodders. Though cereal fodders depressed the yield of groundnut, an overall benefit was observed when yield of both the crops are considered together. The LER gives an accurate assessment of the greater biological efficiency of the intercropping situation. LER values indicated that groundnut recorded yield advantage in all intercropping systems due to crop complementarities. This corroborated the findings of several researchers (Willey, 1979; Reddy and Willey, 1981). Yield advantage in terms of LER and RCC was greater in case of the groundnut/maize association. The higher the LER and RCC value, the greater is the yield advantage. The aggressivity of groundnut is negative; thus, it is considered as the less-dominant crop in the system. Associated cereals were the dominant crops in the present study as measured by the positive value of aggressivity. The data in Table 3 show that among the cereal crop treatments, pearl millet was more dominant than others. The CR value of groundnut was less compared to the associated crops, which indicated that groundnut in the intercropping system is less competitive than the associated cereals. According to Willey and Rao (1980), CR gives a better measure of competitive ability of the crops and is also advantageous as an index over RCC and aggressivity. The data in Table 3 revealed that the CR values of pearl millet and sorghum (two cuts) were greater than maize, and the corresponding CR value of groundnut was also less. This clearly indicates that pearl millet and sorghum were more competitive, and groundnut under these
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two crops was affected more. When monetary advantage was considered, groundnut/maize association gave maximum MAI which might be due to higher LER, RCC and less CR value. 5. Conclusion The study provides information that shading created by tall-growing pearl millet, sorghum and maize on groundnut inhibited the normal nodulation and affected CGR, LAI and NAR in groundnut, resulting in decreased pod yield. However, growing maize between groundnut rows could produce additional green fodder yield in the intercropping system without jeopardizing the pod yield of groundnut and mitigate the fodder scarcity to some extent during the dry season. From this study it has also been found that although groundnut/maize fodder combination is of great economic importance, the choice depends on which cereal is preferred for food and which is better adapted to the particular environment. Crop components in a mixture have differential requirements; therefore, fertilizer use is complicated, particularly rate, time and application of fertilizers in order to obtain the highest economic effect without disturbing the biological function of legumes in nitrogen economy. Research on these aspects needs to be strengthened to obtain the greatest economic return from legume/non-legume intercropping systems. References AICRPO (All India Coordinated Research Project on Oilseeds), 1980. Annual Progress Report on Groundnut. Directorate of Oilseeds Research, Rajendranagar, Hyderabad, Andhra Pradesh, India, p. 42. Bandel, H., Purushotham, S., Shivashankar, K., 1992. Feasibility of raising fodders as intercrops in summer groundnut (Arachis hypogaea L.). J. Oilseeds Res. 9 (2), 326–327. Mal, B., 1998. Forage research in India. The post-independence scenario. Indian J. Agric. Sci. 68 (8), 439–447. Brann, D.E., Juny, G.A., 1974. Influence of cutting management and environmental variation on the yield, but activity and autumn carbohydrate reserve levels of crown vetch. Agron. J. 66, 767–773. Cochron, W.G., Cox, G.M., 1958. Experimental Designs, 2nd ed. Wiley, New York. Devkota, N.R., Rerkasem, B., 2000. Effect of cutting on the nitrogen economy and dry matter yield of lablab grown under
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