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pigeonpea intercropping system in semi-arid tropics of India
Field Crops Research 96 (2006) 90–97 www.elsevier.com/locate/fcr
Growth, competition, yields advantage and economics in soybean/pigeonpea intercropping system in semi-arid tropics of India II. Effect of nutrient management P.K. Ghosh *, M. Mohanty, K.K. Bandyopadhyay, D.K. Painuli, A.K. Misra Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, India Received 4 December 2004; received in revised form 12 May 2005; accepted 20 May 2005
Abstract Low native nitrogen (N) and phosphorus (P) coupled with imbalanced nutrient application is a major constraint limiting productivity of intercropping systems on Vertisols of the semi-arid tropical India. In a 3-year field experiment competition behaviour of component crops for nutrients use in soybean/pigeonpea intercropping system was assessed based on relative yield (RY), relative nitrogen yield (RNY) and relative phosphorus yield (RPY) under three nutrient levels (0 NPK, 100% NPK (N:P:K = 30:26:25 kg ha 1) and 100% NPK + 4 t FYM ha 1). The result showed that before soybean harvest, the RY and RNY of soybean were greater (1.0) than the corresponding values of RY and RNY of pigeon pea (0.6). This implied that competition exists for soil N between the component crops during the first half of the cropping system. It was observed that soybean harvest did not coincide with peak flowering of pigeonpea, the stage when biological nitrogen fixation (BNF) was maximum. Thus, BNF dependency of pigeonpea was low before soybean harvest and the plants suffered from N deficiency more when no fertilizer-N was applied and diminished at a high-N level. Pigeon pea attained its peak flowering after the harvest of soybean and increased its dependency on BNF when soil N was exhausted by soybean. Thus, after the harvest of soybean, RY and RNY of pigeon pea gradually increased and approached 1.0 at maturity at all nutrient levels. The RPY values showed that phosphorus was not the limiting factor to any of the crop in the system even if it was not applied. The study thus suggests that in the soybean/pigeonpea intercropping system, N is a limiting factor for growth of pigeonpea intercrop during the first half of its growth and application of 100% NPK (30 kg N) + 4 t FYM could meet N demand of pigeonpea in N deficient soils as this nutrient management option gave higher yield, root length density and profit under soybean/ pigeonpea intercropping system than 100% NPK and control. # 2005 Elsevier B.V. All rights reserved. Keywords: Competition; Energy use; Intercropping; Nutrient management; Relative yield; Relative nitrogen yield; Relative phosphorus yield
1. Introduction Vertisols of the semi-arid tropics (SAT) are potentially the most productive soils in India and contribute significantly to the national economy. However, productivity potential of large areas of Vertisols in the country (73 million ha) is under-explored primarily because of inadequate management and nutrition-related constraints. The SAT soils are usually low in organic matter, nitrogen * Corresponding author. Tel.: +91 755 2730970; fax: +91 755 2733310. E-mail address: [email protected] (P.K. Ghosh). 0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2005.05.010
and phosphorus. Since organic matter is an important source of N in the soil, these soils are incapable of maintaining N in adequate supply, which affects crop production. Balanced fertilization is thus required for increasing yields in Vertisols of SAT region. Soybean is the most important rainy season crop in Vertisols of the semi-arid tropics of central India. Soybean although a leguminous crop, leaves a net negative N balance in the soil because most of the N and P are accumulated in the edible parts that are usually harvested and not returned to the soil. Conventional soybean cultivation in this region includes its sowing in June after the onset of monsoon rain with conventional tillage practices
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(2 harrowing) and application of di-ammonium phosphate (DAP). Pigeonpea is also an important pulse crop in this region. The availability of early and medium duration varieties of this crop has made their place through intercropping with soybean in this region. Quantifying beneficial or competitive effects of nutrient use in intercropping system is still an important researchable issue. Studies on nutrient management and optimum fertilizer schedule have mainly been on sole cropping of both soybean and pigeon pea (Reddy et al., 1990; Shankaralingappa et al., 2000; Shivran et al., 2000; Saxena et al., 2001; Hati et al., 2001; Ghosh et al., 2004a). Fertilizer recommendations based on sole cropping may not meet the nutrient demand of component crops in the intercropping system, because competition between component crops for nutrient use is more pronounced in the intercropping system (Wahue and Miller, 1978). Further, there are a lot of published information on the nutrient management and nutrient audit on cereal/legume intercropping systems (Bandyopadhyay and De, 1986; Ofori and Stern, 1987; Rerkasem and Rerkasem, 1988; Tobita et al., 1996; Ghosh et al., 2004a,b) but probably few on legume/legume intercropping system. Therefore, there is a need for assessing the competition behaviour between component crops in legume/legume intercropping system for nutrient use and examining appropriate and optimum fertilizer for the system based on competition so that nutrient requirement of each crop in the system is met. The design of experiment and treatments have been explained in the preceding paper (Ghosh et al., 2005a). This paper focuses on assessment of the competition behaviour between soybean and pigeonpea for nutrient use in intercropping based on relative yield (RY) in terms of dry matter, nitrogen and phosphorus accumulation and adoption of suitable nutrient management for soybean/pigeonpea intercropping system.
2. Materials and methods Field experiments were conducted during the rainy (June to October) seasons of 2000, 2001 and 2002 at the research farm of Indian Institute of Soil Science, Bhopal, India. The region has a semi-arid tropical climate and receives an average rainfall of 1005 mm annually. Major part of the rain (88%) is received during June to September. Other weather parameters of the region and rainfall for the crop growing seasons and properties of soil of the experimental site have been described in the previous paper (Ghosh et al., 2005a). The experiment comprising three cropping systems (sole soybean, sole pigeonpea and soybean/pigeonpea intercrop), three tillage practices and three nutrient levels (N0 = 0% NPK, N1 = 100% recommended NPK and N2 = 100% NPK + 4 t farmyard manure (FYM) was laid out in split– split design (Ghosh et al., 2005a). The recommended doses of N:P:K for 100% NPK treatment both for soybean and pigeonpea was 30:26:25 kg ha 1. The NPK and FYM were
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applied every year. The entire dose of nitrogen, phosphorus and potassium was applied at sowing through urea, single super-phosphate and mutriate of potash, respectively. The FYM at 4 t dry weight ha 1 was applied 2 weeks before sowing. Plant samples were collected from 0.5 m2 land area at different stages of crop growth and oven dried at 65 8C until constant weight. Dry matter (DM) was determined based on the fresh weight of sample plants and the moisture content of the subsamples. Data on number and weight of nodules were collected at 50% flowering. Five plants were uprooted with a ball of soil for taking observation on nodulation. Keeping the root portion intact, the ball of soil was washed gently with clean running water followed by cleaning with a camel hairbrush to dislodge soil particles adhering to roots. Nodules from roots were removed, counted and the oven dry mass was measured (Vincent, 1970). Plant samples collected at harvest were analysed for N and P concentration in grain and straw and N and P uptake were determined. The procedures for calculating yield advantage, energy use efficiency and economic index have been described in the preceding paper (Ghosh et al., 2005a). Out of all the inputs for the different operations, manures and chemical fertilizers (NPK) consumed the bulk of the energy for all crops. Though soybean is a legume crop, the agronomic energy requirement for manure and fertilizer application was relatively high (Mandal et al., 2002). It is difficult to ascertain whether less uptake of a particular nutrient is the cause for less yield in intercropping situations. The nutritional relationships between intercrop components were evaluated using relative yield totals (RYT) (Hall, 1974). The RYT for total dry matter (DM) was calculated as (IDMa/SDMa) + (IDMb/SDMb), where IDMa and IDMb are intercrop DM for crop ‘a’ and crop ‘b’ and SDMa and SDMb are sole crop DM for crop ‘a’ and crop ‘b’. This is identical to land equivalent ratio. Relative yield is identical to the partial land equivalent ratio. The RYT for the nutrients was computed similar to that of RYT for total dry matter, in which uptake of corresponding nutrients in stead of dry matter were used in the formula. The RYT, relative N yield totals (RNYT) and relative P yield totals (RPYT) were used to estimate the N and P status of the component crops of the soybean/pigeon pea intercropping system. Theoretical consideration was that (i) if RYT RNYT, N is exploited less by the intercrops compared with other resources indicating that N is a limiting factor in intercropping performance, (ii) If RYT RNYT, N is exploited more by the intercrops compared with other resources indicating that N is not a limiting factor in intercropping performance (Hall, 1974). Similar was the case with RPYT. Statistical analysis of data was carried out using standard analysis of variance (Gomez and Gomez, 1984). The significance of the treatment effect was determined using the F-test. To determine the significance of the difference between the means of two treatments, least significant difference (L.S.D.) was computed at 5% probability level.
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3. Results 3.1. Growth In general, the crop growth rate (CGR) of both crops was higher under sole cropping than intercropping. The effect of nutrient treatment on CGR was not significant up to 30–45 days in soybean and up to 60–75 days in pigeonpea. The combined use of 100% NPK + FYM produced on average 59% higher CGR than the control plots (Fig. 1). Nodule
mass of both the crops also followed the same trend but the magnitude of reduction with no added NPK was more in soybean intercrop than pigeonpea intercrop (Fig. 2). The maximum nodule mass was observed in 100% NPK + FYM plots, though statistically it did not differ from 100% NPK. Effect of nutrient on root length density (RLD) of soybean was significant at surface layer (0–7.5 and 7.5–15 cm). Significant improvement in the RLD of soybean with 100% NPK + FYM compared to 100% NPK and control was observed (Fig. 3).
Fig. 1. Crop growth rate of different crops as influenced by nutrient management. (a) Sole soybean; (b) soybean as intercrop; (c) sole pigeon pea; (d) pigeon pea as intercrop. DAS and ns represents days after sowing and nonsignificant. Vertical bar represens L.S.D. (P = 0.05).
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Fig. 2. Nodule weight under different cropping systems and nutrient management practices. S, IS, P and IP represent sole soybean, intercrop soybean, sole pigeon pea and intercrop pigeon pea while N0, N1, N2 and ns represents no nutrient, recommnded dose of fertilizer, recommended dose of fertilizer plus farmyard manure and nonsignificant. Vertical bar represents L.S.D. (P = 0.05).
3.2. Yield Since treatments year was significant, yield data of each year are discussed. In the year 2000, pigeonpea plants were damaged after germination by water logging due to heavy rain in July. Therefore, yield of only soybean has been reported (data not presented). The integrated use of 100% NPK + 4 t FYM recorded significantly (*P < 0.05) higher seed yield of soybean over 100% NPK and control in 2000. On an average (2001 and 2002), soybean/pigeonpea intercropping system recorded 10 and 50.7% higher seed yield in terms of soybean equivalent yield (SEY) over sole pigeonpea and sole soybean (Table 1). Regardless of the cropping systems, the use of 100% NPK + 4 t FYM produced 14 and 52.7% higher yield over 100% NPK and control, respectively. Effect of interaction of cropping system nutrient was significant (Table 1) during 2001 and
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Fig. 3. Subsoiling effect on root length density distribution of soybean at anthesis. N0, N1, N2 and ns represents no nutrient, recommnded dose of fertilizer,recommended dose of fertilizer plus farmyard manure and nonsignificant. The horizental bar represents L.S.D. (P = 0.05).
2002. At N0, variation in SEY of sole pigeonpea and soybean/pigeonpea intercropping was not noticeable in 2001, while, at N1 and N2 intercropping significantly produced higher SEY than sole pigeonpea and sole soybean in 2001 and 2002 (Table 1). 3.3. Relative yield in terms of dry matter In general, the RY of soybean throughout the growth stages was greater than the RY of pigeon pea at all nutrient levels (Fig. 4). At soybean harvest, the RY of pigeon pea at N0 was about 0.6, while the RY of soybean almost reached 1.0 (Fig. 4). Though the RY of pigeon pea was lower than soybean at all the stages of growth, the differences of RY between the two crops narrowed at N1 and N2 levels as compared to N0. At soybean harvest, the RYof pigeon pea at N1 and N2 was 31–32% higher than that of N0. Similarly, the relative yield total at N1 and N2 was greater than the RYT at N0 in all the stages. After harvest of soybean the RY of pigeon pea improved and at the time of harvest of pigeon pea, it reached about 1.0, particularly at N1 and N2.
Table 1 Interaction effect of nutrient cropping system on soybeana equivalent yield (kg ha 1) Treatment
Sole soybean
Sole pigeonpea
Soybean/pigeonpea intercropping system
Mean
2001 Control 100% recommended NPK 100% NPK + 4 t FYM Mean L.S.D. (P = 0.05)
1050 1390 1597 1369 N = 155
1471 1887 2219 1859 C = 225
1408 2130 2423 1987 N C = 160
1310 1802 2080
2002 Control 100% recommended NPK 100% NPK + 4 t FYM Mean L.S.D. (P = 0.05)
899 1225 1350 1158 N = 120
1395 1650 1775 1601 C = 150
1550 1855 2012 1810 N C = 125
1295 1689 1896
N: nutrient; C: cropping system. a Yields of sole and intercrop pigeon pea were converted to soybean equivalent yield as (yield of pigeon pea unit price of pigeon pea)/unit price of soybean. Thus, SEY in intercropping is yield of intercrop soybean + SEY of intercrop pigeon pea.
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Fig. 4. Seasonal changes in yield of intercrop to sole crop under (a) no nutrient (N0), (b) recommnded dose of fertilizer (N1) and (c) recommended dose of fertilizer and farmyard manure (N2) condition. RY represents relative yield.
Fig. 5. Relative uptake of nitrogen (a) and phosphorus (b) by intercrop to sole crop under different nutrient treatments. N0, N1, N2 represents no nutrient, recommnded dose of fertilizer, recommended dose of fertilizer plus farmyard manure.
3.4. Relative nitrogen yield (RNY) and relative phosphorus yield (RPY)
but significantly (*P < 0.05) higher than sole soybean. The effect of nutrient management on energy use efficiency was not significant. The economic efficiency in terms of benefit:cost ratio (B:C) followed the trend similar to energy use efficiency. Soybean/pigeonpea intercropping registered the highest B:C ratio followed by sole pigeonpea and sole soybean. Net return was also maximum in the intercropping system (Table 2). The combined use of NPK and FYM gave higher net return and B:C ratio than 100% NPK and control.
At soybean harvest, the RNY of soybean was higher than RNY of pigeonpea for all the nutrient levels. The RNY of pigeon pea at N0 was about 0.5 at soybean harvest, while the corresponding RNY values both at N1 and N2 were about 0.6 (Fig. 5). At pigeonpea harvest, its RNY was about 0.9 for all the nutrient levels. In contrast, the RPY of soybean and pigeon pea at soybean harvest did not vary among nutrient levels, though it was higher at N1 and N2. The RPY of pigeon pea was higher (about 0.7) than the RNY of pigeon pea (0.5) at soybean harvest. But at pigeon pea harvest both RNY and RPY values were same. 3.5. Energy use and economics Energy output and energy use efficiency in soybean/ pigeonpea intercropping were comparable to sole pigeonpea
4. Discussion In terms of crop growth rate (CGR), the suppressive effect of pigeon pea on intercrop soybean was not significant indicating that pigeon pea was not an appreciable competitor for soybean for limiting factors. On the contrary, data in Fig. 3 showed that soybean benefited in association with pigeonpea. It is apparent that the deep-rooting ability of
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Table 2 Energy use efficiency and economics as influenced by nutrient management and cropping system Cropping systems
Energy input (MJ ha 1)
Energy output (MJ ha 1)
Net energy (MJ ha 1)
Energy use efficiency (output/input)
Net return (Rs ha 1)
Benefit:cost ratio
Sole soybean Sole pigeonpea Soybean/pigeonpea intercropping L.S.D. (P = 0.05) Control 100% recommended NPK 100% NPK + 4 t FYM L.S.D. (P = 0.05)
6776 6364 5600
20660 90505 78709
13884 84141 73109
3130 5794 6994
11941 22902 27136
8810 17108 20143
3.0 14.2 14.0 2.6 3.77 3.92 3.86 NS
3711 11219 19104 1055 9197 11698 13755 879
1.32 2.00 2.78 0.15 2.02 2.04 2.20 0.12
NS: not significant.
pigeonpea could enhance the possibility of recycling of nutrients, especially nitrogen and phosphorus from the deeper soil layers and therefore improved the nutrient use efficiency of the cropping system by capturing and utilizing nutrient in the upper most soil layer which could otherwise be leached out to deep soil layers (Arihara et al., 1991; Ito et al., 1992, 1993, 1996; Adu-Gyamfi et al., 1993). Benefit to soybean in association with pigeonpea was also assessed in terms of RY, RNY and RPY. The RY, RNY and RPY of soybean at its harvest were about 1.0. This suggested that soybean was not disadvantaged by the intercropping with pigeonpea in terms of growth, and N and P uptake. In contrast, the corresponding RY and RNY of pigeon pea were about 0.6, particularly when fertilizer and manure were not applied. These never reached 1.0 till soybean harvest. The presence of soybean reduced the dry matter yield and N yield of pigeonpea indicating that soybean was a strong competitor with pigeon pea for N during the first half of the cropping system. In this system, it is surmised that fast growing soybean exhausted the soil N quickly, due to which, the slow growing pigeonpea suffered from N deficiency. Further, the RY of pigeon pea was greater than its RNY at soybean harvest. Thus, it is clear that, although pigeon pea is a legume, it suffered from N deficiency in the intercropping system until soybean harvest. This may be attributed to the fact that at soybean harvest, pigeon pea was at the vegetative stage and peak flowering of pigeon pea occurred after harvest of soybean. This suggests that before soybean harvest soil N was fully utilized by soybean and BNF of pigeon pea was not sufficient to meet its N requirement during early growth. This corroborated the findings of Tobita et al. (1994, 1996). Using the concept of RY and RNY in the sorghum/pigeon pea intercropping system, they concluded that before sorghum harvest, pigeonpea suffered from N deficiency and soil N was exhausted by its companion crop: however, pigeon pea increased BNF dependency after sorghum harvest. It may further be noted that though soybean is a legume, its N uptake is high and the crop may respond up to 60 kg N ha 1 (Singh et al., 2001). This is the reason why in the present study soil N is exhausted by soybean as reported by Tobita et al. (1996) in the sorghum/pigeon pea intercropping system. It is apparent from RY and RNY values that once soybean entered its maturity phase, its competitive effect on pigeon
pea was greatly reduced. After the harvest of soybean, the RY and RNY of pigeon pea gradually increased and approached near 1.0 at its maturity at all the nutrient levels. This is attributed to the fact that pigeon pea attained peak flowering after the harvest of soybean and increased its dependency on BNF, and total amount of N in intercrop pigeon pea increased and approached that of sole pigeon pea. Tobita et al. (1996) had similar observation in the sorghum/pigeon pea intercropping system. On the contrary, the RNY and RY of soybean showed no noticeable variation indicating that N was not a limiting factor for its growth when intercropped with pigeonpea even when N was not applied. Pigeonpea utilized soil- and fertilizer-N as efficiently as soybean (Ito et al., 1994; AduGyamfi et al., 1996), thereby inviting a risk of considerable competition for N with component soybean crop. Unless N was supplied either through organic or inorganic sources at the early stage of pigeonpea growth, the crop suffered as evident from less RY and RNY of pigeonpea at N0 (Fig. 4). In the present study, the suppression effect of soybean on pigeon pea, however, was reduced when manures and fertilizers were both applied as indicated by higher RY and RNY (Figs. 4 and 5) and nodule mass of pigeon pea (Fig. 2) in 100% NPK (N1) and 100% NPK + FYM (N2) than in control (N0). Tobita et al. (1996) also observed that soil-N in the sorghum/pigeon pea intercropping system was more limiting at a relatively low amount of fertilizer-N and there was less competition for N between component crops grown in a high-N treatment. Thus, it is clear that the application of a reasonable amount of fertilizer is necessary to meet the N demand of both the crops during the first half of their crop growth and to realize higher yield in soybean/pigeonpea intercropping system. The effect of 100% NPK + FYM on RY, RNY, CGR, nodulation and RLD (Fig. 3) was more pronounced than 100% NPK. Many researchers (Reddy and Willey, 1981; Nambiar et al., 1983, 1986; Ofori et al., 1987; Rerkasem and Rerkasem, 1988; Rerkasem et al., 1988; Ghosh, 2004) have concluded that nearly all legumes fixed less atmospheric N if the soil had high N content through either high native fertility or application of fertilizer to intercropping system. However, in the present study, application of 100% NPK (30 kg N ha 1) + 4 t FYM ha 1 improved nodule mass. Ghosh et al. (2004b) also had similar
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observation in the same soil with 75% NPK + 5 t FYM ha 1 in sorghum/soybean intercropping system. This was attributed to confounding effect of many conditions, viz., (i) the soil of the experimental site is rated as low in available N (145 kg N ha 1), and had less permeable, high bulk density sub surface (15–30 cm) layer, (ii) slowly released N from FYM and repeated applications of FYM provided better soil physical and chemical environment for nitrogenase activity (Misra et al., 1990; Hati et al., 2001), and (iii) soybean often responded up to 60 kg N because of high N accumulation in the edible parts. Therefore, in the soybean/ pigeon pea intercropping system where greater competition between companion crops for N exists, application of 30 kg fertilizer-N in N deficient soil seemed inadequate because pigeon pea also utilized soil-N on par with soybean. The above facts thus suggest that the application of 100% NPK + 4 t FYM ha 1 was not sufficient to raise soil-N to the level affecting nodulation noticeably. Thus, it is apparent that application of 100% NPK + 4 t FYM could meet the N demand and sustain the productivity in the intercropping system (Table 1). The RPY value of both the crops at soybean harvest was the same at N0 but was relatively more in pigeonpea than soybean at N1 and N2. This indicates that both the crops utilized P better than other possible limiting resources. In fact, legumes act as a catalyst to augment availability of native and fixed P. Therefore, P was not limiting for soybean/ pigeonpea intercropping system even at N0 level at the time of soybean harvest. Many workers (Nimje and Seth, 1987; Ae et al., 1990) suggested that phosphorus fertilization to legume helped to enhance the excretion of amino acids in the rhizosphere. Therefore, RPY values of both the crops at N1 and N2, where P was applied, were always higher than that at N0 level even at the early stages of crop growth. It was further observed that at pigeon pea harvest, its RPY further increased (Fig. 5). This suggests that pigeonpea utilized native P better than soybean in the system because it solubilizes otherwise insoluble Ca-P in vertisols by moderating rhizosphere pH by excreting citric acid (Shibata and Katsuya, 2003). In the intercropping system, pigeon pea contributed more biomass yield than soybean. As mentioned earlier pigeon pea, being a deep-rooted crop utilized more of applied nutrient and sub-soil moisture. This positive effect of pigeonpea benefitted associated soybean crop. Jena and Misra (1995) reported that pigeonpea root could utilize soil water up to a depth of 105 cm. These positive effects combined with higher biomass of pigeonpea ultimately contributed to more yield in the intercropping system. The net profit of soybean/pigeonpea intercropping was greater than sole cropping. Higher pigeonpea biomass was mainly responsible for higher profit in this system. Effect of nutrient management on energy use efficiency was statistically neutral, which implies that energy output in terms of biomass yield was compensated by energy input through manures and fertilizers.
5. Conclusion Based on relative yield, relative nitrogen yield and relative phosphorus yield of soybean and pigeonpea in the intercropping system, the study suggests that in N-and Pdeficient Vertisols, only N was the limiting factor during the early part of the cropping system which affected growth of pigeonpea owing to competition with soybean in soybean/ pigeonpea intercropping system. Soil-N was more limiting when no fertilizer-N was applied and diminished at a high-N level. To meet N demand of the intercropped pigeonpea, and sustain the productivity of soybean/pigonpea intercropping system, application of 100% NPK (30 kg N, 26 kg P and 25 kg K) + 4 t FYM is a viable nutrient management option. Alternatively, to reduce the competition for N during the initial stages of growth, the dependence of pigeonpea on biological nitrogen fixation through biofertilizers needs to be increased so that sufficient N would be available for pigeon pea grown on a nutrient-limited Vertisol.
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P.K. Ghosh et al. / Field Crops Research 96 (2006) 90–97 soybean/pigeonpea intercropping system in semi-arid tropics of India. II. Effect of sub-soiling. Field Crops Res. (under review). Gomez, A.K.A., Gomez, A.A., 1984. Statistical Procedures for Agricultural Research. John Willey and Sons, New York. Hall, R.L., 1974. Analysis of the nature of interference between plants of different species. II. Nutrient relations in a Nandi Setaria and Greenleaf Desmodium association with particular reference to potassium. Aust. J. Agric. Res. 25, 749–756. Hati, K.M., Mandal, K.G., Misra, A.K., Ghosh, P.K., Acharya, C.L., 2001. Effect of irrigation regimes and nutrient management on soil water dynamics, evapo-transpiration and yield of wheat in Vertisol. Indian J. Agric. Sci. 71 (9), 581–587. Ito, O., Matsunaga, R., Tobita, S., Rao, T.P., 1992. Rooting behaviour of intercropped pigeonpea Cajanus cajan L. Millspaugh and sorghum Sorghum bicolor L Moench. In: Kutchera, L., Hubl, E., Lichtenegger, E., Persson, H., Sobotic, M. (Eds.), Root Ecology and its Practical Application, vol. 3. ISRR Symposium. Wien University. Bodenkultur, Verein fur Wurzelforschung; A-9020 klagenfurt, pp. 412–422. Ito, O., Matsunaga, R., Katayama, K., Tobita, S., Rao, T.P., Devi, G., 1993. Spatial distribution of root activity and nitrogen fixation in sorghum/ pigeon pea intercropping on an Indian Alfisol. Plant Soil 155/156, 341– 344. Ito, O., Matsunaga, R., Katayama, K., Adu-Gyamfi, J.J., Tobita, S., Rao, T.P., Devi, G., 1994. Nitrate in soil solution under sorghum and pigeon pea plants in mono and intercrops. In: Commission IV. Transactions, 15th World Congress of Soil Science. International Society of Soil Science, Acapulco, Mexico, July 10–16, 5, pp. 48–49. Ito, O., Katayama, K., Adu-Gyamfi, J.J., Devi, G., Rao, T.P., 1996. Root activities and functions in components crops for intercropping. In: Ito, O., Katayama, K., Johansen, C., Kumar Rao, J.V.D.K., Adu-Gyamfi, J.J., Rego, T.J. (Eds.), Dynamics of Roots and Nitrogen in Cropping Systems of the Semi-arid Tropics. JIRCAS International Agriculture Series no. 3, pp. 159–172. Jena, D., Misra, C., 1995. Root zone water balance and yield of different cropping systems under non-irrigated condition. J. Indian Soc. Soil Sci. 43 (3), 455–458. Mandal, K.G., Saha, K.P., Ghosh, P.K., Hati, K.M., Bandyopadhyay, K.K., 2002. Bioenergy and economic analysis of soybean-based crop production systems in central India. Biomass Bioenergy 23, 337– 345. Misra, R.C., Sahu, P.K., Uttaray, S.K., 1990. Response of soybean to nitrogen and phosphorus application. J. Oilseed Res. 7, 6–9. 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. Nimje, P.M., Seth, J., 1987. Effect of phosphorus and farmyard manure on soybean and their residual effect on succeeding winter maize. Indian J. Agric. Sci. 57 (6), 404–409.
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Ofori, F., Stern, W.R., 1987. Cereal-legume intercropping systems. Adv. Agron. 41, 41–90. Ofori, F., Pate, J.S., Stern, W.R., 1987. Evaluation of N2 fixation and nitrogen economy of a maize/cowpea intercrop system using 15N dilution methods. Plant Soil 102, 149–160. 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. Reddy, D.D., Subba Rao, A., SummiReddy, K., Takkar, P.N., 1990. Yield sustainability and phosphorus utilization in soybean-wheat system on vertisols in response to integrated use of manure and fertilizer phosphorus. Field Crop Res. 62, 181–190. 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. Saxena, S.C., Manral, H.S., Chandel, A.S., 2001. Effect of inorganic and organic sources of nutrients on soybean (Glycine max). Indian J. Agron. 46, 135–140. Shankaralingappa, B.C., Shivaraj, B., Sudhir, K., Viswanatha, K.P., 2000. Interaction effect of phosphorus and sulphur on uptake of nitrogen, phosphorus, potassium and sulphur by pigeonpea (Cajanus cajan). Indian J. Agron. 45, 348–352. Shivran, P.L., Ahlawat, I.P.S., Shivran, D.R., 2000. Effect of phosphorus and sulphur on pigeonpea (Cajanus cajan) and succeeding wheat (Triticum aestivum) in pigeonpea-wheat cropping system. Indian J. Agron. 45, 25– 30. Singh, S.P., Bansal, K.N., Nepalia, V., 2001. Effect of nitrogen, its application time and sulphur on yield and quality of soybean (Glycine max). Indian J. Agron. 46 (1), 141–144. Shibata, R., Katsuya, Y., 2003. Phosphorus requisition from non-labile source in peanut and pigeonpea with mycorrhizal interaction. Appl. Soil Ecol. 24 (2), 133–141. Tobita, S., Katayama, K., Matsunaga, R., Adu-Gyamfi, J.J., Ito, O., Rao, T.P., 1996. Soil nitrogen as a limiting factor in the intercropping system of sorghum and pigeonpea. In: Ito, O., Katayama, K., Johansen, C., Kumar Rao, J.V.D.K., Adu-Gyamfi, J.J., Rego, T.J. (Eds.), Dynamics of roots and nitrogen in cropping systems of the semi-arid tropics. JIRCAS International Agriculture Series no. 3, pp. 441–451. Tobita, S., Ito, O., Matsunaga, R., Rao, T.P., Rego, T.J., Johnson, C., Yoneyama, T., 1994. Field evaluation of nitrogen fixation and use of nitrogen fertilizer by sorghum/pigeonpea intercropping on an Alfisol in the Indian semi-arid tropics. Biol. Fertil. Soil 17, 241–248. 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.
Growth, competition, yields advantage and economics in soybean/pigeonpea intercropping system in semi-arid tropics of India II. Effect of nutrient management P.K. Ghosh *, M. Mohanty, K.K. Bandyopadhyay, D.K. Painuli, A.K. Misra Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, India Received 4 December 2004; received in revised form 12 May 2005; accepted 20 May 2005
Abstract Low native nitrogen (N) and phosphorus (P) coupled with imbalanced nutrient application is a major constraint limiting productivity of intercropping systems on Vertisols of the semi-arid tropical India. In a 3-year field experiment competition behaviour of component crops for nutrients use in soybean/pigeonpea intercropping system was assessed based on relative yield (RY), relative nitrogen yield (RNY) and relative phosphorus yield (RPY) under three nutrient levels (0 NPK, 100% NPK (N:P:K = 30:26:25 kg ha 1) and 100% NPK + 4 t FYM ha 1). The result showed that before soybean harvest, the RY and RNY of soybean were greater (1.0) than the corresponding values of RY and RNY of pigeon pea (0.6). This implied that competition exists for soil N between the component crops during the first half of the cropping system. It was observed that soybean harvest did not coincide with peak flowering of pigeonpea, the stage when biological nitrogen fixation (BNF) was maximum. Thus, BNF dependency of pigeonpea was low before soybean harvest and the plants suffered from N deficiency more when no fertilizer-N was applied and diminished at a high-N level. Pigeon pea attained its peak flowering after the harvest of soybean and increased its dependency on BNF when soil N was exhausted by soybean. Thus, after the harvest of soybean, RY and RNY of pigeon pea gradually increased and approached 1.0 at maturity at all nutrient levels. The RPY values showed that phosphorus was not the limiting factor to any of the crop in the system even if it was not applied. The study thus suggests that in the soybean/pigeonpea intercropping system, N is a limiting factor for growth of pigeonpea intercrop during the first half of its growth and application of 100% NPK (30 kg N) + 4 t FYM could meet N demand of pigeonpea in N deficient soils as this nutrient management option gave higher yield, root length density and profit under soybean/ pigeonpea intercropping system than 100% NPK and control. # 2005 Elsevier B.V. All rights reserved. Keywords: Competition; Energy use; Intercropping; Nutrient management; Relative yield; Relative nitrogen yield; Relative phosphorus yield
1. Introduction Vertisols of the semi-arid tropics (SAT) are potentially the most productive soils in India and contribute significantly to the national economy. However, productivity potential of large areas of Vertisols in the country (73 million ha) is under-explored primarily because of inadequate management and nutrition-related constraints. The SAT soils are usually low in organic matter, nitrogen * Corresponding author. Tel.: +91 755 2730970; fax: +91 755 2733310. E-mail address: [email protected] (P.K. Ghosh). 0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2005.05.010
and phosphorus. Since organic matter is an important source of N in the soil, these soils are incapable of maintaining N in adequate supply, which affects crop production. Balanced fertilization is thus required for increasing yields in Vertisols of SAT region. Soybean is the most important rainy season crop in Vertisols of the semi-arid tropics of central India. Soybean although a leguminous crop, leaves a net negative N balance in the soil because most of the N and P are accumulated in the edible parts that are usually harvested and not returned to the soil. Conventional soybean cultivation in this region includes its sowing in June after the onset of monsoon rain with conventional tillage practices
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(2 harrowing) and application of di-ammonium phosphate (DAP). Pigeonpea is also an important pulse crop in this region. The availability of early and medium duration varieties of this crop has made their place through intercropping with soybean in this region. Quantifying beneficial or competitive effects of nutrient use in intercropping system is still an important researchable issue. Studies on nutrient management and optimum fertilizer schedule have mainly been on sole cropping of both soybean and pigeon pea (Reddy et al., 1990; Shankaralingappa et al., 2000; Shivran et al., 2000; Saxena et al., 2001; Hati et al., 2001; Ghosh et al., 2004a). Fertilizer recommendations based on sole cropping may not meet the nutrient demand of component crops in the intercropping system, because competition between component crops for nutrient use is more pronounced in the intercropping system (Wahue and Miller, 1978). Further, there are a lot of published information on the nutrient management and nutrient audit on cereal/legume intercropping systems (Bandyopadhyay and De, 1986; Ofori and Stern, 1987; Rerkasem and Rerkasem, 1988; Tobita et al., 1996; Ghosh et al., 2004a,b) but probably few on legume/legume intercropping system. Therefore, there is a need for assessing the competition behaviour between component crops in legume/legume intercropping system for nutrient use and examining appropriate and optimum fertilizer for the system based on competition so that nutrient requirement of each crop in the system is met. The design of experiment and treatments have been explained in the preceding paper (Ghosh et al., 2005a). This paper focuses on assessment of the competition behaviour between soybean and pigeonpea for nutrient use in intercropping based on relative yield (RY) in terms of dry matter, nitrogen and phosphorus accumulation and adoption of suitable nutrient management for soybean/pigeonpea intercropping system.
2. Materials and methods Field experiments were conducted during the rainy (June to October) seasons of 2000, 2001 and 2002 at the research farm of Indian Institute of Soil Science, Bhopal, India. The region has a semi-arid tropical climate and receives an average rainfall of 1005 mm annually. Major part of the rain (88%) is received during June to September. Other weather parameters of the region and rainfall for the crop growing seasons and properties of soil of the experimental site have been described in the previous paper (Ghosh et al., 2005a). The experiment comprising three cropping systems (sole soybean, sole pigeonpea and soybean/pigeonpea intercrop), three tillage practices and three nutrient levels (N0 = 0% NPK, N1 = 100% recommended NPK and N2 = 100% NPK + 4 t farmyard manure (FYM) was laid out in split– split design (Ghosh et al., 2005a). The recommended doses of N:P:K for 100% NPK treatment both for soybean and pigeonpea was 30:26:25 kg ha 1. The NPK and FYM were
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applied every year. The entire dose of nitrogen, phosphorus and potassium was applied at sowing through urea, single super-phosphate and mutriate of potash, respectively. The FYM at 4 t dry weight ha 1 was applied 2 weeks before sowing. Plant samples were collected from 0.5 m2 land area at different stages of crop growth and oven dried at 65 8C until constant weight. Dry matter (DM) was determined based on the fresh weight of sample plants and the moisture content of the subsamples. Data on number and weight of nodules were collected at 50% flowering. Five plants were uprooted with a ball of soil for taking observation on nodulation. Keeping the root portion intact, the ball of soil was washed gently with clean running water followed by cleaning with a camel hairbrush to dislodge soil particles adhering to roots. Nodules from roots were removed, counted and the oven dry mass was measured (Vincent, 1970). Plant samples collected at harvest were analysed for N and P concentration in grain and straw and N and P uptake were determined. The procedures for calculating yield advantage, energy use efficiency and economic index have been described in the preceding paper (Ghosh et al., 2005a). Out of all the inputs for the different operations, manures and chemical fertilizers (NPK) consumed the bulk of the energy for all crops. Though soybean is a legume crop, the agronomic energy requirement for manure and fertilizer application was relatively high (Mandal et al., 2002). It is difficult to ascertain whether less uptake of a particular nutrient is the cause for less yield in intercropping situations. The nutritional relationships between intercrop components were evaluated using relative yield totals (RYT) (Hall, 1974). The RYT for total dry matter (DM) was calculated as (IDMa/SDMa) + (IDMb/SDMb), where IDMa and IDMb are intercrop DM for crop ‘a’ and crop ‘b’ and SDMa and SDMb are sole crop DM for crop ‘a’ and crop ‘b’. This is identical to land equivalent ratio. Relative yield is identical to the partial land equivalent ratio. The RYT for the nutrients was computed similar to that of RYT for total dry matter, in which uptake of corresponding nutrients in stead of dry matter were used in the formula. The RYT, relative N yield totals (RNYT) and relative P yield totals (RPYT) were used to estimate the N and P status of the component crops of the soybean/pigeon pea intercropping system. Theoretical consideration was that (i) if RYT RNYT, N is exploited less by the intercrops compared with other resources indicating that N is a limiting factor in intercropping performance, (ii) If RYT RNYT, N is exploited more by the intercrops compared with other resources indicating that N is not a limiting factor in intercropping performance (Hall, 1974). Similar was the case with RPYT. Statistical analysis of data was carried out using standard analysis of variance (Gomez and Gomez, 1984). The significance of the treatment effect was determined using the F-test. To determine the significance of the difference between the means of two treatments, least significant difference (L.S.D.) was computed at 5% probability level.
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3. Results 3.1. Growth In general, the crop growth rate (CGR) of both crops was higher under sole cropping than intercropping. The effect of nutrient treatment on CGR was not significant up to 30–45 days in soybean and up to 60–75 days in pigeonpea. The combined use of 100% NPK + FYM produced on average 59% higher CGR than the control plots (Fig. 1). Nodule
mass of both the crops also followed the same trend but the magnitude of reduction with no added NPK was more in soybean intercrop than pigeonpea intercrop (Fig. 2). The maximum nodule mass was observed in 100% NPK + FYM plots, though statistically it did not differ from 100% NPK. Effect of nutrient on root length density (RLD) of soybean was significant at surface layer (0–7.5 and 7.5–15 cm). Significant improvement in the RLD of soybean with 100% NPK + FYM compared to 100% NPK and control was observed (Fig. 3).
Fig. 1. Crop growth rate of different crops as influenced by nutrient management. (a) Sole soybean; (b) soybean as intercrop; (c) sole pigeon pea; (d) pigeon pea as intercrop. DAS and ns represents days after sowing and nonsignificant. Vertical bar represens L.S.D. (P = 0.05).
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Fig. 2. Nodule weight under different cropping systems and nutrient management practices. S, IS, P and IP represent sole soybean, intercrop soybean, sole pigeon pea and intercrop pigeon pea while N0, N1, N2 and ns represents no nutrient, recommnded dose of fertilizer, recommended dose of fertilizer plus farmyard manure and nonsignificant. Vertical bar represents L.S.D. (P = 0.05).
3.2. Yield Since treatments year was significant, yield data of each year are discussed. In the year 2000, pigeonpea plants were damaged after germination by water logging due to heavy rain in July. Therefore, yield of only soybean has been reported (data not presented). The integrated use of 100% NPK + 4 t FYM recorded significantly (*P < 0.05) higher seed yield of soybean over 100% NPK and control in 2000. On an average (2001 and 2002), soybean/pigeonpea intercropping system recorded 10 and 50.7% higher seed yield in terms of soybean equivalent yield (SEY) over sole pigeonpea and sole soybean (Table 1). Regardless of the cropping systems, the use of 100% NPK + 4 t FYM produced 14 and 52.7% higher yield over 100% NPK and control, respectively. Effect of interaction of cropping system nutrient was significant (Table 1) during 2001 and
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Fig. 3. Subsoiling effect on root length density distribution of soybean at anthesis. N0, N1, N2 and ns represents no nutrient, recommnded dose of fertilizer,recommended dose of fertilizer plus farmyard manure and nonsignificant. The horizental bar represents L.S.D. (P = 0.05).
2002. At N0, variation in SEY of sole pigeonpea and soybean/pigeonpea intercropping was not noticeable in 2001, while, at N1 and N2 intercropping significantly produced higher SEY than sole pigeonpea and sole soybean in 2001 and 2002 (Table 1). 3.3. Relative yield in terms of dry matter In general, the RY of soybean throughout the growth stages was greater than the RY of pigeon pea at all nutrient levels (Fig. 4). At soybean harvest, the RY of pigeon pea at N0 was about 0.6, while the RY of soybean almost reached 1.0 (Fig. 4). Though the RY of pigeon pea was lower than soybean at all the stages of growth, the differences of RY between the two crops narrowed at N1 and N2 levels as compared to N0. At soybean harvest, the RYof pigeon pea at N1 and N2 was 31–32% higher than that of N0. Similarly, the relative yield total at N1 and N2 was greater than the RYT at N0 in all the stages. After harvest of soybean the RY of pigeon pea improved and at the time of harvest of pigeon pea, it reached about 1.0, particularly at N1 and N2.
Table 1 Interaction effect of nutrient cropping system on soybeana equivalent yield (kg ha 1) Treatment
Sole soybean
Sole pigeonpea
Soybean/pigeonpea intercropping system
Mean
2001 Control 100% recommended NPK 100% NPK + 4 t FYM Mean L.S.D. (P = 0.05)
1050 1390 1597 1369 N = 155
1471 1887 2219 1859 C = 225
1408 2130 2423 1987 N C = 160
1310 1802 2080
2002 Control 100% recommended NPK 100% NPK + 4 t FYM Mean L.S.D. (P = 0.05)
899 1225 1350 1158 N = 120
1395 1650 1775 1601 C = 150
1550 1855 2012 1810 N C = 125
1295 1689 1896
N: nutrient; C: cropping system. a Yields of sole and intercrop pigeon pea were converted to soybean equivalent yield as (yield of pigeon pea unit price of pigeon pea)/unit price of soybean. Thus, SEY in intercropping is yield of intercrop soybean + SEY of intercrop pigeon pea.
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Fig. 4. Seasonal changes in yield of intercrop to sole crop under (a) no nutrient (N0), (b) recommnded dose of fertilizer (N1) and (c) recommended dose of fertilizer and farmyard manure (N2) condition. RY represents relative yield.
Fig. 5. Relative uptake of nitrogen (a) and phosphorus (b) by intercrop to sole crop under different nutrient treatments. N0, N1, N2 represents no nutrient, recommnded dose of fertilizer, recommended dose of fertilizer plus farmyard manure.
3.4. Relative nitrogen yield (RNY) and relative phosphorus yield (RPY)
but significantly (*P < 0.05) higher than sole soybean. The effect of nutrient management on energy use efficiency was not significant. The economic efficiency in terms of benefit:cost ratio (B:C) followed the trend similar to energy use efficiency. Soybean/pigeonpea intercropping registered the highest B:C ratio followed by sole pigeonpea and sole soybean. Net return was also maximum in the intercropping system (Table 2). The combined use of NPK and FYM gave higher net return and B:C ratio than 100% NPK and control.
At soybean harvest, the RNY of soybean was higher than RNY of pigeonpea for all the nutrient levels. The RNY of pigeon pea at N0 was about 0.5 at soybean harvest, while the corresponding RNY values both at N1 and N2 were about 0.6 (Fig. 5). At pigeonpea harvest, its RNY was about 0.9 for all the nutrient levels. In contrast, the RPY of soybean and pigeon pea at soybean harvest did not vary among nutrient levels, though it was higher at N1 and N2. The RPY of pigeon pea was higher (about 0.7) than the RNY of pigeon pea (0.5) at soybean harvest. But at pigeon pea harvest both RNY and RPY values were same. 3.5. Energy use and economics Energy output and energy use efficiency in soybean/ pigeonpea intercropping were comparable to sole pigeonpea
4. Discussion In terms of crop growth rate (CGR), the suppressive effect of pigeon pea on intercrop soybean was not significant indicating that pigeon pea was not an appreciable competitor for soybean for limiting factors. On the contrary, data in Fig. 3 showed that soybean benefited in association with pigeonpea. It is apparent that the deep-rooting ability of
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Table 2 Energy use efficiency and economics as influenced by nutrient management and cropping system Cropping systems
Energy input (MJ ha 1)
Energy output (MJ ha 1)
Net energy (MJ ha 1)
Energy use efficiency (output/input)
Net return (Rs ha 1)
Benefit:cost ratio
Sole soybean Sole pigeonpea Soybean/pigeonpea intercropping L.S.D. (P = 0.05) Control 100% recommended NPK 100% NPK + 4 t FYM L.S.D. (P = 0.05)
6776 6364 5600
20660 90505 78709
13884 84141 73109
3130 5794 6994
11941 22902 27136
8810 17108 20143
3.0 14.2 14.0 2.6 3.77 3.92 3.86 NS
3711 11219 19104 1055 9197 11698 13755 879
1.32 2.00 2.78 0.15 2.02 2.04 2.20 0.12
NS: not significant.
pigeonpea could enhance the possibility of recycling of nutrients, especially nitrogen and phosphorus from the deeper soil layers and therefore improved the nutrient use efficiency of the cropping system by capturing and utilizing nutrient in the upper most soil layer which could otherwise be leached out to deep soil layers (Arihara et al., 1991; Ito et al., 1992, 1993, 1996; Adu-Gyamfi et al., 1993). Benefit to soybean in association with pigeonpea was also assessed in terms of RY, RNY and RPY. The RY, RNY and RPY of soybean at its harvest were about 1.0. This suggested that soybean was not disadvantaged by the intercropping with pigeonpea in terms of growth, and N and P uptake. In contrast, the corresponding RY and RNY of pigeon pea were about 0.6, particularly when fertilizer and manure were not applied. These never reached 1.0 till soybean harvest. The presence of soybean reduced the dry matter yield and N yield of pigeonpea indicating that soybean was a strong competitor with pigeon pea for N during the first half of the cropping system. In this system, it is surmised that fast growing soybean exhausted the soil N quickly, due to which, the slow growing pigeonpea suffered from N deficiency. Further, the RY of pigeon pea was greater than its RNY at soybean harvest. Thus, it is clear that, although pigeon pea is a legume, it suffered from N deficiency in the intercropping system until soybean harvest. This may be attributed to the fact that at soybean harvest, pigeon pea was at the vegetative stage and peak flowering of pigeon pea occurred after harvest of soybean. This suggests that before soybean harvest soil N was fully utilized by soybean and BNF of pigeon pea was not sufficient to meet its N requirement during early growth. This corroborated the findings of Tobita et al. (1994, 1996). Using the concept of RY and RNY in the sorghum/pigeon pea intercropping system, they concluded that before sorghum harvest, pigeonpea suffered from N deficiency and soil N was exhausted by its companion crop: however, pigeon pea increased BNF dependency after sorghum harvest. It may further be noted that though soybean is a legume, its N uptake is high and the crop may respond up to 60 kg N ha 1 (Singh et al., 2001). This is the reason why in the present study soil N is exhausted by soybean as reported by Tobita et al. (1996) in the sorghum/pigeon pea intercropping system. It is apparent from RY and RNY values that once soybean entered its maturity phase, its competitive effect on pigeon
pea was greatly reduced. After the harvest of soybean, the RY and RNY of pigeon pea gradually increased and approached near 1.0 at its maturity at all the nutrient levels. This is attributed to the fact that pigeon pea attained peak flowering after the harvest of soybean and increased its dependency on BNF, and total amount of N in intercrop pigeon pea increased and approached that of sole pigeon pea. Tobita et al. (1996) had similar observation in the sorghum/pigeon pea intercropping system. On the contrary, the RNY and RY of soybean showed no noticeable variation indicating that N was not a limiting factor for its growth when intercropped with pigeonpea even when N was not applied. Pigeonpea utilized soil- and fertilizer-N as efficiently as soybean (Ito et al., 1994; AduGyamfi et al., 1996), thereby inviting a risk of considerable competition for N with component soybean crop. Unless N was supplied either through organic or inorganic sources at the early stage of pigeonpea growth, the crop suffered as evident from less RY and RNY of pigeonpea at N0 (Fig. 4). In the present study, the suppression effect of soybean on pigeon pea, however, was reduced when manures and fertilizers were both applied as indicated by higher RY and RNY (Figs. 4 and 5) and nodule mass of pigeon pea (Fig. 2) in 100% NPK (N1) and 100% NPK + FYM (N2) than in control (N0). Tobita et al. (1996) also observed that soil-N in the sorghum/pigeon pea intercropping system was more limiting at a relatively low amount of fertilizer-N and there was less competition for N between component crops grown in a high-N treatment. Thus, it is clear that the application of a reasonable amount of fertilizer is necessary to meet the N demand of both the crops during the first half of their crop growth and to realize higher yield in soybean/pigeonpea intercropping system. The effect of 100% NPK + FYM on RY, RNY, CGR, nodulation and RLD (Fig. 3) was more pronounced than 100% NPK. Many researchers (Reddy and Willey, 1981; Nambiar et al., 1983, 1986; Ofori et al., 1987; Rerkasem and Rerkasem, 1988; Rerkasem et al., 1988; Ghosh, 2004) have concluded that nearly all legumes fixed less atmospheric N if the soil had high N content through either high native fertility or application of fertilizer to intercropping system. However, in the present study, application of 100% NPK (30 kg N ha 1) + 4 t FYM ha 1 improved nodule mass. Ghosh et al. (2004b) also had similar
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observation in the same soil with 75% NPK + 5 t FYM ha 1 in sorghum/soybean intercropping system. This was attributed to confounding effect of many conditions, viz., (i) the soil of the experimental site is rated as low in available N (145 kg N ha 1), and had less permeable, high bulk density sub surface (15–30 cm) layer, (ii) slowly released N from FYM and repeated applications of FYM provided better soil physical and chemical environment for nitrogenase activity (Misra et al., 1990; Hati et al., 2001), and (iii) soybean often responded up to 60 kg N because of high N accumulation in the edible parts. Therefore, in the soybean/ pigeon pea intercropping system where greater competition between companion crops for N exists, application of 30 kg fertilizer-N in N deficient soil seemed inadequate because pigeon pea also utilized soil-N on par with soybean. The above facts thus suggest that the application of 100% NPK + 4 t FYM ha 1 was not sufficient to raise soil-N to the level affecting nodulation noticeably. Thus, it is apparent that application of 100% NPK + 4 t FYM could meet the N demand and sustain the productivity in the intercropping system (Table 1). The RPY value of both the crops at soybean harvest was the same at N0 but was relatively more in pigeonpea than soybean at N1 and N2. This indicates that both the crops utilized P better than other possible limiting resources. In fact, legumes act as a catalyst to augment availability of native and fixed P. Therefore, P was not limiting for soybean/ pigeonpea intercropping system even at N0 level at the time of soybean harvest. Many workers (Nimje and Seth, 1987; Ae et al., 1990) suggested that phosphorus fertilization to legume helped to enhance the excretion of amino acids in the rhizosphere. Therefore, RPY values of both the crops at N1 and N2, where P was applied, were always higher than that at N0 level even at the early stages of crop growth. It was further observed that at pigeon pea harvest, its RPY further increased (Fig. 5). This suggests that pigeonpea utilized native P better than soybean in the system because it solubilizes otherwise insoluble Ca-P in vertisols by moderating rhizosphere pH by excreting citric acid (Shibata and Katsuya, 2003). In the intercropping system, pigeon pea contributed more biomass yield than soybean. As mentioned earlier pigeon pea, being a deep-rooted crop utilized more of applied nutrient and sub-soil moisture. This positive effect of pigeonpea benefitted associated soybean crop. Jena and Misra (1995) reported that pigeonpea root could utilize soil water up to a depth of 105 cm. These positive effects combined with higher biomass of pigeonpea ultimately contributed to more yield in the intercropping system. The net profit of soybean/pigeonpea intercropping was greater than sole cropping. Higher pigeonpea biomass was mainly responsible for higher profit in this system. Effect of nutrient management on energy use efficiency was statistically neutral, which implies that energy output in terms of biomass yield was compensated by energy input through manures and fertilizers.
5. Conclusion Based on relative yield, relative nitrogen yield and relative phosphorus yield of soybean and pigeonpea in the intercropping system, the study suggests that in N-and Pdeficient Vertisols, only N was the limiting factor during the early part of the cropping system which affected growth of pigeonpea owing to competition with soybean in soybean/ pigeonpea intercropping system. Soil-N was more limiting when no fertilizer-N was applied and diminished at a high-N level. To meet N demand of the intercropped pigeonpea, and sustain the productivity of soybean/pigonpea intercropping system, application of 100% NPK (30 kg N, 26 kg P and 25 kg K) + 4 t FYM is a viable nutrient management option. Alternatively, to reduce the competition for N during the initial stages of growth, the dependence of pigeonpea on biological nitrogen fixation through biofertilizers needs to be increased so that sufficient N would be available for pigeon pea grown on a nutrient-limited Vertisol.
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