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Effect of irrigation and nitrogen on maize-cowpea fodder intercropping at Ludhiana, India: Advantages and intercrop competition
Field Crops Research, 18 (1988) 177-184
177
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of Irrigation and Nitrogen on Maize-Cowpea Fodder Intercropping at Ludhiana, India: Advantages and Intercrop Competition G.C. AGGARWAL and A.S. SIDHU
Department of Soils, Punjab Agricultural University, Ludhiana 141 004 (India) (Accepted 13 October 1987)
ABSTRACT Aggarwal, G.C. and Sidhu, A.S., 1988. Effect of irrigation and nitrogen on maize-cowpea fodder intercropping at Ludhiana, India: advantages and intercrop competition. Field Crops Res., 18: 177-184. This study was undertaken to examine intercrop competition and the intercropping advantage of maize-cowpea fodder at three irrigation and four nitrogen levels. Another objective was to develop relationships among different measures used for evaluating intercrop competition. The residual effect of intercropping on a following pearl millet fodder crop was also investigated. Yield intercropping advantage was observed at all irrigation and nitrogen levels. Land equivalent ratio values varied from 1.04 to 1.17 for different nitrogen and irrigation levels. There was an advantage in crude protein production similar to that in yield. Intercrop competition was affected by nitrogen and irrigation. The competitive ratio for maize changed from 0.8 at zero nitrogen to 1.46 at 120 kg N/ha. Pearl millet fodder grown after intercrop yielded 42% more than after maize. Relationships were developed for computing relative crowding coefficients and aggressivities from individual crop land equivalent ratios.
INTRODUCTION
Intercropping, practised widely throughout the tropics (Willey, 1979; Waghmare and Singh 1984a,b; Tariah and Wahua, 1985; Natarajan and Willey, 1986), can be an advantageous system due to its better utilization of environmental resources (Sivakumar and Virmani, 1980; Natarajan and Willey 1980; and Reddy and Willey, 1981 ). Many measures have been used for evaluating intercropping advantages and intercrop competition ( Willey, 1979). Recent reports (Baker and Blamey, 1985; Chang and Shibles, 1985) have repudiated the general belief that intercropping is advantageous only at low levels of inputs and technology. Cereal-legume fodder mixtures provide balanced animal feed and also improve soil productivity. However, reports on advantages of intercropping cereal-legume fodders, especially at different levels of inputs, are few. 0378-4290/88/$03.50
© 1988 Elsevier Science Publishers B.V.
178 TABLE 1 Meteorologicalparameters during the growing seasons Year and month 1983 June July August September October
Temperature(°C)
Rainfall (ram)
Evap. (ram/day)
Mean R.H. ( %)
Max
Min
39.0 35.1 33.4 34.0 31.2
24.0 25.8 25.8 24.0 15.5
27.4 200 373 69 4.1
8.6 5.3 3.7 3.6 3.6
45 72 84 79 65
38.7 33.6 33.1 32.1 31.8
28.0 25.3 25.7 21.6 14.0
30 278 291 94 3
9.0 4.8 5.1 4.4 4.3
57 76 82 74 56
1984
June July August September October
'Class A pan average evaporation. This study was undertaken to examine: (1) the effect of nitrogen and irrigation on maize (Zea mays L. ) and cowpea ( Vigna sinensis) fodder intercropping advantages and intercrop competition; (2) the residual effect of such intercropping on a succeeding pearl millet (Pennisetum americanum L. ) fodder crop; and ( 3 ) relationships among different measures used for evaluating intercrop competition. MATERIALS AND METHODS A field experiment was conducted at Ludhiana, India (Lat. 30 ° 5 6 ' N Long. 75 ° 5 2 ' E ) during 1983 and 1984 on a calcareous, Typic Ustochrept, Fatehpur sandy loam soil. The experimental soil was low in organic carbon (0.35%) and available N (162 kg N / h a ) and medium in 0.5N N a i l CO3-extractable P (15.6 kg/ha) and available K (140 k g / h a ) . Soil water content at - 0 . 0 3 3 M P a and at - 1 . 5 M P a water potential was 12.9 and 5.7% (by weight), respectively. Meteorological parameters during the growth seasons are given in Table 1. The effects of three variables, crop system, nitrogen level, and irrigation level, were studied. Sole maize, sole cowpea and a 1:1 maize-cowpea intercrop were fertilized with 0, 40, 80 and 120 kg N / h a (treatments N0....N120) and irrigated at IW/PAN-E ratios (Prihar et al., 1974) of 0.6, 0.9 and 1.2 (IW denotes a fixed amount of 7.5 cm of irrigation water, and PAN-E is the cumulative evaporation from an open pan minus effective rain since the previous irrigation). Irrigations were applied by the border method. H a l f of the N was applied as urea (46% N) at the time of sowing and the rest with the first irrigation (com-
179
mon to all treatments) 20 days after sowing (DAS). Basal doses of P and K were applied at 26.2 kg P and 24.9 kg K/ha, in the forms of single superphosphate and muriate of potash, respectively. All crops were hand-sown in rows 30 cm apart. Intra-row spacing ( 7.5 cm; consequent plant number 444 400/ha) for each crop was the same in intercropping as in sole cropping, and thus the intercropping treatment was a simple replacement. Plot size was 6 m × 3 m. Treatments were combined in a randomized-block design with three replications. Harvesting was done 60 DAS and the yield of green fodder was recorded. The yields of cowpea and maize in the intercrop were recorded separately. Fodder yield was standardized to 80% moisture content (fresh-weight basis). To indicate the relative advantages of intercropping and intercrop competition at any given irrigation or nitrogen level, individual crop land equivalent ratios (LER; Natarajan and Willey, 1986) were calculated using sole-crop yields from the same treatment as the intercrop. Yield advantages of intercropping were assessed from total LER, the sum of the individual crop LERs. For further evaluation of the intercrop system, the residual effect on a following pearl millet crop, sown after harvesting, was also studied. Irrigation treatments became replications for the succeeding pearl millet experiment. Basal doses of 26.2 kg P / h a and 24.9 kg K/ha, but no nitrogen, were applied. The crop was irrigated normally and harvested 60 DAS. The nitrogen content of the three crops was determined (Piper, 1966) for estimating crude protein production.
Relationships among different intercrop competition measures Land equivalent ratio for the ab intercrop is calculated as per Willey, (1979) : LER=La+Lb
L~ = Y~b/ Yaaand Lb = Yba/ Ybb where Y~b and Yb~ are yields of crop a and crop b, respectively, in the ab intercrop, and Y~ and Ybb are yields of sole crops a and b, respectively. L, and/_~ are LERS for individual crops a and b. The relative crowding coefficient for crop a (K~b) in a 1:1 intercrop with crop b is calculated as:
K~b = Yab/( Ya~- Ybb) which can be written as
K.b= ( Y.l, lY..) l ( Ya.IY.a-- Y.JY..) or
K~b=LJ(1--L~)
(1)
180
Similarly, the relative crowding coefficient for crop b (Kba) is Kba = / - ¢ / ( 1 - - / ~ )
(2)
Aggressivity for crop a (Aab) in the intercrop ab is calculated as A~b= Yab/Yaa- YbJYbb which can be written as
A~b=L~-Lb
(3)
Similarly, aggressivity for crop b (Aba) in the intercrop ab is
Ab~=Lb--La
(4)
Thus relative crowding coefficient for both individual crops and intercrop, as well as aggressivity values for the individual crops in an intercrop, can be easily computed from individual crop LERs. RESULTS AND DISCUSSION
A yield advantage of intercropping over sole cropping was observed at all N and irrigation levels (Table 2 ), with LER of 1.09 averaged over all treatments. However, differences in LER values at different levels of N and irrigation were non-significant. Although the relative fodder yield advantage of the intercrop was consistent at all N levels, the relative contribution to yield from maize increased with N level. Rao and Willey (1981) also reported that differences TABLE2
Land equivalent ratio (LER) relative crowding coefficient ( n c c ) aggressivity, and competitive ratio for yields of individual crops and a 1:1 intercrop of maize~cowpea fodder at different levels of irrigation and nitrogen Treatment
1 0.6 1 0.9 I 1.2 LSD (0.05) No N4o Nso N,2o LSD (0.05)
LER
Aggressivity
RCC
Competitive ratio
Cowpea Maize Intercrop Cowpea Maize Intercrop Cowpea Maize
Maize
0.54 0.51 0.51
0.03 0.05 0.06
1.06 1.10 1.12
-0.13 -0.01 0.10 0.20
0.80 0.98 1.21 1.46
0.57 0.56 0.57
1.11 1.07 1.08
ns
ns
ns
0.65 0.55 0.47 0.43
0.52 0.54 0.57 0.63
1.17 1.09 1.04 1.06
ns
ns
ns
ns = not significant.
1.17 1.04 1.04 . 1.06 1.22 0.89 0.75 .
1.33 1.27 1.33 .
. 1.08 1.17 1.33 1.70
.
.
1.56 1.32 1.38 . 2.01 1.43 1.18 1.28 .
-0.03 -0.05 -0.06 .
. 0.13 0.01 -0.10 - 0.20
.
.
181
in L E R values at different fertility levels were statistically non-significant. Likewise, Ahmed and Rao (1982) found that LER values of a maize-soybean intercrop were greater than 1.0 at all N levels and at all locations, although the intercrop advantage declined at higher N levels. Chang and Shibles (1985) reported dry-matter LER values greater than 1.0 under three fertilizer levels at three growth stages. A consistent yield advantage of intercropping sorghum and soybean grain over sole cropping, with a LER of 1.17 averaged over three N levels, was reported by Baker and Blarney (1985). Irrigation frequency did not affect LER ( Table 2 ). This agrees with findings of Rao and Willey (1980) and Natarajan and Willey (1986) that moisture availability has no observable effect on LER.
Competition between intercrops Intercrop competition was affected by both nitrogen and irrigation. Land equivalent ratio for cowpea decreased and that for maize increased with increase in nitrogen; similar results have been reported by Baker and Blamey (1985). Evaluated in terms of relative crowding coefficients as well as aggressivity, cowpea changed from a dominant species at lower N levels to a dominated species at higher N. The behaviour of maize was the reverse of cowpea. The competitive ability of maize was almost equal to that of cowpea at N4o. For quantifying competition between competing crops at different irrigation and nitrogen levels the competitive ratio (Willey and Rao, 1980) was computed, as other measures have some limitations ( Table 2). Nitrogen increased the competitive ability of the maize, increasing from 0.80 at zero N to 1.46 at 120 kg N/ha. Since the competitive ratio values of the two crops are the reciprocal of each other, those for only one of the crops are presented. The results show that cowpea is more competitive than maize only when grown under N and irrigation constraints.
Crude protein production advantage The advantage in crude protein production followed the trend of yield advantage (Table 3 ). Enhanced nitrogen uptake by intercrops has been reported earlier, and has been claimed as the basis of yield benefits from sorghum-legume intercropping (Waghmare and Singh, 1984a).
Sole crop and intercrop yields Sole maize gave the highest fodder yields except at No, and sole cowpea the least (Table 4). Sole cowpea significantly responded to N up to 40 kg N / h a only, whereas increases in yields of sole maize and of the maize-cowpea intercrop were significant up to 120 kg N/ha. However, the contribution of cowpea
182 TABLE 3 Land equivalent ratios for crude protein production of individual crops and 1:1 intercrop of maizecowpea fodder at different nitrogen levels N level
No N4o Nso N12o
Land equivalentratios
Cowpea
Maize
Intercrop
0.70 0.57 0.47 0.40
0.50 0.54 0.57 0.67
1.20 1.11 1.04 1.07
TABLE4 Effectofnitro~nontheyieldofso~andintercrop ~dders(t/ha) Crop
Sole cowpea Sole maize Intercrop Mean
N applied (kg/ha)
Mean
0
40
80
120
21.6 27.9 28.2 25.9
24.4 40.5 35.2 33.4
24.8 48.5 38.9 37.4
25.4 52.8 43.6 40.6
24.1 42.4 36.5
LSD (0.05) for N= 1.4; for fodder= 1.3; for NX fodder=2.5
in intercrop yield (data of separate components of intercrop not given) decreased with increase in N.
Residual effect of cropping system Both the preceding cropping system and applied N at 120 kg/ha had significant effects on the succeeding pearl millet fodder yield (Table 5 ). Pearl millet fodder yield was the highest when grown after cowpea. Averaged over all N treatments, pearl millet grown after the intercrop yielded 42% more than after maize. Yadav (1981) and Waghmare and Singh (1984b) reported a similar effect of intercropping on the succeeding crop. The higher yield of a sole crop succeeding an intercrop has been attributed to better residual fertility (Nair et al., 1979). We found that N uptake by pearl millet (25.5 kg/ha) following the intercrop was 1.3 times that after maize (data not shown). Yields of cereal-legume intercrops have, generally, been found to be less than those of cereal crops, and the results of this study support this (Table 4). Consequently, intercropping has been advocated either for balanced food production or other specific considerations. T h a t approach ignores the beneficial residual effect of intercropping. A rational evaluation of cereal-legume intercropping should be
183 TABLE 5 Residual effect of sole and intercrop fodder and nitrogen on succeeding pearl millet fodder yield (t/ha) Preceding crop
N applied to preceding fodder (kg/ha) 0
40
80
120
Mean
Sole cowpea Sole maize Intercrop
18.9 9.5 16.1
19.0 10.4 14.6
20.0 10.8 15.3
22.5 13.0 15.6
19.9 10.9 15.4
Mean
14.7
14.7
15.4
16.8
LSD ( 0.05 ) for N = 1.4; proceeding crop = 1.2; N X proceeding crop = 2.5 TABLE 6 Fodder yield (t/ha fresh wt.) of the crop sequences at different nitrogen levels Crop sequence
Cowpea--* Millet Maize ~ Millet Cowpea + Maize Millet
N applied (kg/ha) 0
40
80
120
Mean
40.5 37.4 44.3
43.3 50.9 49.8
44.8 59.3 54.2
47.9 65.6 59.2
44.0 53.3 51.7
based on crop-sequence yields. The total crop sequence fodder yield of the intercrop system was comparable to yield of the sole-crop sequence (Table 6). Higher crop-sequence yields from intercropping at low inputs indicate that intercropping is more beneficial under N and irrigation constraints.
REFERENCES Ahmed, S. and Rao, M.R., 1982. Performance of maize-soybean intercrop combination in the tropics: results of a multi-location study. Field Crops Res., 5: 147-161. Baker, C.M. and Blamey, F.P.C., 1985. Nitrogen fertilizer effects on yield and nitrogen uptake of sorghum and soybean, grown in sole cropping and intercropping systems. Field Crops Res., 12: 233-240. Chang, J.F. and Shibles, R.M., 1985. An analysis of competition between intercropped cowpea and maize. II. The effect of fertilization and population density. Field Crops Res., 12: 145-152. Nair, K.P.P., Patel, U.K., Singh, R.P. and Kaushik, M.K., 1979. Evaluation of legume intercropping in conservation of fertilizer nitrogen in maize culture. J. Agric. Sci., Camb., 93: 189-194. Natarajan, M. and Willey, R.W., 1980. Sorghum-pigeonpea intercropping and the effects of plant population. 2. Resource use. J. Agric. Sci., Camb., 95: 59-65. Natarajan, M. and Willey, R.W., 1986. The effects of water stress on yield advantages of intercropping systems. Field Crops Res., 13: 117-131.
184 Piper, G.S., 1966. Soil and Plant Analysis. Hans Publications, Bombay, India, 368 pp. Prihar, S.S., Gajri, P.R. and Narang, R.S. 1974. Scheduling irrigation to wheat using pan evaporation. Indian J. Agric. Sci., 44: 567-571. Rao, M.R. and Willey, R.W., 1980. Evaluation of yield stability in intercropping : Studies on sorghum/pigeonpea. Exp. Agric., 16: 105-116. Rao, M.R. and Willey, R.W., 1981. Stability of performance of a pigeonpea-sorghum intercropping system. In : Proc. International Workshop on Intercropping, 10-13 January 1979, ICRISAT, Hyderabad, India. ICRISAT,Patancheru, A.P., pp. 306-317. Reddy, M.S. and Willey, R.W., 1981. Growth and resource use studies in an intercrop of pearl millet/groundnut. Field Crops Res., 4 : 13-24. Sivakumar, M.V.K. and Virmani, S.M., 1980. Growth and resource use of maize, pigeonpea and maize-pigeonpea intercrop in an operational research watershed. Exp. Agric., 16 : 377-386. Tariah, N.M. and Wahua, T.A.T. 1985. Effects of component populations on yields and land equivalent ratios of intercropped maize and cowpea. Field Crops Res., 12 : 81-89. Waghmara, A.B. and Singh, S.P., 1984a. Sorghum-legume intercropping and the effects of nitrogen fertilization. 1. Yield and nitrogen uptake by crops. Exp. Agric., 20: 251-259. Waghmare, A.B. and Singh, S.P., 1984b. Sorghum-legume intercropping and the effects of nitrogen fertilization. 2. Residual effect on wheat. Exp. Agric., 20: 261-265. Willey, R.W., 1979. Intercropping-Its importance and research needs. Part 1. Competition and yield advantages. Field Crop Abstr., 32: 1-10. Willey, R.W. and Rao, M.B., 1980. A competitive ratio for quantifying competition between intercrops. Exp. Agric., 16: 117-125. Yadav, R.L., 1981. Intercropping pigeonpea to conserve fertilizer nitrogen in maize and produce residual effects on sugarcane. Exp. Agric., 17: 311-315.
177
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of Irrigation and Nitrogen on Maize-Cowpea Fodder Intercropping at Ludhiana, India: Advantages and Intercrop Competition G.C. AGGARWAL and A.S. SIDHU
Department of Soils, Punjab Agricultural University, Ludhiana 141 004 (India) (Accepted 13 October 1987)
ABSTRACT Aggarwal, G.C. and Sidhu, A.S., 1988. Effect of irrigation and nitrogen on maize-cowpea fodder intercropping at Ludhiana, India: advantages and intercrop competition. Field Crops Res., 18: 177-184. This study was undertaken to examine intercrop competition and the intercropping advantage of maize-cowpea fodder at three irrigation and four nitrogen levels. Another objective was to develop relationships among different measures used for evaluating intercrop competition. The residual effect of intercropping on a following pearl millet fodder crop was also investigated. Yield intercropping advantage was observed at all irrigation and nitrogen levels. Land equivalent ratio values varied from 1.04 to 1.17 for different nitrogen and irrigation levels. There was an advantage in crude protein production similar to that in yield. Intercrop competition was affected by nitrogen and irrigation. The competitive ratio for maize changed from 0.8 at zero nitrogen to 1.46 at 120 kg N/ha. Pearl millet fodder grown after intercrop yielded 42% more than after maize. Relationships were developed for computing relative crowding coefficients and aggressivities from individual crop land equivalent ratios.
INTRODUCTION
Intercropping, practised widely throughout the tropics (Willey, 1979; Waghmare and Singh 1984a,b; Tariah and Wahua, 1985; Natarajan and Willey, 1986), can be an advantageous system due to its better utilization of environmental resources (Sivakumar and Virmani, 1980; Natarajan and Willey 1980; and Reddy and Willey, 1981 ). Many measures have been used for evaluating intercropping advantages and intercrop competition ( Willey, 1979). Recent reports (Baker and Blamey, 1985; Chang and Shibles, 1985) have repudiated the general belief that intercropping is advantageous only at low levels of inputs and technology. Cereal-legume fodder mixtures provide balanced animal feed and also improve soil productivity. However, reports on advantages of intercropping cereal-legume fodders, especially at different levels of inputs, are few. 0378-4290/88/$03.50
© 1988 Elsevier Science Publishers B.V.
178 TABLE 1 Meteorologicalparameters during the growing seasons Year and month 1983 June July August September October
Temperature(°C)
Rainfall (ram)
Evap. (ram/day)
Mean R.H. ( %)
Max
Min
39.0 35.1 33.4 34.0 31.2
24.0 25.8 25.8 24.0 15.5
27.4 200 373 69 4.1
8.6 5.3 3.7 3.6 3.6
45 72 84 79 65
38.7 33.6 33.1 32.1 31.8
28.0 25.3 25.7 21.6 14.0
30 278 291 94 3
9.0 4.8 5.1 4.4 4.3
57 76 82 74 56
1984
June July August September October
'Class A pan average evaporation. This study was undertaken to examine: (1) the effect of nitrogen and irrigation on maize (Zea mays L. ) and cowpea ( Vigna sinensis) fodder intercropping advantages and intercrop competition; (2) the residual effect of such intercropping on a succeeding pearl millet (Pennisetum americanum L. ) fodder crop; and ( 3 ) relationships among different measures used for evaluating intercrop competition. MATERIALS AND METHODS A field experiment was conducted at Ludhiana, India (Lat. 30 ° 5 6 ' N Long. 75 ° 5 2 ' E ) during 1983 and 1984 on a calcareous, Typic Ustochrept, Fatehpur sandy loam soil. The experimental soil was low in organic carbon (0.35%) and available N (162 kg N / h a ) and medium in 0.5N N a i l CO3-extractable P (15.6 kg/ha) and available K (140 k g / h a ) . Soil water content at - 0 . 0 3 3 M P a and at - 1 . 5 M P a water potential was 12.9 and 5.7% (by weight), respectively. Meteorological parameters during the growth seasons are given in Table 1. The effects of three variables, crop system, nitrogen level, and irrigation level, were studied. Sole maize, sole cowpea and a 1:1 maize-cowpea intercrop were fertilized with 0, 40, 80 and 120 kg N / h a (treatments N0....N120) and irrigated at IW/PAN-E ratios (Prihar et al., 1974) of 0.6, 0.9 and 1.2 (IW denotes a fixed amount of 7.5 cm of irrigation water, and PAN-E is the cumulative evaporation from an open pan minus effective rain since the previous irrigation). Irrigations were applied by the border method. H a l f of the N was applied as urea (46% N) at the time of sowing and the rest with the first irrigation (com-
179
mon to all treatments) 20 days after sowing (DAS). Basal doses of P and K were applied at 26.2 kg P and 24.9 kg K/ha, in the forms of single superphosphate and muriate of potash, respectively. All crops were hand-sown in rows 30 cm apart. Intra-row spacing ( 7.5 cm; consequent plant number 444 400/ha) for each crop was the same in intercropping as in sole cropping, and thus the intercropping treatment was a simple replacement. Plot size was 6 m × 3 m. Treatments were combined in a randomized-block design with three replications. Harvesting was done 60 DAS and the yield of green fodder was recorded. The yields of cowpea and maize in the intercrop were recorded separately. Fodder yield was standardized to 80% moisture content (fresh-weight basis). To indicate the relative advantages of intercropping and intercrop competition at any given irrigation or nitrogen level, individual crop land equivalent ratios (LER; Natarajan and Willey, 1986) were calculated using sole-crop yields from the same treatment as the intercrop. Yield advantages of intercropping were assessed from total LER, the sum of the individual crop LERs. For further evaluation of the intercrop system, the residual effect on a following pearl millet crop, sown after harvesting, was also studied. Irrigation treatments became replications for the succeeding pearl millet experiment. Basal doses of 26.2 kg P / h a and 24.9 kg K/ha, but no nitrogen, were applied. The crop was irrigated normally and harvested 60 DAS. The nitrogen content of the three crops was determined (Piper, 1966) for estimating crude protein production.
Relationships among different intercrop competition measures Land equivalent ratio for the ab intercrop is calculated as per Willey, (1979) : LER=La+Lb
L~ = Y~b/ Yaaand Lb = Yba/ Ybb where Y~b and Yb~ are yields of crop a and crop b, respectively, in the ab intercrop, and Y~ and Ybb are yields of sole crops a and b, respectively. L, and/_~ are LERS for individual crops a and b. The relative crowding coefficient for crop a (K~b) in a 1:1 intercrop with crop b is calculated as:
K~b = Yab/( Ya~- Ybb) which can be written as
K.b= ( Y.l, lY..) l ( Ya.IY.a-- Y.JY..) or
K~b=LJ(1--L~)
(1)
180
Similarly, the relative crowding coefficient for crop b (Kba) is Kba = / - ¢ / ( 1 - - / ~ )
(2)
Aggressivity for crop a (Aab) in the intercrop ab is calculated as A~b= Yab/Yaa- YbJYbb which can be written as
A~b=L~-Lb
(3)
Similarly, aggressivity for crop b (Aba) in the intercrop ab is
Ab~=Lb--La
(4)
Thus relative crowding coefficient for both individual crops and intercrop, as well as aggressivity values for the individual crops in an intercrop, can be easily computed from individual crop LERs. RESULTS AND DISCUSSION
A yield advantage of intercropping over sole cropping was observed at all N and irrigation levels (Table 2 ), with LER of 1.09 averaged over all treatments. However, differences in LER values at different levels of N and irrigation were non-significant. Although the relative fodder yield advantage of the intercrop was consistent at all N levels, the relative contribution to yield from maize increased with N level. Rao and Willey (1981) also reported that differences TABLE2
Land equivalent ratio (LER) relative crowding coefficient ( n c c ) aggressivity, and competitive ratio for yields of individual crops and a 1:1 intercrop of maize~cowpea fodder at different levels of irrigation and nitrogen Treatment
1 0.6 1 0.9 I 1.2 LSD (0.05) No N4o Nso N,2o LSD (0.05)
LER
Aggressivity
RCC
Competitive ratio
Cowpea Maize Intercrop Cowpea Maize Intercrop Cowpea Maize
Maize
0.54 0.51 0.51
0.03 0.05 0.06
1.06 1.10 1.12
-0.13 -0.01 0.10 0.20
0.80 0.98 1.21 1.46
0.57 0.56 0.57
1.11 1.07 1.08
ns
ns
ns
0.65 0.55 0.47 0.43
0.52 0.54 0.57 0.63
1.17 1.09 1.04 1.06
ns
ns
ns
ns = not significant.
1.17 1.04 1.04 . 1.06 1.22 0.89 0.75 .
1.33 1.27 1.33 .
. 1.08 1.17 1.33 1.70
.
.
1.56 1.32 1.38 . 2.01 1.43 1.18 1.28 .
-0.03 -0.05 -0.06 .
. 0.13 0.01 -0.10 - 0.20
.
.
181
in L E R values at different fertility levels were statistically non-significant. Likewise, Ahmed and Rao (1982) found that LER values of a maize-soybean intercrop were greater than 1.0 at all N levels and at all locations, although the intercrop advantage declined at higher N levels. Chang and Shibles (1985) reported dry-matter LER values greater than 1.0 under three fertilizer levels at three growth stages. A consistent yield advantage of intercropping sorghum and soybean grain over sole cropping, with a LER of 1.17 averaged over three N levels, was reported by Baker and Blarney (1985). Irrigation frequency did not affect LER ( Table 2 ). This agrees with findings of Rao and Willey (1980) and Natarajan and Willey (1986) that moisture availability has no observable effect on LER.
Competition between intercrops Intercrop competition was affected by both nitrogen and irrigation. Land equivalent ratio for cowpea decreased and that for maize increased with increase in nitrogen; similar results have been reported by Baker and Blamey (1985). Evaluated in terms of relative crowding coefficients as well as aggressivity, cowpea changed from a dominant species at lower N levels to a dominated species at higher N. The behaviour of maize was the reverse of cowpea. The competitive ability of maize was almost equal to that of cowpea at N4o. For quantifying competition between competing crops at different irrigation and nitrogen levels the competitive ratio (Willey and Rao, 1980) was computed, as other measures have some limitations ( Table 2). Nitrogen increased the competitive ability of the maize, increasing from 0.80 at zero N to 1.46 at 120 kg N/ha. Since the competitive ratio values of the two crops are the reciprocal of each other, those for only one of the crops are presented. The results show that cowpea is more competitive than maize only when grown under N and irrigation constraints.
Crude protein production advantage The advantage in crude protein production followed the trend of yield advantage (Table 3 ). Enhanced nitrogen uptake by intercrops has been reported earlier, and has been claimed as the basis of yield benefits from sorghum-legume intercropping (Waghmare and Singh, 1984a).
Sole crop and intercrop yields Sole maize gave the highest fodder yields except at No, and sole cowpea the least (Table 4). Sole cowpea significantly responded to N up to 40 kg N / h a only, whereas increases in yields of sole maize and of the maize-cowpea intercrop were significant up to 120 kg N/ha. However, the contribution of cowpea
182 TABLE 3 Land equivalent ratios for crude protein production of individual crops and 1:1 intercrop of maizecowpea fodder at different nitrogen levels N level
No N4o Nso N12o
Land equivalentratios
Cowpea
Maize
Intercrop
0.70 0.57 0.47 0.40
0.50 0.54 0.57 0.67
1.20 1.11 1.04 1.07
TABLE4 Effectofnitro~nontheyieldofso~andintercrop ~dders(t/ha) Crop
Sole cowpea Sole maize Intercrop Mean
N applied (kg/ha)
Mean
0
40
80
120
21.6 27.9 28.2 25.9
24.4 40.5 35.2 33.4
24.8 48.5 38.9 37.4
25.4 52.8 43.6 40.6
24.1 42.4 36.5
LSD (0.05) for N= 1.4; for fodder= 1.3; for NX fodder=2.5
in intercrop yield (data of separate components of intercrop not given) decreased with increase in N.
Residual effect of cropping system Both the preceding cropping system and applied N at 120 kg/ha had significant effects on the succeeding pearl millet fodder yield (Table 5 ). Pearl millet fodder yield was the highest when grown after cowpea. Averaged over all N treatments, pearl millet grown after the intercrop yielded 42% more than after maize. Yadav (1981) and Waghmare and Singh (1984b) reported a similar effect of intercropping on the succeeding crop. The higher yield of a sole crop succeeding an intercrop has been attributed to better residual fertility (Nair et al., 1979). We found that N uptake by pearl millet (25.5 kg/ha) following the intercrop was 1.3 times that after maize (data not shown). Yields of cereal-legume intercrops have, generally, been found to be less than those of cereal crops, and the results of this study support this (Table 4). Consequently, intercropping has been advocated either for balanced food production or other specific considerations. T h a t approach ignores the beneficial residual effect of intercropping. A rational evaluation of cereal-legume intercropping should be
183 TABLE 5 Residual effect of sole and intercrop fodder and nitrogen on succeeding pearl millet fodder yield (t/ha) Preceding crop
N applied to preceding fodder (kg/ha) 0
40
80
120
Mean
Sole cowpea Sole maize Intercrop
18.9 9.5 16.1
19.0 10.4 14.6
20.0 10.8 15.3
22.5 13.0 15.6
19.9 10.9 15.4
Mean
14.7
14.7
15.4
16.8
LSD ( 0.05 ) for N = 1.4; proceeding crop = 1.2; N X proceeding crop = 2.5 TABLE 6 Fodder yield (t/ha fresh wt.) of the crop sequences at different nitrogen levels Crop sequence
Cowpea--* Millet Maize ~ Millet Cowpea + Maize Millet
N applied (kg/ha) 0
40
80
120
Mean
40.5 37.4 44.3
43.3 50.9 49.8
44.8 59.3 54.2
47.9 65.6 59.2
44.0 53.3 51.7
based on crop-sequence yields. The total crop sequence fodder yield of the intercrop system was comparable to yield of the sole-crop sequence (Table 6). Higher crop-sequence yields from intercropping at low inputs indicate that intercropping is more beneficial under N and irrigation constraints.
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