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Effect of row arrangement on light interception and yield in sorghum-pigeonpea intercropping

Summary Two experiments examined the effect of improving the distribution of the pigeonpea plants in sorghum-pigeonpea intercropping by having an alternate row arrangement of the two orops (SP) instead of the two sorghum: 1 pigeonpea row arrangement (SSP) that was studied earlier. One experiment was under conditions of good moisture supply (a deep Vertisol site in the high rainfall year of 1978) but the other experienced early moisture stress and had much lower end-of-season soil moisture storage (an Alfisol site in 1979). In 1978 the proportional sorghum yield was not affected by row arrangement (86 and 85% of the sole crop yield for the SSP and SP treatments respectively). Under the drier Alfisol conditions of 1979, the proportional sorghum yield was lower, probably because of the increased competitive ability of the drought resistant pigeonpea, and it was adversely affected by the alternate row arrangement (72% for SSP and 60% for SP). Compared with the SSP arrangement, the SP arrangement increased the level of light interception by the intercropped pigeonpea immediately after the sorghum harvest from 30 to 48 % in 1978 and from 44 to 60 % in 1979; the total energy intercepted during the whole post-sorghum period was increased by 23 and 12 % in the 2 years, respectively. However, these improvements in canopy cover were associated with only small increases in total dry matter of the intercropped pigeonpea at final harvest, from 69 to 74 % of the sole crop in 1978 and from 60 to 65 % in 1979. The increase in seed yield was even less than that in total dry matter in 1978 (from 90 to 93% of the sole crop) but similar in 1979 (71 to 76%); the value of this increase in 1979 was insufficient to offset the decrease in sorghum yield. None of the increases in total dry matter or seed yield of pigeonpea reached significance. It is concluded that with a good moisture supply alternate rows could be an alternative to the 2 sorghum: 1 pigeonpea arrangement, though it offers no additional yield advantage. With poorer moisture supply, alternate rows are not a worthwhile option because of the risk of reducing sorghum yield to an extent that cannot be offset by the small increase in pigeonpea yield.