The effects of water stress on yield advantages of intercropping systems

Abstract

Two experiments are reported in which a line-source irrigation system was used to study the effects of a range of moisture regimes (S1 to S5 in order of increasing stress due to insufficiency of moisture) on sole crops of sorghum, millet and groundnut, and intercrops of 1 row sorghum : 2 rows groundnut (SGG), 1 row sorghum : 3 rows groundnut (SGGG), 1 row millet : 1 row groundnut (MG), 1 row millet : 2 rows groundnut (MGG), 1 row millet : 3 rows groundnut (MGGG), and 1 row sorghum : 1 row millet (SM). The dry matter yield advantages of intercropping compared with sole cropping ranged from 8 to 30% for the millet/groundnut systems, 0 to 19% for the sorghum/groundnut systems and 5 to 15% for the sorghum/millet system; moisture stress had no consistent effect on these dry matter advantages. For reproductive yields, all the intercropping systems showed some increase in relative advantages with increase in stress because of higher harvest indices in intercropping than in sole cropping. Largest advantages were 93% for SGG at S5 moisture regime and 78% for MGG at S4 moisture regime, both of these being significantly greater than advantages at S1. The level of stress giving peak advantages depended on crop combination and crop proportions. It is emphasised that all intercropping treatments were of ‘replacement’ type in which the plant population of each crop was only a proportion of that of its sole crop and total population was equivalent to that in either of the sole crops. It is suggested that if total populations in the intercrops are higher than in the sole crops then, under stress conditions, intercropping yields could well be less than sole crop yields because of increased competition for moisture