Row arrangement and nitrogen effects on growth yield of sorghum-legume intercrops

Sorghum [Sorghum bicolor L. Moech] production in eastern Uganda is largely done in intercrops with legumes, especially beans [Phaseolus vulgaris], groundnuts [Arachis hypogea], Pigeon pea [Cajanus cajan] and Cowpea [Vigna unguiculata L. Walp]. However, the overall intercrop yields have declined especially in the region (cowpea <200, groundnut <800 and sorghum <1000 kg ha-1). A study was conducted on-station at Serere Agricultural and Animal Production Research Institute (SAARI) and on-farm Nyero and Atoora sub-countries in Kumi and Soroti districts, respectively for two seasons to assess the effect of row arrangement and N rate on sorghum-legume intercrops productivity (groundnut and cowpea). Treatments included row arrangement, namely, alternate (1 row of sorghum by 1 of legume) versus staggered (2 rows of sorghum by 2 rows of legume), N rate (0 and 40 kg N ha-1), and intercrop legume species (groundnut vs cowpea). Study site soils were suboptimal in organic matter (1.9-2.35%), total N (0.1-1.5%) and Bray I P (3.0-3.5 mg kg1). Sorghum-groundnut intercrop row staggering considerably improved sorghum above ground dry weight, head weight and grain yield. There was no significant (P>0.05) grain yield difference between sole sorghum (4,826 kg ha-1) and the groundnut grown sorghum (4,232 kg ha-1). In contrast, intercropping cowpea with sorghum affected sorghum yield (3,105 and 4,826 kg ha-1 for sorghum- cowpea and sole sorghum respectively), irrespective of N rate and row arrangement. Legume productivity was consistently greater (P<0.05> under staggered (2x2 rows) than under the alternate (1x1) arrangement. Groundnut was generally more productive (P<0.05) than its cowpea counterpart, irrespective of N.rate. Sorghum-groundnut intercropping depressed (P<0.05) groundnut peg to pod transformation, pod filling, dry matter and grain yield. Surprisingly, poor groundnut yields were obtained with N application in the rows (847 kg ha-1) compared to sole groundnut (1,043 kg ha-1). For cowpea, alternating rows had no influence on yield irrespective of N rate. Water use efficiency was 1.18 and 1.63 for the alternate and staggered plots, respectively, while N use efficiency was -1.14 versus 5.75 for the respective treatments. Alternation of sorghum-cowpea rows led to a equivalent ratio (LER) of 1.21. While staggering produced 1.68. The ground intercrop led to LER to 1.51 for the alternated rows and 1.74 for the staggered.