Planting Density and Geometry Effect on Canopy Development, Forage Yield and Nutritive Value of Sorghum and Annual Legumes Intercropping

Abstract

Forage sorghum (FS) (Sorghum bicolor L.) is a major forage in crop–livestock production systems. It has low crude protein (CP) and is rich in fiber. Its forage quality can be improved by mixing with legumes rich in CP. Achieving a greater legume contribution to achieve higher CP over monocrops is a challenge for intercropping. Field trials were conducted with lablab (Lablab purpureus L.), pigeon pea (Cajanus cajan L.) and cowpea (Vigna unguiculata), grown with sorghum as mixed 1:1 (sorghum: legumes) and 2:2 (sorghum: legumes) rows. The sorghum plant density was 250,000 and 190,000 plants ha−1. Periodic crop biomass, leaf area index (LAI) and light interception (LI) were measured, together with forage mixture quality at final harvest. The LAI and LI values were greater for lablab and cowpea intercrops in the 1:1 configuration. Legume forage yield contributed up to 10–12% of the total dry matter (DM). A significant improvement in legume biomass was observed for a sorghum population at 190,000 plants ha−1 with paired rows (2:2) of either lablab or cowpea. Sorghum and total forage yields were higher in both 1:1 and 2:2 configurations with 250,000 plants ha−1. The CP concentration of the forage mixture was 62–75 g kg−1 DM. The acid and neutral detergent fibers and the digestibility of the forage mixture were not improved to any great extent. The results suggested that sorghum planted at normal populations with paired rows of lablab or cowpea can improve sorghum–legume intercrop productivity.