Relative Yield Totals and Yield Components of Intercropped Sorghum and Soybeans

A 2-year field study was conducted to determine how total grain yield per unit of land area could be maximized by intercropping sorghum (Sorghum bicolor (L.) Moench) and soybeans (Glyycine max (L.) Merrill). These two species are being intercropped more frequently through-out the world to increase protein yield per unit of area and utilize available moisture. Grain yields, yield components, and relative yields were analyzed. Two sorghum cultivars, grain type ‘DeKalb BR-44’ (semi-dwarf) and dual purpose ‘DeKalb FS-16’ (tall), were intercropped with soybean cultivars ‘Calland’ (Group III) (constant plant density) at 16 sorghum population densities, ranging from 1.38 to 33 plants/m². The soil was a Flanagan series, a fine, montmorillonitic, mesic Aquic Argiudoll. Intercropping changed the response patterns of sorghum yield components as plant population changed and reduced yields of FS-16 and BR-44 by 14 and 74%, respectively. Sorghum yield components were reduced more in mixtures of BR-44 than in mixtures of FS-16; with number of heads per plant being the most affected. Intercropping also reduced the compensatory alterations in sorghum yield components as population changed. In mixtures, tillering ability and population density were the main determinants of grain yield. Highest yields in monoculture were obtained at densities higher than 25 plants/m² for FS-16. and between 12 and 15 plants/m² for BR-44. Grain yields of both sorghum cultivars increased linearly with increases in plant population in the mixture, lntercropping soybeans with FS-16 and BR-44 reduced soybean yields by 75 and 17%, respectlvely; primarily due to reduced pod number. Relative yield curves indicated that the highest relative yield totals might be obtained by planting soybeans 5 cm apart between rows of sorghum planted at a density of 5 plants/m² at a spacing of 74 ✕ 74 cm.