Effects of Intercropping on Soybean N2-Fixation and Plant Composition on Associated Sorghum and Soybeans1
- T. A. T. Wahua and
- D. A. Miller2
Sorghum (Sorghum bicolor (L.) Moench) and soybean (Glycine max (L.) Merrill) are being intercropped in tropics so that crops more effectively utilize water; there is better weed control, and soil fertility is improved. A field experiment was conducted to determine the effects of sorghum-soybean intercropping on soybean N2-fixation and plant composition of both crops. The soil was a Flanagan series, a fine, montmorillonitic, mesic Aquic-Argiudoll. Soybeans were intercropped with tall and semi- dwarf sorghum cultivars at 16 population densities from 1.38 to 33. plants/m2. Soybean N2-fixation was estimated by acetylene reduction. Various plant parts were analyzed for present N.
Nitrogen-fixation by soybeans grown with tall sorghum was reduced 99% due to reduction in number of nodules per plant (77%), weight per nodule (50%), and specific nodule activity, SNA, (96%). Soybean dry matter and seed percent oil were also reduced by 87 and 8%, respectively. Soybean percent seed protein and leaf N were unaffected by intercropping.
Soybeans grown with semi-dwarf sorghum fixed 2.64 times more N than plants in monoculture but produced 40% less dry matter and 3% less oil in seed. Percent seed protein and leaf and stem N of soybeans were unaffected by intercropping. The increase in N2-fixation was probably due to increases in number of nodules per plant (62%) and SNA (364%). Possible involvement of allelo- pathy, NO3- absorption, delayed senescence, and inter- specific mechanical support was considered.
Protein yield of intercropped tall and semi-dwarf sorghum was reduced by 15 and 71%, respectively. Only in the dwarf cultivar did intercropping increase percent seed protein by 15%. Sorghum grain oil was unaffected by intercropping.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © . .