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Agronomy Journal Abstract -

Effects of Intercropping on Soybean N2-Fixation and Plant Composition on Associated Sorghum and Soybeans1


This article in AJ

  1. Vol. 70 No. 2, p. 292-295
    Received: June 3, 1977

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  1. T. A. T. Wahua and
  2. 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.

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