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This article in AJ

  1. Vol. 70 No. 2, p. 292-295
     
    Received: June 3, 1977
    Published: Mar, 1978


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doi:10.2134/agronj1978.00021962007000020018x

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

  1. T. A. T. Wahua and
  2. D. A. Miller2

Abstract

Abstract

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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