Fixation and Excretion of Nitrogen by Tropical Legumes1
- Akinola A. Agboola and
- Adeboyejo A. A. Fayemi2
Since earlier investigations revealed that interplanted legumes competed with a late crop of corn (Zea mays L.) and suggested that legumes were incapable of benefiting associated nonlegumes over the same growing period, relatively short-season legumes, calopo (Calopogonium mucunoides), cowpea (Vigna sinensis), and greengram (Phaseolus aureus), were interplanted with corn in the early cropping season to measure their effects on both the early planted and the late-planted corn crops.
Two days after harvesting the intercrops of corn and legumes, soil samples from the 0- to 15- and 15- to 30-cm depths were collected from the unfertilized plots of control (no legume), cowpea, greengram, and calopo order to determine in the greenhouse the soil N status. Two other greenhouse experiments were conducted to check the N-fixing and N-excreting ability of the legumes.
The investigations showed that calopo, cowpea, and greengram fixed N when planted alone and when interplanted with corn. Cowpea and calopo interplanted with corn did not benefit the early corn crop, but as green manure they were an important source of N for the corn in the late-cropping season. On the other hand, greengram interplanted with corn in the early season increased yield of the early corn crop but contributed very little to the yield of the late corn crop.
The data also revealed that tropical legumes are capable of fixing large quantities of N under improved conditions. Calopo, cowpea, and greengram fixed equivalents of 450, 354, and 324 kg/ha, respectively, when inoculated and grown in a complete nutrient culture (except for N) as compared to 370, 157, and 63 kg/ha, respectively, when not inoculated and grown in unfertilized soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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