Summary
Sources of N used by cropped and intercropped cowpeas and rice were determined by the 15N isotope-dilution technique. The biological efficiency of intercropping cowpeas and rice was assessed by calculating the land equivalent ratio of dry matter yield, total N, and uptake of N. A reduced N uptake by both cowpeas and rice during mixed cropping was attributed to mutual competition, with both crops competing effectively for the scarce environmental resources. The lack of a significant difference in the uptake of fertilizer and soil N by mixed-crop rice and cowpeas is an indication that the soil N was sufficient and that the mixed cropping did not create any imbalance in soil and fertilizer N uptake. The land equivalent ratio ranged between 120% and 180% for shoot dry matter and total N, showing that biological efficiency was increased by intercropping cowpeas with rice. The proportion of N derived from the atmosphere by mono- and intercropped cowpeas was not significantly different, showing that the potential of cowpeas to fix N2 was independent of the cropping system, since the rice did not stimulate the cowpeas to fix more N2.
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Okereke, G.U., Ayama, N. Sources of nitrogen and yield advantages for monocropping and mixed cropping with cowpeas (Vigna unguiculata L.) and upland rice (Oryza sativa L.). Biol Fertil Soils 13, 225–228 (1992). https://doi.org/10.1007/BF00340580
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DOI: https://doi.org/10.1007/BF00340580