Nitrogen accumulation in three legumes and two cereals with emphasis on estimation of N2 fixation in the legumes by the natural15 N-abundance technique
1990
Yoneyama, T | Nambiar, P T C | Lee, K K | Srinivasa Rao, B | Williams, J H
N accumulation and natural "N ahundance in three legumes (groundnuts, cowpeas, and soybeans) and in two cereals (sorghum and maize) were investigated over two seasons in Alfisols with and without N fertilization. Using the N uptake and natural "N abundance of non-nodulating plants as the indication of N derived from soil and fertilizer, the per cent N derived from atmospheric N2 was calculated for nodulated plants. In the first experiment, the groundnut genotype contained 85% atmospherc-derived N, but the percentage decreased with N application, Estimates of atmosphere-derived N by the N-difference and 15~-abundanctee chniques gave identical results. The percentages of atmosphere-derived N estimated by the two methods at different stages of groundnut growth were also similar. In the second experiment, atmosphere-derived N was estimated in plants grown with 0-200 kg ha-' applied N. The estimated atmosphere-derived N ranged from 42% to 61 % for groundnuts from 33% to 77% for cowpeas, and from 24% to 48% for soybeans, depending on the amount of N applied. Inoculation with a Bradyrhizobium strain increased the percentage of atmospherederived N in soybean plants grown without any fertilizer N. The natural "N abundance of sorghum and maize was very close to that of the non-nodulating groundnut, suggesting that these cereals can be used as reference plants in the estimation of atmosphere-derived N by the natural "N-abundance method.
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