Importance of exchangeable and nonexchangeable soil nh4+ in nitrogen nutrition of lowland rice
1985
KEERTHISINGHE, G. | DE DATTA, S. K. | MENGEL, K.
In lowland rice (Oryza sativa L.) soils, NH4-N is considered the most important inorganic nitrogen form. Therefore, we examined the influence of NH4 fertilizer application and N uptake of the crop on the level of exchangeable and nonexchangeable soil NH4 Field experiments at three sites in major rice-growing areas in the Philippines showed that NH4 fertilizer application was clearly reflected by an increase of exchangeable and nonexchangeable soil NH4, while N uptake resulted in a decrease of both NH4 fractions. We found major NH4 contributions from nonexchangeable soil NH4 only in Maligaya silty clay loam, which is rich in vermiculite. On all soils in the wet and dry seasons the exchangeable soil NH4 was depleted during the first 8 wk of crop growth, indicating that this fraction is easily available to the crop. The net release of exchangeable and nonexchangeable NH4 throughout the growth period ranged from 0 to 100% of the N uptake of rice and depended greatly on soil and weather conditions. In the wet season most of the N taken up by the crop could be accounted for by the net release of NH4, whereas in the dry season most of the N taken up by the crop originated from soil organic N.
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