Abstract
A transplanted crop of IR36 rice (Oryza sativa L.) was grown in greenhouse pots on three different soils [cation exchange capacity (CEC) 5 to 62 cmol (Na+) kg-1 soil] in two different experiments. Efficiency of 15N-labeled urea incorporated into presubmerged wet soils was compared with that of 15N-urea broadcast on dry soils (air-dry soil, moisture content 40 to 50 g kg-1 soil) followed by submergence and puddling. With wet soil application, 15N loss varied between 35% and 50%, whereas it was less than 20% with dry soil application. Nitrogen-15 loss increased with an increase in the rate of N applied and a fall in soil CEC, especially with wet soil application. Variations in 15N loss followed the buildup of water-soluble N (urea-N + NH4 +-N) in floodwater, i.e., the potential N loss. Lack of correlation between 15N loss and potential N loss with dry soil application was attributed to increased susceptibility to nitrification-denitrification of urea deep-placed by infiltrating water. Data on N loss were consistent with the findings on N use efficiency. Whether measured by grain yield response, N uptake, apparent recovery, or 15N recovery, a striking improvement in N use efficiency occurred when urea was applied to dry soil prior to submergence instead of to puddled wet soils. As the duration of submergence between urea application to dry soil and transplanting was increased from 0 to 7 days, improvement in 15N recovery by plant and accompanying grain yield response decreased.
On an overall basis, this greenhouse research has demonstrated the principle that total N loss from rice fields is predominantly controlled by the proportion of applied urea entering the floodwater. The research also provides basic information on improving current N management practices in irrigated lowland rice culture.
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Katyal, J.C., Gadalla, A.M. Fate of urea-N in floodwater. Plant Soil 121, 31–39 (1990). https://doi.org/10.1007/BF00013094
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DOI: https://doi.org/10.1007/BF00013094