Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil |
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Authors: | Sakorn Phongpan Somsak Boondown Rob Wetselaar |
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Affiliation: | (1) Agricultural Chemistry Division, Department of Agriculture, 10900 Bangkok, Thailand;(2) Pathum Thani Rice Research Center, 12110 Pathum Thani, Thailand;(3) CSIRO Division of Water and Land Resources, G.P.O. Box 1666, A.C.T. 2601 Canberra, Australia |
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Abstract: | Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH3) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH3 could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha–1 in dry season and 3.0–4.1 Mg ha–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The15N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH3 volatilization was probably responsible for the poor efficiency of broadcast urea in this study. |
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Keywords: | Acid sulfate soil floodwater properties grain yield 15N balance N use efficiency Oryza sativa L urea |
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