Nitrogen-15 and sulfur-35 balances for fertilizers applied to transplanted rainfed lowland rice |
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Authors: | A. Satrusajang P. Snitwongse R. J. Buresh D. K. Friesen |
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Affiliation: | (1) Department of Agriculture, Isotope Laboratory, Division of Agricutural Chemistry, 10900 Bangkok, Thailand;(2) International Fertilizer Development Center (IFDC), P.O. Box 2040, 35662 Muscle Shoals, AL, USA |
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Abstract: | A field experiment was conducted on a poorly-drained Aeric Paleaquult in northeastern Thailand to determine the effect of N and S fertilizers on yield of rainfed lowland rice (Oryza sativa L.) and to determine the fate of applied15N- and35S-labeled fertilizers. Rice yield and N uptake increased with applied N but not with applied S in either sulfate or elemental S (ES) form. Rice yield was statistically greater for deep placement of urea as urea supergranules (USG) than for all other N fertilizer treatments that included prilled urea (PU), urea amended with a urease inhibitor (phenyl phosphorodiamidate), and ammonium phosphate sulfate (16% N, 8.6% P).The applied15N-labeled urea (37 kg N ha–1) not recovered in the soil/plant system at crop maturity was 85% for basal incorporation, 53% for broadcast at 12 days after transplanting (DT), 27% for broadcast at 5–7 days before panicle initiation (DBPI), and 49% for broadcast at panicle initiation (PI). The basal incorporated S (30 kg ha–1) not recovered in the soil/plant system at crop maturity was 37% for sulfate applied as single superphosphate (SSP) and 34% for ES applied as granulated triple superphosphate fortified with S (S/GTSP). Some basal incorporated15N and35S and some broadcast15N at PI was lost by runoff. Heavy rainfall at 3–4 days after basal N incorporation and at 1 day after PI resulted in water flow from rice fields at higher elevation and total inundation of the 0.15-m-high15N and35S microplot borders. Unrecovered15N was only 14% for 75 kg urea-N ha–1 deep placed as USG at transplanting. This low N loss from USG indicated that leaching was not a major N loss mechanism and that deep placement was relatively effective in preventing runoff loss.In order to assess the susceptibility of fertilizer-S to runoff loss, a subsequent field experiment was conducted to monitor35S activity in floodwater for 42 days after basal incorporation of SSP and S/GTSP. Maximum35S recoveries in the floodwater were 19% for SSP after 7 days and 7% for S/GTSP after 1 day. Recovery of35S in floodwater after 14 days was 12% for SSP and 3% for S/GTSP.This research suggests that on poorly drained soils with a low sorption capacity, a sizeable fraction of the fertilizer S and N remains in the floodwater following application. Runoff could then be an important mechanism of nutrient loss in areas with high probability for inundation following intense rainfall. |
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Keywords: | Nitrogen balance sulfur balance Oryza sativa L. urea elemental S runoff leaching Thailand |
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