Phosphorus mass balances for successive crops of fertilised rainfed rice on a sandy lowland soil
2005
Pheav, S. | Bell, R.W. | White, P.F. | Kirk, G.J.D.
Raising and sustaining rice yields in the rainfed lowlands requires an understanding of nutrient inputs and outputs. On sandy lowland rice soils, managing phosphorus (P) supply is a key factor in achieving increased yields and sustainable production. Phosphorus inputs, rice yields, and crop P uptake were used to quantify P requirements of rice: together with results on soil P fractions, P balance sheets were constructed over five consecutive cropping seasons on a sandy Plinthustalf near Phnom Penh, Cambodia. Grain yields ranged from 665 to 1557 kg ha(-1) with no added P. Average yields increased significantly with P fertiliser application over five consecutive crops by 117, 139 and 140% when the phosphate fertiliser was applied at 8.25, 16.5 and 33 kg P ha(-1), respectively. Without added P fertiliser, a net loss of 1.2 kg P ha(-1) per crop was estimated with straw return and 2.0 kg P ha(-1) per crop with straw removed from the field, whereas, with added P fertiliser, there was a net P gain in the soil of 5.6 or 9.5 kg ha(-1) per crop when straw was removed and returned to the soil, respectively. After one crop, the addition of P fertiliser significantly (P < 0.01) increased recovery in all soil P fractions. Across five successive crops, repeated application of 16.5 and 33 kg P ha(-1) rates resulted in progressive P accumulation in the soil, especially a labile NaOH-Po pool, but had no effect on yields and P uptake of rice. By contrast, 8.25 kg P ha(-1) per rice crop was generally adequate for grain yields of 2.5-3.0 t ha(-1) and to maintain soil P pools.
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