Infulence of Phosphorus, Nitrogen and Organic Fertilizers on Rice Yield and Available Soil Phosphorus

Abstract

Several experiments were carried out to clarify the effects of fertilizer management on response of rice yield and phosphorus accumulation in rice soils during 1990-1996. The first experiment was conducted on the farmer fields in the lower north region in 1990-1991. The treatments were comparison between fertilizer rates of 12-0-0 and 12-7.5-0 kg N-P2O5 -K2O/rai for clayey soils and 12-0-4 and 12-7.5-4 kg N-P2O5-K2O/rai for loamy soils. The second experiment was comparison of fertilzer rates: 0-0-4, 4-0-4, 8-0-4, 12-0-4, 16-0-4 and 12-7.5-4 kg N-P2O5 -K2 O/rai responsed to RD23 and KDML 105 yield and accumulated available soil P. The experiment was conducted at the Phitsanulok Rice Research Center (PSDLRRC) in 1990-1996. The third experiment was analysis of rice soils obtained from long term application of organic fertilizers with and without chemical fertilzer which was conducted in 1974/1976 at PSLRRC. The last experiment was analysis of P sorption coefficient of major rice soil series in the lower north region.
The results showed that application of phosphate 7.5 kg NP2O5 -K2O/rai increased 10-25% rice yield in a loamy soil with P content below 7 ppm. while the rice yield response was less or none in a clayey soil with P content higher than 7 ppm. Phosphate application 7.5 kg-P2O5/rai/year (1990-1996) gave approximately 50% of accumulated available soil phosphorus higher than the control at PSLRRC. Long term rice straw compost application (1976-1992) gave 55-240% of accumulated available soil P higher than the control treatment and more P accumulated when combined application with chemical fertilizer. Rice hull and rice hull ash gave less or none accumulated available soil P.
Phosphorus coefficient of major rice soil series in the lower north region was 145-689 P2O5/100 g soil; phosphorus coefficient of clayey soils were higher than that of loamy soils.