Use of phosphorus sorption characteristics for determining rate and type of phosphorus fertilizers for growing rice on ongkharak soil with residual lime

Abstract

A study on the response of rice, RD. 43 variety, grown on Ongkharak soil with residual lime to rates of phosphate calculated from P adsorption characteristics such as P adsorption capacity with the value of 802 mg P kg-1 (Pmax), half of Pmax (401 mg P kg-1), 0.2 mg P L-1 (398 mg P kg-1) and the rate of 157 mg P kg-1 recommended by DOA and to different types of phosphate fertilizer, including tripple super phosphate and rock phosphate was conducted. Fifteen days old rice seedling was transplanted in pot under greenhouse cover. Urea and KCl at the rates of 504 and 260 mg kg-1 were used as top dressing for all treatments and the former at the rate of 98 mg kg-1was applied at flowering stage. Results revealed that using of TSP as well as applying P at the rate of Pmax (802 mg P kg-1) gave significantly better vetgetative growth and higher seed yield than did the applications of rock phosphate and other rates of P. In addition, the TSP and Pmax rate tended to lower soil P adsorption. Application of TSP at 3.96 mg kg-1gave the highest seed yield of 264.9 g pot-1 whereas addition of RP at the equivalent amount of P contrastingly gave a lower seed weight (20.1 g pot-1). No P application gave the slowest vegetative growth and the lowest seed yield (7.5 g pot-1).