Availability of phosphate fertilizer on azolla in paddy soil
1992
Prayoon Swatdee (Department of Agriculture, Bangkok (Thailand). Soil Science Div. Soil Microbiology Research Group)
Two soil series varying in the adsorption capacity were evaluated for the availability of P to Azolla after the application of phosphate fertilizer. The two soil series use are Rangsit (Rs) which is the acid sulfate soil and the Roiet (Re) which is low humic grey soil. The experiments were carried out in both pot and field. The field experiments were conducted at Ubon Ratcha Thani Rice Research Center in Re soil series and at Pathum Thani Rice Research Center in Rs soil series. P32 labelled triple super phosphate at 37.5 kg P2O5/ha was split applied to Rs and Re soils in pot experiment. Azolla pinnata was used to evaluate the availability of P. The adsorption capability of P was higher in Rs soil than Re soil. Split application of p fertilizer at 10 days interval could alleviate the adsorbed P to acid soil which resulted in increasing Azolla biomass comparable to normal soil condition. Azolla could increase paddy yield equivalent to fertilizer N at 37.5 kg N/ha. The utilization of P by Azolla was more efficient in Re soil than the Rs soil. Basal application of phosphate fertilizer resulted in higher amount of P adsorbed to soil. Thus in acid sulfate soil, more frequent split application of phosphate fertilizer is recommended than in low humic grey soil.
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