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Phosphate sorption-desorption behaviour and phosphorus release characteristics of three contrasting lowland rice soils of Cambodia

Pheav, S., Bell, R.W., White, P.F. and Kirk, G.J.D. (2002) Phosphate sorption-desorption behaviour and phosphorus release characteristics of three contrasting lowland rice soils of Cambodia. Cambodian Journal of Agriculture, 6 . pp. 39-54.

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Abstract

Understanding the P sorption and release characteristics of different soils can help in determining fertiliser P requirements for the growth of rice (Oryza sativa L.). Glasshouse and laboratory experiments were undertaken to observe the long-term release characteristics of P from added fertiliser for the early growth of rice, and also to determine P sorption-desorption behaviour of three contrasting lowland soils from Cambodia: Prateah Lang (Plinthustalf), Koktrap (Plinthaquult) and Toul Samroung (Endoaqualf). In the pot experiment, rice was treated with four P rates (0, 5, 10 and 20 mg/kg soil) and grown over five successive cropping cycles, each of six to eight weeks. Phosphorus sorption desorption isotherms were constructed by equilibrating with 0, 10, 20 and 40 mg P/1 in 0.01 M CaCl2 solution at 25 oC.

On the sandy Prateah Lang (PL) and clayey Toul Samroung (TS) soils, addition of 10 mg P/kg soil was adequate in the first crop for maximum tiller number, plant height, total dry matter, P concentration, and total P uptake. By contrast, about 20 mg P/kg was needed for the maximum growth and total P uptake on the clayey acid Koktrap (KT) soil. After two crops, plant growth progressively declined at all P levels, but the decrease in yields and total P uptake on the clayey TS and KT soils was slower than for plants grown on the sandy PL soil.

Resin-P extractable was the smallest P fraction compared to other major soil-P (NaOH-Pi, NaOH-Po and Residual-P) pools in all soil groups, but recovery from the Resin-P pool was higher in the sandy PL soil than in the clayey TS and KT soils. The declining amounts recovered from all the extractable soil P fractions, especially major soil P (NaOH-Pi and Po and Residual-P) pools with succeeding rice crops grown on all the soils could be attributed to continued reactions of the added P fertiliser by soils in addition to plant P uptake during each plant-growing cycle.

The clayey KT and TS soils sorbed five-fold more P than the sandy PL soil in oxidized conditions. Phosphorus desorption was initially greatest from the sandy PL soil: but with increasing numbers of soil extractions, the release of sorbed P declined faster than in the clayey KT and TS soils. The cumulative desorbed P was greater from the clayey KT and TS soil than from the sandy PL soil. The greater P sorbed by the clayey soils should ensure a longer duration of the residual P effect.

Publication Type: Journal Article
Murdoch Affiliation: School of Environmental Science
Publisher: Cambodian Agricultural Research and Development Institute.
Copyright: © Cambodian Agricultural Research and Development Institute.
URI: http://researchrepository.murdoch.edu.au/id/eprint/18121
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