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The response of upland rice to phosphorus on drained soils subjected to different periods of prior flooding

Seng, V., Bell, R.W.ORCID: 0000-0002-7756-3755, Willett, I.R. and Nesbitt, H.J. (2002) The response of upland rice to phosphorus on drained soils subjected to different periods of prior flooding. Cambodian Journal of Agriculture, 6 . pp. 15-23.

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Low rice yields following intermittent loss of soilwater saturation are believed to involve, on occasions, P deficiency but the possible mechanisms have not been studied in detail. In the present pot experiments, two acid lowland soils from Cambodia (Koktrap -black clay soil and Prateah Lang- sandy soil) were treated with P either before or after flooding to investigate the effect of the timing of P application on its effectiveness for upland rice growth. Phosphate fertiliser (45 mg P/kg soil) was added to both soils before flooding for periods of 0, 1, 2 and 4 weeks, or after drying the flooded soils. After air-drying and crushing, the soils were wet to field capacity and the upland rice grown in them for six weeks.

The addition of P 4 weeks before flooding decreased shoot dry matter in the sandy soil and in the black clay soil after only 1 week of flooding. But when P was added after drying the soils, shoot dry matter was not decreased regardless of the period of prior soil flooding. Soil pH increased and redox potential (Eh) decreased during flooding, resulting in an increase in acetate extractable Fe and the phosphate sorption capacity of soils. There was a close relationship between P sorbed and acetate extractable Fe (r2=0.96–0.98). Olsen and Bray-1 extractable P strongly correlated with shoot dry matter and shoot P concentrations indicating that P, the availability of which was controlled by the period of prior flooding, limited the growth of upland rice.

It was concluded that phosphate fertiliser added before flooding was relatively ineffective in increasing growth in the upland rice. This was attributed to the increase in occlusion of P within ferric oxyhydroxides formed during subsequent oxidation of the soils. Decrease P availability may also have been associated with a greater phosphate sorption capacity of the soils during flooding and drying of soils. The implications of this for P supply to rice in intermittently flooded lowlands, and for P fertilizer requirements of pre- and post-rice upland crops are discussed.

Item Type: Journal Article
Murdoch Affiliation(s): School of Environmental Science
Publisher: Cambodia Society of Agriculture
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