Residual effects of rock phosphate and triple superphosphate on production of deepwater rice on acid sulfate soil
1988
Thongbai, P. | Puckridge, D.W. | Sangthong, P. | Sattarasart, A. (International Rice Research Inst., Bangkhen, Bangkok (Thailand))
A long-term experiment initiated in 1984 assessed the response of deepwater rice to annual dressings of 8.7 kg available P/ha or to the residual effects of a single application of 35 or 140 kg available P/ha. Rock phosphate (1.8% available P, 16% total P) and triple superphosphate (TSP) (19.6% P) were used. All phosphate treatments produced more than the untreated check. After the first year, the highest yields were from the residual effects of the initial application of rock phosphate equivalent to 140 kg available P/ha. Soil analyses after three crops gave total soil P values approximating those predicted, but indicated that rock phosphate contributed more available P to the soil than its specified content, possibly released by soil acidity. Available P from TSP was rapidly fixed. For each year, there was a highly significant curvilinear correlation between P uptake by plants and soil Bray 2-P.
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