Use of radioisotope P-32, chemical soil analyses and plant test to assess plant available phosphorus in Pakchong, Lampang and Satuk soil series
1994
Mesak Milintawisamai
Study was conducted to assess phosphorus availability of 3 soil series, namely Pakchong, Lampang and Satuk soil series by five methods. The methods were Bray-II method, Ammonium Lactate method, extraction with water, E-value method and L-value method. E-value was estimated by adding P-32 to exchange with phosphorus in the soils. L-value was estimated by adding P-32 labelled phosphate fertilizer followed by growing corn and soybean on the soils. Furthermore, comparisons were made among counting P-32 in soil and plant extracts by a liquid scintillation counter with cocktail, by a liquid scintillation counter without cocktail and by a gas-filled counter. Bray-II P and Ammonium Lactate-P were highly correlated (r=0.9849). The E-value increased with the time of reaction and became constant at 14 days, 7 days and 2 hours in the cases of Pakchong, Lampang and Satuk soil series, respectively. The E-value of Satuk soil series was highly correlated with Bray-II P (r=0.8182). The L-value was suitable for evaluating available phosphorus of the 3 soil series when using corn as a phosphorus extractor. The correlation coefficients of L-value and Bray-II P were 0.9997, 0.9573 and 0.9968 for Pakchong, Lampang and Satuk soil series, respectively. The amount of P-32 counted by a liquid scintillation counter without adding cocktail gives correlation coefficients of 0.9988 and 0.9989 with those counted with cocktail and those counted by a gas-filled counter, respectively.
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