Research and development for cereal crop [rice] production: Soil and fertilizer [Major inorganic phosphate fraction controlling extractability of four soil P test methods in paddy soils on the Central Plain [in Thailand]]
Paiboon Prabuddham | Somsak Vangnai | Piya Duangpatra (Kasetsart Univ., Bangkok (Thailand). Faculty of Agriculture. Dept. of Soils)
In 1979, 4 subprojects were initiated. They are (a) Rice yield evaluation by plant analysis; (b) Fertility evaluation of paddy soils by soil test; (c) Transformation of soil phosphate in paddy soils; and (d) Influence of fertilizers on milling quality and some nutritive quality of milling products. These 4 subprojects are under active investigation. Among them, combination of subproject was good enough for preparation of the complete report on "Major inorganic phosphate fractions controlling extractability of four soil P test methods in paddy soils on the Central Plain". Fractionation of 40 paddy soils of the Central Plain into Al-P, Fe-P, Ca-P and Re-P (reductant soluble P) In-P (inorganic-P), O-P (organic-P) and T-P (total-P) were carried out in all air dried soil samples. Four soil P test methods namely, Bray II's, Olsen's, N. Carolina's and Al-Abbas Barber's were also investigated. simple correlation and stepwise regression analysis were used as a justing tool for the major soil P contributor of the P test methods. The results can be summarized as: (1) Dominant soil P forms relative to T-P were in the order : Fe-P (52.5%) Re-P (27.5%) Ca-P (11.4%) Al-P (8.6%), (2) Extractability of the P test methods are in the order: Al-Abbas - Barber-P (47.0 ppm) Olsen-P (7.1 ppm)--Bray II-P (5.9 ppm) N. Carolina-P (1.1 ppm) and (3) Fe-P is the major inorganic P controlling extractability of all soil "available" P tests studied except the N. Carolina-P which Ca-P is the major contributor
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