In a laboratory experiment, the changes of extracted phosphorus (DEP) in 33 limed and non-limed soils were determined 7 and 30 days after fertilisation with P, as well as DEP and DEPCa indices were evaluated as related to P sorption and to certain soil properties. The concentration of available phosphorus in the soils was measured in 0.03 M CH3COOH extract by the Nowosielski method. The changes of the available P in the soil (DEP) calculated per unit of applied P were expressed as the incline of the curve, presenting the linear dependence between P added and P extracted. The increase of concentration of P by 1 mg per 1 dm3 of the soil (the invers of DEP value) measured after 7 days incubation was obtained after the addition of 3-4 mg P per dm3 and 7-14 mg of P dm-3 of the soil in soils of poor and high sorptivity, respectively. In the present investigations the simple indices of P sorption estimated for one P rate (e.g., PSI200 andPSI1500) were significantly correlated with DEP and DEPCa, being therefore good indices of the prognosis of available phosphorus changes in fertilised soil, and useful in commercial soil tests.
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