Strontium Chloride-Citric Acid Extraction Evaluated as a Soil-Testing Procedure for Phosphorus

Abstract

The 0.02 M SrCl2-0.05 M citric acid solution (Sr-citrate) was developed for the simultaneous determination of availability indices for P and other plant nutrients from soils. The objective of this study was to compare the Sr-citrate extracting solution with the water, NaHCO3, Bray 1, Bray 2, Mehlich 3, and 0.1 M HC1 soil tests as extractants for soil P, and as predictors of plant-available P for oat (Avena sativa L.) and corn (Zea mays L.) in the glasshouse. The Srcitrate solution extracted more P than did water, or the Olsen, Bray 1, and Mehlich 3 solutions in acidic and neutral to calcareous soils but less than the Bray 2 and 0.1 M HCl solutions. The amounts of P extracted from 34 soils by the Sr-citrate procedure were very closely related to that extracted by the six other solutions and, in particular, to the amounts extracted by Olsen (r = 0.97** [significant at P = 0.01]) and Mehlich (r = 0.96**) solutions. The Sr-citrate solution was among the best in predicting uptake of P and the relative dry-matter accumulation by oat and corn from both acidic (pH < 6.5) and higher pH soils. The relationships between the amounts of soil P extracted by the seven procedures and plant uptake were particularly improved when the clay content or the effective cationexchange capacity and, to a lesser extent, the maximum buffering capacity were included in multiple-regression equations. The Srcitrate extractant can simultaneously extract NO3-N, P, K, SO4-S, and micronutrients from acid and calcareous soils. The results of this study show that Sr-citrate procedure has definite advantages over standard extraction procedures in the evaluation of the amount of plant-available P in soils. View complete article To view this complete article, insert Disc 5 then click button8