Automated Analysis of Soil Extracts for Phosphorus, Potassium, Calcium, and Magnesium

Abstract

Abstract An automated method is described for determining P in double acid (0.05N HCI + 0.025N H2SO4) and Bray P1 (0.025N HCI + 0.03N NH4F) soil extracts and K, Ca, and Mg in double acid and 1N ammonium acetate soil extracts. Comparisons are made between double acid and Bray P1 soil extraction methods for removal of P from a Freehold sandy loam soil that had been differentially fertilized with P fertilizers. Comparisons are also made between the double acid and ammonium acetate soil extraction methods for removal of K, Ca, and Mg from the same soil that had been differentially fertilized and limed with K fertilizers and pulverized–dolomitic limestone, respectively. Comparisons are made between automated and atomic absorption determinations of K, Ca, and Mg in standard solutions and double acid and ammonium acetate soil extracts. Bray P1 soil extractant removed 30–73% more P than did the double acid soil extractant from Freehold sandy loam soil. Ammonium acetate extractant removed about 25% more K from soil than did the double acid extractant. Double acid soil extractant removed more Ca from the soil than did ammonium acetate extractant, particularly at high soil Ca levels. Greater amounts of Ca were found in both types of soil extracts by the automated than by atomic absorption techniques. Double acid extractant removed more Mg from soil than did ammonium acetate extractant. The 2 instrumentation methods produced similar results for Mg and K analyses of both soil extract types.