A new soil test for simultaneous extraction of macro‐ and micro‐nutrients in alkaline soils

Abstract

A new soil test was developed for simultaneous extraction of NO₃, P, K, Zn, Fe, Cu and Mn from alkaline soils. The new extraction solution is 1 M in ammonium bicarbonate (NH₄HCO₃), 0.005 M in Diethylene Triamine Pentaacetic Acid (DTPA) and has a pH of 7.6. The new extracting solution should be stored under mineral oil. Ten grams of soil are weighed out into 125 ml Erlenmeyer flasks. Two 2.5 ml scoops of Fisher G carbon black (to remove color for colorimetric determination of nitrates) are added to each soil, followed by 20 ml extracting solution. The soil mixture is then shaken on an Eberbach reciprocal shaker for 15 minutes at 180 cycles per minute. The extract is then filtered through a Whatman 42 filter paper or its equivalent for NO₃, P, K, Zn, Fe, Cu and Mn determinations. The results obtained with the new procedure are highly correlated with results obtained with Olsen's P test, ammonium acetate K test, and Lindsay and Norvell's DTPA‐Zn, Fe, Cu and Mn test. Regression equations between the levels of nutrients extracted by the new procedure and those extracted by the procedures mentioned above were developed. These equations were used to calculate index values for nutrients extracted by the new extraction procedure based on values used at the Colorado State University Soil Testing Laboratory for the standard extraction procedures. The new procedure extracted about the same amounts of K and Fe as ammonium acetate and DTPA, respectively, from soils having low to marginal levels of these elements. However, it extracted about half as much P as NaHCO₃ and about 0.5 PPM more Zn, 0.8 PPM more Mn, and 0.3 PPM more Cu from soils having low to marginal levels of these elements.