Estimation of Some Macro-Nutrients by a New Multi-Nutrient Soil Extractant (OM-MES-VERA) and Its Relationship with Conventional Soil Test Methods

For saving the expenses and time involved in the routine soil testing, a novel multi-nutrient soil extractant (OM-MES-VERA) comprising 0.0025 M EDTA +0.01 M oxalic acid +0.02 M acetic acid +0.02 M maleic acid +0.02 M 2-(N-Morpholino) ethane sulfonic acid (MES) + 0.1% polyacrylamide with final pH (6.0) has been developed. This extractant was used to assess the availability of macronutrients from soil and compared with the conventional soil test methods. In a laboratory evaluation with diverse soils (n = 32), OM-MES-VERA extracted K similar to 1 M ammonium acetate (pH 7.0) but extracted significantly lower amounts of inorganic N (NH4+ + NO3−), P, S, Ca and Mg compared to conventional alkaline KMnO4 hydrolysable N, Olsen’s- or Bray’s- P, 0.15% CaCl2 extractable S, 1 M ammonium acetate extractable Ca and Mg, respectively. Interestingly, the absorbance ratio (OD465/OD665) of OM-MES-VERA extracts significantly correlated with the conventional alkaline KMnO4 hydrolysable N (R2-value = 0.386, Significant at p ≤ .01) and additional inclusion of clay and organic C contents, pH and electrical conductivity led to an improved prediction of N (R2-value = 0.501, significant at p ≤ .01). Other macronutrients (P, K, S, Ca, Mg) extracted by OM-MES-VERA could be successfully regressed on the conventional soil test values (R2-value 0.342–0.633, all significant at p ≤ .01). The soil test values by OM-MES-VRA and conventional methods were correlated with soil properties. Further greenhouse and field studies are required to prove the suitability of OM-MES-VERA extractant for assessing the availability macronutrients.