Evaluation of Ammonium Bicarbonate–Diethylene Triamine Penta Acetic Acid as a Multinutrient Extractant for Acidic Lowland Rice Soils

Abstract

Simultaneous extraction of nutrients using ammonium bicarbonate–diethylene triamine penta acetic acid (ABDTPA) extractant has been successful for highland soils, but its potential for lowland soils is still uncertain. This study evaluated the suitability of ABDTPA extractant to determine available phosphorus (P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) in lowland rice soils of Sri Lanka. Available nutrients were analyzed both by conventional and ABDTPA methods, using the original ABDTPA (1∶2 soil–extractant) method as well as a modified (1∶4 soil–extractant) method. Conventional methods tested were Olsen, Bray 1, and FeO strip for available P; neutral NH4OAc extraction for exchangeable Ca, Na, K, and Mg; and DTPA extraction for available Zn, Cu, Fe, and Mn. Nutrient content and uptake by plants were determined by a pot experiment with rice (Oryza sativa). Nutrients extracted by the conventional methods and ABDTPA methods correlated well, in general, for all nutrients. Highly significant correlations were observed between plant uptake and extractable nutrients by 1∶2 and 1∶4 ABDTPA methods for P (r=0.85***and 0.73***, respectively), K (r=0.79*** and 0.66***, respectively), Na (r=0.86*** and 0.78***, respectively), Zn (r=0.66*** and 0.60***, respectively), Mn (r=0.72*** and 0.84***, respectively), and Fe (r=0.74*** and 0.68***, respectively). Calcium and Mg extracted by ABDTPA showed a poor relationship with their respective plant uptake. The ABDTPA method was as effective as or even better than the conventional methods in evaluating fertility status of lowland rice soils with respect to most nutrients. Replacing the conventional methods by the single ABDTPA multielement extractant will reduce the time and cost of soil analysis.