Evaluating suitability of chemical extractants for measuring available soil potassium under long term conservation agriculture

The research was driven by concerns over the skewed application of nitrogenous fertilizers and the threat to potassium (K) mining and the sustainability of the rice-wheat cropping system in the Indo-Gangetic plains. The objective was to identify potential K extractants as affected by different crop establishment methods and optimum nutrient levels. A split-plot experimental setup was established in 2012 with four levels of crop establishment methods and three nutrient management levels. Soil potential K extractants and critical concentration using Cate and Nelson was evaluated with twelve extractants: distilled water, 0.01 M calcium chloride (CaCl 2 ), 0.1 M barium chloride (BaCl 2 ), 1 N ammonium acetate (NH 4 OAc), 0.03 M sodium tetraphenyl boron (NaTPB), ammonium bicarbonate- diethylenetriamine tetraacetic acid (AB-DTPA), Mehlich I, Mehlich III, 0.002 M strontium chloride (SrCl 2 ), 0.02 M SrCl 2 + 0.05 M Citric acid and finally 1 N boiling nitric (HNO 3 ) acid. 1 M NaOAc showed a strong correlation with 0.03 M NaTPB ( r = 0.979 ** ), relative yield ( r = 0.927 ** to 0.984 ** ), plant K-uptake ( r = 0.930 ** to 0.974 ** ) and soil indices ( r = 0.913 ** to 0.97 ** ). Whereas, 0.002 M SrCl 2 was poorly correlated ( r = 0.231 NS to 0.641 * ) with soil and plant indices and had a lower soil K critical concentration (24 mg kg − 1 ). Unlike commonly used 1 N NH 4 OAc, 1 M NaOAc, and multinutrient extractants (AB-DTPA, Mehlich I, and Mehlich III) are better indices of relative yield and plant available K. Treatments with residue retention in both seasons and optimum K fertilization (60 kg K 2 O ha − 1 ) outperformed others in terms of crop yield and plant available K.