Evaluation of chemical extraction methods for available potassium in rice soils of Meghalaya.

摘要

Different extractants were used to determine the most reliable soil test method in the assessment of potassium (K) availability in soils of Meghalaya, India. A total of 53 soil samples were collected during 2003-04 from rice-growing areas representing six districts of Meghalaya, namely: Ri-Bhoi (21), Jainta Hills (6), East Khasi Hills (8), West Khasi Hills (6), West Garo Hills (7) and South Garo Hills (5). These soils were analysed for various forms of K, viz., water soluble, exchangeable, non-exchangeable, lattice and total K. The dry matter yield of rice (cv. Shah Sarang-1) increased significantly with the addition of K at 75 kg/ha across all the soils with a yield response of 20-110% and relative yield of 48-83%. Total K in the soils varied from 1200 to 3950 mg/kg. Water soluble K was low in all the soils with values from 7 to 66 mg/kg. The highest available K was extracted with 1.0 N HNO₃ ranging from 47 to 334 mg/kg. Exchangeable K alone accounted for 52.3% variation to the NH₄OAc extractable K, while the inclusion of solution, non-exchangeable, lattice and total K influences the observed variation to an extent of 18.5% to the regression. Water soluble and exchangeable K showed highly significant relationship with K uptake by rice, indicating that these two forms mainly contributed in K nutrition of rice. Ammonium acetate extraction method for estimation of available K was found to be better than the other methods.