Bioavailable potassium in river-bed sediments and release of interlayer potassium in irrigated arid soils

Crop responses to applied potassiun fertilizers are erratic in many arid and semi-arid soils. The potassium supplying potential of river-bed sediments and release of interlayer potassium from eleven alkaline soils were measured in two separate experiments. Sediments from the Chenab and Ravi Rivers in Pakistan were exhausted of potassium by successively growing wheat, maize, mungbean, and wheat in them for a total of 200 days, using Hoagland solution to supply optimum amounts of other nutrients. Cumulative plant dry matter yield was significantly greater on the Chenab sediments. The quantities of potassium supplied to plants from the sediments of the two rivers were also significantly different. Interlayer potassium was extracted for 1231 minutes from a Udic Haplustalf (Pindorian series) by twelve different solutions each with the same electrolvte content (100 cmol). The sodium adsorption ratios (SAR) of the solutions were adjusted to 5, 10, 25, and 50, each with Ca:Mg ratios of 25:75, 50:50 or 75:25, using solutions of sodium, calcium and magnesium chloride. The potassium released from the soil was inversely related to solution SAR. Increasing proportions of magnesium relative to calcium in solution favoured the release of potassium, except in the SAR 5O solution. Significantly different quantities of potassium were extracted by various solutions. Maximum potassium (442 mg/kg) was extracted by SAR 5 solution with a Ca:Mg ratio of 25:75. Interlayer potassium subsequently removed by this solution trom 11 alkaline soils ranged from 407 to 499 mg/kg. The potassium released from all but three of the soils was related to their clay content (r = 0.72; n = 8). The release of potassium from the soils followed the Elovich function. The intercept (X1) and slope (X2) estimated for the function was related to potassium released (y) by the equation: y = -1.13 + 2.74X1 - 0.014X2 (r = 0.998; n = 8) The results imply that river sediments treated with irrigation water containing magnesium and sodium ions can contribute substantial amounts of available potassium for plant growth.