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Potassium Supply Characteristics of Thirty-three Soils as Influenced by Seven Rates of Potassium

Dep. of Agronomy, Louisiana State Univ., Baton Rouge, LA 70803

S. A. Barber^*

Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907

*Corresponding author.

ABSTRACT

Limited information is available on the effect of applications of multielement fertilizer materials on the concurrent changes in K_l (soil-solution K) and K_s (exchangeable K). The objectives of this research were to: (i) investigate the relative increases in both K_l and K_s after addition of graded amounts of a 3-4-7.5 solution fertilizer; and (ii) determine if the changes in K_l and K_s with fertilizer additions were related to some measurable physical or chemical property of the soil. Thirty-three surface soils were equilibrated moist for 3 wk after addition of 0, 21, 42, 104, 208, 415, and 1245 mg K per kg of soil. High rates of application were used because they occur when the same total amount of K is placed in a small fraction of soil, e.g., band application. Values of K_l were determined from water-displaced soil solution. Values of K_s were obtained from K extracted with 1.0 M NH₄OAc at pH 7.0 minus K_l, where is the volumetric water content g^–1 of sample. The increase in K_l with K addition was described by K_l = ax^c + d, where x is the amount of added K and a and d are regression constants. Values of c, the curvilinearity coefficient, varied from 1.00 (linear) to 1.59. The increase in K_s with K addition was described by K_s = g + hx. The value g represents the amount of exchangeable K in the untreated soil. Values of h, the slope, varied from 0.42 to 1.13. The coefficients describing the relation of both K_l and K_s to added K were not correlated with any of the measured soil properties. There was no significant correlation between c and h. Characterization of the changes in K_l and K_s after addition of K gives information useful for determining the effectiveness of K placement.

Contribution from Purdue Univ. Agric. Exp. Stn. This research was supported in part by a grant from the Fluid Fertilizer Foundation. Submitted as Purdue Journal Paper no. 12078.

Received for publication July 10, 1989.

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