| The ability of a soil to supply potassium (K) depends on the K concentration in solution, and on the K present as exchangeable K (EK) and non-exchangeable K (NEK). Twenty one soils from Arkansas were analyzed (i) to characterize their K adsorption-desorption, and (ii) to understand their ability to release or fix K. Estimated cation exchange capacity (CEC) was greater than analyzed CEC (P < 0.05). Fine-textured soils had the largest CEC and the largest extractable-K (P < 0.05) compared to coarse- and medium-textured soils. Non-exchangeable K evaluated with sodium tetraphenyl boron (NaBPh4) increased as the incubation time was extended ( P < 0.05), with fine-textured soils having more NEK than the other two soil textures. Quantity/Intensity curves for K were also developed. Fine-textured soils had the largest potential buffering capacity [90 cmol kg-1/(cmol L-1)1/2] compared to coarse- [10 cmol kg-1/(cmol L-1) 1/2] and medium-textured soils [13 cmol kg-1/(cmol L-1)1/2] (P < 0.05); whereas coarse- and medium-textured soils were not different (P > 0.05). Three soils with different textures (Desha, Guthrie, and Steprock-Linker complex) were selected to conduct a greenhouse study to understand their K dynamics. Winter wheat (Triticum aestivum L. 'Coker 9553') was grown in 30 pots per soil for 82 days. Nitrogen was supplied as Ca(NO 3)2 (40 kg ha-1 of N for six weeks), and K was supplied as KCl (0, 40, 80, 120, 160 and 200 kg ha-1 of K2O). Total dry matter (DM) increased as K rate increased for the Guthrie and Steprock-Linker complex soils, but total DM decreased as K increased when adding more than 40 kg ha-1 of K2O in the Desha soil. Final soil extractable-K increased linearly as K rate increased ( P < 0.05). Results confirm that fine-textured soils have the greatest potential to provide or fix plant-available K. |
