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Effect of Soil Organic Matter Accumulation on Potassium and Ammonium Quantity-intensity Relationships¹

ABSTRACT

Quantity-intensity (Q/I) relationships for potassium (K⁺) and ammonium (NH₄⁺) in a Maury silt loam soil (fine-silty, mixed, mesic, Typic Paleudalfs) under long-term conventional and no-tillage management were investigated to determine changes in solute-soil interactions brought about by differential organic matter accumulation. To obtain differences in organic matter content, representative soil samples were collected from a field experiment that was established in the spring of 1970, involving treatments of conventional tillage with no nitrogen (N) fertilizer (CT-control) and no-tillage with 336 kg N ha^–1 applied annually (NT-high N). The results of the study reveal that K⁺ and NH₄⁺ equilibrium concentration ratios (CR^k*, CR^NH*₄) along with the linear potential buffering capacities (PBC^K, PBC^NH₄) were greatly affected by soil organic matter accumulation resulting from no-tillage and N addition. CR^K* and CR^NH*₄ were higher in the NT-high N than the CT-control system (19.61 and 12.11 vs 6.61 and 2.15 [(mol L^–1)^1/2 x 10³], respectively). Furthermore, the PBC^k was slightly greater but not significantly different in the NT-high N (28.4) than the CT-control system (26.3) [cmol(+) kg^–1)/(L mol^–1)^1/2]. Potential buffering capacity for NH₄⁺ (PBC^NH₄) was significantly smaller in the NT-high N (17.5) than the CT-control system (26.0). The affinity of the NT-high N soil exchange phase for both K⁺ and NH₄⁺ was significantly lower than that of the CT-control exchange phase. The affinity for K⁺ exhibited by NT-high N system was significantly greater than that for NH₄⁺ (1.71 vs. 1.23). In CT-control systems only slight differences (statistically nonsignificant) were observed in affinities for NH₄⁺ and K⁺ (2.62 vs. 2.47). Potential buffering capacity for NH₄⁺ and K⁺ appeared to be a function of the affinity of the exchange phase for each cation and the magnitude of the cation exchange capacity (CEC). Despite higher CEC values in the NT-high N system, a proportional increase in the PBC was not observed because the NT-high N exchange phase exhibited a lower affinity for NH₄⁺ and K⁺ ions than the CT-control did.

¹ Contribution from the Dep. of Agronomy, Univ. of Kentucky Agric. Exp. Stn., Lexington, KY 40546. The investigation reported in this paper (no. 85-3-120) is in connection with a project of the Kentucky Agric. Exp. Stn. and is published with the approval of the director.

² Associate Professor, Assistant Professor, and Professor of Agronomy, respectively. Univ. of Kentucky, Lexington, KY 40546-0091.

Received for publication July 12, 1985.

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