Soil potassium mobility and uptake by corn under differential soil moisture regimes

This study examined the effects of soil moisture on soil K mobility, dynamics of soil K, soil K fixation, plant growth and K uptake. A pot experiment, with and without corn (Zea mays L.), was conducted over a 16-d duration using a Yolo silt loam treated with two soil moisture regimes, i.e. constant moisture vs. wetting-drying (W-D) cycles. Soil K dynamics were determined using both ion exchange resin and direct extraction of soil solution. Soil K mobility increased significantly with soil moisture content (theta(v)) and there was a positive curvilinear relationship between theta(v) and effective diffusion coefficient (D-e), suggesting that more K+ can diffuse to the plant roots at sufficient soil moistures. Increase in D-e could be attributed to the decrease of impedance factor. During W-D cycles, soil solution K concentration increased as soil solution volume decreased, but soil solution K and NH4+-extractable K pools decreased. In the constant moisture regime, available K pools decreased over the 16-d duration, but to a lesser extent than in W-D regime. The W-D cycles significantly enhanced K fixation and reduced available K pools in the soil in contrast to the constant moisture regime. Potassium fixation by the soil showed a biphasic pattern under the W-D regime, with a rapid fixation within the first 2 d after re-wetting, followed by a slower fixation. In the soil with constant moisture, K fixation was rapid during the first 8 h after wetting the soil, and then proceeded so slowly that no significant K fixation was observed after 4 d. The W-D cycles decreased root and shoot growth and K uptake by corn compared to constant moisture condition. Our results support the hypothesis that W-D cycles enhance soil K fixation, reduce soil K mobility and plant growth, and therefore reduce plant K+ uptake.