This study examined the effects of soil moisture on soil K mobility, dynami
cs 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 us
ing 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 u
sing 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 effecti
ve diffusion coefficient (D-e), suggesting that more K+ can diffuse to the
plant roots at sufficient soil moistures. Increase in D-e could be attribut
ed to the decrease of impedance factor. During W-D cycles, soil solution K
concentration increased as soil solution volume decreased, but soil solutio
n 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 exten
t 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, fo
llowed 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 cy
cles decreased root and shoot growth and K uptake by corn compared to const
ant moisture condition. Our results support the hypothesis that W-D cycles
enhance soil K fixation, reduce soil K mobility and plant growth, and there
fore reduce plant K+ uptake.