Aim <p>This study aims to obtain information on the exchangeable kinetics of potassium (K) between the soil and solution phases to improve the understanding of soil K behavior.</p> Methods <p>Coupling the diffusive gradient in thin film technique (DGT) with the DGT induced flux in soil (DIFS) model revealed the spatial heterogeneity and seasonal dynamics of soil K availability and recharge rates in a rice-oilseed rape rotation system, for the first time at the field scale. This approach enabled the in situ evaluation of soil K bioavailability.</p> Results <p>The resupply ratio (R) remained consistently below 0.90, indicating that K uptake of rice and oilseed rape relied partially on solid-phase K resupply. Soil acidification in the rhizosphere promoted labile K (LK) release, thereby enabling high replenishment efficiency despite low available K content. K fertilization enhanced soil K supply capacity and shorten solution K transport distance by expanding available K pools and augmenting recharge ability. DIFS model showed that during the rice season, soils exhibited higher resupply ratio, faster desorption rates, and shorter response times, which enhanced LK mobilization and supply capacity. Conversely, limited replenishment of solid-phase K during the oilseed rape season caused an increased dependence on K fertilization.</p> Conclusion <p>C_DGT content were significantly positively correlated with crop K uptake (<i>p</i> &lt; 0.01), demonstrating the utility of this approach for assessing soil K availability. Soil environment limits the supply of soil labile K recharge; therefore, K fertilization strategies in rice-oilseed rape rotations must be rationally tailored to seasonal crop demand and soil supply limitations.</p>