Soil available water and plant growth in relation to K:Na ratio

•Application of treatments included different K:Na ratios created clay dispersion.•Pore size decreased due to migration of dispersed clay particles toward the pores.•Increase in plant available water because of increase in small pores. The effect of K:Na ratio on plant available water (PAW), least limiting water range (LLWR), integral water capacity (IWC), penetration resistance and plant growth was assessed in this study. Treatment solutions including different K:Na ratios at two electrical conductivity levels (EC = 3 and 6dSm−1) were applied into an agricultural loamy soil in pots using capillary rise from the bottom, and the soil in the pots were kept at a water content close to field capacity for one month. In addition, maize was planted into the treated soils in three replicates. PAW, LLWR and IWC were calculated by soil available water calculator (SAWCal) software based on measurements of soil water retention and penetration resistance. In our study, LLWR was limited by PAW. The results showed that PAW of the treated soils increased significantly with increasing K:Na ratio in comparison with the control soil at both EC levels, due to increasing clay dispersion with increasing K:Na ratio. A reduction in the soil pore size due to migration of dispersed clay particles into soil pores could be a possible reason for the increase in PAW. Positive relations were found between PAW and meso-porosity and micro-porosity at both EC. Maize growth significantly increased with increasing PAW at EC = 6dSm−1. It can be concluded that the application of different K:Na ratios induced different degrees of dispersion of clay particles, which presumably migrated into soil pores, changing the soil pore size distribution towards smaller pores. This increased PAW in our studied soil, with positive effects on plant growth.