Temporal Evolution of Soil Hydraulic Properties in a Cropping Season: Drivers and Hydrological Impacts

Soil hydraulic properties (SHPs) are fundamental to the accuracy of land-surface, hydrological and agro-hydrological models. Most modelling studies assume static SHPs due to limited information on how climate and anthropogenic factors drive their temporal fluctuations. This study aims to address this gap by investigating the temporal variation of SHPs in a cropping season (rice and wheat) under different fertiliser and irrigation management practices, identifying the key factors controlling this variability, and understanding the resulting impacts on hydrological processes. Experiments were conducted at an agricultural plot at IIT Kanpur, India, located within the Ganga Basin under no-tillage conditions. The temporal variability was analysed in soil organic carbon ($\mathrm{OC}$) content, bulk density (${\rho }_b$), saturated hydraulic conductivity ($K_{\mathrm{sat}}$) and soil water retention curve (SWRC) for the period 2022–2023. The highest variability was observed in $K_{\mathrm{sat}}$. The maximum change in $K_{\mathrm{sat}}$ value for the study duration was observed to be $160\%$ at 25 cm depth. The saturated water content, ${\theta }_{\mathrm{sat}}$ remained consistent across both crops. Trend analysis revealed a significant negative temporal trend in soil $\mathrm{OC}$ for both cropping seasons, irrespective of the fertiliser treatment. Plant root depth, irrigation and evapotranspiration significantly influenced SHP variability across all crops and fertiliser treatments. The temporal evolution of SHPs suggests dynamic shifts in infiltration rates, water retention and water redistribution throughout the cropping season. Further, simplified relationships were developed to predict the SHPs at any given time for the two crop seasons, with an $R^2$ up to 0.98. These findings enhance our understanding of the dynamic nature of SHPs and their controlling factors.