Effect of Salinity on Root Water Uptake in Paddy and Wheat: A Comparative Study and Parameter Estimation

Soil salinity poses a significant challenge to agricultural productivity, especially in arid and semiarid regions, where the accumulation of excessive salts in the root zone impedes water uptake and adversely affects crop growth. A comprehensive understanding of the effects of salinity on root water uptake is essential for developing optimized irrigation practices and promoting sustainable crop production. This research investigates the effect of varying salinity levels on the root water uptake (RWU) pattern using nonlinear Ojha and Rai RWU model. Experiments were conducted at six salinity levels (0.5, 5, 10, 15, 20, and 25 dS/m), on paddy (Oryza sativa L.) and wheat (Triticum aestivum), within a controlled experimental environment. The optimization algorithm was tested using synthetically generated soil moisture data, demonstrating a strong agreement with the actual values which confirms the efficacy of the model. The results indicate decrease in nonlinear RWU pattern parameter β and the root depth, with increase in salinity levels. The β parameter varies from 1.953 to 1.825 for paddy and from 1.543 to 1.348 for wheat at salinity levels of 0.5 dS/m and 25 dS/m, respectively. Root depth for paddy decreases by 35.98% and 51.47% for wheat crop, comparing minimum and maximum salinity levels. The simulated moisture profiles using the optimized β values are in strong agreement with the field-observed soil moisture content across the different layers in the root zone. Moreover, irrigation with highly saline water (25 dS/m) resulted in an approximate reduction of 81% in peak RWU recorded for paddy and 56% for wheat, compared to irrigation with low salinity water (0.5 dS/m). The coefficient of determination (R2) and Nash Sutcliffe efficiency (NSE) values for soil moisture variation across different salinity levels range from 0.887 to 0.941 and 0.846 to 0.908 for paddy and 0.872 to 0.955 and 0.828 to 0.913 for wheat respectively, indicating the efficacy of the model even under high salinity stress. As a result of higher osmotic stress, the soil moisture depletion decreases for both crops with the elevating salinity levels. This study advances the application of the nonlinear Ojha and Rai RWU model by incorporating an optimization-based approach to estimate the nonlinearity parameter (β), improving its applicability in saline-irrigated conditions. Additionally, a comparative analysis of paddy and wheat under varying salinity levels provides new insights into crop-specific responses, establishing its usefulness in salinity-affected irrigation systems.