Water uptake, active root volume, and solute leaching under drip irrigation: A numerical study

The use of saline water for irrigation is based on the concept that increasing irrigation water quantity may offset in part the negative effects associated with higher salinity. The main goals of this paper were (1) to investigate the impact of the controllable variables, the relative quantity (Q(r)), and the quality (C-0) of the irrigation water on water uptake, active root volume, and solute leaching under daily drip irrigation in fine (clay) and coarse (sandy) textured soils; (2) to test the hypothesis that the reduced active root zone associated with salt accumulation may further reduce water uptake by plant roots; and (3) to assess consequences of using (C-0-Q(r)) substitutions based on the FAO recommendations on salinity control with respect to agricultural and environmental aspects. Novel findings of this study suggest that in the clay soil mean water extraction rate, S-w is quite robust to C-0-Q(r) substitutions, and the decrease in transpiration, T, induced by increasing C-0 is mainly due to the decrease in the soil volume providing most (90%) of the root water uptake, Vs. In contrast, in the sandy soil, Vs may increase with C-0-Q(r) substitutions, and the decrease in T is mainly due to the decrease in Sw, induced by osmotic pressure head reduction. Consequently, in the clay soil, a simultaneous increase of Q(r) and C-0 based on the FAO substitution curve may lead to an increase in root uptake efficiency, T/V-s, while it may cause the opposite effect in the sandy soil. Furthermore, compensation for the adverse effects of increasing C-0 on relative transpiration, T-r, by C-0-Q(r) substitutions is more efficient in the clay soil than in the sandy soil. The C-0-Q(r) substitution approach may lead to an increase in the salt load leached below the root zone, thus increasing the potential for polluting groundwater resources. Results of the present study suggest that for both soils, from both agricultural and, particularly, environmental points of view, irrigation with high-quality water which may comply with economical criteria is desirable.