Crop yield response to water - Cra

figure 7 The root zone depicted as a reservoir with indication of the equivalent water depth (Wr) and rootzone depletion (D r ).Evapo-transpiration (ET)Irrigation (I)Rainfall (P)Runoff(RO)Stored soil water (mm)0.0Field capacityD rW r Permanent wilting point0.0Root zone depletion (mm)TAWCapillaryrise(CR)Deeppercolation(DP)but increases exponentially with depth, so that infiltration, evaporation and transpirationfrom the top soil layers can be described with sufficient detail.To simulate water movement in and out of the soil profile, AquaCrop considers surface runoff,infiltration, capillary rise, soil evaporation and crop transpiration. To simulate the redistributionof water into a soil layer, the drainage out of a soil profile, and the infiltration of rainfall and/or irrigation, AquaCrop makes use of an exponential drainage function that describes thedeclining water movement between saturation and field capacity. Upward water movementfrom a groundwater table to the soil profile is described by an exponential relationshipbetween the capacity for capillary rise and the height above the groundwater table. Theamount of water that moves upward depends not only on the depth of the groundwater tablebut also on the wetness of the top soil and the hydraulic characteristics of the soil layers. Byconsidering the water fluxes in response to the processes listed above, the soil-water contentis updated at the end of the daily time step in each of the 12 compartments (for full detailssee Raes et al., 2011).While performing the water balance, AquaCrop also deploys the salt balance. Salts enter thesoil profile by capillary rise from a saline groundwater table or together with the irrigationwater. Salts are leached out of the soil profile by excessive rainfall or irrigation. Vertical saltmovement in a soil profile is described by assuming that salts are transferred downwards bysoil-water flow in macro pores as simulated by the drainage function. Since the solute transportin the macro pores bypass the soil water in the matrix, a diffusion process is consideredto describe the transfer of solutes from macro pores to the soil matrix. Therefore the soil28crop yield response to water