UC Riverside

Accurate estimation of evapotranspiration (ET) and its partitioning into transpiration and evaporation is fundamental for improving water management practices in water-limited environments and under deficit irrigation conditions. This investigation was conducted to estimate the water balance and ET components of subsurface drip (SDI) irrigated Chardonnay wine grapes for two seasons (2010–2011 and 2011–2012) using a numerical model (HYDRUS-2D). Treatments involved the application of different volumes [51% (I1), 64% (I2), 77% (I3), and 92% (I4) of normal application] of water for irrigation. A modified version of the FAO-56 dual crop coefficient approach was used to generate daily transpiration and evaporation as inputs to the HYDRUS-2D model. The calibrated and validated model produced estimates of actual evapotranspiration (ETCact), actual transpiration (Tpact), and actual evaporation (Esact), and deep percolation under varied irrigation applications. The model-simulated values were then used to estimate actual crop coefficients (Kcact and Kcbact), and water productivity of wine grape under different deficit irrigation conditions. Seasonal ETCact simulated by HYDRUS-2D for different treatments varied between 239 and 382 mm. However, seasonal evaporation accounted for 44–59% of seasonal ETCact losses in different treatments. The modelled daily transpiration rate in I4 treatment (Tp4act) varied from 0.11–2.74 mm/day. Deep percolation accounted for 35–40% of the total water applied by rainfall and irrigation. The mean value of actual crop coefficient (Kcact) estimated by HYDRUS-2D simulated ETC act over the two seasons was 0.27, which matched with other investigations. Similarly, values of Kcbact for initial, mid and end stages were 0.13, 0.27 and 0.14, respectively. Monthly values of evaporation coefficient (Ke) ranged from 0.1 to 0.32, with a mean value of 0.18. Water productivity with respect to ET losses (WPETC) ranged from 5.9 to 6.2 kg/m3 of water use. However, water productivity for transpiration (WPTC) almost doubled as compared to WPETC in all treatments. The impact of deficit irrigation on berry juice composition (Brix, pH and titratable acidity) was lower than the inter-seasonal variability. These results can help develop better irrigation management strategies for SDI irrigated wine grapes under water scarce conditions.