A rapid decline in water table of the Ogallala aquifer necessitates water conservation farming practices in Texas High Plains (THP). Deficit irrigation (DI) and biochar amendment strategies are widely adopted to sustain agriculture in semi-arid regions like THP. Although these practices are studied individually, research involving the combined effect of these factors is lacking, especially in THP. The goal of this study was to investigate the effect of DI and biochar application on soil water depletion, root distribution, and water use efficiency of cucumber in West Texas. A two-year field study was conducted in a split-plot design with irrigation levels as the main plots: I1[100% crop evapotranspiration (ETc) replacement before mid-season (EBM))-100% ETc replacement after mid-season (EAM), I2 (80% ETc EBM- 60% ETc EAM), I3 (60% ETc EBM - 80% ETc EAM), I4 (40% ETc EBM-40% ETc EAM)] and biochar rates [ 0 t/ha,15 t/ha, and 20 t/ha] as sub-plots with four replications. Results showed that I4 had the largest and I1 had the least soil water depletion, and the differences in water depletion among irrigation levels were significant up to 1-m soil depth. Root length density (RLD) and root surface area density (RSAD) were significantly higher in I1 followed by I2 and I3, and these parameters were the least in I4. Water Use Efficiency (WUE) showed I2 being the most water productive DI treatment with an average increase of 5% compared to I1. Biochar didn't influence water depletion, RLD, and WUE but significantly increased RSAD compared to non-amended plots. Thus, deficit irrigation level I2 can be a potential alternative irrigation to full irrigation for enhancing water productivity of cucumber in the THP. More pronounced biochar effects could be expected in long term studies.
