Deficit irrigation and surface residue cover effects on dry bean yield, in-season soil water content and irrigation water use efficiency in western Nebraska high plains

Considering ground water pumping restrictions and unpredictable amount of water available for irrigation from year to year, Nebraska Panhandle producers are facing a challenge to reduce their irrigation water usage and practice deficit irrigation. Among irrigated crops in the region, dry bean (a major cash crop and critical to crop rotation systems) has relatively low water use and is capable to withstand periods of stress. Consequently, two experiments within six consecutive growing seasons (2010–2015) were conducted to determine the impacts of multiple irrigation scenarios (full irrigation, deficit irrigation, and rainfed) and two soil surface conditions (bare soil versus crop residue) on dry bean production, irrigation water use efficiency, and temporal soil water dynamic within the crop root zone. Dry bean yield ranged from 0.41 to 4.07 Mg ha⁻¹ during the six years of the study (2010–2015). The results (2012–2015) indicated that reducing irrigation water by 25% on average increased irrigation water use efficiency (I_WUE) by 26% and only caused 6% yield reduction in relative to the full irrigation treatment scenario. However, applying only 50% crop evapotranspiration requirement (ETc) resulted in significant yield reduction (30% reduction on average) in 5 out of 6 years compared to the full irrigation treatment (p < 0.05). Our results indicate that temporal in-season rainfall and ETc demand variabilities along with the per-season soil water content status should be carefully analyzed in order to target the appropriate growth stage(s) for more severe deficit irrigation scenarios. When pre and early season rainfall was abundant deficit irrigation treatments imposed before flowering outperformed treatments targeting after flowering. However, under normal and dry conditions yield decline was more pronounced due to severe early season (before flowering) water stress compared to late season (after flowering) water stress. In two of three years plots with bare soil significantly (p < 0.05) outyielded plots covered with residue. Average yield across irrigation treatments was 14% lower for plots with residue cover (average yield: 2.15 Mg ha⁻¹) compared to bare soil plots (average yield: 2.51 Mg ha⁻¹). Overall, the dynamic of soil water content within root zone and I_WUE in plots covered with residue was similar to that in bare soil plots across irrigation treatments throughout the growing seasons.