ABSTRACT. Several factors, including multi-year drought
77). A linear relationship between the cumulative ET w and fraction of season (function of days after emergence) was found. This relationship developed for a given location could be used to extrapolate seasonal ET w for in-season irrigation management. Poor correlation was found between CWP and other variables such as total irrigation, rain + irrigation, and total water. The results of this study can provide useful information for soybean irrigators to make better management decisions under deficit irrigation conditions.
Keywords. Crop water productivity, Deficit irrigation, Evapotranspiration, Limited irrigation, Soybean, Water stress.everal factors, including multi-year drought, declining aquifer levels, and new water regulations, are reducing availability of irrigation water in the semi-arid area of west-central Nebraska. Since many farmers in this area now do not have enough water to meet the seasonal water requirements of agronomic crops such as corn and soybean, maximizing the yield produced per unit of water under deficit irrigation conditions is becoming crucial to the long-term viability of the local and state economy. Deficit irrigation has been suggested as an alternative strategy for making better use of irrigation water. For instance, Zwart and Bastiaanssen (2004) reviewed measured crop water productivity (CWP) (yield per unit of seasonal evapotranspiration) for several crops around the world and concluded that the CWP could be significantly increased if irrigation was reduced and crop water deficit was intentionally induced. Similarly, Schneekloth et al. (1991) compared the yields of soybean under dryland, deficit irrigation (limited to 150 mm) and full irrigation at North Platte, Nebraska, using sprinkler irrigation. They found the same yields for the deficit and full irrigation treatments during a three-year study. Deficit irrigation increased dryland yields from 0.4 to 2.8 Mg ha −1 , while full irrigation only increased yields by 0 to 0.4 Mg ha −1 over the deficit irrigation treatment. Deficit irrigation represented an average seasonal water savings of 119 mm compared with full irrigation. For the same location, Hergert et al. (1993) found that during a field experiment conducted from 1983 to 1991, an allocation of 150 mm of irrigation, which represented 53% of the water applied to a full irrigation treatment, produced an average soybean grain yield of 88% of that obtained using full irrigation.When water is limited, it is important to maximize storage of rainfall in the soil profile and to use techniques to conserve soil water, such as conservation tillage, terraces (where needed), improved residue management, and effective weed control programs. It is also important to select crops and crop rotations that conserve water, and use irrigation water efficiently by minimizing losses that do not contribute to crop S
