Barley Productivity, Carbon Isotope Discrimination and Nitrogen Utilization Efficiency as Affected by Moisture Level

A field experiment was conducted to determine barley productivity, carbon discrimination analysis and Nitrogen Utilization Efficiency (NUE) under rainfed and Supplemental Irrigation (SI) conditions for two seasons. The treatments consisted of two water (rainfed and SI) and two N (zero and 50 kg N ha-1) levels. At harvest, barley grain yield was recorded and shoot and grain samples were taken for chemical analysis, dry matter determination and carbon and nitrogen isotope compositions analysis. Grain yield increased with SI and with N addition under SI only suggesting the soil moisture is the more limiting growth factor. Nitrogen uptake was higher with SI in both seasons and with N in the second season. Grain and N uptake derived from fertilizer were higher with SI in both seasons. SI increased the soil moisture and therefore, increased the NUE in the second season only but not in the first drier season. Carbon isotope discrimination was higher with SI and decreased with N application. Carbon isotope discrimination correlated positively with grain yield and shoot dry matter in the second season only and with the Water Use Efficiency (WUE) in the first drier season. Therefore, it can be concluded that SI increased barley production and NUE. In addition, carbon isotope discrimination can be used as tools for predicting barley production in relatively wet season and WUE in the drier season