Lentil Response to Nitrogen Application and Rhizobia Inoculation

Lentils (Lens culinaris L.) are an important component of the dryland farming systems in the western USA. Optimum nitrogen (N) management can enhance yield and quality of lentils. We conducted a field (at two locations, one with previous history of lentil and the other one without lentil history) and a greenhouse study to evaluate response of lentil to the application of rhizobium inoculant and starter N (control, 22 kg N ha^?1 in the form of urea [U], 22 kg N ha^?1 in the form of slow-release or environmentally safe nitrogen [ESN], and 22 kg N ha^?1 U + 22 kg N ha^?1 ESN). In both, the field and the laboratory studies, lentil yield did not respond positively to the experimental treatments. Lentil average yield was 1216 and 1420 kg ha^?1 at the field condition. In this rain-fed system, lentil yield was mainly limited by moisture availability, and the application of an external N did not contribute to the yield enhancement. Both of these treatments, however, increased protein content. Compared to the control, the application of rhizobium plus U and ESN enhanced protein content by about 34% (from 23.1 to 30.9%). The application of U+ESN also considerably increased postharvest residual nitrate (NO₃)-N in the soil, which can be easily leached and creates environmental pollution. Briefly, the application of U+ESN increases lentil protein content, but more efforts are needed to optimize N management in lentils in order to reduce the environmental concerns in the shallow soil.