Optimal Nitrogen Fertilizer Rates to Maximize Seed Yields from the Perennial Grain Crop Intermediate Wheatgrass (Thinopyrum intermedium L.).

Perennial crops have been proposed as a solution to a number of environmental issues related to agriculture including greenhouse gas (GHG) emissions, nitrogen (N) fertilizer pollution, and soil loss (Glover et al., 2010). Intermediate wheatgrass (Thinopyrum intermedium L.; IWG) is an introduced cool-season forage grass that has been bred over the last 10 years for high seed quality and yield. The dense, dynamic root system of IWG introduces new complexities for managing fertility to maximize grain yields. We tested the effect of various nitrogen N fertilizer rates on IWG seed and vegetative biomass yield at five different locations for four years. In 2013, the average agronomically optimum N fertilizer rate (AONR) for maximizing grain yield was 79 kg N ha^-1; however, AONR varied substantially by location ranging from 54 – 111 kg N ha^-1. The predicted grain yield at AONR was 880 kg ha^-1, and ranged from 687 – 1101 kg ha^-1 for site-level estimates. Grain yields decreased and lodging increased in response to high N fertilizer rates. Analysis of 2014 data will show how IWG stand maturity influences grain yield responses to N fertilization. This information is critical for determining the economic feasibility and potential for broad-scale deployment of perennial crops across the US Upper Midwest.