Managing the soil profile NO 3-N through crop selection and irrigation is an important consideration for the sustainable production of cellulosic biofuel feedstock crops. Data from two seasons were collected and analyzed from a 4-yr study conducted in Prosser, WA, to assess the effect of biofuel feedstock grasses and irrigation levels on soil profile NO 3-N. The experimental design was a split plot with three replications. The main plots had three irrigation levels (60, 80, and 100% evapotranspiration, ET), and the subplots contained three cultivars of switchgrass ( Panicum virgatum L.) and gamagrass ( Tripsacum dactyloides L.) cultivars. Soil and root samples were collected in fall 2011 (Season1) and winter of 2012 (Season2). Soil profile NO 3-N concentrations were highest at the lowest irrigation levels. In Season1, the soil profile NO 3-N concentration averaged over depths was 1.7 mg kg -1 for the switchgrass cultivars and 5.6 mg kg -1 for gamagrass. In Season2, the concentrations were 1.4 and 2.2 mg kg -1 for the switchgrass cultivars and gamagrass, respectively. We found a significant correlation between switchgrass root mass and soil profile NO 3-N; r=0.63-Kanlow; r=0.58-Blackwell; and r=0.46-Shawnee. Our results suggest that soil profile NO 3-N was lower under the switchgrass cultivars than gamagrass. More root mass and NO 3-N were accumulated at lower irrigation levels. The results reported here can help in developing practical decision tools for managing fertilizer N in biomass biofuel crops.
