Nitrogen Removal by Orchardgrass and Smooth Bromegrass and Residual Soil Nitrate

Nitrogen removal by cool‐season grasses may aid in capturing excess N from animal confinement operations or phytoremediation. Limited information exists on the N dynamics of these grasses near the asymptote of the N response curve. The objectives of this study were to evaluate N removal, residual soil NO3–N, and apparent N recovery in orchardgrass (Dactylis glomerataL.) and smooth bromegrass (Bromus inermisLeyss.) at annual N rates of 224, 448, and 672 kg ha−1Species × harvest interactions were observed in both years, but no species × N rate interactions occurred. Orchardgrass removed 352 and 505 kg N ha−1yr−1at the 448 N rate compared with 207 and 371 in smooth bromegrass in 1999 and 2000, respectively. In a dry year, orchardgrass (r2= 0.41) and smooth bromegrass (r2= 0.31) exhibited linear N uptake. In a year with adequate rainfall, a quadratic relationship was observed for orchardgrass (R2= 0.92), while smooth bromegrass had linear uptake (r2= 0.66). Greater N removal was observed in orchardgrass partly because of superior fall growth, when 99 and 82 kg N ha−1were removed in 1999 and 2000 at the 448 N rate compared with 23 and 15 kg N ha−1in smooth bromegrass. These removal rates accounted for 28 and 16% of the seasonal total in 1999 and 2000 in orchardgrass and 11 and 4% in smooth bromegrass. Orchardgrass N removal exceeded smooth bromegrass in a three‐cut system, and this difference was enhanced by utilizing the fall growth period to capture residual soil N.