Nitrogen Fertilization and Harvest Timing Affect Switchgrass Quality

Abstract

Early season switchgrass (Panicum virgatum L.) can be used as animal feed and mature late-season biomass as a biofuel feedstock. However, nitrogen (N) application and harvest timing effects on the quality of both end-use need further evaluation. This study evaluated the changes in nutritive quality for animal feed and biofuel feedstock, under different N application rates (0 to 235 kg N ha−1 yr−1) and different harvest times at a fixed N rate. Plant N removal increased with increasing N application rate (P < 0.05). The largest single difference (27%) was found between 0 and 33.6 kg N ha−1 application rates. Nitrogen removal decreased during subsequent harvests at a fixed N rate (P ≤ 0.0001). Forage quality was affected by N rates, although it was especially impacted by harvesting time. Fibers and most minerals in the biomass increased as accumulated growing degree days (AGDD) increased (P ≤ 0.0001), but N and total digestible nutrients (TDN) decreased as AGDD increased (P ≤ 0.0001). High crude protein and minerals with low fiber are desired forage qualities and the opposite is true for biofuel feedstock. Earlier harvests are beneficial for hay production or livestock grazing, and late-season harvests are better for biofuel production.