Nitrogen Fertilization Response in FIVE Bioenergy CROP Systems in the North-Central United States.

The effect of nitrogen fertilization on yield and quality of five perennial bioenergy feedstocks cropping systems: 1) switchgrass (Panicum virgatum L.); 2) giant miscanthus (Miscanthus × giganteus Greef & Deuter ex Hodkinson & Renvoize); 3) a native grass mixture (5 species); 4) an early successional field; and, 5) a restored prairie (18 species); was investigated at two sites in the north-central US region. The study sites were located in Michigan (KBS, 42˚23’47” N, 85˚22’26” W) and Wisconsin (ARL, 43˚17’45” N, 89˚22’48” W). A randomized complete block (RCBD) with 5 replicates and split-plots was used as the experimental design. Nitrogen fertilizer at 0 kg ha^-1 and 56 kg ha^-1 was applied to split-plots for each cropping system since 2010. Data were collected for growing seasons from 2010-2016. No dry matter yield response to N fertilization was detected in switchgrass at either location throughout the study. Giant miscanthus exhibited a positive yield response to N fertilization at both KBS and ARL (P=0.0003 and P< 0.0001). Nitrogen fertilization effect in the polyculture treatments largely depended on which species were dominate in the cropping system with grasses being more responsive than forbs. Giant miscanthus had the highest nitrogen fertilizer use efficiency among five cropping systems evaluated in this study (KBS: 0.03347 Mg kg^-1 N; ARL: 0.11639 Mg kg^-1 N). Nitrogen fertilization significantly reduced glucose and xylose levels in biomass from the warm-season grass cropping systems. Total ethanol yield on land area basis (Mg ha^-1) was driven more by biomass quantity than quality.