Biomass Production and Energy Content of Grass and Alfalfa Mixture in CRP Land Affected By Nitrogen and Harvesting Time in Central Montana.

Biomass from Conservation Reserve Program (CRP) can be used for biofuel feedstock. But there is no information how harvesting time and nitrogen application rate affect amount and quality of biomass in grass and alfalfa mixed pastureland for biofuel feedstock in central Montana. Therefore, we carried out an experiment to investigate the effect of harvesting times and N application rates on biomass yields, species and major cell wall composition and energy content, and post-harvest major soil nutrient content. The experiment was executed from 2009 – 2012 in mixed grass and alfalfa CRP land in central Montana in split plot design with three replications. Nitrogen application rates were (0, 56, and 112 kg N ha^-1) assigned to main plots and subplots were harvesting times (July and October). Averaged over years, increased nitrogen application rates increased total dry biomass (alfalfa plus grass) significantly from 3175 kg ha^-1 at 0 kg N ha^-1 to 3685 kg ha^-1 at 112 kg N ha^-1. The percentage of alfalfa dry biomass reduced significantly from 47% at 0 kg N ha^-1 to 35% with the application of 56 kg N ha^-1. But this situation was reversed for grass. Nitrogen application rates did not affect cellulose, hemicellulose, lignin and energy content of the biomass. Early harvesting (July) significantly increased total dry biomass and percentage of alfalfa by 27% and 82%, respectively, compared to late harvesting (October). Cellulose, hemicellulose, lignin and energy density of biomass were significantly higher for October than July harvest. However, because of more biomass in July harvest, more total energy per hectare was obtained with the application of 112 kg N ha^-1 than October. For October harvest, the maximum total dry biomass and energy content per unit area was achieved at lower N fertilization rate (56 kg ha^-1). October harvesting tends to increase residual available soil nitrogen, phosphorus and potassium perhaps due to remobilization. It can be concluded that harvesting in October provide elongated time for wildlife habitat achieving one of the envisioned objective of CRP. In addition, harvesting in October tends to minimize nutrient mining and reduce transportation cost of biomass per unit energy content to the processing facility than July. Economic analysis should follow to make recommendation.