Biomass from Conservation Reserve Program (CRP) land can be used as a lignocellulosic bioenergy feedstock. This experiment investigated the effect of harvest timing and N rate on changes in species composition, biomass, cell wall composition, energy content, and post-harvest soil nutrient content. The experiment was conducted from 2009 to 2012 in grass and alfalfa (Medicago sativa L.) mixed CRP land in central Montana in a split-plot design with three replications. The main-plot treatments were three N rates (0, 56, and 112 kg N ha-1), and subplot treatments were two harvest timings (July and October). Averaged across years, application of 112 kg N ha-1 significantly increased total (alfalfa plus grass) biomass from 3175 to 3685 kg ha-1. As the N application rates increased, the species composition shifted, with an increase in grass and a decrease in alfalfa contributions to biomass. The increased N rates also increased N uptake in the grass but not the alfalfa. Nitrogen fertilization did not affect cell wall composition for grass or alfalfa. July harvesting significantly increased total biomass and the contribution of alfalfa by 27 and 82%, respectively, compared with October harvesting. October harvested biomass had higher cellulose, hemicellulose, lignin, and energy content than July harvest per unit biomass, yet energy per hectare was higher for the July harvest due to the higher biomass yield. Because the October harvest provided higher energy content, it would contribute to reduced biomass storage and transportation costs. In addition, October harvest reduced biomass ash and minimized soil nutrient mining.
ASJC Scopus subject areas
- Agronomy and Crop Science