Biomass Yield Potential, Feedstock Quality, and Nutrient Removal of Perennial Buffer Strips under Continuous Zero Fertilizer Application

Abstract. Perennial-based buffer strips have been promoted with the potential to improve ecosystem services from riparian areas while producing biomass as livestock feed or as a bioenergy feedstock. Both biomass production and nutrient removal of buffer strips are substantially influenced by the vegetation types for the multipurpose perennial buffers. In this 2016–2019 study in Western Illinois, two perennial cropping systems, including forage crops composed of cool-season grass mixtures (forage system) and bioenergy crops made up of warm-season grass mixtures (bioenergy system), were used to establish buffer strips for assessing biomass production, feedstock quality, nutrient removals, and buffer longevity. Treatments for this study reflecting agronomic practices included 1) two harvests occurring in summer (at anthesis) and fall (after complete senescence) and 2) one harvest in fall for forage system (2- vs. 1-cut forage), and 3) one fall harvest for bioenergy system (1-cut bioenergy). Successively harvesting without any fertilizer input resulted in a yield decline in forage biomass over three years by approximately 30 % (6.3 to 4.4 DM Mg ha^-1 with the rate of 1.0 Mg ha^-1 yr^-1) in the 2-cut forage and by 35 % (4.9 to 3.2 DM Mg ha^-1 with the rate of 0.9 Mg ha^-1 yr^-1) in the 1-cut forage systems. The feed quality also decreased over the years by showing declined rates of 12.9 (crucial protein), 0.9 (calcium), 0.7 (copper), and 1.3 (zinc) g kg^-1 DM yr^-1. Empirical models predicted enteric CH₄ emissions from cattle ranged from 225.7 to 242.6 g cow^-1 d^-1 based on the feed nutritive values. In contrast, bioenergy biomass yield increased by 27 % from 4.9 to 6.7 DM Mg ha^-1 with consistent quality (cellulose ~ 397.9 g kg^-1; hemicellulose ~ 299.4 g kg^-1), corresponding to the increased total theoretical ethanol yield from 1.8×10³ to 2.4×10³ L ha^-1 (~33 % increase). Annual nutrient removals of N, P, K, Ca, and Mg were significantly higher in the forage systems (e.g., 2-cut: 52.6~106.9 kg-N ha^-1; 1-cut: 44.5~84.1 kg-N ha^-1) than those in the bioenergy system (e.g., 25.9~34.4 kg-N ha^-1); however, the removal rate declined rapidly over three years (e.g., ~49 % reduction) as the annual biomass yield declined in the forage systems. This on-farm field study demonstrated the potential of the perennial crop used as buffer strip options for biomass production and buffer sustainability at the edge of the field.