Impact of nitrogen and phosphorous on biomass yield, nitrogen efficiency, and nutrient removal of perennial grasses for bioenergy

Abstract Perennial grasses are the promising source of bioenergy in South America which could provide several environmental benefits such as reduction in the greenhouse gasses emissions and reduction of nutrients and soil losses. Our objective was to determine the impact of N and P fertilization on biomass yield, N use efficiency (NUE), apparent N recovery (ANR), and nutrient removal (NR) on three perennial grasses: elephantgrass (Pennisetum purpureum Schum.), giant reed (Arundo donax L.), and switchgrass (Panicum virgatum L.). Four fertility treatments were evaluated in a 8-year field study in northwestern Uruguay: 1. control (No fertilizer), 2.100 kg N ha−1 year−1, 3.100 kg P2O5 ha−1 year−1, and 4.100 kg N + 100 kg P2O5 ha−1 year−1. Across years, elephantgrass had the highest biomass yield followed by giant reed and switchgrass (18.9, 16.3, and 14.1 Mg ha−1, respectively). Biomass yield increased 46% when N fertilizer was added, compared to the control. A low response was detected for P fertilization on all grasses, probably for initial P soil content (≥9 g kg−1). Elephantgrass had the highest NUE (70 kg kg−1 N), however, it had the highest total NR on these eight years (899, 226, and 2800 kg ha−1 for N–P–K, respectively) among the grasses, indicating a potential for increased fertilization input over time. Switchgrass had the lowest average ANR (19%) and NR (334, 45, and 166 kg ha−1, respectively). Therefore, even though switchgrass presented the lowest biomass yield, it is an excellent option as low-input bioenergies grass for temperate regions.