Biomass Yield and Nutrient Responses of Switchgrass to Phosphorus Application

Abstract

Increasing desire for renewable energy sources has increased research on biomass energy crops in marginal areas with low potential for food and fiber crop production. In this study, experiments were established on low phosphorus (P) soils in southern Oklahoma, USA to determine switchgrass biomass yield, nutrient concentrations, and nutrient removal responses to P and nitrogen (N) fertilizer application. Four P rates (0, 15, 30, and 45 kg P ha−1) and two N fertilizer rates (0 and 135 kg N ha−1) were evaluated at two locations (Ardmore and Waurika) for 3 years. While P fertilization had no effect on yield at Ardmore, application of 45 kg P ha−1 increased yield at Waurika by 17% from 10.5 to 12.3 Mg ha−1. Across P fertilizer rates, N fertilizer application increased yields every year at both locations. In Ardmore, non-N-fertilized switchgrass produced 3.9, 6.7, and 8.8 Mg ha−1, and N-fertilized produced 6.6, 15.7, and 16.6 Mg ha−1 in 2008, 2009, and 2010, respectively. At Waurika, corresponding yields were 7.9, 8.4, and 12.2 Mg ha−1 and 10.0, 12.1, and 15.9 Mg ha−1. Applying 45 kg P ha−1 increased biomass N, and P concentration and N, P, potassium, and magnesium removal at both locations. Increased removal of nutrients with N fertilization was due to both increased biomass and biomass nutrient concentrations. In soils of generally low fertility and low plant available P, application of P fertilizer at 45 kg P ha−1 was beneficial for increasing biomass yields. Addition of N fertilizer improves stand establishment and biomass production on low P sites.