PR - Economic Costs Of Soil Nutrient Mining And Benefits From Plant Nutrient Recycling: The Case Of Switchgrass Produced For Bioenergy Feedstock

Few attempts have been made to account for the potential costs associated with soil nutrient mining or the potential benefits associated with nutrient remobilization in switchgrass pastures established and managed as a dedicated bioenergy feedstock crop. Continuous soil nutrient mining could result in declining yields and profitability in the long-run and ultimately final exit out of switchgrass production. The objective of this study was to determine the cost associated with nutrient mining and the potential benefits associated with nutrient remobilization associated with one and two-cut switchgrass harvest systems in the southern Great Plain, USA. Data collected from a four-year, two-location agronomic field trial that evaluated two harvest systems, five N rates, and fixed rates of P and K applications were used for analysis. A standard forage analysis was used to determine the concentrations of N, P and K nutrients in the feedstock harvested. Cost of mining (or benefit of recycling) was estimated by comparing two separate economic models. Model 1 follows the conventional economic approach of utilizing yield response to treatments levels of N, P and K. Model 2 follows an approach that accounts for the costs and benefits associated with the N, P and K concentrations removed by the plants at harvest. Results from the convention economic approach indicate that producers should harvest twice per year, lending the system to mine significant quantities of N, P and K. When the benefits and costs associated with total nutrient uptake from plants were accounted, assuming a $110 Mg-1 for feedstock, the results indicate a producer would be better off harvesting twice (once in the summer and again in the winter), and the non-market economic tradeoff between nutrient mining and long-run soil sustainability was $8.70 Mg-1.

Keywords: Switchgrass, bioenergy, economic sustainability, cellulosic feedstock, nitrogen, harvest system