Biomass From Buffers: A Win-Win for Climate and Water Quality?.

Researchers have hypothesized that biomass crop production in vegetative buffers can simultaneously produce biofuel feedstock, sequester C, and improve water quality performance. This win-win hypothesis, however, hinges on whether the landowner chooses to maximize biomass yield or not. When cropland is converted to vegetative buffer, the permanent vegetation stabilizes soil, increases soil C, and traps nutrients, pesticides, and sediment in runoff from uplands. Biomass harvesting in buffers can enhance the nutrient trapping function by exporting nutrients contained in biomass and renewing vigorous nutrient-accumulating plant growth. Perennial biomass crops, such as switchgrass and hybrid poplar and willow trees, have been reported to export as much as 143 kg N ha^-1 yr^-1 and 26 kg P ha^-1 yr^-1. However, nutrient scavenging by biomass crops will be diminished if fertilizer is applied for increasing biomass yield. For example, maximum biomass yield of switchgrass has been reported to be achieved when fertilizer N is applied at rates as high as 187 kg N ha^-1 yr^-1 beyond the amount of N that would be exported in the biomass crop. Excess nutrients are likely to leach and further degrade water quality. Pesticide application to buffers for controlling diseases, pests, and weeds carry additional water quality risks, especially in riparian settings. Water quality benefits of growing biomass crops in buffer zones will not accrue without some limitations placed on production practices.