The impact of cropping on primary production in the US great plains

Land use and altered carbon dynamics are two of the primary components of global change, and the effect of land use on carbon cycling is a crucial issue in regional scale biogeochemistry. Previous studies have shown that climate and soil conditions control net primary production (NPP) at regional scales, and that agricultural land use can influence NPP at local scales through altered water availability and carbon allocation-patterns. However, few studies have attempted to quantify the effect of cultivation on NPP at regional scales, and no studies have examined this relationship for the most heavily cultivated region of the United States, the Great Plains. We quantified current regional aboveground and belowground productivity (including cultivation) for nine years on a county basis from (1) USDA agricultural census data, and (2) STATSGO range site production values. By comparing these data with values of native vegetation NPP (precultivation) derived from STATSGO, we estimated that cultivation is increasing regional NPP by similar to 10%, or 0.046 Pg C/yr. In addition, we examined the relationship between cultivation of particular crops and NPP change and characterized the influence of individual crops on primary productivity.