Nitrogen, Phosphorus, and Potassium Removal in Sweet Sorghum Grown for Biofuel.

Sweet sorghum (Sorghum bicolor (L.) Moench) is gaining attention as a possible bioenergy feedstock in the Midwestern U.S. Continued research into the sustainable production of sweet sorghum is essential to making it a viable crop to supplement maize and perennial grasses. Sweet sorghum is drought tolerant, has high nitrogen-use efficiency, and is well-suited for widespread production in the U.S. To better determine the crop’s uptake and use of nitrogen, phosphorus, and potassium in sustainable dryland systems, a three-year study (2009-2011) was conducted in central Missouri measuring the N, P, and K content of above-ground dry matter in two sorghum cultivars (Dale, Top 76-6) across five N fertilizer rates ranging from 0-224 kg ha^-1 under rain-fed conditions.  Nutrient uptake was affected by annual differences in precipitation, whereby in years with high precipitation greater nutrient content was observed. Nutrient content, especially total nitrogen, and removal from the field, were highly dependent on N fertilizer application.  Consequently, in order to maintain soil fertility, fertilizer recommendations will need to be developed that account for the removal of these nutrients in the harvested biomass.