This Is AuburnElectronic Theses and Dissertations

Development of Fertilizer Recommendations for Native Biofuel Crops and Nutrient Release from Cattle Feces




Brown, Richard

Type of Degree



Agronomy and Soils


Plant biomass is a viable raw material for renewable energy production. The use of perennial grasses is a possible option, however information on their nutrient management in the southeastern U.S. is deficient. The objective of this study was to determine the response of switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) to different levels of nitrogen (N), phosphorus (P), and potassium (K) fertilization. The study was conducted during 2007-2009 near Brewton, Alabama, USA on the ‘Rate of NPK’ plots (circa 1954) that have been maintained at various levels of soil fertility. Plots were planted in 2007 and allowed one year to establish a stand before the experiment began. In the spring of each year, varying rates of N, P, and K were applied to both grasses. Nutrient concentration data was collected throughout the growing season by sampling plant tissue, and dry matter yield (DMY) was obtained by a once-a-year harvest in November of both years. Dry matter yield showed a diminishing returns response to N fertilization while no response was observed for P or K. Maximum agronomic yield (MAY) was attained at 155 and 161 kg N ha-1 for big bluestem and switchgrass, respectively. Economic analysis showed net return increased with N fertilization at high and low biomass prices for switchgrass, while an increase was only observed only at the high biomass price for big bluestem. Nutrient removal for all elements in both species increased with rate of fertilizer applied. Apparent N recovery (ANR) was calculated and switchgrass displayed a diminishing return response ,while responses for big bluestem varied. Since yield showed no response to P or K fertilization, nutrient concentration data were analyzed for N treatments only, and decreased across the growing season. Concentration of N varied between 0 and 158 kg N ha-1 indicating that plant tissue sampling, when taken early enough in the growing season, can detect N deficiency. Cattle (Bos taurus) manure has been historically used as a soil amendment to increase fertility, but information on the impacts of cattle defecation in pastures on soil fertility is lacking. A study was conducted in Auburn, AL from 2008 to 2009 to measure nutrient release from dairy feces. Feces and soil samples were collected throughout two seasons in the winter of 2008-2009 and the summer of 2009. Results indicated that N, P, K, calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn) were released from feces at different rates throughout the experiment. Season affected the release rate of all nutrients. Feces retained small amounts of each nutrient after an initial decline. An increase in soil nutrients across time was observed for all elements except Cu. Rates of nutrient response varied by element and was affected by season. The results suggested that feces can have an effect on the soil nutrient status.