Nitrogen leaching loss from poultry manure amendments to corn production systems

Background/Question/Methods

In the Chesapeake Bay Watershed, geographically concentrated poultry production has led to manure and nutrient excesses that contribute to eutrophication and hypoxia in the bay. Manure almost always remains close to its source, causing high nitrogen (N) loads to enter the watershed. Proposed techniques for minimizing N losses to the environment from manure applied to crops include composting and biochar production. Compost and biochar are relatively recalcitrant compared to raw manure, thus may lead to greater N retention in the soil and lower rates of N leaching. The purpose of this study was to determine the effects of these poultry manure amendments on the timing and magnitude of N losses to the environment. Two replicated field sites in high and low manure production areas of the watershed simulated typical farming practices for the area. At each site, plots were treated with urea, raw manure, compost, and biochar. Soil samples of various depths up to 1 m were taken at three time points throughout the growing season from each site and analyzed for N content in the forms of ammonium and nitrate. 

Results/Conclusions

Differences in weather and soil characteristics between the two sites affect both the timing and amount of N leaching. The site in Delaware is characterized by sandy soils and high precipitation. Soils at the Pennsylvania site have higher clay and silt content, with lower precipitation. Nitrate and ammonium concentrations differed across sampling time points, and reflected the timing of fertilizer additions and plant nutrient uptake. Results reflect differences in site characteristics, especially soil type, with greater leaching losses from the sandy soil. Differences among fertilizer amendments are also reflected in groundwater N concentrations. Site variation seems to have the highest impact on amendment N losses. Urea and manure amendments tended to have higher N leaching losses, while losses from the control and compost plots were lower. The highest ammonium concentrations were found more frequently at shallow depths, while the highest nitrate concentrations were found in deepest samples. Our results suggest that manure amendments do differ in timing and amount of N leaching, and that site characteristics have a large impact on these patterns.