Citation:

Smith, H., T. Williams, S. Pearlstein, J. Compton, AND J. Morse. Comparing Post-Harvest Soil Nitrogen and Carbon Cycling and Content in Tall Fescue Fields Under Conventional and Enhanced Efficiency Fertilization. AGU, Washington, DC, December 10 - 14, 2018.

Impact/Purpose:

Portland State University scientists are collaborating with US EPA and Willamette Valley farmers and fertilizer companies to examine the broad ecosystem effects of enhanced efficiency fertilizers on crop yield, N leaching and trace gas production on active production farmland. National Science Foundation's Research Experience for Undergraduates student Hillary Smith is conducting solil sampling to determine the surplus N in the soil after harvest, as well as soil carbon and nitrogen contents and cycling processes. This work will add a broader ecosystem context to the ongoing collaboration. The results of soil analyses, along with crop yields, are an important step towards establishing best practices for application of nitrogenous agricultural fertilizers to mitigate their environmental and health impacts.

Description:

Synthetic nitrogen (N) fertilizers have enabled massive gains in global agricultural productivity, but widespread use of excessive amounts of chemical fertilizers has resulted in diminished air and water quality. Human health problems can arise from elevated levels of these agricultural pollutants, including N oxides in the atmosphere and nitrate in drinking water. Ecosystems are also adversely affected by excess reactive N from agriculture that leaches into water bodies, causing eutrophication events, while global climate change is impacted by emissions of nitrous oxide (N2O). Parts of the Southern Willamette Valley, Oregon, have been designated as a Groundwater Management Area due to high nitrate levels in groundwater, with observed high nitrate leaching below some grass seed crops. To inform more efficient fertilizer practices, our study compared grass seed yield and residual soil N after harvest in four tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) grass seed fields under conventional and enhanced efficiency fertilizer treatments (slow-release urea pellets, Nutrisphere-N®). Three soil samples (0-15 cm) per treatment in each field were collected and analyzed to characterize soil physical and chemical properties, including pH, texture, bulk density, and organic matter content. Residual N content was measured by extraction with 2M KCl, while potential rates of net N mineralization, net nitrification, and respiration were determined following 10-day incubations. Potential denitrification was estimated using the denitrification enzyme activity assay. The effects of fertilizer treatment on crop yield varied by site, with two fields having 8% and 24% greater grass seed yield under conventional fertilizer practices, while the other two fields had 49% and 43% greater yields from enhanced efficiency fertilizer. Results of soil analyses, along with crop yields, are an important step towards establishing best practices for application of nitrogenous agricultural fertilizers to mitigate their environmental and health impacts.

Record Details: