Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 22, 1997
Publication Date: N/A
Interpretive Summary: The ability of agricultural crops to retain nutrients is critical for obtaining optimal crop productivity with minimal environmental contamination. The application of agricultural fertilizers has been linked to nitrate contamination of ground water. This problem has increased interest in using uncultivated riparian ecosystems as buffers between agricultural fields and surface waters. Riparian buffer strips have been shown to reduce the amount of nitrate moving to subsurface waters. This study indicates that fertilizer N losses, amounting to 12.5% of the applied fertilizer N, from poorly drained grass seed crops may be lost through soil denitrification (conversion of nitrate to N gases). Further research is needed to determine the fate and processing of nitrate in the riparian buffer zone at this site. Nutrient and microbiological data suggest that the riparian zone could potentially process nitrate through denitrification and thus maintain low nitrate levels and higher water quality compared to the adjacent agricultural field.
Technical Abstract: The factors that affect denitrification of fertilizer N were determined in cultivated riparian (CR) soils cropped to perennial ryegrass and noncultivated naturally vegetated riparian soils (NCR) of poorly drained grass cropping systems in western Oregon. Denitrification in the NCR was low compared to the CR using the Acetylene Inhibition method. The CR soil denitrification was consistent over the growing season averaging between 269 to 280 g N2O-N ha**-1 d**-1 during the measurement period depending on soil type. Denitrification was positively correlated to soil NH4-N level in the CR. The greater denitrification of the CR likely reflects fertilizer applications in contrast to no fertilizer addition to the NCR. Nitrate-N levels in the CR averaged 5 to 12 times higher than those of the NCR. The microbial biomass was 4 times larger in the NCR soils and may have functioned as a significant sink for N reducing denitrification. Multivariate factor analysis using orthogonal factor rotation showed that approximately 83% of the observed variance in denitrification was explained by grouping experimental variables by microbial activity, N2O-N emission, temperature, and nitrification. The grouping of soil variables was useful in explaining the importance of different soil processes in regulating denitrification. This study indicates that significant N losses, amounting to 12.5% of the applied fertilizer N, from poorly drained grass seed cropping systems may be lost through denitrification (conversion of nitrate to N gases).