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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #339820

Title: Soil nutrient variability and groundwater nitrate-N in agricultural fields

item Logsdon, Sally
item Cole, Kevin

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2018
Publication Date: 6/15/2018
Publication URL:
Citation: Logsdon, S.D., Cole, K.J. 2018. Soil nutrient variability and groundwater nitrate-N in agricultural fields. Science of the Total Environment. 627:39-45.

Interpretive Summary: The amount of nutrients in soil varies across the landscape and as a result of management practices. This study showed that uneven swine manure management resulted in an area of high nutrient levels in the surface soil. Due to dry weather conditions, there were no runoff events for several months after application, so the high phosphorus levels were not lost in runoff or erosion. Nitrate that leached to the groundwater declined over the growing seasons for five of nine monitored wells, as expected. Nitrate levels in groundwater remained high at the other four sites, perhaps due to long-term manure applications. This information is important to scientists and well as those developing best management practices.

Technical Abstract: Landscape and management often result in uneven nutrient loads within a field. The hypotheses of this study are that 1) phosphorus accumulates at low areas in the landscape adjacent to waterways, and 2) nitrate at lower landscape positions will be decreased in the subsoil due to denitrification and leaching losses. The purpose of this study was to determine if high nutrient loads accumulate in zones close to outlets (waterways, ditches, tiles, etc.) with potential to contribute to offsite loss of nutrients. Soil was sampled within transects in two fields, and three wells were installed in each field. The transects were close to grassed waterways, and runoff was monitored in one of the fields. The data show the hypotheses were not consistently correct. Surface nutrient concentrations related more to management than landscape in a field that had recent swine manure application before sampling, and showed a zone of high nutrient load. Due to dry conditions after manure application in the fall of 2012, runoff did not occur until 2013, and P loads were in the expected range. Another field did show a relation between landscape factors and nutrient levels in the surface soil. However, in this field groundwater nitrate levels were highest in the low elevation site closest to the waterway, contrary to the hypothesis. Groundwater nutrient levels were a result of several factors reflecting both local soil and management, and surface and subsurface lateral transport across the landscape.