Dual-isotope approach for assessing agricultural management effects on nutrient dynamics: Proof of concept

Authors: Bos, Janae; Williams, Mark; Penn, Chad; Smith, Douglas

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2022
Publication Date: 8/12/2022
Citation: Bos, J.H., Williams, M.R., Penn, C.J., Smith, D.R. 2022. Dual-isotope approach for assessing agricultural management effects on nutrient dynamics: Proof of concept. Agrosystems, Geosciences & Environment. 5:e20306. https://doi.org/10.1002/agg2.20306.
DOI: https://doi.org/10.1002/agg2.20306

Interpretive Summary: Intensive agricultural management can result in a surplus of soil nitrogen and phosphorus that can impair water quality for years to decades after agricultural inputs cease. In this study, we use a multi-isotope approach to examine changes in soil isotopic signature resulting from agricultural intensification and long-term nutrient additions to fields in the Texas Blackland Prairies ecoregion. Both N and P isotopes have the potential to yield new insights into soil nutrient transformations and aid in the tracing of diffuse nutrient pollution. We compared isotopic signatures across land use (remnant prairie vs. row crop) and nutrient source (fertilizer vs. poultry litter). Results showed that soil del15N varied between land use at the study onset likely due to greater N loss and cycling in row crops, with differences between row-cropped fields becoming apparent following application of litter to one field. In contrast, soil del18Op in row-cropped fields only differed from the prairie following the long-term nutrient trial; however, signatures were similar irrespective of P source. Findings highlight the utility of a multi-isotope approach for quantifying N and P dynamics within soil systems. Coupled with knowledge of long-term nutrient management practices this approach could be useful for identifying and tracing diffuse nutrient losses within agricultural landscapes.

Technical Abstract: In this study, we utilize a multi-isotope approach combining del15N with the highly novel analysis of del18O of phosphate (del18Op). Our objective was to examine changes in soil nutrient concentration and isotopic signal resulting from long-term fertilization (2002-2017) of row-cropped fields receiving either fertilizer or poultry litter in the Texas Blackland Prairies ecoregion. We also compared fields to a remnant prairie receiving no nutrient inputs. Soil del15N varied between land use at the study onset likely due to greater N loss and cycling in row crops, with differences between row-cropped fields becoming apparent following application of litter to one field. In contrast, soil del18Op in row-cropped fields only differed from the prairie following the long-term nutrient trial; however, signatures were similar irrespective of P source. Findings highlight the utility of a multi-isotope approach for quantifying N and P dynamics within soil systems. Coupled with knowledge of long-term nutrient management practices this framework could be useful for identifying and tracing diffuse nutrient losses within agricultural landscapes.