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

Abstract

Abstract Quantifying the impact of long‐term agricultural management on nutrient fate and transport is critical for developing sustainable management solutions. In this study, the utility of a dual‐isotope approach, combining soil δ15N with analysis of δ18O of phosphate (δ18Op), was assessed at the Riesel Watershed in the Texas Blackland Prairies. The objective was to examine changes in soil nutrient concentration and isotopic signal from fields with contrasting nutrient source (inorganic fertilizer vs. poultry litter) and land use (remnant prairie vs. row crops) over a long‐term study (2002–2017). Results showed that soil δ15N varied between land use at the study onset likely because of 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 δ18Op in row‐cropped fields only differed from the prairie following the long‐term nutrient trial; however, signatures were similar irrespective of P source. Results from this proof‐of‐concept study highlight the potential of a dual‐isotope approach for quantifying nutrient dynamics within soil systems when coupled with knowledge of long‐term management practices. Findings and study limitations also emphasize the need for future research and application of a dual‐isotope framework in agricultural landscapes for identifying and tracing nutrient fate and transport.