PEDOGENIC CONTROLS ON NITRATE LEACHING IN CULTURED COLORADO SOILS

Abstract

Nitrate leaching from irrigated agriculture remains a major driver of groundwater contamination and non-point source pollution in semi-arid regions of Colorado. While management practices influence nutrient dynamics, this study demonstrates that pedogenic soil properties exert the dominant control on nitrate mobility and retention. Through detailed pedon characterization and integration of long-term deep nitrate data from the South Platte Basin (10 years) and short-term data from the Arkansas Basin (2 years), we applied Principal Component Analysis (PCA), linear mixed-effects modeling, and segmented regression threshold analysis to identify soil properties governing nitrate behavior across contrasting pedogenic settings. Results indicate that total calcium carbonate (CaCO₃), total nitrogen (TN), and clay content are the most influential predictors of nitrate concentration in the South Platte Basin, where finer-textured soils and stronger horizon development constrain nitrate mobility. Clay distribution and total nitrogen near the site mean represented the threshold point where nitrate persistence increased more dramatically, while elevated carbonate levels restricted vertical percolation, promoting lateral flow and retention within the profile. In contrast, the Arkansas Basin model showed no statistically significant linkages, likely reflecting both the limited two-year dataset and weaker pedogenic development in its coarser parent materials. These findings underscore that nitrate leaching potential in the South Platte Basin’s furrow-irrigated systems is governed by the interaction between nutrient availability and soil hydrologic architecture rather than by management alone. Fertilizer management dictates the quantity of nitrate at risk for transport, but the subsurface structure, shaped by clay illuviation, carbonate accumulation, and horizon continuity, ultimately determines its fate. Pedologically informed nutrient and irrigation management, supported by long-term datasets and site-specific monitoring, is essential to improving nitrogen use efficiency and protecting groundwater quality in Colorado’s irrigated agroecosystems.