Phosphorus and organic matter enrichment in snowmelt and rainfall–runoff from three corn management systems
The physical nature of sediment transport favors the movement of smaller and less dense materials, typically resulting in greater (enriched) sediment total phosphorus (TP) and organic matter (OM) concentrations than those of the parent soil. In rainfall–runoff, residue cover significantly influenced P enrichment, with the median TP enrichment ratio (TP ER ) for corn-grain (1.4) being significantly greater ( p = 0.007) than that for corn-silage (0.8) and manured corn-silage (1.0) fields, which were similar. While greater P enrichment was observed in snowmelt compared to rainfall–runoff, attributable to correspondingly high OM ER values, TP ER was unaffected by treatment differences ( p = 0.60). The OM enrichment was much higher (~ 10×) during snowmelt (9.7) compared to rainfall–runoff (0.97). Low flow rates over frozen surfaces may have favored enhanced transport of OM and clay-sized particles in snowmelt. Crop residue contributions from corn-grain systems favor greater transport of organic P forms (i.e., low dissolved reactive P/total dissolved P ratios) whereas inorganic P dominance was observed in silage fields. Additional intra-event runoff data generated for fields with different crop-row orientations (contour vs. up-and-down the slope) provided more insights into the temporal dynamics of P enrichment process. The TP ER values were generally inversely related to flow rate and soil loss. This study addresses crucial knowledge/information gaps on the role played by the mode of runoff generation (rainfall–runoff vs. snowmelt) and field roughness conditions (due to crop residue, crop-row orientations) on P enrichment from row-cropped agricultural systems.