Sediment-bound total organic carbon and total organic nitrogen losses from conventional and strip tillage cropping systems

Global carbon (C) and nitrogen (N) cycles are closely linked to erosion and hydrologic processes. By reducing tillage erosion and runoff, sediment-bound C and N losses can be reduced. Published studies represent only a few soil types and regions and rarely directly compare tillage practices. The objective of this study was to quantify concentrations and sediment-bound total organic carbon (TOC) and nitrogen (TON) loads and enrichment ratios in runoff from 0.2-ha fields in rotational cotton (Gossypium hirsutum L.)-peanut (Arachis hypogea L.) production during a 7-yr study within a southeastern USA coastal plain landscape. The Ultisoils at the study site have loamy sand to sandy loam texture surface horizons. The fields were in either continuous conventional tillage (CT) or strip tillage (ST) and were at upper, middle, and lower landscape positions. Sediment-bound TON and TOC concentrations were significantly greater from ST than CT fields as were the TOC and TON enrichment ratios. However, due to greater surface runoff and sediment loss, TON and TOC loads were significantly greater from CT than ST fields. The CT and ST loads were significantly different at the upper and middle but not at the lower landscape position. Enrichment ratios, 14 to 19 for TON and 8 to 12 for TOC, were several-fold greater than reported in the limited available literature, where studies focused on finer textured surface soils. Our findings have highlighted the site-specific nature of erosion processes, how they affect sediment-bound C and N loss in agricultural landscapes, and how reducing tillage may impact sediment C and N dynamics. The observed enrichment ratios can be used to modify or adjust values used in current erosion models and improve their suitability for use in the region and elsewhere where surface soils have sandy texture and when practices like ST are implemented.