Location: Southeast Watershed ResearchTitle: Sediment-bound total organic carbon and total organic nitrogen losses from conventional and strip tillage cropping systems Author
Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2017
Publication Date: 5/3/2017
Citation: Endale, D.M., Potter, T.L., Strickland, T.C., Bosch, D.D. 2017. Sediment-bound total organic carbon and total organic nitrogen losses from conventional and strip tillage cropping systems. Soil and Tillage Research. 171:25-34. Https://doi:10.1016/j.still.2017.04.004.
DOI: https://doi.org/10.1016/j.still.2017.04.004 Interpretive Summary: Carbon (C) and nitrogen (N) play essential roles in influencing soil health and hence crop productivity and environmental quality. Recently, interest has peaked about the possible role of soil for carbon retention and for the mitigation of climate change. Soil erosion and deposition greatly influences the distribution of soil carbon and nitrogen within a landscape. There is a wide margin in estimates of the net effect of soil erosion on the carbon cycle, ranging from retention to loss, because of gaps in our understanding of the fate of eroded soil carbon. Cropping management effect on soil organic carbon and nitrogen redistribution by erosion and deposition in complex landscapes remains poorly studied. We conducted a seven-year study (2003-2009) to quantify and assess how much total organic carbon (TOC) and total organic nitrogen (TON) was attached to sediment (concentrations as %), how this compared with that in the parent soil (enrichment ratio ER), and how much mass left fields, from a cotton-peanuts rotational cropping system with a winter rye crop managed under conventional tillage (CT) and strip tillage (ST) in the Atlantic Coastal Plain, an important agricultural region in southeastern USA with sandy soils. The TON concentration in sediment was O.7% from ST compared with 0.3% from CT, and the TOC concentration was 8.5% from ST compared with 3.8% from CT. Similarly, the enrichment ratio for TON was 19.3 form ST compared with 13.9 form CT, and the enrichment ratio for TOC was 12.1 from ST compared with 8.1 from CT. On the other hand, due to greater sediment loss from CT, the mass in pounds per acre of TON lost from CT was 0.16 compared with 0.10 from ST and the mass of TOC lost from CT was 2.00 compared with 1.12 from ST. These differences were all significant. The observed enrichment ratios are several-fold greater than reported in the limited available publications pointing to the need for additional research on ER in sandy soils. The implication of this research is that reduced losses with sediment from ST resulted in increased storage of TOC and TON. The research also highlights the site-specific nature of erosion processes and how they affect the loss or retention of C and N in agricultural landscapes. 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 soils are sandy.
Technical Abstract: Soil erosion and sediment loss with runoff are closely linked to global carbon and nitrogen cycles. Reducing tillage has been shown to reduce erosion and runoff sediment-bound carbon (C) and nitrogen (N) losses. However, published studies represent only a few soil types and regions and rarely directly compare tillage practices. In addition, little related published information exists on the loamy sand and sandy loam soils that are characteristic of the Atlantic Coastal Plain region of the southeastern USA. Our objective was to quantify and assess differences in concentrations (as %), enrichment ratios, and loads of sediment-bound total organic carbon (TOC) and total organic nitrogen (TON) from a cotton (Gossypium hirsutum L.)-peanuts (Arachis hypogea L.) rotational cropping system with rye (Secale cearale) cover crop managed under conventional tillage (CT) and strip tillage (ST) in a Coastal Plain landscape. The study was conducted from 2003 to 2009. The experimental fields were set up to include upper, middle and lower landscape positions. Concentrations and enrichment ratios for TON and TOC were greater in sediment from ST than CT but, due to greater sediment loss, TON and TOC loads were greater from CT than ST. Across landscape positions, the median concentration in sediment from ST was 0.74% for TON and 8.51% for TOC compared with 0.31% and 3.81%, respectively, from CT. Similarly the median enrichment ratio in sediment from ST was 19.28 for TON and 12.07 for TOC compared with 13.92 and 8.06 respectively, of CT. On the other hand, the median TON load in kg ha-1 was 0.18 from CT and 0.11 from ST, and the median TOC load was 2.24 from CT and 1.26 from ST. Differences were all significant at a of 0.05. Generally, differences were also significant at the upper and middle landscape positions but not at the lower landscape position in some cases. The observed enrichment ratios are severalfold greater than reported in the limited available literature but, by enlarge, the literature values come from more loamy soils. The implication of this research is that reduced losses with sediment from ST resulted in increased storage of TOC and TON. The research also highlights the site-specific nature of erosion processes and how they affect the loss or retention of C and N in agricultural landscapes. 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 soils are sandy. These results add to the suite of advantages other research has shown of cropping practices that adopt strip tillage with winter cover crop in the Coastal Plain of southeastern USA in terms of improved productivity and environmental quality.