Surface-soil aggregation and organic C and N fractions under paired grassland and cropland sites in the southeastern USA

Authors: Franzluebbers, Alan; VAN VLIET, STEPHAN - Utah State University; YOUNG, SIERRA - Utah State University; POORE, MATT - North Carolina State University

Submitted to: Grassland International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2023
Publication Date: 5/15/2023
Citation: Franzluebbers, A.J., Van Vliet, S., Young, S., Poore, M. 2023. Surface-soil aggregation and organic C and N fractions under paired grassland and cropland sites in the southeastern USA. Grassland International Congress Proceedings. p. 125-128. https://doi.org/10.52202/071171-0029.
DOI: https://doi.org/10.52202/071171-0029

Interpretive Summary: Ecosystem services from pasture-based livestock farming systems have been relatively poorly characterized. Evidence is emerging that perennial grasslands can provide a diversity of ecosystems services, including soil organic carbon storage, that help protect agricultural production and the environment to which it depends. An ARS scientist in Raleigh, North Carolina collaborated with investigators from North Carolina State University and Utah State University (formerly at Duke University) to determine soil chemical, physical, and biological properties between paired cropland and pasture sites in three different ecoregions of the southeastern US. Evidence was strong that soil organic carbon and nitrogen, soil-test biological activity, and soil aggregation were improved under well-managed perennial pastures than under cropland. These results will be useful to farmers, farm advisors, and policy makers to appreciate the value of perennial pastures in agricultural landscapes.

Technical Abstract: Grasslands are expected to deliver ecosystem services by sequestering soil organic C, improving soil health and water quality, and minimizing soil erosion. Data to support these ecosystem services from contemporary managed grasslands are relatively scant, and so on-farm measurements would help bolster assessment across more diverse environmental settings. This study was conducted to compare soil properties from paired land-use of croplands and grasslands in a diversity of Major Land Resource Areas – the Piedmont, Blue Ridge, and Blackland Prairie of the southeastern USA. Four separate pastures on three collaborating farms were sampled at depth of 0-10 cm. Four samples from a neighboring cropland field were paired with these pastures. A variety of soil chemical, physical, and biological properties were determined. Soil chemical properties were occasionally different between land management systems on one of the three farms, but few consistent differences occurred across farms. Dry-stable mean-weight diameter (MWD) was not different between paired land management systems, but water-stable MWD was dramatically reduced at all three locations with cropland compared with pasture. Soil stability index (water-stable MWD divided by dry-stable MWD) averaged 0.64 mm/mm under cropland and 0.91 mm/mm under pasture, suggesting that pastures had a highly stable soil surface that was resistant to erosion and likely contributed to high water infiltration. Soil organic C and N fractions (i.e., total, particulate, and mineralizable) were all significantly greater under pasture than under cropland, indicating that these pastures were indeed storing more C and N, and contributing to greater soil biological activity. This study provides evidence that well-managed grasslands can sequester soil organic C and N, improve soil surface stability conditions to foster water infiltration and reduced runoff, and may have important implications for habitat development for soil-dwelling organisms.