Sand is the unifying textural component with surface-soil carbon and nitrogen fractions across undisturbed land uses in North Carolina

Authors: Franzluebbers, Alan

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2024
Publication Date: 1/1/2025
Citation: Franzluebbers, A.J. 2025. Sand is the unifying textural component with surface-soil carbon and nitrogen fractions across undisturbed land uses in North Carolina. Soil Science Society of America Journal. Vol 89, Issue 1. https://doi.org/10.1002/saj2.70011.
DOI: https://doi.org/10.1002/saj2.70011

Interpretive Summary: Estimating potential changes in soil organic matter with implementation of grassland management in North Carolina and surrounding states could be improved with better understanding of how moderately and slowly changing portions of organic matter react as a function of soil texture. Greater soil organic matter will help control soil erosion, enhance nutrient cycling, and provide habitat for biodiversity. A scientist in the Plant Science Research Unit collected soils from private farms throughout North Carolina under grasslands and woodlands. Soil organic matter was strongly associated with soil texture, in which organic matter was greatest with least amount of sand and lowest with the greatest amount of sand. In addition, soil density was greatest with greatest amount of sand. These functional relationships between soil texture and organic matter will be useful for scientists to better predict the implications of improved management on soil organic matter. Farmers and landowners can use this information as a practical guide for how much carbon might be stored in soil based on soil texture conditions on their farm.

Technical Abstract: Soil organic matter concentrations are associated with soil texture in some but not in all studies. Why there are variable responses to soil texture can have logical reasons, the most obvious of which are inconsistent historical land uses, interactions with climatic and landscape settings, and management variations within a land use. In an evaluation of surface soils (0-10-cm depth) under consistently undisturbed land use from 648 sites across relatively narrow climatic variations in North Carolina, large soil texture variations were assembled into structured populations (n=27) of sand and clay categories (n=24). Sand concentration varied from 220 to 881 g/kg, silt concentration varied from 67 to 517 g/kg, and clay concentration varied from 47 to 360 g/kg (5 to 95% limits). Overwhelmingly, total, particulate, and non-particulate organic C and N fractions were more statistically associated with sand concentration than with clay concentration alone. Sand concentration is the inverse of clay + silt summation and is a necessary feature when determining particulate organic C and N. Soil bulk density and sieved soil density were also more associated with sand concentration than clay concentration alone. This study confirmed there was no saturation limit for the accumulation of non-particulate organic C and N (sometimes labeled mineral-associated organic matter). Therefore, sand concentration should be considered the best indicator of soil textural influence on soil organic matter properties.