Surface-soil carbon and nitrogen mineralization under cropland, grassland, and woodland in Virginia

Authors: Franzluebbers, Alan

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2025
Publication Date: 4/10/2025
Citation: Franzluebbers, A.J. 2025. Surface-soil carbon and nitrogen mineralization under cropland, grassland, and woodland in Virginia. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.70050.
DOI: https://doi.org/10.1002/saj2.70050

Interpretive Summary: Conservation land management is critical for enhancing the capacity to produce food and fiber, balancing ecological components of the landscape, and preserving environmental quality. Potential soil nitrogen mineralization is a key indicator of the nutrient supplying capacity through organic matter cycling mediated by soil microbial activity. An ARS scientist in Raleigh North Carolina conducted a field survey of soil microbial activity conditions under conventional-till cropland, no-till cropland, grassland, and woodland on 31 farms in central and western Virginia. Potential soil microbial activity was generally greatest under grassland management and lowest under conventional-till cropland with no-till cropland and woodland intermediate. The quantity of nitrogen potentially supplied through mineralization of surface-soil organic matter was substantial and followed the same order as microbial activity. Accumulation of nitrate in soil during laboratory incubations was low under woodland and some grassland soils, suggesting that specific microorganisms responsible for this conversion were being inhibited. These results will be useful for farmers, agricultural advisors, and scientists to understand the benefits of land-use systems on productivity and environmental outcomes.

Technical Abstract: Long-term management of crop and grazing lands can be expected to change the functioning of soil. Minimizing soil disturbance with conservation management is critical to changing surface soil organic matter conditions, but less is known of how canopy structure (plant species, residue quality) may be affecting C and N properties and processes over time. A diversity of soils from 31 farms in the piedmont and mountain regions of Virginia were sampled at 0-10-cm depth to assess soil C and N mineralization and associated properties. Basal soil respiration was 53 +/- 21% greater under conservation land uses of grassland and woodland than under cropland. Residual inorganic N was greater under no-till cropland (24 kg ha-1) than under conventional-till cropland (10 kg ha-1), but soil C and N mineralization were not different (partly due to few observations under conventional-till cropland). Net N mineralization was 38 +/- 14% greater under grassland than under woodland. Residual soil ammonium-N was strongly associated with biologically active soil C and N properties despite relatively low concentrations and residual soil nitrate-N was minimally associated with these properties. Apparent nitrification during laboratory incubation (g NO3-N g-1 mineralized N) was high in all cropland soils (1.03 +/- 0.08), inhibited in some grassland soils (0.88 +/- 0.18), and dramatically inhibited in most woodland soils (0.31 +/- 0.32). The combination of high net N mineralization and reduced nitrification provides mechanisms for maintaining productivity while minimizing N losses to the environment in long-term conservation land uses.