Soil aggregation and surface-soil properties under grazed pastures and conservation land uses in Virginia

Authors: Franzluebbers, Alan

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Water quality protection of the Chesapeake Bay continues to be a high priority in the Mid-Atlantic region. Nutrient runoff and sediment transport are key attributes that must be limited to further improve water quality. An ARS scientist in Raleigh, North Carolina collected soil from 31 different farms in Virigina under grazing lands, no-till croplands, and woodlands to assess soil aggregation and other soil-surface characteristics that indicate potential soil erosion and runoff. Grasslands were one of the best land uses for soil aggregation characteristics, equal to that of woodlands and greater than that of croplands. Of managed grasslands, pastures that were at least 10 years old led to the best soil aggregation, total soil N, and soil-test biological activity. Stocking rate was not definitive in its influence on surface-soil characteristics due to few observations at the lowest and highest rates. Most intensive rotational stocking led to reduced soil aggregation characteristics, but levels were generally high in all stocking methods. Pasture nitrogen fertilization was not always necessary to elevate soil conditions. These results will be important for agricultural advisors, farmers, extension specialists, and scientists in the region to promote more efficient, soil conserving practices for agriculture to protect water quality in the Chesapeake Bay and other surrounding watersheds.

Technical Abstract: Grazed pastures supporting ruminant livestock have not been well characterized. However, growing interest in holistic management of compromised watersheds suggests that grazing lands deserve more attention for their capacity to provide ecosystem services. Relatively little is known about how grazing management affects soil aggregation and other surface-soil properties on private lands in the eastern US. This study investigated the effects of land use (conventional-till cropland, no-till cropland, grassland, and woodland) on soil aggregation, bulk density, sieved soil density, total soil N, and soil-test biological activity on 31 private farms distributed across the western half of Virginia. Soil stability index followed the order (p < .05): conventional-till cropland (0.60 mm/mm) < no-till cropland (0.78 mm/mm) < woodland (0.85 mm/mm) = grassland (0.89 mm/mm). Surface soil characteristics improved with pasture age due to organic matter recycling from residual forage mass and animal excreta. Increases in total soil N and soil-test biological activity helped create water-stable aggregation and reduce soil bulk density. Soil stability index was optimized with moderate stocking rate of 0.5 to 1.1 Mg live weight/ha. Stocking method did not affect soil aggregation or bulk density. Soil stability index declined with increasing N fertilization. Soil aggregation characteristics were generally not affected by organic amendment, quantity of hay fed on farm, or occasional hay harvest from pastures, mostly because aggregation was high overall across management variables. Well-managed grazed pastures in Virginia are creating desirable conservation agricultural land uses to protect watershed quality.