Evaluating Conservation Agricultural Management for Soil Health Outcomes in Southeastern Virginia

Abstract

Improving soil health in agricultural soils is vital as the effects of climate change and an increasingly affluent population are putting a strain on land resources. Conservation agricultural practices such as cover cropping and conservation tillage systems (e.g., strip tillage, minimal tillage, or no tillage) are implemented to improve soil properties, but soil health outcomes in Coastal Plain cropping systems have been inconsistent and may take decades or longer to occur. Improving soil health and agricultural prosperity in the region requires: a better understanding of the rate and magnitude of response in soil properties to different types of management; and a better understanding of the interaction between management types, soil health parameters, and crop yield. In this study, four tillage systems (in order of decreasing intensity: conventional tillage > strip tillage > minimal tillage > and no tillage) and three winter cover rotations (in order of decreasing expected biomass input: high-biomass cover crop > winter cash crop > and fallow) were tested in a split plot design. For the first objective of this study, bulk density, penetration resistance (as depth to root restrictive layer), total organic carbon, carbon stocks, saturated hydraulic conductivity, and yield were measured repeatedly over a seven-year period to better understand the longitudinal response of these properties to management. Bulk density and saturated hydraulic conductivity showed a greater temporal variation in the more intensive tillage practices (strip tillage and conventional tillage) in the top 5 cm. Depth to root restrictive layer was consistently highest in the deep tillage treatments (strip tillage and minimal tillage). The change in soil organic carbon concentration between 2018 and 2022 in the top 5 cm was numerically greater in the strip tillage (0.67%) and no tillage (0.68) than the conventional tillage was 0.18%. In 2022, the carbon stocks were significantly increased in all three conservation tillage treatments compared to conventional tillage. Yield was significantly increased by winter cover in the years that a legume/non-legume cover crop mix was implemented. For the second objective of this study, the effects of 6 years of management were evaluated for total organic carbon, active carbon, short-term carbon mineralization, aggregate stability, and crop yield. These parameters were then correlated to determine drivers in soil health outcomes. Total organic carbon was increased in the strip tillage treatment (1.13% in 2021 and 1.61 % in 2022) compared to conventional tillage (0.83% in 2021 and 1.09% in 2022) in the top 5 cm. In 2022, total organic carbon under cover crop (1.51 %) and cash crop (1.46 %) treatments were also significantly higher than the fallow (1.33 %) in the top 5 cm. Active carbon results followed a similar but weaker trend in both years. Percent aggregate stability was improved by minimal tillage (47%) in 2022 compared to conventional tillage (41%). The findings from the correlation analyses suggest that total organic carbon concentration, soil texture, and tillage were all prominent drivers in improving soil health outcomes. These results demonstrate the relatively slow response of many soil physical properties to management, highlight the need for consistent management to improve properties, and emphasize the need to take measurements at different times of the year. This information can be used to develop more sustainable and resilient cropping systems in the Coastal Plain.