No-till and cover crop impacts on soil carbon and associated properties on Pennsylvania dairy farms

Authors: Dell, Curtis; SALON, PAUL - NRCS; FRANKS, CAROL - NRCS - RETIRED; PLOWDEN, YURI - NRCS

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2007
Publication Date: 5/12/2008
Citation: Dell, C.J., Salon, P., Franks, C., Plowden, Y. 2008. No-till and cover crop impacts on soil carbon and associated properties on Pennsylvania dairy farms. Journal of Soil and Water Conservation. 63(3):136-142.

Interpretive Summary: The use of conservation practices in crop production is recommended to prevent soil erosion on susceptible land. Adopting soil conservation practices can help to reduce levels of carbon dioxide in the atmosphere and the potential for climate change. Reducing or eliminating tillage can slow the break down of plant residues and allow more of the carbon in plant residues to become soil organic matter rather than to be returned to the atmosphere as carbon dioxide. Building soil organic matter can also improve conditions for plant growth by increasing the soil’s nutrient holding capacity and improving soil structure. However, the expected increases in soil carbon are based largely on results of research on small plots, and there have been few reports that verify the gains in soil carbon in commercial farm fields after conservation practices are implemented. Additionally, very little information is available for dairy forage systems where almost all the above ground plant material is harvested, limiting the amount of crop residue that can become soil organic matter. To address these concerns, an on-farm study was conducted on seven central Pennsylvania dairy farm fields where rotations of silage corn and alfalfa were grown on similar soils using either conventional tillage or no-till planting, both with and without winter cover crops (cereal rye). Soil was sampled from three depths 0 to 5, 5 to 10, and about 36 to 41 cm, and soil organic matter carbon and nitrogen and several soil properties were measured. Fields where no-till was used had approximately 50 percent more carbon in the upper 5 cm of soil compared to tilled fields, but carbon accumulations below 5 cm were similar among fields. This indicates that about 0.3 MT/ha/yr of carbon have accumulated in these fields since the introduction of no-till. Soil aggregate stability (resistance to breakdown by water) and cation exchange capacity (nutrient holding) were proportional to the amount of carbon. Cover crops had no detectable impact on carbon accumulations, but tended to increase organic matter nitrogen. Fields with the combined use of no-till and cover cropping had the greatest soil aggregate stability. Other measured soil properties did not vary consistently with tillage or cover cropping. Findings of the study indicate that no-till production of silage corn, in rotation with alfalfa, on commercial dairy farms is likely to result in the anticipated increase in soil organic C (0.1 to 0.5 MT/ha/yr) and enhancement of some soil properties. Greater soil C accumulations under no-till, despite little input of above ground residue due to forage harvest, suggest that root residues are the key organic matter source.

Technical Abstract: The use of conservation practices in crop production, especially no-till planting, is generally expected to result in sequestration of C as soil organic matter and contribute to the reduction of CO2 inputs to the atmosphere. However, expectations are almost exclusively based on findings from plot-scale research and have not been widely validated by measurements on commercial farms. Additionally, research focusing on soil C sequestration potential in dairy forage systems is limited. To address these concerns, an on-farm study was conducted on seven central Pennsylvania dairy farms fields. Soil was sampled following corn in alfalfa/silage corn rotations on Hagerstown or Hublersburg soils where either conventional tillage or no-till was used, with and without cereal rye cover crops. Organic C and N in particulate (POM) and mineral-associated (MIN) pools, bulk density, water stable aggregates, available water content, cation exchange capacity (CEC), and pH were measured at three depths of the soil profiles (0-5 cm, 5-15 cm, and the upper Bt horizon). Fields where no-till was used had approximately 50 percent more C in POM and MIN pools in the upper 5 cm of soil compared to tilled fields, but C accumulations below 5 cm were similar among fields. This suggests of C sequestration rate of approximately 0.3 MT/ha/yr since the introduction of no-till. Soil aggregate stability and CEC were proportional to C pool sizes. Rye cover crops had no detectable impact on C accumulations, but tended to increase POM and MIN-N. Fields with the combined use of no-till and cover cropping had the greatest aggregate stability. Other measured soil properties did not vary consistently with tillage or cover cropping. Findings of the study indicate that no-till production of silage corn, in rotation with alfalfa, on commercial dairy farms is likely to result in the anticipated increase in soil organic C (0.1-0.5 MT/ha/yr) and enhancement of soil properties. Greater soil C accumulations under no-till, despite little input of above ground residue due to forage harvest, suggest that root residues are the key organic matter source.