No-till and other conservation tillage practices have proven successful in controlling soil erosion and providing other benefits. But if carbon sequestration is the goal, conservation tillage alone is not the solution.
New research1,2,3 utilizes deep soil samples and micro-meteorological techniques to obtain a better understanding of carbon dynamics, whereas earlier research relied solely on shallow soil sampling, which provides an incomplete assessment of carbon storage in agricultural soils.
Different tillage practices influence the vertical distribution of carbon in the soil. No-till maintains crop residues within the upper few inches of the soil surface, while conventional tillage buries residues deeper in the soil profile. Therefore, no-till results in more carbon storage in the surface soil, and conventional tillage results in more carbon storage in the subsurface soil.
However, looking at the entire soil profile (16 inches) demonstrates that soils under various tillage methods contain similar amounts of carbon - no method of tillage has a clear advantage over another. Conservation tillage reduces disturbance to the soil and leaves crop residue on the soil surface, whereas conventional tillage buries crop residues. Therefore, when placement of crop residues in the soil profile and the amount of soil disturbance are taken into account, it appears the same amount of carbon is stored regardless of tillage practices.
Cover Crops Store Carbon
Methods of accurately measuring soil carbon stocks are still evolving.4 However, it is clear that cover cropping, when used as a complimentary practice with no-till, sequesters carbon in agricultural soils. Cover crops are grasses, legumes and forbs planted to provide seasonal soil cover when the soil would otherwise be bare - before the main crop emerges in the spring or after fall harvest. Cover crops sequester carbon by adding biomass both on the soil surface and below-ground. A 12-year University of Illinois study showed that adding cover crops to all tillage treatments increased soil organic carbon stock gains by 30% for no-till, 10% for chisel plowed and 18% for moldboard-plowed plots.5
Planting in late summer allows perennial cover crops to generate substantial biomass throughout the fall and again in the spring. Winter rye is a good choice because it is more resistant to decay than other cover crops such as oats or barley.
Recent tillage surveys conducted in Minnesota show that farmers are using conservation tillage more frequently than in the past, particularly in corn and soybean rotations. Soil erosion control, water quality improvement, and lower production costs are among the many environmental and economic benefits associated with conservation tillage practices.
Issues of carbon sequestration notwithstanding, BWSR encourages the use of conservation tillage to protect soil quality reduce soil erosion, and improve water quality in local waterways.
1. Baker, J.M., T.E. Ochsner, R.T. Venterea and T.J. Griffis. 2007. Agriculture, Ecosystems & Environment 118 (1-4): 1-5.
2. Dolan, M.S. et. al. 2006. Soil & Tillage Research 89 (2): 221-231.
3. Christopher, S.F. and R. Lal. 2009. Soil Science Society of America Journal 73 (1): 207-216.
4. Olson, K., M. M. Al-Kaisi, R. Lal and B. Lowery. 2014. Soil Science Society of America Journal 78 (2): 348.
5. Olson, K, S.A. Ebelhar and J.M. Lang. 2014. Open Journal of Soil Science 4: 284-292.