Are you looking to build your soil carbon? Then you’ll have to do more than simply switch to no-till, research shows.
‘Soil carbon’ refers to carbon held within the soil, usually as organic matter. By increasing the capacity of soil to sequester (or store) carbon, farmers and ranchers can reduce agriculture’s contribution to climate change. Field tillage affects soil carbon by exposing the soil surface to wind and water erosion; exposing buried organic matter to water, air, and microorganisms; and moving surface material below ground.
The dustbowl gave birth to the modern soil conservation movement. Since then, various conservation tillage approaches – meaning any method that retains crop residue and results in at least 30% of the soil surface being covered after planting – have been endorsed to avoid tilling’s negative impacts.
Conservation tillage practices include no-till, chisel plowing, single-disc passes, and others. There is widespread support for these practices when used for achieving many conservation outcomes. However, their usefulness in capturing soil carbon is less certain.
In particular, no-till’s carbon sequestration merits are in contention. Our 2013 review of carbon sequestration research found no conclusive evidence that any conservation tillage practice exhibited an advantage over conventional practices.* Although touted as a generic “best management practice,” there is strong indication of no-till’s unsuitability for poorly drained, clay, and cool soils.
Last month, senior university researchers from Iowa, Illinois, Ohio, and Wisconsin determined that no-till’s carbon sequestration efficacy could not be substantiated. Researchers reviewed hundreds of published soil science and tillage literature assessing (a) the sequestration, storage, retention, and loss of soil carbon; over (b) a rooting depth of 1-2 meters; over (c) long time frames; and coming to (d) conclusions on both sides of the no-till coin.
The lack of agreement on no-till’s carbon sequestration efficacy points us to the importance of using other conservation measures for achieving carbon sequestration goals and the importance of cropping systems. In corn and soybean crop rotations, no-till must be used in partnership with cover crops, small grains, and forages. Soil type and slope need to be taken into consideration, and strategies for sequestering carbon deep in the soil profile where it is more stable need to be adopted.
* You can learn more about soil carbon by reading our report Banking on Carbon here.
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