A meta study of two key food-producing regions in South Asia and sub-Saharan Africa concluded that conservation agriculture has minimal impact on carbon sequestration — meaning it won’t do much to combat climate change. However, it found that conservation farming does increase soil carbon near the surface of soils, slows erosion and improves water retention, offering a strategy for climate-change adaptation.
The study, which analyzed 76 papers on the topic, was published in the journal Agriculture, Ecosystems & Environment. It was carried out by scientists at Britain’s Rothamsted Research, and at the International Maize and Wheat Improvement Center (CIMMYT) in the UK, India and Zimbabwe.
The study, “Does conservation agriculture deliver climate change mitigation through soil carbon sequestration in tropical agro-ecosystems?” focused on studies in the Indo-Gangetic Plains, the breadbasket of South Asia, and sub-Saharan Africa, where yields of staple corn are extremely low and further threatened by climate variability and change.
“Findings showed that there was a general trend for soil carbon to be slightly increased under conservation agriculture compared to conventional practices, but the magnitude was less than is often claimed and there were a significant number of cases where there was no measurable increase,” said a statement from Rothamsted and CIMMYT.
Conservation agriculture is often said to lock up, or sequester, carbon in soil and contribute to the mitigation of climate change by keeping the soil covered with crop residues or cover crops, and diversifying crop systems. While the method can improve soil quality, reduce erosion and retain soil moisture, “the authors concluded that claims for conservation slowing climate change were overstated,” the statement said.
In regions where nitrogen fertilizer is used at high rates, such as the Indo-Gangetic Plains, improved management of nitrogen will often deliver greater reductions in greenhouse gas emissions than conservation agriculture, the study found.
It also found compelling evidence that “crop diversification (either through crop rotation or integration of tree-based elements) may deliver more soil carbon sequestration than reduced tillage or crop residue retention.”
Another paper, “Limited potential of no-till agriculture for climate change mitigation,” published in 2014 in Nature Climate Change, reached similar conclusions. It noted that no-till systems concentrated soil carbon in the top layers of soil, instead of increasing the overall level. It found no-till would thus have a limited impact on sequestering carbon and combatting climate change, though it did deliver other soil benefits. No-till farming techniques are often used with herbicide-resistant crops such as GMO corn and soybeans.