No-till farming, a key conservation agriculture strategy that avoids conventional ploughing and otherwise disturbing the soil, may provide environmental benefits, but not a boost in crop yields, according to a review of research by experts at the University of California Davis.

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UC Davis researchers said that their review is possibly the largest such comparative study undertaken in agriculture. The results suggest that the approach may only lead to yield increases in drier areas. Elsewhere, yields could even fall as a result of adopting the practice (yields were between six and nine percent lower in wetter climates).

No-till has been promoted worldwide in recent years, as a core principle of conservation agriculture. Although opponents of the method have criticised no-till, including claiming it leads to higher input use, the FAO has been broadly supportive, arguing that many claims made against the practice are "misconceptions."

FAO has described no-till as a "Necessary, but not a completely sufficient condition to arrive at truly sustainable agriculture."

Even so, commenting as the UC Davis review was published in Nature this week, co-author Cameron Pittelkow said, "The big challenge for agriculture is that we need to further increase yields but greatly reduce our environmental impacts. The common assumption that no-till is going to play a large role in the sustainable intensification of agriculture doesn't necessarily hold true, according to our research findings."

No-Till's role in conservation agriculture

Conservation agriculture is currently practiced on 125 million hectares of land globally, an area almost as big as the total U.S. cropland. Three key principles guide the concept: minimizing soil disturbance (of which no-till farming is part), protecting the soil with cover crops or leftover crop residue, and rotating crops. The overarching idea is to create a productive agriculture system that is sustainable in the long term.

Though the researchers identified that no-till often led to yield reductions, they found that these reductions were minimised when other sustainable principles, such as crop rotation and residue retention were also practiced. They said this highlighted the importance of implementing all three conservation agriculture principles as part of an integrated management system rather than relying on no-till alone.

When adopted in dry climates, and in combination with the other two principles of conservation agriculture, no-till farming performed significantly better than conventional tillage, likely due to the higher retention of soil moisture. The areas identified as 'dryland ecosystems', and therefore most suited to no-till, are home to 38 percent of the world's population, according to the UC Davis researchers.

UC Davis Plant Science professor Chris Van Kessel said, "No one has ever stated that there would be a significant decline like this. Our findings suggest that broad implementation of conservation agriculture may not be warranted in all areas, particularly where residue retention and crop rotation practices are hard to implement."

However, though yield may be reduced in some circumstances as the result of a transition to no-till agriculture, other benefits of the practice identified by research include reduced soil erosion, increased soil biodiversity and reduced emissions through carbon sequestration. These goals all sit comfortably with other aims of conservation agriculture.

Professor Dick Godwin, who has studied no-till arable systems in Britain and whose research will be released by Harper Adams University next month, recently said, "My research has shown that no-till practices can offer significant potential operational, economic, soil and environmental benefits for the UK."

"However," Prof Godwin added, "This comes with a number of challenges for improved management, many of which are being successfully addressed by current practitioners."

He said more research may be needed to "Look into the control of grass weeds, slugs and snails, and to further improve the operation of equipment in wet soils with high residue loads."