Researchers assess productivity limits of conservation agriculture

Plowing a Minnesota field

No-till farming, a key principle of conservation agriculture, has received strong international support to help address global food security challenges in recent years, but a new analysis suggests that it is not as beneficial as often assumed unless additional steps are implemented.

The findings, recently published in the journal Nature, demonstrate that no-till farming, or direct planting of crops with minimum soil disturbance, is restricting rather than enhancing global crop production and sustainable intensification efforts.

Two research fellows from Northern Arizona University’s Center for Ecosystem Science and Society, Kees Jan van Groenigen and Natasja van Gestel, contributed to the study.

The authors synthesized current scientific evidence at a global scale from hundreds of field trials across 48 crops and 63 countries to compare no-till to conventional tillage practices, representing the largest assessment to date on this topic.

“Hundreds of studies have looked at the effect of no-till practices on yield. But, because these studies were done on so many different systems, for many different crops and in many different climates there was no agreement on the effect of no-till,” van Groenigen said. “For that reason, we decided to collect all the data we could find on the subject to see if we could discern patterns.”

The team found that no-till negatively impacts crop yields at the global scale and often leads to yield declines compared to conventional tillage systems. However, they discovered that the negative impacts of no-till are minimized when it is combined with the other two principles of conservation agriculture, residue retention and crop rotation. In these cases it can produce equivalent or greater yields than conventional tillage.

Van Gestel explained it as a unique pattern that emerged through the assessment. “No-till practices reduced yield by 6 percent, but this yield gap was lessened when people also rotated crops and left plant residue in the field after harvest,” van Gestel said. “So, if you want to go the sustainable route, more is indeed better, and farmers should employ all three practices jointly: no-till, crop rotation and residue retention.”

She added, “In fact, in dry climates, we actually found that no-till increased yields in systems that also applied crop rotation and residue retention. This could be linked to better soil moisture retention because the higher yields in no-till soils happened when irrigation practices were absent.”

Van Gestel said areas that will suffer from more intense drought with climate change could therefore particularly benefit from using all three practices.

“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,” said Chris van Kessel, professor of plant sciences at UC Davis and co-author of the study.