With herbicide resistance on the rise, there is a renewed emphasis on soil tillage as a critical component of integrated weed management.

Although tillage is the subject of an ongoing debate - with studies released this month by NASA and the European Conservation Agriculture Federation emphasising the role minimising soil disturbance and building up soil carbon can play in reducing greenhouse gas emissions from farming - a newly published paper by researchers from the U.S. has backed tillage as a major means of suppressing weeds. The study stresses that, when it comes to weeds, timing matters and when tillage occurs can significantly impact both weed density and the composition of the weed community that emerges from seeds in the soil.

The paper, published in the journal Weed Science, looks at the impact of tillage on four sites in the northeastern U.S. that were tilled every two weeks during the growing season. Six weeks after each tillage cycle, researchers sampled random plots - 196 in total - to measure the density and species of weed seedlings.

They found that total weed density tended to be greatest when soil was tilled early in the growing season. In fact, more than 50 percent fewer weeds emerged after late-season tillage than after early-season tillage.

The composition of the weed communities in the test fields was also impacted by tillage timing. After early-season tillage there was greater unevenness among various weed species, with some species clearly dominating. After late-season tillage, the distribution among weed species tended to be much more even.

"Our results suggest that farmers may be able to better manage weed communities and to mitigate the impact of weeds on crop yields by adjusting the timing of their tillage, crop rotation and other cultural management practices," says Matthew Ryan of Cornell University, a member of the research team.

Full text of the article can be read here.