Emerging weed resistance increases tillage intensity and greenhouse gas emissions in the US corn-soybean cropping system

Between 1998 and 2016, tillage intensity across the US corn-soybean cropping systems shifted from a decreasing to an increasing trend. The decreasing tillage intensity is correlated to the wide adoption of herbicide-tolerant crops, whereas the tillage reintensification is found to be related to the emergence of herbicide-resistant weed species after 2008. The growing tillage intensity resulted in increased GHG emissions and undermined the GHG mitigation achievements from other activities or other sectors. Tillage is a common agricultural practice that helps prepare the soil and remove weeds. However, it remains unknown how tillage intensity has evolved and its effect on net greenhouse gas (GHG) emissions. Here, using a process-based modelling approach with a multi-source database, we examined the change in tillage intensity across the US corn-soybean cropping systems during 1998-2016 and the impact of tillage intensity on soil GHG emissions. We found that tillage intensity first decreased and then, after 2008, increased, a trend that is strongly correlated with the adoption of herbicide-tolerant crops and emerging weed resistance. The GHG mitigation benefit (-5.5 +/- 4.8 TgCO(2)e yr(-1)) of decreasing tillage intensity before 2008 has been more than offset by increased GHG emissions (13.8 +/- 5.6 TgCO(2)e yr(-1)) due to tillage reintensification under growing pressure of weed resistance. As weed resistance persists or grows, tillage intensity is anticipated to continue rising, probably increasing GHG emissions. Our results imply that farmers' choices in managing herbicide resistance may help mitigate agricultural GHG emissions, underscoring the importance of an alternative strategy to control weeds.

Automated summary

Between 1998 and 2016, the tillage intensity in the US corn-soybean cropping systems shifted from a decreasing to an increasing trend. The decrease in tillage intensity was due to the adoption of herbicide-tolerant crops, while the increase was related to the emergence of herbicide-resistant weed species after 2008. The growing tillage intensity resulted in increased greenhouse gas (GHG) emissions.