Conservation tillage under threat in the United States

Conservation tillage, after being widely adopted in the past few decades, is now threatened by the development of herbicide resistant weeds. Of the 157.7 million ha of cropland across the United States (U.S.) in 2012, approximately 127.5 million ha were harvested. Roughly 44% of total cropland area used conservation tillage practices, including no-tillage. In 1989, there were approximately 0.34 ha of conservation tillage for every hectare of conventional tillage, including reduced tillage. By 2012, the ratio had grown to 1.64 ha of conservation tillage for every hectare of conventional tillage. New technology, such as herbicide-resistant crops, greatly helped to increase the adoption rate of conservation tillage practices, yet current herbicide-resistant weed challenges are a real and expanding threat to conservation tillage. Produc- ers are faced with difficult management decisions regarding herbicide-resistant weeds. Despite many of these ha currently being under United States Department of Agriculture (USDA)– Natural Resources Conservation Service (NRCS) conservation program contracts, the difficulty of controlling herbicide-resistant weeds places many ha at risk of being converted to higher-intensity tillage systems. The shift to higher-intensity tillage facilitates burial of small weed seed and/or the increase of pre-emergence and pre-plant incorporated herbicide activ- ity to control problematic weeds, especially in dry-land crop production. However, in the past decade in the U.S., there has been a renewed interest in cover crops and their management for both carbon sequestration and agronomic purposes. Start- ing in the late-1990s, scientists at the USDA – Agriculture Research Service (ARS) National Soil Dynamics Laboratory in Auburn, Alabama initiated research using a Brazilian style cover crop management technique utilizing a roller-crimper, in conjunction with herbicides, to terminate mature cover crops. High residue cover crops are increasingly being incorporated into integrated pest management recommendations to help alleviate herbicide resistance selection pressure through their weed suppressive characteristics.