An increase in tillage practices in the recent past showed greenhouse gas (GHG) emissions also increased, according to research published in the journal Nature Food.
Scientists Chaoqun Lu, Zhen Yu, David A. Hennessy, Hongli Feng, Hangin Tian and Dafeng Hui examined two fluctuations in the recent past of U.S. tillage, a decrease in tillage from the years 1998 to 2008, and a subsequent increase in tillage between 2008 and 2016. The decreases were observed in both carbon dioxide (CO2) and nitrous oxide (N2O). Researchers focused exclusively on tillage practices in corn-soybean rotations.
When tillage was on the wane with the widespread introduction of herbicide-resistant crops, GHG emmissions decreased by an annual rate equivalent to 4.6 terragrams (Tg) of CO2 per year. A terragram (Tg) is a unit equal to 1 million tonnes.
However, as tillage increased in the second period — which corresponds to the discovery of herbicide-resistant weeds — GHG emissions rose faster than they had declined, the equivalent to about 2.7 Tg of CO2 per year.
The decrease era (1998-2008) was fueled by increasing adoption of no-till practices at the expense of both conventional till and conservation till (strip-till, ridge-till, min-till, and mulch till) practices in the Mississippi River basin, the Corn Belt, the lower Mississippi alluvial valley and small pockets on the East Coast. The net decrease in GHG during this year was equivalent to 61 Tg of CO2.
The increase era (2008-2016) was led by decreasing no-till practices in the South and lower Midwest, as well as more intense tilling the the central and northern Midwest. During this period, the net increase of CO2 was equivalent to 110 Tg of CO2 per year, erasing the gains of the decrease period.
Illinois, Indiana, Nebraska, North Dakota and Minnesota all reported high swings in practices across the years.
The researchers report that uncertainty about the most recent period (2016 to today) remains high, and point out that herbicide-resistant weeds, which appear to have driven farmers back to tilling during the increase period, remain an area of concern.