Conservation Tillage: The Search for Sustainable Agriculture
With both the global population and temperatures on the rise, there is an ever-growing need for the development of ways to help feed the masses while reducing greenhouse gas emissions. Conservation tillage appeared to be the answer to both, however, a recent study by Lognoul et al. (2016) calls into question the viability of this practice as a method of climate change mitigation.
Conventional vs Conservation Tillage Practices
Conventional tillage practices involve the removal of previous plant residue from the fields and cause a large disruption to the soil. There are different types of conservation tillage; but only reduced tillage, which has a minimal amount of soil disruption, was examined in this particular study. While the effects of conservation tillage are variable amongst different systems, a review by Busari et al. found that these practices are far more environmentally friendly than conventional tillage practices. Many benefits are associated with the use of these new tillage systems, such as decreased runoff, evaporation and soil erosion, as well as more resilient plants (Busari et al., 2015). Most importantly, conservation tillage practices are thought to hold the potential for carbon sequestration in the soil, notably within the top 30 cm (Johnson et al., 2007). Conservation tillage, in particular the “no-till” system, has been promoted around the world as the sustainable alternative to traditional agricultural practices (Busari et al., 2015).
A New Insight into the Impact of Reduced Tillage by Lognoul et al. (2016)
Lognoul et al. sought to compare the CO2 and N2O soil fluxes of two sites, one grown under reduced tillage and the other under conventional, to examine the effect of long-term tillage treatments. They also wanted to see how these fluxes could be related to the properties of the soil. There have been conflicting results on how exactly tillage practices affect greenhouse gas fluxes from agricultural soils, which was the driving factor in why Lognoul et al. underwent this study that looked at fields grown under these tillage treatments for seven years rather than the year or two most other studies employed.
Their study was run in Gembloux, Belgium on two parcels of a corn maize field; each undergoing one of the two treatments, conventional or reduced tillage, since 2008. They employed the use of an automated dynamic closed chamber system, which ran continuously from June 16 to October 15, 2015. They chose to take continuous measurements in order to get a more accurate depiction of N2O emissions, as these can experience high spatial and temporal variability, with irregular peaks in emissions that could be missed under a measurement schedule. A series of 8 chambers were run in sequence under a 4.5 hour closing cycle. Other factors, which they were hoping to relate to these fluxes of N2O and CO2 (such as soil temperature moisture) were also measured.
The results of their study showed a surprising outcome for a practice considered to be environmentally friendly. Both N2O and CO2 fluxes were significantly higher under reduced tillage than those under conventional tillage. Reduced tillage was found to have doubled soil respiration and the mean CO2 flux, while the mean N2O fluxes were 10 times greater than those from soils with conventional tillage, which Lognoul et al. believe may be attributed to higher levels of organic carbon and nitrogen in the soil under reduced tillage. These healthier soils could experience greater soil respiration and therefore higher greenhouse gas fluxes due to increased microbial activity and root respiration.
Taking a Closer Look at Current Conservation Practices
The findings of this study by Lognoul et al. present a troubling issue: if reduced tillage actually produces greenhouse gas emissions much greater than conventional tillage, do the other benefits, such as reduced fuel usage and less soil erosion, outweigh the detrimental effects of these increased fluxes? In their concluding remarks, Lognoul et al. (2016) call into question whether or not reduced tillage can truly be considered a beneficial practice for the climate and recommend that future studies should examine current conservation practices for any potential sources of harm to the environment.