Contributed by Drew Lyon, Endowed Chair Small Grains Extension and Research, Weed Science, Washington State University
In my mind, the purpose of a blog is to throw out ideas and have them discussed. With that objective in mind, I would like to discuss the sustainability of no-till annual cropping systems.
I attended my first no-till conference in 1990, the year I started my job as an assistant professor and Extension Dryland Cropping Systems Specialist at the University of Nebraska-Lincoln Panhandle Research and Extension Center in Scottsbluff. I had received my Ph.D. in Agronomy/Weed Science from the University of Nebraska-Lincoln in August of 1988. After a 13-month stint as a Technical Services Representative for American Cyanamid Company in Michigan, I started my job in Scottsbluff. As a weed science graduate student, I had not attended any no-till conferences, but in my new dryland cropping systems position, I thought it was important for me to attend these conferences and see what I could learn. So, in the summer of 1990, I attended the Great Plains No-Till Conference in Bismarck, ND.
I was impressed by all the positive results presented in favor of no-till crop management throughout the Great Plains, but also a bit surprised by the lack of any negative results. In my scientific training, I had come to expect counter arguments and viewpoints on almost every topic, but I heard none. As a weed science graduate student in the 1980s, several of my fellow students at the University of Nebraska were studying atrazine resistance in several weed species. We learned that overreliance on herbicides, especially on just a few herbicides, for example, atrazine, would inevitably result in herbicide resistance in weeds. At the time, no-till systems in the Great Plains were highly dependent on atrazine. It was cheap and effective, and it was used on a lot of acres. Roundup (glyphosate) was not cheap in the 1980s and 1990s, and it was used mostly for grass control because it was too expensive to use the rates needed for broadleaf weed control. In my mind, the Achilles heel of no-till at that time was its near total dependence on atrazine. This was bound to fail, and yet nobody was talking about it at the conference.
In the 2000s, glyphosate went generic, which greatly reduced its cost, and a plethora of new herbicides came to the market. This was just what no-till systems needed to remain viable. However, the Achilles heel did not disappear. Overreliance on herbicides in no-till cropping systems quickly resulted in one herbicide after another losing efficacy as weeds developed resistance to them. Now, however, there is no flood of new herbicides coming to the market to replace the herbicides we are losing to resistance. We are becoming more and more reliant on fewer and fewer effective herbicides, which will only hasten their demise as effective tools.
I have always been skeptical about the long-term sustainability of strict no-till cropping systems. While my research in western Nebraska convinced me of the many benefits that no-till systems provide, including reduced soil erosion and increased soil water capture and storage, I also saw the benefits of occasionally, and strategically, using tillage as part of an integrated weed management system. I also saw that successful no-till systems, like successful organic systems, needed to include sophisticated crop rotations to manage weeds. No-till winter wheat-fallow was just not going to work for long. I believe in bringing as many tools as possible to the fight with weeds. Voluntarily leaving all tillage out of a weed management plan sounds like tying one arm behind your back. It may be an interesting challenge, but unless you really up your game in every other dimension of integrated weed management, I’m not going to put money on you winning the 15-round boxing match with weeds.
I don’t have the answer for how much tillage is needed to keep weeds in check, delay herbicide resistance, and do as little harm to soil health as possible, but I’m pretty sure that never tilling is not sustainable in the long-term. More research is needed to better understand the effects of occasional tillage on different soils. Most tillage research compares always tilling to never tilling because treatment differences reveal themselves quickly. A young faculty member needing to get tenure and promotion cannot wait for 10 to 20 years to publish results from a study where tillage only occurs every 6 to 10 years. In addition to weed control, occasional tillage may also be helpful when applying soil amendments such as ag-lime, gypsum, manure, or biochar, thus killing the proverbial two birds with one stone. While tillage has been used too much in the past, and with dire consequences, I think there is still a role for tillage in an integrated weed management program.
I bet at least a few of you don’t agree with me. Please share your arguments with us. I think it is an argument worth having, even if nobody’s mind is ultimately changed.