Pete recently retired as a professor at Colorado State University after teaching for 30 years. He served as the president of the Soil Science Society of America, and spent his career researching ways to apply the principles of soil science to better manage dryland agroecosystems.
The following interview has been edited for clarity and length.
Steve Rosenzweig: The Dust Bowl was a major disaster for farmers in the Great Plains. How did it happen?
Gary Peterson: The people that came out to the West were accustomed to farming where there was plenty of water, and so they used tillage methods that left the soil bare. Bare soil in an environment like ours with wind and with intensive rains when they do come is subject to vast erosion. It actually caused them to go broke. Many of them had to move off the land. They lost everything they had, and it was a socially very upsetting time.
SR: Why should we care about soil erosion?
GP: Well soil erosion decreases soil productivity. The surface of the soil is the most fertile part. So when you lose that in a dust storm, it decreases the value of the land. And once you're in a dust storm on the Great Plains some place, you don't have much trouble understanding why you don't want it to happen. It's unhealthy with the dust in the air, it decreases the value of your land, and your neighbors don’t like you… it doesn't take much to figure out you don't want erosion. And if you happen to have a water erosion event, and your topsoil is on the neighbor's field, it makes for unhappy people.
SR: What lessons came out of the Dust Bowl?
GP: Well the lesson is that you need to keep cover on the soil. The biggest step has been the no-till system where you actually use herbicides to control weeds instead of tillage. And as you use the herbicides, you don't till, you keep the residues on the top, you save enough water that you can put another crop into the system like corn or millet or sunflower. And as a result then you get better use of the water and avoid that wasteful time.
SR: Why is crop residue cover on the soil surface so important?
GP: It does several things. First one is with the residue on top, you decrease raindrop impact so you get a better chance of getting the water into the soil. The residues take the energy out of the raindrop. Then the second thing is the mulch on top decreases the evaporation rate, and so as a result then you get a better chance of conserving the water there when you want to use it for a crop.
SR: You said that by conserving the water, you are able to put more crops into the system. Why would you want to put more crops into a crop rotation?
GP: The major challenges are still about how to make a profit in a very risky environment. Because 2 years out of 10 in many cases you're going to get a zero crop and there's also hail hazards, so the biggest challenge is how do you keep going? So you have to have some good years in between. Corn requires it's water at a different time than wheat, and sunflower different than either of those, and so if you have more crops in your system, the chances are that you're going to get one crop at least is pretty good. In the old days it was only wheat, basically wheat-fallow. So with extra crops in the rotation, you reduce risk.
SR: Much of the research you conducted over the course of your career concerned fallow periods in crop rotations. Can you tell me what you’ve learned after several decades of studying fallow?
GP: Well, fallow is anytime you don't have a plant in the field, but the biggest challenge in dryland agriculture is summerfallow. You have periods of time during the hottest months when you don't have any cover on the land, and that's the worst part of fallow. It started as a way to reduce risk. When the farmers first came here and they didn't have no-till techniques, they were only able to grow one crop every other year by saving enough water in the fallow year to decrease the risk of crop failure. But summerfallow is very inefficient. For example if you receive 16 inches of rain during a fallow period, you might be lucky if you saved 1/4 of that in the soil. So, 75% would be lost to evaporation or to weed use, so it's a very inefficient system.
SR: What would a resilient dryland cropping system look like to you?
GP: To me? Oh that's a big question. I would like to have system where wheat would only appear in the system every four to five years, and in the meantime then I might use crops like corn, millet, sunflower, and then forage crops. Annual forages that you can plant, harvest, and get off in time to plant say another wheat crop. A lot of people don't want to bring animals back in the system because it complicates life, but the forage crop doesn't hail out very easy. If you're depending on a grain crop and you're depending on it to set seed, the forage crop doesn't do that. It doesn't have a high water demand period of flowering or anything like that, so you can do better with a small amount of rain. And if you get one of those intense hails, it just knocks it down a little bit but you've still got something. Forage crops are more forgiving in a system because you don't have to try to produce grain at a particular time so you're not as sensitive to rainfall timing.
SR: When you talk to producers, how do you convince them that diverse crop rotations are the way to go?
GP: Oh it's easy. ‘How would you like to make better use of the water that falls out of the sky? How do you get more plants, how do you get more production from every drop of water that falls on your farm?’ And right away the lights go on, and the benefits are that you get the biodiversity and you also get erosion control. And everybody wants erosion control, but they don't want to pay for it. But if you can make money, that's the way to do it. I don't think it is just farmers. I think the way to the heart of every businessman is how you make profit. And in this case, it's like you're making money while you're improving the situation.
Steve Rosenzweig is a PhD Candidate at Colorado State University. This interview was conducted as part of a film project to document emerging innovations in dryland agriculture, which can be viewed here.