Last summer, Dr. Joel Gruver sat down with a group of farmers in northern Iowa to exchange ideas about cover crops. The self-described “student of cover crops” from Western Illinois University offered tips from his experiences and fielded questions for four hours.
Gruver’s research over the years on cover crops in both organic and conventional farming systems has taught him that covers are a key tool in organic systems, but have valuable roles to play in all farming systems. Here are other bits of information and advice gleaned from the informal conversation.
1. If you wait until after harvest to plant cover crops, you’ve often lost more half of the growth potential for the fall. Look online for growing degree days for your area. For example, in Aledo, Illinois, when you compare average growing degrees (base 40 F) between August 1 and December 1, you see that 50% of the degree days occur before September 1 and 80% occur before October 1.
2. Continuous no-till or strip till are the best systems to combine with cover crops. That’s because the less tillage done, the more growing season you have for cover crops and the more opportunity to harness the soil loosening effects of cover crop roots.
3. If you’re not growing something green on your land over the entire growing season, you’re missing an opportunity to grab carbon from biomass production. You have 4 months of growing season for growing corn and soybeans, but there are at least 3 more months of growing season in the heart of the Corn Belt you can take advantage of with cover crops. That extra growth will help build soils and reduce nutrient losses in water leaving the farm.
4. Your soil care goal should go beyond not losing topsoil to erosion to actually building topsoil. While many farmers have made dramatic progress in slowing soil erosion, the target should go well beyond the “tolerant” or “T” figure of 3 to 5 tons of soil loss per acre per year. Cover crops are a key to moving from tolerable topsoil loss to building topsoil -- green lands give blue water!
5. Be aware of the differences of soils on your farm and how your management improves or degrades soil health. It’s not uncommon in a drought for yield monitors to jump 50 bushels an acre as the combine crosses an old hedgerow or fence-line that has soils with higher organic matter. Soil test nutrient levels are often lower in fertility in an undisturbed fence row, but organic matter is normally much higher.
6. We’ve lost half the organic matter on most prairie soils. That’s been through decomposition as well as from soil erosion. The decomposition is accelerated by tillage and other farming practices like liming and drainage.
7. Tillage may temporarily increase water infiltration, but the long term effect is normally more surface ponding and water runoff during storms. Prove this to yourself -- go out to a tilled field and one with cover crops and no-till during or right after a rain. See what sticks to your shoes in each case. This is really a better indicator of infiltration than many more complicated tests you might use.
8. The science is clear -- cover crops can reduce nitrate leaching at a lower cost than other practices being used. They’re more effective than edge-of-field practices, and have the added bonus of building soils that edge-of-field nitrate reduction practices don’t address.
9. The number one way to make cover crops pay is to graze them. You’ll immediately see reduced feed costs for cattle -- putting some green out there is cheaper than storing hay. Consider aerial seeding -- in soybeans, get the seed on before the bean leaves drop to be sure the seed gets to the soil.
10. Experiment with cover crop combinations using small amounts of seed and a push planter. We’ve seen better radish biomass when we planted peas with them, and we’ve learned as you plant radishes earlier, you should lower the rate. We’ve learned radishes will smother about anything. And, we’ve seen you get the best weed suppression with narrow rows. These are the kinds of things you can learn by experimenting and testing in a small area using a push planter, rather than making a larger investment.
11. You can use your corn planter for cover crops -- it may be the best system you can use. Planters and drills get the best seed-to-soil contact, which is especially important in a dry summer and fall. On the other hand, aerial or high-boy seeding has the advantage of giving the seed a head start, with germination and growth earlier in the year.
12. Haphazard cover crop management will lead to train wrecks. If you’re not committed to paying the same attention to detail for cover crops you use for growing corn and soybeans, you may not be a good fit for cover cropping. If you’re not sure you’re ready to devote time and energy to manage covers carefully but still want to give it a try, opt to follow the simplest and safest recommendations for first-timers.
Betts writes from Johnston, Iowa.