Even a short time without living roots in the soil can impact your farm ecosystem. If you practice no-till religiously, you are probably quite familiar with this concept. Although at King’s we generally don’t preach no-till orthodoxy, we do believe in maximizing time with living roots growing in soil. You may have heard of beneficial fungal organisms like mychorrhizae that form symbiotic relationships with plant roots. In the end, the fungal hyphae greatly expand their hosts’ ability to reach water and nutrients. To thrive and get the nutrients they need, though, they require access to living roots almost continuously. The living root system also exhudes labile organic compounds that feed a multitude of soil organisms in the rhizosphere.
To accomplish all this, many no-tillers “plant green” – establishing a cash crop into a living cover crop before spraying to kill it or just after using a roller-crimper to mechanically kill and flatten it. As a result, the lifecycles of the two crops overlap.
Keeping a live root zone to support soil life and health is just the beginning. Unlike a dead residue mat, a living crop doesn’t foster and transmit soil borne disease effectively. It also doesn’t harbor pests like slugs that look to the emerging seedling as its only food source. The overlap of the two growing crops creates a window of biodiversity, and each increase in biodiversity raises the system’s defenses.
- At a basic level, it helps manage timing. It makes more time for double-cropping, so you have less worry about rushing to get the cover crop chopped or incorporated before planting. It removes the primary tillage operation from the schedule (but you still have to fit in rolling or spraying at the same time or later on).
- Not only is soil quality improved, but so is soil moisture management. Living crops anchor moisture in soil and hold it in their own tissues to prevent surface runoff or leaching. Plus, they help take up some extra moisture in wet early springs, which may make it easier to get equipment in the field earlier to plant.
- Managed correctly, it can simplify weed control. A thick, actively growing cover crop is already competitive with weeds. When you plant correctly and control the crop at the right time (so the cover crop does not become the weed), you have left no window for weeds.
- Always know what you’re dealing with. Account for the thickness of the cover, whether standing or rolled, and be sure you have enough down pressure to cut through it and the root mass. Stop and get off the drill to check seed-to-soil contact and seed depth. Make sure the seed furrow is closing properly. It also helps establishment to plant into moist soil that is high in organic matter.
- If it can be rolled, the cover crop will be much more manageable. Rolling is still considered “planting green”, but since it has been crimped and flattened (and possibly sprayed, in a conventional setting), it’s less likely to get caught up in the planter or drill.
- In many cases, the short few weeks of extra growth time come at the point when the cover crop is growing fastest. As spring temperatures warm and the crop breaks dormancy, the growth curve shoots up. According to No-till Farmer, “Research has shown that by using this practice, cover crop biomass can easily be doubled.” More crop growth means more soil carbon, which greatly improves infiltration and cuts down on soil erosion and runoff. Fewer nutrients are lost as well, as the roots continue growing and uptaking nutrients almost until the new crop can take over. If it’s a legume like hairy vetch or crimson clover, it has that much more time to fix nitrogen.
- Hairpinning problems are reduced. Cutting through live green material is actually much easier than cutting through dying residue that is still rubbery and not yet crisp and dry. It also turns out to be somewhat easier than cutting through fully dead residue. Manure can be applied to the living crop ahead of planting, as well, and is less likely to form an impenetrable plaster-like layer the way it might when applied to dying, matted residue.
- Some equipment tweaks can make your life easier. Cover crop rollers can be mounted on some corn planters that flatten the cover crop to the soil surface, parting the plants so that double disk openers have less material to cut through. This also means less competition and shading as the new crop establishes. If you have a crop like hairy vetch that is very prone to tangling, you may also find it helpful to raise up the closing wheels so the vetch doesn’t wrap around them.
- If the cover crop has a high C:N ratio (such as mature rye) you will have to optimize soil fertility – and possibly even add 30-50 extra units of N/acre so that crop residue can break down faster and won’t tie up nitrogen as much.
- Understand how rapidly C:N ratio can change. Crops that look small in early spring mature in a matter of weeks, rapidly increasing their lignin content, and along with it, the time they take to break down and return nutrients to the soil. Slow N release over the course of the season can be a benefit, though, if you have plenty to start out with.
We did this in our Lancaster County, PA corn research plots last spring, planting the corn no-till into a growing cover crop of hairy vetch and crimson clover. Manure was spread before planting green. The May 4 date was good for the planting timeline of the corn, but the legumes were at pre-bloom stage, about 12 inches high. The hairy vetch was not yet long and viney enough to tangle with the corn planter, but we did sacrifice a good amount of nitrogen that would have been fixed if we had waited a few more weeks. We learned that we had to consider both the physical challenges to planting and the growing degree days lost or gained for corn at different planting dates. Planting green often involves a direct tradeoff between the growth of the cover crop and the growth period of the main crop, and you will find that you have to manage more closely to maximize the main crop.