After a long dry fall of 2017, Old Man Winter held on longer than we are accustomed to this spring. Whether your purpose for planting a cover crop was for erosion control, soil moisture management, nutrient sequestration, grazing, or nitrogen fixation, the growth we hoped for largely has not fulfilled our expectations. Many producers who invested the time and money into seeding cover crops are scratching their chins and wondering what they can do for cover crop management in this late spring.
What sort of options are there for extending the spring growth period to achieve the goal? The choices range from terminating before planting as you have always done to simply waiting to plant a little later. In between those choices is an option called “planting green”.
Planting green means planting your cash crop into a cover crop that is still alive and letting the cash and cover crop grow at the same time, for “a period of time”. The management issue will be deciding how long that “period of time” is. Optimizing moisture in the soil profile is what you will base your decisions on.
For erosion control it is optimum to grow a cereal rye cover crop to a 14 to 18-inch height. The plants will have more lignin or carbon in the stem and endure longer into the growing season. Your goal is to have the cover crop maintain surface cover that can deflect the impact of raindrops on bare soils until crop canopy is achieved.
Soil moisture management with cover crops comes into play in excessive rainfall springs and low areas that are problematic every year. In either situation, the key is to monitor rainfall received and soil moisture used as the cereal rye can remove a lot of moisture quickly when temperatures warm up and growing conditions are excellent.
If grazing is your goal you may want to consider selecting a shorter season maturity cash crop that allows you to plant a little later in the spring. With good management you may be able to graze the cover crop to your desired level, remove the livestock, then plant your corn “green”. Let the cover crop regrow to the stage where it will uptake herbicide effectively and then burn it down. Excessive spring rainfall may lead to some tracking by livestock so having a backup plan in case that develops is advisable.
If you planted a multi-species cover crop with an overwintering legume component you would ideally want to let the legume grow until nitrogen is being fixed for corn plants to use. That again could require either a shorter season variety allowing later planting and/or planting green as discussed earlier.
Newcomers to no-tilling corn into cover crops into lower organic matter soils may want to consider terminating a cereal rye cover crop a little earlier to avoid any allelopathy issues or excess moisture and nutrient competition to the corn plant from the grass cover crop. In furrow pop up fertilizer and/or starter fertilizer with extra nitrogen will help mitigate the early nutrient competition.
Plant corn a minimum of 2 ½” deep into the cover crop and make sure you have sufficient down pressure to close the seed furrow. The more you increase your soil organic matter with no-till and cover crops, the easier your soil is to work with.
Planting soybeans green into a cereal rye cover crop is the easier part of the continuous no-till and cover crop system. Soybeans are a legume and tolerate competition from the grass cover crop well. Planting soybeans 2 ½” deep into the living cereal rye root system that is supporting an active arbuscular mycorrhizal fungi population will allow the beneficial fungus to colonize the germinating bean roots and protect them from other pathogenic fungal diseases.
The biomass from the cereal rye with aggressive living roots combined with the existing corn residue makes for a carbon charged growing season. The rye has sequestered the leftover nitrates from the corn crop, so the soybean plants go to work immediately fixing nitrogen. This is the leg of the corn/soybean rotation where you can increase soil organic matter more.
Some cover crop is always better for the soil than no cover crop. A cereal rye cover crop with just 12 inches of growth can have a root system 24 to 36 inches deep so there will be soil health improvement benefits from the cover crop at all stages of growth. The link between the sun and soil is the living plant with roots exuding the plant sugars created by photosynthesis that feed the soil biology. The more time there is living roots in the soil the more your soil thrives.