By James Hoorman, Hoorman Soil Health Services
Some cooler temperatures are coming and some rain has occurred. Most farmers are hoping for more rain to get their crops out of the ground and growing. One thing, where ever the soil had higher amounts of soil organic matter (SOM), the crops emerged and are growing much better. Every 1% SOM holds about 0.5 to 0.8 inches of rain, which helps crops germinate and grow until they get their roots established. Building SOM requires getting more roots in the soil. No-till and cover crops are two ways to build SOM and reduce adverse weather.
As wheat harvest approaches, farmers may be considering double cropping soybeans. In a dry year, soybeans may not be the best option, but letting wheat stubble remain bare promotes weeds. Many cover crops can grow and thrive with little soil moisture including buckwheat, cowpeas for nitrogen, and teff (forage crop). Diverse cover crop mixtures help each germinate and get needed nutrients. Planting cover crops after wheat is a safer bet when moisture is lacking.
The late David Brandt in his last interview with No-till Farmer gave several tips on using cover crops. A big benefits to using cover crops is fighting weeds. Weeds will grow in poor conditions because they are the first colonizers of disturbed (tilled )soil. Weeds do not add much SOM and they compete with the main crop for sunlight, water, and nutrients. Most weeds do not promote beneficial microbes for our grain crops. The best weed fighters are cereal rye, daikon radish, sorghum species, and buckwheat. Diverse cover crops can reduce weed populations by suppressing weed populations while improving beneficial soil organisms.
Brandt’s second tip is select multiple species of cover crops to accommodate a large growing window. In North Dakota research, multiple species planted together thrived while single species seldom grew during dry conditions. Multiple species have different root systems (deep, shallow), so they do not directly compete for water and nutrients. Growing at different elevations, they capture sunlight at different angles, allowing multiple species to grow together. Some species grow well in the summer, others late summer and early fall, and others will grow after a frost occurs. Growing multiple species of cover crops is the easiest and fastest way to improve SOM.
The third option is to grow and capture nitrogen (N). Many clovers and legumes are capable of producing from 100#-200# of nitrogen. Hairy vetch, common vetch can add 200# N, cowpeas winter peas, and sweet clover up to 150#N, and crimson clover, white clover, Sunn Hemp up to 100# N. After a dry year, excess unused N can be captured by grass cover crops like cereal rye, annual rye grass, barley, teff, oats, and brassicas like radish, kale, and rape. Capturing N and building SOM can be as valuable as producing double crop soybeans in a dry year. Unfortunately, growing soybeans without a carbon source (grass) tends to make your soil hard and less productive.
Brandt’s fourth option was to experiment with reducing crop inputs especially harmful herbicides by using a crimper crop roller. Glyphosate (Roundup) is a chelator of many beneficial micro-nutrients. A mechanical way to terminate cover crops is to use a crimper to roll cover crops flat to terminate cover crops. Three cover crops that can not be terminated with a crimper are annual ryegrass, red clover, and alfalfa. Most cover crops crimp the best when they start to bloom or come into head, which maximizes root development and nitrogen formation on legumes and clovers. If it gets too dry in the spring, terminate early with a burndown herbicide. Farmers have several new and old burn down options that avoids glyphosate use (Harpe, Sharpen, Liberty, 2-4D, Gramoxone (paraquat), Reviton).
A fifth option is to try inter-seeding cover crops into existing crops. In the fall; farmers are using drones, airplanes, helicopters, and highboy applicators to seed cover crops before the main crop is harvested. At least 1-2 inches of rain is required to get the cover crops to thrive before winter sets in. Most cover crops need a minimum of 60 days growth to survive the winter. Inter-seeding cover crops into corn, between the rows is another option, but not recommended in a dry year. The best time to inter-seed in corn is when the corn has four to no more than 5 true leaves (V4-V5). If its really dry, the cover crop either will not germinate, or if the dry period occurs later in the summer, sometimes the cover crop can compete for moisture. Timing and weather conditions are critical when making this decision. These are all tips for making soils more resilient to adverse weather conditions.