Use of Cover Crops for Soil Health, Rehabilitation and Crop Performance
By K.W. Campbell
How healthy is the soil used in your cropping systems? If it’s low in carbon levels and organic matter, then the soil profile is typically low in beneficial biological organisms. It might be time to remedy the situation with the use of a cover crop.
The advantages of cover crops are realized over an extended time frame where organic matter, water infiltration, beneficial soil microorganisms, and nitrogen levels in soil are increased and soil compaction layers, water and wind erosion, and weed competition are decreased.
In 2016, the Sustainable Agriculture Research and Education program conducted a national survey of cover crop usage throughout the U.S. Insight from the 2,020 farmers across the country found yield increases in corn and beans following cover crops. Multi-year data showed yield boosts increased as cover crops are planted year after year. Specifically, corn yields increased an average of 3.4 BPA (1.9%) and soybeans increased 1.5 BPA (2.8%) after cover crops. Also, corn yield increases rose to 8.3 BPA, and soybeans yields rose to 2.4 BPA, respectively, after cover crops had been used for more than four years.
There are three main categories of cover crops: grasses, legumes and brassica.
Grasses are the most widely used cover crops in corn and soy crop systems with rye, triticale, and wheat being the most common. Cereal rye is quite common in the upper Midwest as the residue levels in the spring are more manageable and easy to terminate prior to crop planting. Grasses are excellent nitrogen scavengers and often reduce nitrate runoff into water supplies. They are also excellent at preventing soil erosion, and they produce copious amounts of biomass to increase soil organic matter.
The primary value of legumes is to fix nitrogen in the soil. The amount of nitrogen added back into the soil is dependent on the legume species and is proportional to the species’ biomass. Popular legume cover crops include lentils, crimson clover, hairy vetch, and field peas.
Brassica cover crops have become much more common in the Midwest due to their tendency to generate large tap roots, which are ideal for breaking up soil compaction layers. Common brassicas include forage radishes, turnips, and mustards. Most of these brassica species winter-kill in Midwestern states that experience freezing temperatures.
When is the right time to establish cover crops?
Method and timing depend on the cover crop, farming operation, and the seasonal environment. Legumes and brassicas are typically planted in season during a nitrogen side-dress application time frame. Also, high-clearance machines can be used after corn canopy closure. Grasses and grass-legume mixtures can be done at crop maturity, but again, high clearance machines or aerial application equipment is needed.
Depending on latitude, grass and legume cover crops may be planted post-harvest or even during the harvest. An example cover crop mixture for post-harvest could include:
- 50% rapeseed
- 20% radish
- 30% turnip seed
- Seeding rate of five pounds per acre
- Planted first week of September
If you are planting cover crops after harvest, winter weather in the Midwestern states will kill off the cover crop prior to spring planting, so the cover crop residue can supply organic matter to the soil profile, break up compaction layers, and provide additional nitrogen to the soy/corn crop throughout the season.
This time of year is a good time to think about cover crops and work it into your budget and 2018 cropping plan. Talk to your AgVenture Yield Specialist to see if cover crops are the right fit for your operation.