Cover crop application in row crops

by Tamara Scully

For the growing number of farmers utilizing cover crops in their operations, a key challenge has been getting cover crop seeds planted in a timely fashion without disturbing or encroaching upon the main crop. There are variety of cover crop application methods – all with pros and cons –which can be utilized to get the seed to soil contact needed for successful cover cropping.

Some benefits of planting a cover crop include reduced soil erosion and nutrient runoff, increased biodiversity, enhanced water management, weed, pest and disease control, nitrogen fixation, carbon sequestration and soil-building. If those benefits aren’t enough, consider that properly managed cover crops have recently been shown to increase yields of corn, soy and wheat crops. By enhancing the overall soil health, crop production increases.

Terminating a cover crop before planting a cash crop, or planting a cover crop after the primary crop is harvested, can be effective management methods. But co-mingling the cover crop and the cash crop, by interseeding one directly into the other as it grows is an option which, according to a recent Sustainable Agriculture Research and Education (SARE) nationwide study of farmers, is growing. Of the farmers surveyed, 80 percent grew commodity crops, while the other 20 percent grew horticultural crops.

As per the study report:

“Approximately three out of four cover crop acres in the survey were planted after harvesting a cash crop, but the practice of inter-seeding covers into growing cash crops is an emerging trend – 27 percent of the respondents said they seeded cover crops at side dress fertilization time or in late summer.

“At the other end of the cycle, ‘planting green’ – seeding cash crops directly into living, green cover crops, then terminating the covers – had been tried or used by 39 percent of the respondents.”

Aerial seeding

A large New Jersey initiative, undertaken by Natural Resources Conservation Service (NRCS) and North Jersey Resource, Conservation and Development (North Jersey RC&D), involved aerial seeding 10,000 acres of cover crops across farmland in four counties over the past five years.

“We take care of all the logistics,” Christian Bench, North Jersey RC&D Agricultural Specialist, said. “The cover we are getting is great, when we have the rains and it sets them [the seeds] in.

“Aerial seeding of cover crops at 65 pounds of seed per acre into corn stands has resulted in 75 percent cover crop germination,” Bench said. Seeding into soybeans occurs at 50 percent leaf drop, allowing more sunlight to penetrate for better germination rates.

In three of the five years the program has aerial-seeded cover crops, there was more than 50 percent coverage the following spring, the minimum considered successful. In the remaining two years, rain – which needs to fall within a narrow window after seeding – did not happen, and the coverage rate fell below 50 percent.

The aerial seeding, done in late August or early September, requires the use of coated seeds for proper dispersal, as light seeds will scatter. Heavy corn residues can cause a problem with aerial seeding, impacting the growth of the cover crop. Harvest equipment can damage the cover crop seedlings.

Although expensive, aerial seeding runs no risk of cash crop damage, limits soil compaction and can seed 700 acres per day. The planes have a carrying capacity of 3,300 pounds, and coordination between neighboring farms reduces inefficiencies.

North Jersey RC&D coordinates the seeding of the cereal rye, annual ryegrass, tillage radish and crimson clover mix, and covers the farmers’ up-front out of pocket expenses not covered by the USDA-NRCS Environmental Quality Insurance Program (EQIP).

High crop spreader

An existing high clearance spreader can be modified to inter-seed cover crops into standing crops. Cover crops are sown into soy in August, and into corn when it’s at the V5-V6 stages of growth.

“This is a method that farmers can do. The equipment is out there,” Bench said, or there is the option to hire custom services. The cost ranges from $12 – $15 per acre, and 150 acres can be seeded per day. There is very good seed to soil contact, although “you’re still broadcasting, as with the aerial,” so rain timing after seeding remains critical.

Concerns include the inconsistent spread pattern, with skipped spots, sometimes seen to be as wide as 60 feet. If producers try to overlap when spreading, there is the risk of increased crop damage. If there are no previous tracks in the field, the risk of crop damage is increased.

Another concern is soil compaction, which is “counter-intuitive to what cover cropping is all about,” he said.

Interseeder

An interseeder drill can be used to sow cover crops into standing corn. It can also side dress nitrogen or apply herbicides while seeding, reducing compaction and time, and allows for adjustable row spacing. Germination rates are typically high with this method, although cash crop damage, particularly on headlands, can occur as the equipment moves through the field. Not all types or widths of corn planter are compatible with an interseeder drill, which can seed about 50 acres/day.

Timing of drilling in a wet year can be tricky. In trials inter-seeding cover crops into corn plots, there has been “varied success. Timing is tricky. Drill set-up is tricky. The overall canopy shade is really, really tricky,” Bench said.

Post-harvest options

Post-harvest drilling using existing equipment is another way to get a cover crop planted, though the timing of the harvest can make it difficult to sow more than one species of cover crop. It is often challenging to plant any brassicas or legumes, Bench said, but rye can be planted a bit late and still catch up in the spring.

Heavy crop residues can make the drilling difficult. Post-harvest drilling can be done at rates of about 100 acres/day, and the cost is less than aerial seeding but more than with a high crop spreader. Seed size is not an issue.

Common equipment, such as a field cultivator, can be retrofitted with seed tubes and a seed box arm for multi-species cover crop seeding post-harvest. A sprayer can be modified and retrofitted as well. Both require another pass through the field, and the proper timing to avoid crop damage will be important.

“Drilling is the way to go to establish cover crops. This creates great seed to soil contact,” Bench said.

When it comes to cover crops, “something is better than nothing,” he said, and opting to keep the ground covered throughout the year brings lasting benefits, whether seeding post-harvest or inter-seeding into an existing cash crop.

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