Organic no-till with cover crops
by Sally Colby
Organic farming traditionally involves some degree of tillage, primarily for weed management. Because tillage interferes with the accumulation of organic matter that’s vital for soil building and successful crops, researchers are working to find an alternative.
Dr. Andrew Smith, chief scientist at Rodale Institute, said tillage is effective for crop production but it’s labor, energy, time and equipment intensive. Farmers know it takes about 20 years to accumulate one millimeter of topsoil, and many conventional farmers use no-till methods to protect this valuable soil asset. But without tillage, weed management in organic farming remains a challenge.
Smith said Rodale research projects have seen yields in organic systems comparable to conventional farming systems. Practices include tilling in a cover crop (green manure) and organic inputs such as compost. Another practice is a stale seed bed, which allows weeds below the soil surface to germinate and then be killed prior to establishing the cash crop, minimizing soil disturbance. Smith said while these methods are effective, they don’t contribute to the regenerative aspect of organic farming.
“No-till with no cover crops is no good,” said Smith as he described the farming systems trial initiated by the Rodale Institute 1981 and still in use today. “In 2008, we implemented no-till in all the systems already in place.”
Smith described the three systems Rodale studied: first, a conventional system that follows standard practices with input recommendations from Penn State – typically a corn/soybean rotation. The legume system is an organic system that relies solely on leguminous cover crops such as vetch and clover along with rye for fertility. The manure system closely resembles a livestock operation with inputs such as composted manure as well as a more diverse crop rotation that includes a perennial phase of alfalfa and orchardgrass.
“In 2008, all of these included a no-till phase,” said Smith. “In 2015, we added a conservation conventional system. While the conventional no-till has been continuous no-till since 2008, it’s had no cover crops. The conservation conventional includes rye as a cover crop and wheat in the rotation.”
In all systems except the manure system, researchers didn’t see a benefit of increased soil organic carbon with no-till, adding that in general, soil health indicators generally follow a trend of no soil health improvement simply due to practicing no-till. “Cover cropping takes crop rotation, organic inputs and a perennial phase to aerate soil,” he said. “No-till by itself slows the degradation of soil but it doesn’t regenerate or build soil health.”
Gardeners often use straw mulch to suppress weeds, but that practice isn’t efficient for large-scale crop production. However, growing the weed-suppressing mulch in the field where the cash crop will be grown is a viable option.
Smith said when farmers started adopting organic no-till systems, they used implements such as cultipackers and stalk choppers that had been used successfully in conventional farming in combination with herbicides. However, if the rolled down crop wasn’t effectively killed, it often grew back and became a weed in the planned crop. Flail mowers were proven to be effective in killing cover crops and left a suitable level of weed-suppressing mulch. “However, because it was chopped,” said Smith, “we found it breaks down later in the season and allows weeds to emerge.”
A roller crimper has similar crimping action to a haybine, and the water-filled drum has sufficient weight to kill the crop. The roller crimper can be mounted on the front with a no-till planter behind for a one-pass system. “We now have a cover crop on top of the soil protecting the soil,” said Smith. “Our studies show we retain more moisture, so in years of drought we get better crop production. We’re moving toward more regenerative.”
Smith explained the schedule for an organic no-till system. A winter annual cover crop is planted in autumn, then the cover crop is terminated in late spring at planting time. Timing is an important consideration for termination. “It’s very important to terminate the cover crop when it has switched from a vegetative phase to the reproductive phase,” he said. “If you roll and crimp cereal rye before it forms a head and started to shed pollen, it would stand right back up after rolling. If you wait until it’s starting to shed pollen and has gone into reproductive phase, you can get effective kill.” A hairy vetch cover crop should be terminated when about 75% to 100% of the plant is flowering.
The Rodale team planted corn into hairy vetch in 2013 using a front-mounted roller crimper and a no-till planter with additional weight behind. Smith said he prefers not to use row cleaners, noting that in an organic system, it’s preferable to remove cleaners to prevent any areas where weeds might emerge within the row. Several weeks after planting, the thick mat of hairy vetch has broken down, providing nitrogen for the emerging corn crop. A month later, the corn crop canopy quickly suppresses any weeds that might be emerging.
In comparing standard plow and till corn production to no-till, Smith counted nine passes through the field with plow and till. Yield was 143 bushels/acre. No-till requires two passes: rolling/planting and harvest. “With no-till, we went through the field twice,” said Smith. “We rolled and planted, then harvested and had 160 bushels/acre. There’s significant reduction in time and cost in that system.”
A 2016 farming systems comparison trial resulted in 200 bushels/acre in the organic system – a record for the area. The conventionally tilled system yielded 140 bushels/acre, meeting the county average. Considering the substantial price premiums for organic corn, reduced costs can mean significant profits for the farm.
In a no-till cover crop system, cover crop establishment is critical. “We’ve been using cereal rye planted in fall before [next year’s] soybean crop, and hairy vetch planted in mid to early fall before corn,” said Smith. “Studies show that cereal rye produces the largest amount of biomass and gives us the best weed-suppressing mulch. Hairy vetch produces the greatest amount of nitrogen to provide fertility for the corn.”
Timely planting of cover crops ensures sufficient biomass in spring when it’s time to plant the cash crop. Smith said it’s critical to have weeds well under control when establishing cover crops so newly emerging weeds aren’t a problem in spring.
Careful planning of the rotation is key to success. For a corn crop, there isn’t enough time to get rye established to get good weed-suppression. The solution is to plant rye, then oats the following year and take the oats off in July. “That gives us enough time to get rye established in September before soybeans,” said Smith. “We try to get the soybeans off by October 1; that leaves time to plant wheat. Wheat is taken off in July, then hairy vetch is planted before corn the next year.” Such a schedule allows large planting windows, allowing farmers to get into fields when conditions are good.