Organic No-Till Cover Crops

 

Rye and hairy vetch cover crop. Photo Kathryn Simmons

Organic no-till cover crops are grown to flowering (or very close), killed without tilling or chemicals, and left to become dead mulch for the next crop. The food crops are planted into the dying residue. We have used no-till cover crops for Roma paste tomatoes, which are transplanted in early May. We don’t need early-ripening for these, making them a good no-till food crop. This method enabled us to have 1 year in 10 as a no-till year.

Four ways to kill cover crops without herbicides or tilling

  1. Winter-killed cover crops for early spring food crops
  2. Mow-killed cover crops.
  3. Crimped and rolled cover crops use special tractor equipment. A crimping roller is more successful than a smooth roller. I have also seen photos of an energetic human-powered method involving a T-post lying on the ground across a bed, with two well-coordinated people, one at each end of the T-post, lifting the post with a loop of rope or twine, setting the post back down a few inches further forward and stepping on it.
  4. Mowed and tarped cover crops, kept covered until the roots of the cover crop are dead. With this method, the cover crop or weeds can be killed at any stage of growth. I’m still learning about this, so I won’t say more this time.
We can no longer rely on our winter cover crop oats getting winter-killed. March photo by Pam Dawling

Organic no-till benefits to the soil

  • Soil is kept covered, reducing erosion.
  • Soil compaction is reduced by having fewer tractor passes. Labor, fuel and machinery costs are also reduced.
  • Soil layers are not inverted, the soil micro-organism habitat is undisturbed, the root channels of the cover crops are undisturbed, and the number of earthworms and microbes increases.
  • Soil structure improves, organic matter increases and the cover crop biomass is conserved, rather than burning up as quickly as it would if incorporated.
  • Soil can absorb and retain more water, making it more resilient in drought. Yields are higher under drought conditions than on tilled soil.
  • Soil retains cooler temperatures into the summer, increasing root growth.
  • No new weed seeds are brought to the surface.
  • Some pathogens and pests may be suppressed.
  • Mulch grows in situ – no need to haul and spread.
  • Legumes in the cover crop mix can provide all the nitrogen the next crop needs. The cost of N from vetch seed is half the cost of N from fertilizers.
  • Legumes are a slow-release fertilizer: 15% of the nitrogen in the vetch is in the roots, in position in the soil for the new transplants. 50% becomes available to the food crop as the soil warms in spring and early summer; 50% remains for the following season.
  • Hairy vetch activates plant genes that increase disease tolerance and plant longevity, giving tomatoes an extra 2 to 3 weeks of production
  • Use of agricultural plastics is reduced.
  • If spring is wet, it may be possible to mow, when you couldn’t till.
  • Crops such as pumpkins are cleaner than those grown on bare soil.
Hairy vetch cover crop.
Photo Southern Exposure Seed Exchange

Suitable cover crops for no-till

  • When choosing winter annual cover crops, consider cold-tolerance, the length of the growing season, and efficacy in fixing nitrogen and producing biomass. Do you want a winter-killed cover crop (oats, sorghum-sudangrass) or a hardy one (winter wheat or winter rye)?
  • Using a mixture of grasses and legumes helps limit the loss of N from the cover crop through leaching or denitrification. Generally, use a grass/legume mix in a 2:1 ratio, although you can use higher amounts of legumes, up to 1:1. Hairy Vetch, Austrian Winter Peas, Crimson Clover are all suitable.
  • There are advantages to including more than one legume in the mix – in unusual weather, one may struggle, while the other does better. 

No-till cover crops for early spring vegetables

  • Frost-tender cover crops can be used before early spring no-till food crops. Some growers say it is best to mow or roll the cover crop at around the first frost date, to provide a more uniform mulch in the spring. Weeds may be a problem and the soil will be colder than bare soil — this may work for cabbage and broccoli.
  • For the very earliest spring crops, forage radish, lab-lab bean or bell beans will die back and leave almost bare soil. While they are growing, they suppress weeds.
  • BUT fast-maturing spring vegetables will not do well with no-till cover crops unless you add N fertilizer, as they need nitrogen more quickly than can be got from no-till cover crops early in the year when the soil is cold.
Winter rye and crimson clover cover crop
Photo by McCune Porter

No-till cover crops before suitable late spring vegetables

  • A 1994 USDA trial of various no-till cover crop mulches for tomatoes found that hairy vetch (without added nitrogen fertilizer, and without any weeding) out-yielded plastic-and-fertilizer plots by about 25%, and out-yielded fertilized bare soil by 100%.
  • Late-spring transplanted crops such as late tomatoes, peppers, eggplant, Halloween pumpkins, or successions of cucumbers and squash can do very well after a winter-hardy legume-grass mix no-till cover crop.
  • I have read that transplanting eggplant into crimson clover (sown in the fall before) will reduce flea beetle outbreaks, but I have yet to try it. Mowing after early bud stage will kill crimson clover.
  • At the Coastal Plain Experiment Station in Tifton, Georgia, they have trialed peanuts planted into crimson clover.
  • If you have machinery or hand tools for seeding into no-till cover crops, direct seeded crops are possible.
Rows of Roma paste tomatoes, some on bioplastic, some no-till. Credit Bridget Aleshire

Our example: Paste tomatoes in a mow-killed no-till cover crop mix

  1. We find a plot that will be available in early September: Our spring broccoli and cabbage finish in early July. We follow them with a round of buckwheat summer cover crop.
  2. Then, on September 7–14, we sow winter rye, Austrian winter peas and hairy vetch. 5 oz HV, 1.5 oz AWP, 2.5 oz Rye per 100 sq ft (5 g HV, 5 g AWP, 8 g rye/m2.)
  3. It is vital to grow a solid stand of cover crops for high biomass. The goal is to have the vetch be about 4″ (10 cm) tall before hard frosts of 22°F (-5.5°C) stop growth.
  4. We do not till in this cover crop in spring, but in early May, we mow it very close to the ground using our hay mower (5/1-5/5), just before our tomato transplanting date. We want the cover crop to stay in long aligned stems, not be chopped up small. For small patches, a scythe is better than a weed-whip, for the same reasons
  5. This kills the cover crops. If mowed too early, they will not die. The vetch should be flowering. Rye should be at the soft dough stage – bite a kernel.
  6. We let the mulch wilt for a day, making it easier to work with, before transplanting. We measure and set out stakes and ropes to mark the rows.
  7. We transplant the tomatoes into the dying mulch with as little disturbance of the cover crop as possible.
  8. The vetch and peas (if plentiful) supply all the nitrogen the tomatoes need. We do not add any compost or other fertilizer. The peas reduce the incidence of Septoria leaf spot in the following tomato crop.
  9. In our humid climate the dead no-till mulch keeps weeds away for 6 -10 weeks, by which time it has mostly biodegraded. In climates that are drier or cooler than ours, the mulch will last longer.
  10. In July we roll hay between the rows, to top up the mulch. We plant the tomato rows 5.5 feet (1.7 m) apart and the plants are staked and woven, so we can snugly fit big round bales of hay down the aisles.
  11. This crop doesn’t finish until the frost, and we have all the posts to remove before we can sow a cover crop, so the winter following the paste tomatoes, we usually grow rye with Austrian winter peas.
The Roma paste tomatoes later in the year.
Photo Kathryn Simmons
Roma tomatoes in an earlier year, with rolled hay mulch. Photo Twin Oaks
Plentiful harvest of Roma paste tomatoes. Photo Twin Oaks COmmunity

Cautions about no-till planting

  • Cold-hardy cover crops need time in spring to grow to optimal size before mowing – they are not suitable for early spring food crops
  • Untilled soil in spring is colder than tilled soil: growth of anything you plant in it will be slower, and harvests delayed. Not good for warmth-loving crops such as watermelons!
  • The rate of nitrogen release from the cover crop will be slower than from an incorporated cover crop
  • Transplanting into untilled soil is harder work than planting into loose tilled soil
  • The timing of sowing, rolling or mowing and planting is critical. The wrong weather can jinx your plans
  • If the cover crop stand is poor, weeds will germinate – have a Plan B. Usually this will involve tilling, adding compost and then finding another mulch
  • There may be some regrowth of the cover crop, if mowing was too high, irregular or poorly timed. If needed, mow between the crop rows a couple of weeks later
  • There may be more fungal diseases and slugs
  • In arid zones, it is necessary to wet the mulch weekly to release the nutrients. Drip irrigation won’t do that
  • Hand-seeding into untilled soil is tricky – winter snow and ice can leave soil quite compacted. Unsuitable for small seeded, closely-spaced vegetables. Pumpkins and squash can be direct seeded in crimped and rolled (or mowed) winter rye.
  • Initial hopes for no-till cover crops – that it would be possible to grow vegetables organically without ever tilling again – were unrealistically high

No-till tractor equipment

  • For mowing cover crops, we use our hay mower/conditioner rather than our (rotary) bush-hog, as it cuts close to the ground and lays the cover crop down without chopping it into small pieces. This helps it last longer, and be easier to transplant into. Flail-mowers are recommended over lower-speed sickle-bar mowers, which can get tangled with long vetch vines
  • Roll-killing leaves a longer-persisting mulch than mowing, although there may be problems with re-growth. Adding a method of crimping the stems increases the effectiveness. Hairy vetch is harder to kill by rolling than crimson clover.
  • Ron Morse designed a No-Till and Reduced Till Planting Aid, consisting of a heavy coulter and shank assembly with a wavy coulter behind the shank to slice the mulch and leave a 2″-3″ (5-7.3 cm) strip of prepared soil, for planting in a separate operation.
  • Transplanters are available that are designed for use with thick organic mulches.
  • Direct seeding of large-seeded crops is possible using equipment to open a narrow slot deep enough for the seeds. No-till seeders are harder to find: an example has a toolbar planter, 15″ (38 cm) fluted disk blades to cut through the vetch mat, 15″ (38 cm) double disk opener, 12″ (30 cm) cast-iron closing disks, plastic seed pressers and extra weights.

More on no-till

At the Pasa 2022 conference I went to the workshop On-Farm Experience with Organic No-Till, by Sam Malriat from Rodale.

Sam pointed out that no-till methods sequester carbon in the soil, but simply never tilling does not improve the soil. He recommended we not be obsessive about no-till, but move towards reducing tillage. Sometimes shallow tillage can be a good choice, adding value by incorporating organic matter. OM and soil water capacity can be increased enormously by using cover crops, compost or manure, grazing, or a good crop rotation.

You need a very solid, heavy cover crop stand, to provide a thick mulch when terminated. There is a lot of difference in thickness of mulch from rye sown in August and in October. You also need a very competitive cash crop; a successful method of planting into the cover crop residue, and a back-up plan in case something goes wrong. For example, sowing corn into rolled and crimped hairy vetch does not work well, because corn is a heavy feeder and is not very competitive. A better idea is to undersow the corn at V5 or V6 (stages of vegetative growth) with white clover or crimson clover in September (in PA). It’s very important to get good seed to soil contact, and enough moisture. The clover grows after the corn dies. If the clover is left growing into the second year, cabbage can be transplanted into it.

Rye termination timing: When to successfully crimp

“Interested in no-till production, but unsure of how to manage cover crops so they don’t become a problem for the crop that follows?
The most common management concern is when to crimp your cover crop to get a good kill but prevent it from setting seed. Getting the timing right on crimping small grain cover crops like rye isn’t difficult, but it does take a little attention to its growth stage. See this three-minute video for a quick run-down on which stages to look for in order to get that timing right.”

Winter rye headed up. Mow or turn it under very soon! Don’t let it shed seed.
Photo Pam Dawling

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