Many vegetable producers grow fall-planted cover crops to improve soil health and protect the soil from winter erosion. Overwintering cover crops like rye and vetch can be difficult to kill and take weeks to decompose, delaying spring planting. Winter-killed cover crops like oats create a mulch which keeps soils cool and wet. Tilling dead oat residue warms and dries out the soil for early plantings. But tillage destroys some of the soil health benefits of the cover crop, and decomposing small grain residue may release nitrogen too slowly for early crops.
Ray Weil and Natalie Lounsbury's pioneering work with forage radishes at the University of Maryland could provide a solution to the vegetable grower's winter cover crop dilemma. When planted in August, forage radishes suppress winter weeds and scavenge left-over nitrogen keeping nutrients out of groundwater. Succulent radish tissue melts away quickly when the ground thaws leaving dark soil to absorb spring warmth and little residue to interfere with planting equipment. Quickly decomposing radishes might also release nitrogen when early vegetables need it.
No-till planting of early spring vegetables into winter-killed radishes may preserve the benefits of winter cover crops without compromising early season income. To test this hypothesis Lounsbury and Weil secured a Sustainable Agriculture Research and Extension (SARE) grant. They compared oats, radish and radish oat cover crops on tilled and un-tilled seedbeds at two research stations in Maryland where they measured cover crop and tillage effects on soil water, temperature, N dynamics, potential planting date and crop responses for four different vegetable crops, focusing primarily on spinach. Along with Extension Educator collaborators they worked with eight farmers in Maryland and three farmers in Pennsylvania to trial no-till planting into winter killed cover crops on real farms in real conditions.
Research station trials were carried out at two sites for two years. Spinach was planted after radish, oat and radish/oat cover crops with and without tillage. Photo Credit Natalie Lounsbury.
Can we eliminate spring tillage, speed soil warming, capture nutrients and prevent erosion by planting spring crops into winter killed radish? (Can we no-till spring vegetable crops into winter killed cover crops)?
Sometimes. The results from experimental sites and farmer experience were mixed. When forage radish was planted in mid-to-late August in Maryland and had adequate fall growth, no-till planting some early vegetables (spinach, peas, beets) worked very well. In other cases, no-till planting was not feasible because heavy, lower organic matter soils tended to crust or become compacted over the winter. At other farms the field was too weedy after the winter killed radishes to attempt no-till. This may have been because radish cover crops were planted too late, did not have enough nutrients, or were in wet soils. When radish cover crops are not grown in optimal conditions they do not create a dense canopy early enough in fall to shade out any fall germinating weeds. These weeds take off once the cover crop winter-kills.
Spinach planted into tilled (left) and untilled (right) radish. In the heavy, low tilth soil at this farm no-tilled soil crusted quickly making it difficult to make the Jang seeder penetrate and resulting in patchy emergence. Photo Credit Tianna DuPont.
How do no-tilled vegetable yields compare to tilled fields?
No-till spinach tended to do well, comparable to spinach after tilled in covers. At an experiment site in Maryland's Piedmont region, no-till planted spinach after forage radish produced statistically equivalent yields to plantings after tilled in radish in one year, and out-yielded all other treatments in a second year. That is good news. In some conditions no-till spinach may be able to match up to spinach after tillage. However, results are site and farm specific, and no-till plantings did not yield well at a site on Maryland's Coastal Plain. Most farms did not have replicated trials, and results from single strips were mixed. No-till planting of beets, peas, and spinach after forage radish were reported to work well in some cases, but not in others, largely due to establishment problems. This may be a result of soil conditions or planting equipment, or both.
Yield in thousands of pounds per acre. Yields marked with different letters are statistically different.
Does no-till delay maturity?
Of the crops we worked with, spinach and peas seemed to do the best after no-till. Some other crops including kohlrabi and lettuce matured more slowly when planted into winter killed cover crop residue of radishes or oats when there was no tillage. This may be because the soil stayed colder. Tillage "fluffs" the soil leaving air pockets that warm up faster than dense soil particles. Temperature influences both microbial activity and plant growth.
Tilled (left) no-tilled (right). Photo Credit Natalie Lounsbury.
Do winter killed covers give us warm enough spring soil temperatures?
The warmer the soil, the quicker seeds will germinate. Seeds that 'jump' out of the ground are less likely to rot or be consumed by soil insects. No-till planting into thick cover crop mulch can be difficult in the northeast because the soils stays cold, blanketed and shaded by the thick layer of cover crop material insulation. Radish cover crops, on the other hand, leave very little residue after they are killed by winter low temperatures. Lounsbury and team hoped that this relatively bare dark soil would capture the sun's rays and warm up more quickly. They found that although tilled ground which had had no cover crop warmed up the quickest, untilled radish and radish-oat cover crop ground warmed up as quickly as untilled bare ground. Five weeks after planting, crops that were planted into un-tilled radish had experienced 20% greater growing degree hours than those that had been planted into un-tilled oats.
Dark exposed soil where winter-killed radishes leave the ground relatively open warm up faster than where there is a layer of cover crop residue. Photo Credit Dave Liker, Gorman Farm.
Fields with no cover warmed up faster than fields with oat cover crop residue. Radish residue fields were intermediate.
Can winter killed cover crops keep nutrients from leaching over the winter and release them for spring crops?
Winter cover crops can be fabulous nutrient sponges, capturing what otherwise might have leached deep into the soil where cash crops cannot get it and keeping nitrogen out of the water table. For example, a vigorous rye cover crop can capture up to 100 lbs per acre of nitrogen. Radish cover crops are especially efficient nutrient scavengers capturing up to 200 lbs per acre of nitrogen. But are the cover crops releasing this nitrogen when the plants need it? Lounsbury found that nitrogen from radish became available as soon as the soil warmed in the spring, March in 2012 and April in 2013. This contrasted with oats, which contributed no increase in available nitrogen in early spring compared to a bare fallow. The beginning of nitrogen release from radish seems to correlate with when crops start to need significant nitrogen for growth, for example the 2-4 leaf stage in spinach.
Examples from the Farm.
Gottschell Farm, Coopersburg PA Gottschell Farm is a 1.5 acre farm in Coopersburg PA which retails to thirty CSA members, the Emmaus Farmers market, an on-farm stand and to local restaurants. Oats is the stand-by winter cover on the farm. In 2011 and 2012 Steve and Nicole experimented with fall planted radish before spring spinach. Late in the fall of 2011 the stand of radish cover crop looked decent. But tiny chickweed plants were visible in the understory. The warm winter of 2011-12 was cold enough to kill the radish cover crop, but warm enough that chickweed flourished. After the radish cover crop died back the chickweed grew in thick making it inadvisable to attempt no-till. In 2012 Nicole planted the radish cover earlier, August 25, and by late fall groundcover was 96-98%. In the spring of 2013 winter-killed radish plots had very few weeds and only a little radish residue. Nicole seeded directly into the winter killed radish with a hand-pushed Jang Seeder after only a light raking. The spinach germinated well in both no-tilled and tilled radish cover crop plots. Nicole said, "The spacing looks beautiful. It is really nice and even. I'm very impressed." Unfortunately due to an untimely spring hail storm we were not able to compare yields at this site.
Radishes were planted Aug 25, 2012 at 15.5 lb/A in two plots. At the same time oats were planted in another plot which is their standard practice. Gottschell Farm.
Winter-killed radish Gottschell Farm February 13, 2013.
Spinach no-till planted with a Jang seeder (left) had similar stands as those seeded into radish that had been roto-tilled first (right). April 29, 2013. Gottschell Farm.
Beech Grove Farm, Williamsport PA Eric and Anne Nordell seeded radish and oat, onto ridges August 13, 2011. Their goal with early cover crop planting was to maximize cover crop growth. The cover crops grew well and the oats were headed out by the time they winter-killed. Cover crop growth for both oats and radish was adequate to suppress weeds over the winter, and weed pressure at this farm is already very low. In the spring, they seeded a variety of different vegetable crops onto the top of ridges. The soil dried down quicker in the spring where the radish cover crop had grown, allowing for an earlier planting date of the spring vegetables. However, the soil dryness and clay content made it difficult to penetrate the soil with a hand-held push seeder. They had to perform a very shallow and light tillage operation with a rotary hoe to loosen the top 1-2 inches of soil prior to seeding the spring vegetable crops. Also, in order to no-till seed, they had to rake away cover crop residue on the ridges that had been fall planted to oats. Even with the oat residue raked off the ridges, spinach germination was noticeably spottier and slug damage noticeably higher after oat cover crops compared to after radish cover crops. Likely due to a reduced stand, no-till seeded spinach yields were lower after oats compared to after radish cover crops. The Nordells also observed that the spinach on radish ridges was a very deep green, perhaps indicating nitrogen release from the decaying radish roots.
In 2012, the Nordells seeded cover crops onto ridges later (August 30) in order to reduce the oat biomass to more manageable levels. In 2012 they also shallow tilled 1-2 inches and they still had to quickly rake aside some dead oat residue in order to seed the very earliest spinach. In 2012 stand vigor, quality and yield was better on oat compared to radish ridges. Eric and Anne reported that the soil tilth was better under the oat cover crop due to the fibrous root system aggregating the soil and the more durable cover crop residue helping to retaining soil moisture. In 2012, the Nordells felt that leaf lettuce did equally well on ridges after oat as radish, but they felt quality was not always quite as nice after radish. They also observed somewhat smaller size and yield of Carola potatoes after radish than after oats.
Overall the Nordells plan to continue experimenting with fall planted, winter killed cover crops before spring vegetables. They recommend planting oats in early September rather than in mid-August like you would radish in their area. Oats planted too early created too much residue and cool, slug infested soil.
**Note plots were not replicated in on-farm trials. Yield and stand differences are reported as averages only.
Oats and radishes planted in strips at Beech Grove Farm. In plots shown above oats were broadcast. Ridges were formed and then 2 rows of radish seeded. Photo Credit Charlie White.
Oats broadcast in fall. Residue cut and rotary hoed on ridgetop in spring, Beech Grove Farm. Photo Credit Charlie White.
2 rows radish on ridgetops. 1 row oats between ridges. No spring tillage. Beech Grove Farm. Photo Credit Charlie White.
Gorman Farms, Laurel MD At Gorman Farms Dave Liker seeded radish cover crops in mid-August in 2012. In the spring he no-till planted peas into the dead radish residue using a Matermac tractor mounted seeder. The Matermac can deal with significant residue. "The double disks opened the soil like a pizza cutter," Dave said. The field, which tends to be wet, was just dry enough to plant without fearing compaction, but was too damp to get good closure in the furrow. These conditions are exactly the conditions under which tillage can cause damage to soil structure, and no-till seeding can avoid that problem. The peas germinated well. "It was one of our best crops of peas," Dave said. The weed suppression in the early spring was impressive but it was very difficult to cultivate later on. They generally use a basket weeder to cultivate peas. However the dried out radish husks on the soil surface clogged the cultivator making it impossible to do tractor mounted weed control with his tools. After radish there was also a "rock hard bed," Dave said which meant damage to the cultivator rather than ability to throw soil into the row with the cultivator. Another difficulty Dave ran into was rotation. They seeded so much forage radish on the farm it was difficult to rotate away from brassicas.
A MaterMacc seeder has no trouble planting into radish "residue." Photo credit: Dave Liker, Gorman Farm.
The planter did not get good closure of the furrow and they had to cover the seed by dragging a foot along the row. Photo credit: Dave Liker, Gorman Farm.
Tips for No-till Planting Spring Vegetables into Winter Killed Residue
Early planting for weed suppression: The mechanism of weed suppression is light exclusion by the rapidly growing forage radish. In Maryland radish needs to be established by the last week of August to get adequate canopy closure for weed suppression.
Adequate fall radish growth: The correct seeding rate is important for optimal growth and weed suppression. The suggested seeding rate is 8-10 lbs/acre drilled and 12-14 lbs/acre broadcast. Growth can be hindered if there is not enough residual fertility (radish scavenges nutrients, but if nutrients aren't there, it can't scavenge enough for full development), conditions are too wet (radish does not like "wet feet" and will not grow well in poorly drained soils), or there are insufficient crop stands. Insufficient crop stands can occur with seeding that is either too heavy resulting in competition between plants or too light, resulting in bare patches. Radish generally establishes quickly and easily, but some care should always be taken in planting cover crops- just like one would take care to plant cash crops, providing good seed-soil contact.
Weed suppression: If there are visible patches of ground 8 weeks after planting, there will not be adequate weed suppression for no-till planting without herbicides.
The soil in spring is well enough aerated: In low "tilth" soils with few soil aggregates rainfall can quickly compact soil. Soils with a nice crumbly texture which forms pockets to hold air and water and is less easily compacted will more easily support no-till spring planting.
Effective spring planting equipment. Forage radish leaves very little "residue" on the soil surface in spring, which means that under some conditions, it is possible to plant no-till even with simple push seeders. In other soil conditions, however, push seeders such as the Jang and Earthway will skate over a quickly dried out upper crust of the soil surface. Without even penetration and seed to soil contact emergence will be spotty. Heavier duty seeders such as the Mater Mac seeder have no trouble planting into radish "residue." In some soil conditions, press wheels may need to be adjusted for adequate furrow closing.
The right spring crop. We have had a lot of success with spinach, and farmers have had success with peas and beets. At least one farmer reported that carrots didn't work very well. There may be delayed maturity of some crops with the no-till planting. We experienced this with some lettuce and kohlrabi trials.
Weeding in no-till planting: Weed suppression only lasts until mid-April (in MD) and then some weeding may be necessary. Hand weeding and using a hoe is relatively easy. The radish carcasses can get in the way. The soil can be hard and form a surface crust. The no-till surface makes mechanical weeding difficult. Basket weeders do not work. Even knives tend to get tangled in the radish carcasses.
This project was funded by Northeast SARE (LNE11-312). Research is continuing and updates can be found on the project's website and blog at www.notillveggies.org. Check out the website for videos, photos and 2014, 2015 results. For questions by phone feel free to contact Tianna at (610) 746-1970
By Tianna DuPont, Charlie White Penn State Extension; Natalie Lounsbury, Ray Weil, University of Maryland; Eric and Ann Nordell, Beech Grove Farm; Nicole Shelly, Gotschell Farm; Dave Liker, Gorman Farms