Spring Planted Cover Crops for Vegetable Rotations

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

One principle of managing for improved soil health is that you should always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted and provide soil health benefits where vegetables are not scheduled until late May or the month of June.

The most common grass family cover crop options for mid to late March or early April planting are spring oats, and annual ryegrass. Plant oats 90-120 lbs per acre and annual ryegrass at 20-30 lbs per acre.

Mustard family (Brassica) cover crop options for late March or early April planting include yellow mustards, white mustards, brown mustards and oriental mustards. Companies also offer blends of several mustard species. Mustards are generally planted at 10-20 lbs per acre. Rapeseed and canola are another mustard family option for spring planting at 5-12 lbs per acre. Forage radishes and oilseed radishes can also be spring planted at a rate of 4-10 lbs per acre. Arugula is an additional mustard family option planted at 4-7 lbs per acre.

In the legume family, field peas are another option for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian field peas are larger seeded and used as a spring cover crop planted alone at 120-140 lbs per acre. An often-forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs per acre, for mixtures 6-10 lbs per acre.

Mixtures also can be used. Research has shown that you get the best soil health benefits from mixing three species from different plant families. Commonly a grass is mixed with a legume and with a mustard family crop. Examples would be spring oats, field peas, and forage radish; or annual ryegrass, red clover, and mustard. Reduce seeding rates of each component when using in mixtures. Companies often offer preblended mixture for these uses.

Many of the mustards have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties include Pacific Gold, Idagold, and Kodiak. Biofumigant blends include Caliente and Mighty Mustard. Biofumigant rapeseed varieties include Dwarf Essex and Bonar.

To use as a biofumigant, mustards will be allowed to go to full growth (early flowering) and then are chopped with a flail chopper (cut fine) and incorporated with a tractor mounted rototiller or other tillage tool for complete incorporation. Chopping releases the biofumigant compounds in the plants. Ideally the area then should be rolled with a cultipacker or overhead irrigated to seal in the biofumugant.

Finely chopped biofumigant cover crop ready for incorporation. Chopping releases the biofumigant compounds in the plants.

When used as a biofumigant, mustards should be grown as a crop. You need to add 60-100 lbs of nitrogen per acre to produce the maximum biomass. Nitrogen is also required to produce spring oats and annual ryegrass at similar rates. When planting mixtures with peas, nitrogen rates should be reduced.

Several spring-planted cover crops have been used specifically to address nematode infested soils. This includes “Nemat” arugula and “Image” radish. Mustards such as Caliente 199 have been used to reduce Phytophthora infestations.

Spring planted cover crops shown including mustards, rapeseed, radishes, and arugula.

DECCnetwork.com and Visiting Cover Crop Demonstration Sites

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

UD and DSU currently have sites set up for anyone to come and visit cover crop demonstrations. These sites have different cover crop species and planting dates to evaluate cover crop growth and development. These sites are listed online at http://www.deccnetwork.com/, which include the locations as well as a description of what has been planted. As these cover crops grow and the cash crops are planted this coming spring, these sites will be available to check on their progress and evaluate them for yourself.

Soybean Burndown – If You Haven’t Sprayed Yet, Good Luck

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

If you have already burned down your soybean fields, be sure to look at them before planting and decide if you are going to need another application of a burndown herbicide (glyphosate or paraquat) due to newly emerged weeds. Even if you included a residual herbicide with your burndown, you need to check to be sure that no weeds have started to emerge.

For those fields that have not been burned down, you have a few things to consider. If you have marestail/horseweed you have two options, 2,4-D or Sharpen to tankmix with glyphosate. Most formulations of 2,4-D used at a pint have a restriction of 15 days preplant, but the 1 pt rate is not going to be very effective on taller horseweed plants. Some formulations of 2,4-D will allow 1 lb acid equivalent (1qt of a 4lb gal) as close as 15 days to planting. Be sure to check the labels. Sharpen use on coarse-textured soils with less than 2% organic matter needs to be applied 30 days before soybean planting due to potential crop injury. Medium to fine textured soils treated with 1 oz of Sharpen has no waiting period, while there is a 15-day interval with the 1.5 oz rate. Horseweed plants beginning to bolt will need at least the 1.5 oz rate for effective control.

Be aware that if you use Sharpen, the label does not allow another group 14 herbicide (Valor, Authority product, or Reflex) within 30 days on coarse-textured soils with low organic matter or 14-days for all other soil types.

Many of the soybean fields may have had a rye cover crop in them. While the rye will help with weed control by suppressing the growth of weeds or preventing weed emerging, it requires very thick mulch of a cover crop to be highly effective. So scout your cover crop fields to determine what the best approaches for weed management are.

Killing Cover Crops

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

It is important to be sure cover crops are dead prior to planting. Once the crop has emerged there are fewer options for killing the cover crop. The cool, overcast weather has further complicated terminating cover crops. All herbicides need actively growing plants to be effective, and the recent weather has slowed (or reduced) herbicide activity. Allow 7 to 10 days for glyphosate to achieve maximum effectiveness and scout to be sure burndown programs were successful. Tankmixtures with triazine herbicides or mixtures containing Valor (flumioxazin) can reduce glyphosate effectiveness under poor growing conditions. On the other hand, tankmixing a triazine with paraquat can improve overall effectiveness. When tankmixing, analyze each component herbicide to avoid a reduction in effectiveness. Some growers are planting first and spraying the cover crop after planting. This is a unique situation that requires the proper planter and attachments to manage the residue, and paying close attention to be sure the cover crop does not take up too much moisture before planting. We will be evaluating this concept of “planting green” this spring for both corn and soybeans.

Terminating Forage Radish (aka Tillage Radishes)

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

When we had weather similar to this winter’s a few years ago and many of the forage radishes survived, I did not have much luck with killing radishes with herbicides. My concern is the likelihood of radishes regrowing if only the foliage is removed. I am thinking that we need to be sure the crown portion of the plant is also killed. With lack of experience on how to kill radishes, I don’t have any sure-fire approaches.

Some folks say that mowing will terminate these plants. We did not have a mower that would allow us get the blades low enough to remove the crown. Likewise, disking was not sufficient to kill the radishes either.

Glyphosate is not very effective on radishes. So in areas where it is appropriate to use 2,4-D that is the product I would suggest (at a rate of 1 qt for 4lb/gal). Tankmixing it with glyphosate to control rye and other species.

Situations where 2,4-D is not appropriate are more challenging. Paraquat (2 qts) with a triazine herbicide (simazine, atrazine or metribuzin) would be a suggestion.

If the triazines interfere with crop rotation, then only paraquat, but a second application maybe needed.

I would suggest killing the radishes early because: 1) we don’t have a sure-fire approach and this allows time to retreat if needed; 2) allows for the root to start to break down so it won’t interfere with planting; and 3) radishes will be killed before they start to flower and produce seeds.

However, farmers should also walk their fields and see how many radishes are really alive, there may not be as many as they think. In addition, if they planted mixed species, they need to weigh the pros and cons of terminating the field. Terminating the radishes will also kill other species.

Planting Spring Cover Crops for Vegetable Rotations

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

One principle of managing soil for improved health is to always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted in March or early April to provide soil health benefits where vegetables and field crops are not scheduled until late May or the month of June.

The most common cover crop options for late March or early April planting include spring oats, mustards and annual ryegrass. Plant oats 90-120 lbs per acre, mustards at 10-20 lbs per acre, and annual ryegrass at 20-30 lbs per acre.

Field peas are another option for spring planting. We are somewhat south of the best zone for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian or spring field peas are larger seeded and used as a spring cover crop planted alone at 120-140 lb/A.

Mixtures also can be used. Field peas are well adapted to mixing with spring oats or with annual ryegrass. Reduce seeding rates of each component when using in mixtures. Recommended seeding rates are 70 lbs of oats per acre and 40 lbs/A of Austrian winter peas or 80 lbs/A of Canadian or spring field peas.

Many mustard family crops have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties and blends include ‘Pacific Gold’, ‘Idagold’, ‘Caliente’, ‘Trifecta’, and ‘Kodiak’. Other mustard family crops serve as non-hosts, trap crops, or deterrents for pests. In research at the University of Delaware biofumigation using early spring planted biofumigant crops such as ‘Image’ radish, ‘Dwarf Essex’ rapeseed, or ‘Nemat’ arugula showed potential for managing root knot nematode populations. When used as a biofumigant, mustard family cover crops should be grown to achieve maximum biomass by adding 60-100 lbs of nitrogen per acre. Nitrogen is also required to produce high biomass with spring oats and annual ryegrass at similar rates.  When planting mixtures with peas, nitrogen rates should be reduced.

An often forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs/A, for mixtures 6-10 lbs/A.

Cover Crops that Did Not Winter Kill

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Many Delmarva vegetable growers plant cover crops that winter kill. This reduces costs for crop destruction prior to planting early spring vegetables. With the mild January and February temperatures, many cover crops have not fully winter killed, including fall planted spring oats, forage radish, and some mustard species. For vegetable growers seeking to have early areas for spring planting, this will require that these cover crops be killed by non-selective herbicides or tillage. This will also limit the potential to plant no-till vegetables into these areas.

Radish cover crop that did not winter kill.

Another concern is with higher risk of seed corn maggot damage to early planted vegetables. The following is a reprint of an article from Joanne Whalen in 2016 on this issue with some additions regarding terminating cover crops in italics.

“Seed Corn Maggot in Spring Planted Vegetables”

Warm daytime temperatures in late February and March followed by cooler spring temperatures may result in very favorable conditions for seed corn maggot (SCM) infestations. Spring planted vegetables most susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. SCM overwinter as pupae in the soil and adult flies start emerging in our area in late February and early March. SCM larvae (maggots) can cause damage by burrowing into seeds, cotyledons and the below ground hypocotyl tissue of seedlings. Maggots can also burrow into the main stems of plants.

There are other maggots that can attack spring planted crops; however, the SCM generally occurs earlier in the season and has the widest host range.

As most are aware, there are no rescue treatments for maggots, once damage is found it is too late to control them. Cultural control options to consider include: (a) avoid planting into fields where animal manure was recently applied and/or where a green manure was recently incorporated – this will be an issue with cover crops that did not winter kill; (b) early disking or plowing under of crop residues to ensure that they are completely decomposed before planting – this should take place 2-4 weeks before planting; (c) good weed management; and (d) planting seeds as shallow as possible to encourage quick emergence. Chemical control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. In addition, if conditions are favorable for seed corn maggot, a combination of a seed treatment and soil insecticide (where labeled) may be needed to provide effective control. Please refer to the Commercial Vegetable Recommendations for available control options. (http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/)

Seed corn maggot damage to a pea seedling.

Cover Crop Decisions for Vegetable Growers Part 2

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Vegetable growers should take time to revisit their rotations and plans for the next growing season. Decisions on fall rotational crops or cover crops will need to be made soon.

Start by listing your goals. Some possible goals for vegetable rotations include:

  • Returning organic matter to the soil. Vegetable rotations are tillage intensive and organic matter is oxidized at a high rate. Cover crops help to maintain organic matter levels in the soil, a critical component of soil health and productivity. Brassicas and winter legumes provide the most biomass followed by ryegrasses and then rye.
  • Providing winter cover. By having a crop (including roots) growing on a field in the winter you recycle plant nutrients (especially nitrogen), reduce leaching losses of nitrogen, reduce erosion by wind and water, and reduce surface compaction and the effects of heavy rainfall on bare soils. Cover crops also compete with winter annual weeds and can help reduce weed pressure in the spring.
  • Providing fall and early winter cover and then winter killing. The use of winter killed cover crops are very useful when early spring (March or April) plantings of vegetable crops such as potatoes, peas, cole crops, early sweet corn, or early snap bean crops are being planned. By winter killing, cover crop residue is more manageable and spring tillage and planting can proceed more quickly.
  • Reducing certain diseases and other pests. Cover crops help to maintain soil organic matter. Residue from cover crops can help to increase the diversity of soil organisms and reduce soil borne disease pressure. Some cover crops may also help to suppress certain soil borne pests, such as nematodes, by releasing compounds that affect these pests upon decomposition. One system would be planting mustards in August or early September, tilling them into the soil to provide some biofumigation in October, and then planting a small grain crop for winter cover. Spring planted mustards can also work ahead of later spring planted vegetables.
  • Providing nitrogen for the following crop. Leguminous cover crops, such as hairy vetch or crimson clover, can provide significant amounts of nitrogen, especially for late spring planted vegetables. Hairy vetch is particularly well suited for no-till systems and can provide full nitrogen requirements for crops such as pumpkins and partial requirements for crops such as sweet corn, tomatoes, or peppers.
  • Improving soil physical properties. Cover crops help to maintain or improve soil physical properties and reduce compaction. Roots of cover crops and incorporated cover crop residue will help improve drainage, water holding capacity, aeration, and tilth. The use of large tap rooted cover crops such as forage radish or oilseed radish are particularly well adapted to these uses.
  • Setting up windbreaks in the fall for spring planted vegetables. Small grain crops will overwinter and grow tall enough in to provide wind protection for spring planted vegetables. Rye has been the preferred windbreak because tall types are still available and it elongates early in the spring. While barley is also early, tall varieties are not generally available. Wheat and triticale are intermediate and later.
  • Developing no-till, bio-strip-till, and bio-bed preparation systems. There is much opportunity to increase the amount of no-till and bio-tillage systems. The key will be selecting the right cover crop for the desired system. Rye, crimson clover, subclover, tillage radish, spring oats, and other cover crops have been used successfully for no-till vegetables. One innovative system that uses a combination of winter killed covers and standard covers is bio-strip-till. In this system, a high biomass cover crop such as rye or vetch is planted with strips of forage or oilseed radish in rows where spring planting will occur. Another system uses rye strips with forage radish planted where the beds will be next year.

Cover crop planting windows vary with crop and timely planting is essential to achieve the desired results. There are many cover crop options for late summer or fall planting including:

Small Grains
Rye is often used as a winter cover as it is very cold hardy and deep rooted. It has the added advantage of being tall and strips can be left the following spring to provide windbreaks in crops such as watermelons. Rye makes very good surface mulch for roll-kill or plant through no-till systems for crops such as pumpkins. It also can be planted later (up to early November) and still provide adequate winter cover. Wheat, barley, and triticale are also planted as winter cover crops by vegetable producers.

Spring oats may also be used as a cover crop and can produce significant growth if planted in late August or early September. It has the advantage of winter killing in most years, thus making it easier to manage for early spring crops such as peas or cabbage. All the small grain cover crops will make more cover with some nitrogen application or the use of manure.

To get full advantage of small grain cover crops, use full seeding rates and plant early enough to get some fall tillering. Drilling is preferred to broadcast or aerial seeding.

Ryegrasses
Both perennial and annual ryegrasses also make good winter cover crops. They are quick growing in the fall and can be planted from late August through October. If allowed to grow in the spring, ryegrasses can add significant organic matter to the soil when turned under, but avoid letting them go to seed.

Winter Annual Legumes
Hairy vetch, crimson clover, field peas, subterranean clover, and other clovers are excellent cover crops and can provide significant nitrogen for vegetable crops that follow. Hairy vetch works very well in no-till vegetable systems where it is allowed to go up to flowering and then is killed by herbicides or with a roller-crimper. It is a common system for planting pumpkins in the region but also works well for late plantings of other vine crops, tomatoes and peppers. Hairy vetch, crimson clover and subterranean clover can provide from 80 to well over 100 pounds of nitrogen equivalent. Remember to inoculate the seeds of these crops with the proper Rhizobial inoculants for that particular legume. All of these legume species should be planted as early as possible – from the last week in August through the end of September to get adequate fall growth. These crops need to be established at least 4 weeks before a killing frost.

Brassica Species
There has been an increase in interest in the use of certain Brassica species as cover crops for vegetable rotations.

Rapeseed has been used as a winter cover and has shown some promise in reducing certain nematode levels in the soil. To take advantage of the biofumigation properties of rapeseed you plant the crop in late summer, allow the plant to develop until early next spring and then till it under before it goes to seed. It is the leaves that break down to release the fumigant-like chemical. Mow rapeseed using a flail mower and plow down the residue immediately. Never mow down more area than can be plowed under within two hours. Note: Mowing injures the plants and initiates a process releasing nematicidal chemicals into the soil. Failure to incorporate mowed plant material into the soil quickly, allows much of these available toxicants to escape by volatilization.

Turnips and mustards can be used for fall cover but not all varieties and species will winter over into the spring. Several mustard species have biofumigation potential and a succession rotation of an August planting of biofumigant mustards that are tilled under in October followed by small grain can significantly reduce diseases for spring planted vegetables that follow.

More recent research in the region has been with forage radish. It produces a giant tap root that acts like a bio-drill, opening up channels in the soil and reducing compaction. When planted in late summer, it will produce a large amount of growth and will smother any winter annual weeds. It will then winter kill leaving a very mellow, weed-free seedbed. It is an ideal cover crop for systems with early spring planted vegetables such as peas. Oilseed radish is similar to forage radish but has a less significant root. It also winter kills. Brassicas must be planted early – mid-August through mid-September – for best effect.

Cover Crop Mixtures
There is significant interest in cover crop mixtures to the point where 6 – 8 different species are being mixed together. As fall cover crop season is upon us, there are a number of considerations that growers interested in using mixtures should be aware of.

Cover crop species are commonly grouped into six major categories: 1) cool season grasses; 2) cool season legumes; 3) cool season broadleaves 4) warm season grasses; 4) warm season legumes; and 6) warm season broadleaves. In theory, a successful mixture will combine species from as many categories as practical based on the planting season. For late summer/fall planting we will be limited to 1, 2, and 3 above.

In addition, cover crop species can also be placed into groups based on the benefits they offer. This includes nitrogen fixation, nutrient (particularly nitrogen) uptake and recycling, compaction reduction, disease suppression, biofumigation, weed control, biomass accumulation, use as a mulch, winter killing to facilitate early spring plantings, and other benefits.

The first step in creating a mixture is to list the available species that can be used for the time of the year. For example, for late summer and fall planting this would include small grains (wheat, barley, rye, winter oats, triticale), ryegrasses, rapeseed, winter annual legumes (crimson clover, hairy vetch, winter hardy field peas, subclover, many other clovers). If winter killed crops with extended fall growing seasons are desired then radishes, mustards, and spring oats would be examples of selections.

The second step would be to list what soil health attributes or other cropping system needs should be prioritized. For example, if a mulch for no-tilling vegetables into next spring is a priority then high biomass cover crops that decompose more slowly such as cereal rye or triticale should be in the mixture. Conversely, if early spring planting is the goal then winter killed cover crops should be in the mixture. If compaction needs to be addressed then radishes or other species in the Brassica family should be in the mix. If nitrogen fixation is a priority then a high N fixing potential legume such as hairy vetch should be included.

The final step would be to develop seeding rates for each mixture component. This is critical because too much of one component can outcompete other components and limit their survival or limit their usefulness in the mixture. Unfortunately there is little actual science to guide seed rate determinations for complex mixtures. A number of seed companies supply mixtures and can be consulted.

An example of a potential September seeded cover crop mixture for Delaware with many winter hardy species is: rapeseed, ryegrass, cereal rye, crimson clover, and hairy vetch. A multi-species example with combinations of winter killed and winter hardy species is: radish, mustard, spring oats, triticale, crimson clover, and field peas.

Growers will need to do some experimentation on their own farms with different mixtures and seeding rates to determine what works best for their farm, growing conditions, and rotations.

Cover Crop Decisions for Vegetable Growers I: Basic Considerations & Winter Killed Cover Crops

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

With cover crop season coming up, vegetable growers will have decisions to make on what cover crops to plant and how best to grow and use them. The following is the first in a series revisiting this topic.

Cover crop acreage has been growing in the region, largely due to nutrient management efforts and cost share programs. In the last 2 years, there has been an emphasis on growing cover crops for soil health benefits and programs are underway from NRCS and Conservation Districts to increase cover crop plantings for soil improvement.

Nutrient management goals and soil health goals are not necessarily the same. In nutrient management based cover crop programs, the goals are to have crops that can take up residual nitrogen and also provide cover to reduce erosion losses. Non-legumes predominate, with most of the acres planted in small grains such as rye with some recent use of radishes (Maryland programs are non-legume based while Delaware conservation district programs allow for the use of legumes). No fertilizer can be used with cover crops in these programs. In this case the answer to the question above is that a cover is being grown. While there will be soil health benefits, they are not maximized.

In contrast, when soil improvement is the primary goal, the cover crops are grown as crops. You are growing plants to maximize the benefits they provide. To increase organic matter and improve soil health the main goal is to produce maximum biomass above ground and below ground. A secondary goal would be to provide different types of organic matter (such as with cover crop mixtures) to support a diverse soil microbial environment.

In other cases the goals will be different. With leguminous cover crops a goal may be to maximize the amount of nitrogen fixed. With soil compaction reducing crops such as radishes, the goal is to maximize the amount of “biodrilling” – the amount of tap roots being produced. With biofumigant crops, the goal is to maximize the production of fumigant-like chemicals the crops produce. With mulch based systems, the goal is to maximize above ground biomass.

What these soil improvement and specific use goals have in common is the need to treat the cover crop as a crop in order to optimize plant growth. This includes seeding at the proper rate to achieve optimal stands, planting at the right time, using seeding methods to get maximum seed germination and plant survival, having sufficient fertility to support good plant growth, providing water during dry periods, managing pests (insects, diseases, weeds), and inoculating legumes. If cover crop mixtures are being used, the ratios of seeds being planted must be considered to have the best balance of plants in the final stand.

The best cover crop stands are obtained with a drill or seeder that places the seed at the proper depth, at the proper seeding rate, with good soil to seed contact. Fertilization and liming programs should be used to support season-long growth – fertilizers and other soil amendments will be necessary in most cases. Nitrogen will need to be added for non-legumes.

When the crop is terminated is also key. The cover crops should be allowed to grow to the stage that maximizes the benefits they have to offer before killing the crops. Allowing a winter cover to grow for an extra week in the spring can make a large difference in the amount of biomass produced.

Cover crops that put on significant growth in the fall and then die during the winter can be very useful tools for vegetable cropping systems. These winter killed cover crops add organic matter, recycle nutrients, improve soil health, and allow for earlier spring vegetable planting.

Winter killed cover crops that are late summer and fall planted include spring oats, several mustard species, and forage and oilseed radish. Earlier planted summer annuals (millets; sorghums, sudangrasses, and hybrids; annual legumes such as sun hemp or forage soybeans; buckwheat and many others) can also be used as winter killed species. Timing of planting will vary according to the species being used and winter killed species selection will depend on when fields will be available for seeding. Summer annuals should be planted in late July or during August for use in a winter killed system to obtain sufficient growth.

Spring oats and mustard species can be planted from late August through September. For best effect, forage and oilseed radishes should be planted before the middle of September. Spring oats, radishes and mustards are not suited for October or later planting because they will not produce adequate fall growth.

All of the winter killed non-legumes mentioned above will benefit from the addition of 30-60 lbs of nitrogen.

The following are several options for using winter killed species with vegetables:

1) Compaction mitigation for spring planted vegetables. Where there are compacted fields, the use of forage radishes has worked very well as a winter killed cover crop by “biodrilling”. The extremely large taproot penetrates deep into the soil, and after winterkilling, will leave a large hole where future crop roots can grow. Oilseed radish also provides considerable “biodrilling”. Winter killed radishes works well with spring planted crops such as spinach, peas, early sweet corn, and early snap beans. One issue with radishes is that in mild winters they may not fully winter kill.

2) Early planted vegetables. A wide range of early planted vegetables may benefit from winter killed cover crops. For example, peas no-till planted or planted using limited vertical tillage after a winter killed cover crop of forage radish, oilseed radish, or winter killed mustard have performed better than those planted after conventional tillage. Early sweet corn also has potential in these systems as do a wide range of spring vegetables including spinach, potatoes, and cabbage. Winter killed radishes and mustards also have the advantage of outcompeting winter annual weeds leaving relatively weed free fields and also in recycling nutrients from the soil so that they are available in the spring for early crops (decomposition has already occurred).

3) Mixed systems with windbreaks for plasticulture. By planting planned plasticulture bed areas with winter killed cover crops and areas in-between with cereal rye you can gain the benefits of these soil improving cover crops and eliminate the need make tillage strips early in the spring. The winter killed areas can be tilled just prior to laying plastic.

4) Bio-strip till. By drilling one row of forage or oilseed radish and other adjacent rows with rye or other small grains, you can create a biodrilled strip that winter kills and that can be no-till planted into the spring without the need for strip-till implements. This opens up dozens of options for strip tilling (seed or transplanted) spring vegetables.

Cover Crops – A Soil Health Strategy to Prepare for Climate Change

Jennifer Volk, Extension Environmental Quality and Management Specialist; jennvolk@udel.edu

Did you know that you might already be employing strategies to help your operation prepare for climate change? Turns out that some of the same best management practices that have been utilized for decades for their benefits to the environment are also excellent tools to help combat and prepare for a changing climate.

It is pretty well known that cover crops are one of the best agricultural practices for improving water quality due to their ability to reduce nitrogen running off and leaching from agricultural fields. Depending on the varieties and mixtures used, cover crops can also suppress weed and insect pests. But, it is their ability to improve soil health that makes cover crops an excellent tool in the adaptation tool box for climate change.

One of the greatest benefits of cover crops is their ability to improve soil tilth. The root systems of cover crops, legumes especially, promote beneficial fungi (mycorrhizae) and other microorganisms in soil. These fungi and microorganisms help bind soil aggregates and well-aggregated soils allow for more water infiltration and retention and ultimately increase a soil’s capacity for plant available water. This is important given that we are anticipating hotter annual average and summer temperatures, warmer nights, and more hot, dry days in the future – all of which will likely lead to an increase in water demand by crops. Cover crops can help improve soil moisture conditions which could provide protection to crops during the hot dry conditions to come.

Cover crops also decrease risks of erosion through several pathways. First, the plants themselves hold the soil in place but the cover they provide also protects the soil from wind and raindrops. Additionally, since cover crops contribute to better aggregation of soils, the particles are more closely bound together and less susceptible to erosive forces. And, because more water can filter through well-aggregated soils, less water runs off, reducing the potential for soil to move with it. These are important benefits as climate projections indicate that precipitation will be more intense in the future and intense rains have a higher probability of eroding soils.

Finally, cover crops are often reported to increase soil carbon due to the stable organic matter left behind by woody and fibrous grains, grasses, and non-legumes. But, other agronomic practices could counteract this benefit, especially tillage. Conventional tillage not only breaks up the soil aggregates that improve soil tilth, but it also creates more soil surface area for microorganisms to decompose organic matter ultimately decreasing soil carbon. So, best results for soil health come when you utilize cover crops and minimal tillage systems together.

Because cover crops can help build soil carbon, they can in effect sequester carbon from the atmosphere, offsetting a portion of the carbon being emitted to the atmosphere which is causing climate change in the first place. A recent Natural Resource Defense Council Report, “Climate-Ready Soil: How cover crops can make farms more resilient to extreme weather risks,” (https://www.nrdc.org/sites/default/files/climate-ready-soil-IB.pdf) reports that if cover crops are used on half of the corn and soybean acres in the top 10 agricultural states, more than 19 million metric tons of carbon will be captured by those soils each year and that is equivalent to taking four million cars off of the road.

Granted, it takes a long time to increase the organic content of soil, so there are no false claims that cover crops will produce changes overnight. Rather, using cover crops can be thought of as a long-term strategy to protect and improve your soil health – which works in the context of climate change since that too is a long term process. The healthier your soil, the more prepared your operation will be to deal with changing climate conditions. So, why not start using cover crops today to help prepare your soil for the future!

Sign up for cover crop cost share at the Kent and Sussex County Conservation Districts began June 13th and runs through August 5th.  The New Castle Conservation District will begin accepting applications for cover crops on Monday, August 1st and will accept them through August 31st or until funds are no longer available. Call your local district to learn more:

New Castle County, call 302-832-3100, extension 3

Kent County, call 302-741-2600, extension 3

Sussex County, call 302-856-3990 extension 3

In addition to their standard cover crop cost share program, the Sussex Conservation District offers two additional programs. One is their air seeder program which allows you to utilize their air seeder to plant your cover crop into your standing cash crop. They are also taking applications for an NRCS Regional Conservation Partnership Project that will give participants farming in the Chesapeake Bay watershed a $25 per acre bonus when they plant cereal rye or a cereal rye mix.