Strip-Till, Biological Strip-Till and No-Till Systems Using Cover Crops for Seedless Watermelon Production

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

Strip-Till, Biological Strip Till, and No-Till Systems Using Cover Crops for Seedless Watermelon Production

Seedless watermelons are the most important fresh market vegetable crop on the Delmarva Peninsula with over 5,000 acres grown annually on over 150 farms

Considerable production costs are incurred to grow seedless watermelons including transplants, plastic mulch, drip tape, irrigation (pumping), fertilizers, and pest control. Over 95% of seedless watermelons are grown on black plastic mulch in a tillage and input intensive system.

Current systems require several tillage operations prior to laying plastic. Heavy tillage reduces organic matter levels in the soil by increasing decomposition rates, destroys soil structure, and negatively affects soil health. Compacted areas between beds allow water to accumulate and can increase disease pressure in wet years as evident with the high amounts of Phytophthora fruit rot in watermelon fields on Delmarva in 2017.

Plastic mulch use adds extra cost to production, requires addition labor and time to apply, requires hand labor and machine use for removal, and must be disposed of in landfills. Degradable mulches are available and do offer another option for watermelons, however there is a high up-front cost in their use.

In a standard production system, over 130 lbs. of nitrogen are applied using inorganic nitrogen sources, another input cost (manufactured from fossil fuels), There are a minimum of 4 trips across the field with tillage and plastic laying equipment with associated fuel cost.

There is increased interest in no-till and strip till systems using killed cover crops for seedless watermelon production for later season plantings (late May and June) to reduce costs, reduce the risk of Phytophthora fruit rots, and maintain soil health. Another option is to transplant into barley stubble after harvest in June. These systems will not produce early watermelons but can improve the economics of later plantings.

No-till production of transplanted vegetable crops has been researched and demonstrated on-farm over the last two decades and no-till systems have been shown to be as productive as plasticulture based systems.

Research by Johnson and Taylor in Delaware in the 1990s showed the potential for no-till transplanting vegetable crops into rye cover, using a rolling corn stalk chopper to roll kill the rye (newer systems use a chevroned roller/crimper specifically designed to roll kill cover crops). Vegetables successfully grown with this method included pumpkins, cantaloupes, watermelon, tomatoes, and peppers. Additional studies looked at cover crop systems and no-till transplanting of vegetables into hairy vetch, crimson clover, hairy vetch-rye-crimson clover mix, and subterranean clover cover crops. This research showed that crops of squash could be grown with no additional nitrogen in killed legume covers.

Chevron bladed roller crimper for rolling cover crop prior to transplanting.

The University of Delaware conducted additional research evaluating no-till and biological strip till methods for seedless watermelon production. The goal was to reduce input costs while maintaining productivity, eliminate plastic mulch in production, maintain or improve soil organic matter and soil health, provide a portion of nitrogen fertilizer biologically, decrease fruit rots and other diseases, and decrease machine and labor costs.

Use of forage radish in a biological strip till system (winter killed forage radish strips with rye in between) was demonstrated for seedless watermelon and cantaloupe production at the University of Delaware in 2013. Additional research was conducted at the University of Delaware in 2014 with biological strip till using rye, hairy vetch, crimson clover and mixed systems with winter killed forage radish strips.

Biological Strip Till Systems in 2015
A one-acre plot was dedicated to this study. Cover crops were planted in early September 2014 for the 2015 study. A biological strip till system uses a one row strip of forage radish surrounded by the cover crop on either side. This is accomplished by blocking or dedicating seed meters in a drill. A diagram is shown below:

C C C C C C R C C C C C C C

(C = Cover Crop. R = Forage Radish)

Cover crop combinations are given in the treatments below. The forage radish winter killed and deteriorated, leaving a strip with holes (the biological strip till). Cover crops were rolled using a roller crimper after rye headed but before anthesis and when full biomass was achieved with legumes. Additionally, non-selective and pre-emergence herbicides were applied after rolling. Seedless watermelons and pollinizer plants were set by hand. It has been shown that transplants can be set directly in the hole left by the forage radish that winter kills. Drip irrigation was used in both the plasticulture and biological strip till systems.

Treatments with the single row of tillage radish in the middle and cover crops on either side included:

1)       Roll killed rye

2)       Roll killed vetch

3)       Roll killed crimson clover

4)       Killed subterranean clover

5)       Roll killed rye-vetch

6)       Roll killed rye-crimson clover

7)       Black plastic mulch (control)

Results indicate that biological strip till systems, when planted later in the season, can be a viable alternative to plasticulture systems. The best cover/radish combination for weed management was the rye/crimson clover mix.

Yield of seedless watermelons in a biological strip till system by variety and cover crop, Georgetown, DE 2015

Tillage Based Strip Till
Tillage based strip till systems can also being used to grow seedless watemelons. In this system strips are tilled using a strip tillage implement with coulters or with mini rotavators. Transplants are set with a transplanter designed to go through some trash or that punches holes in the ground for the transplant.

Strip-till Implement

No-till for Seedless Watermelons
No-tilling into rolled cover crop or into barley stubble can also be successful with seedless watermelons. The key to success with this system is to have soils in good condition that will allow a no-till transplanter to function properly (cut a slot and then close around the transplant). To make this function, soils need to have a sufficient moisture level at transplanting.

All Systems
In each of these systems, addition of a legume cover crop such as hairy vetch or crimson clover can provide a portion of the nitrogen to grow the watermelon crop (credit 60-90 lbs of N/acre). Thick cover crop stands producing high amounts of biomass will serve as a mulch for weed control and will also serve to keep fruit off the ground, limiting fruit diseases. Good transplant to soil contact at planting is essential and equipment must be set up correctly to achieve this. Additional fertilizers can be applied before or at planting and can be sidedressed.

Strip-till and no-till production systems are adapted to overhead irrigation. Drip tape can be applied in strip till systems using properly modified equipment to place in the ground next to plants. Surface applied drip tape is not recommended.

The biggest challenge in each of these systems is weed management, especially in the row. Non-selective herbicides are used before transplanting along with a residual program. Other residuals can be applied between rows with a shielded sprayer. Post emergence applications are limited to grass materials or shielded applications. Irrigation is necessary to activate residual herbicides. See the 2018 Mid-Atlantic Commercial Vegetable Production Recommendations for specific guidance http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/.

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.

Comments on Burn-Downs for No-Till Soybeans

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

There are a lot of different issues going on in soybean fields. These are some thoughts based on recent phone calls and observations in the field.

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 may not have gotten the rain to activate those herbicides.

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. 2,4-D at a pint has a restriction of 15 days preplant, but the 1 pt rate is not going to be very effective on taller horseweed plants. 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.

A lot 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 the best approaches for weed management.

Finally, I have been asked why the burndowns may not have worked in some of the fields. First, and foremost consider how effective the burndown is on the plants/cover crop present. Paraquat is generally not very effective on grass species or on some of the broadleaf weeds once they are more than a few inches tall. Glyphosate is not very effective on legumes, mustards, henbit, or annual ryegrass. So maybe the herbicide used was not the right choice.

There can be issues with tankmixing. While a triazine herbicide such as atrazine, simazine or metribuzin can increase the control of paraquat, these herbicides can reduce the effectiveness of glyphosate under some circumstances. So be careful about tankmixing.

Was there adequate coverage? While glyphosate can perform well at volumes well under 15 gal/A, that may not be adequate coverage for heavy weed pressure or trying to control smaller weeds under the cover crop. And paraquat should be applied in higher spray volumes. Was the burndown sprayed with large droplet sizes? While increasing droplet sizes can reduce drift, it can also reduce coverage. So things like air-induction nozzles or drift control agents can reduce spray coverage, which in turn reduce performance. Finally, all these herbicides seem to work better when the sun is shining and that has not happened much in our area over the past month.

Many things can work against you when trying to control weeds. Planning ahead, scouting, and allow time to retreat under these challenging conditions will improve success.

Field Crops Growers Can Conserve Nitrogen in Poultry Litter While Retaining Benefits of No-Till

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu and Amy Shober, Extension Nutrient Management and Environmental Quality Specialist; ashober@udel.edu

There are many benefits of long term no-till. However, using surface applications of poultry litter in no-till has several drawbacks. The following are some thoughts on how to manage poultry manure to reduce nutrient losses while maintaining some of the benefits associated with no-till.

No-till has been shown to reduce erosion losses from fields and, therefore, reduce the transport of nutrients attached to soil particles that would subject to erosion. Phosphorus losses are reduced considerably upon initial adoption of no-till. Nitrogen losses from surface flow are also reduced, but a significant portion of nitrogen in runoff exists in a soluble form rather than a particulate form. Over time, surface additions of poultry litter in continuous no-till leads to a buildup of soil P at the surface, which can increase soluble P losses in surface runoff. In addition, surface applications of poultry litter do not conserve the ammonium fraction. If litter is not incorporated shortly after application, much if not all of the ammonium can be volatilized and lost to the atmosphere as ammonia gas; only the organic fraction remains, thus reducing the fertilizer (and economic) value of the manure. Long term no-till provides significant soil quality and productivity benefits by increasing organic matter in soils. Tillage will greatly reduce organic matter accumulation by increasing oxidation rates. Balancing the benefits of long term no-till with the disadvantages of P surface buildup and ammonia losses when poultry manure is surface applied is difficult.

However, there are some management options that provide many of the benefits of no-till (such as reduced erosion and organic matter accumulation) while conserving ammonium N in applied poultry litter and reducing stratification of P. A number of farmers in Delaware have adopted the use of special minimum tillage tools, including aerators, vertical tillage devices (Turbotill), and “no-till harrows”. These devices allow for partial incorporation of poultry litter, which helps to conserve some of the ammonium N and reduce P stratification. The action of these devices is such that much of the benefits of no-till remain. Surface cover is reduced minimally, ensuring that erosion rates will not increase significantly; in some cases infiltration rates are improved further reducing erosion potential. Organic matter oxidation is increased under minimum tillage, but organic matter accumulations will be higher than what is expected when using standard tillage practices.

Another innovation that is on the horizon is a poultry litter injector. A narrow furrow is opened; the dry poultry litter falls into the slot and then the slot is closed again with closing wheels. The process of litter injection is expected to better maintain no-till benefits, conserve most of the ammonium N, and reduce surface P stratification than minimal tillage options.

Our current recommendation is to apply poultry litter and use an aerator, vertical tillage device, or no-till harrow to do a partial incorporation, while leaving as much crop residue as possible. Once poultry litter injectors become available, farmers may want to adopt that technology, if economically viable (cost of purchase and operation is less than the benefits received).

No-Till and Vertical Tillage for Processing Vegetables

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

No-Till Processing Vegetables
There is increased interest in no-till production of processing vegetables. No-till production is possible for most of our common processing vegetables. However, success will depend upon a number of factors. For spring planted crops, soil temperature and emergence will be the dominant issue. For summer plantings, especially into small grain stubble, soil seed contact and stand emergence will be a major issue. When planting any vegetable crop no-till into cover crops, residue management is a major challenge and for all mechanically harvested crops, contamination by previous crop residue at harvest is a common concern along with harvest recovery.

No-Till Peas
Research at the University of Delaware in 2012 showed that peas planted into winter-killed cover crops yielded equal to or better than peas planted conventionally (March planting). Yields were highest in plots where forage radish or oil seed radish winter killed. No-till peas after winter killed mustards also performed well. In contrast, peas no-tilled after winter killed spring oats did not perform as well as conventionally planted peas. It should be noted that 2012 was exceptionally warm in March. Success with early no-tilled peas will depend upon soil temperature and ground cover. Lower residue systems such as winter killed radishes or soybean stubble would be best adapted for no-till peas.

No-Till Sweet Corn
Sweet corn can be successfully no-tilled. However, a major concern for early planted no-till sweet corn into decaying crop residue or killed cover crops is seed corn maggot. Even with insecticidal seed treatments, seed corn maggot can overwhelm early plantings in some conditions and reduce stands significantly. In a 2012 experiment, April planted processing sweet corn planted into killed forage radish cover crop performed poorly when compared to conventional plots due to losses to seed corn maggot. Another issue is cold soils and delayed emergence. While most processing sweet corn varieties compensate well for reduced stands, early no-till plantings are still at risk for reduced yields. No-till sweet corn will be most successful from mid-May onward. Use of row cleaners can help to make no-till more successful in early planted systems.

No-Till Lima Beans
Lima beans have been successfully no-tilled in the past. The main issue has been with residue at harvest. In 2012 trials, no-till lima beans did not perform as well as conventionally planted lima beans after wheat. This difference was most pronounced where stubble was close mowed prior to planting versus planting into standing stubble. Trials in 2013 will focus on stubble height in no-till systems after small grain with lima beans.

No-Till Snap Beans
Snap beans have been successfully no-tilled. In discussions with growers and green bean processors, green beans no-tilled into barley stubble performed very well. We will be evaluating no-till snap beans in 2013 in different stubble heights after barley. Early planted snap beans (April and May) also have the potential to be no-tilled into areas with winter killed cover crops and we will be evaluating no-till snap beans after winter killed forage radishes in 2013. Early terminated small grain cover crop would also be a possibility with no-till snap beans.

Using Vertical Tillage with Processing Vegetables
Growers are interested in the use of vertical tillage tools with processing vegetables. The success of this system will depend on the type of cover prior to planting. In 2012 research, vertical tillage prior to pea planting performed as well or better than conventional tillage in areas with winter killed forage radishes. Processing sweet corn performed equal to conventionally planted sweet corn in vertically tilled ground again after a winter killed forage radish crop. Research in 2013 will look at vertical tillage in a number of crop residues and processing crops.

No-Till and Strip-Till Fresh Market Vegetables

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

Most fresh market vegetable crops are either grown under conventional tillage or plasticulture systems requiring significant tillage. From a soil health perspective organic matter is the driver for healthy soils and the more the soil is worked, the faster that organic matter is decomposed and lost from soils.

One solution for this dilemma is using no-till, where organic matter can be conserved or increased. The best success story with no-till vegetables has been with pumpkins, which are commonly direct seeded through a killed cover crop mulch (often hairy vetch or rye) or through crop residue (most commonly barley or wheat small grain stubble). The mulch provided keeps pumpkins off of the ground and has greatly reduced fruit diseases and improved quality. Other seeded crops such as sweet corn and snap beans have been successfully no-tilled in the region.

No-till also has been shown to work with transplanted crops. Systems were developed and tested for tomatoes on hairy vetch and for numerous crops transplanted through small grain cover from peppers to cantaloupes. There were several no-till transplanters developed and we tested one at UD back in the 1990s.

Incorporating leguminous cover crops into these systems can reduce nitrogen needs for the vegetable crop being grown. In the pumpkin no-till into hairy vetch system, typically no additional N will be needed.

There are several reasons why no-till has not been more widely adopted for vegetable crops. No-till vegetables cannot be grown for early crops which are often the most profitable, due to soil temperatures remaining cooler, longer. Establishment can be an issue, especially through thick cover crop mulches. Weeds are controlled partially by the mulches and herbicides can be used for residual control; however, weed escapes can be problematic because cultivation is not available as a tool. Certain pests such as slugs, mites, and several insects can be an issue in no-till. Drip irrigation is also more difficult to use in no-till.

An alternative that combines some of the benefits of no-till with conventional tillage is strip-till, where cover is maintained between rows and a 6-12 ft tilled strip is where vegetables are seeded or transplanted. Strips can be formed with narrow rotary cultivators or with strip till coulters. This allows for earlier crops and for better establishment. A subsoiler can be run in the strips to improve root development. Management of the strip area needs to be planned ahead of time so that cover crops do not get too large – strips are formed when cover crops are small. There is also potential to install drip irrigation in the strips. In a strip-till system weed management is critical and residual herbicides will be critical.

Research has shown that for many vegetables, yields in strip till and no-till are comparable or higher than similar season conventional or plasticulture production.

The following are some of the keys to success with no-till fresh market vegetables:

1) Well drained soils are best for no-till and strip-till.

2) Fields to be no-tilled or strip-tilled should have minimal weed seed banks and little or no perennial weed problems.

3) An effective cover crop is required for no-till and strip-till systems to work. The cover crop should produce enough biomass to cover the soil and provide mulch that limits light and weed germination. Winter cover crops that have worked well for vegetable no-till in our area are hairy vetch, crimson clover, rye, vetch-rye combination, ryegrass, and subterrenean clover. For late summer no-till vegetable crops, several of the millets have provided good cover.

4) The cover crop should be easy to kill by chemical or mechanical means and have little or no-regrowth potential. Proper timing of cover crop kill is necessary to avoid reseeding in no-till systems. For strip-till systems, strips need to be formed early in the growth stage of the cover.

5) Attention needs to be paid at planting in no-till systems to provide good soil-seed contact for direct seeding or root placement and firming for transplants.

6) Provision should be made for moving residual herbicides into the soil through the mulch cover. This may require overhead irrigation.

7) Provision should be made to manage weed escapes. This may require spot spraying or hand weeding.

 

Soil Health and Vegetable Production

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

Experienced growers and crop advisors know that one of the keys to vegetable productivity is a healthy soil. According to the Cornell Soil Health Group, “Soil health describes the capacity of a soil to be used productively without adversely affecting its future productivity, the ecosystem or the environment.” “Soil health emphasizes the integration of biological with chemical and physical measures of soil quality that affect farmers’ profits and the environment.”

From a biological standpoint, soil health relates directly to the root environment and organisms that inhabit the soil. A healthy soil for vegetables will be one that has few limits to root growth; supports high numbers of beneficial soil organisms, such as earthworms; supports a diverse microbial community with high levels of beneficial bacteria, fungi, Actinomycetes, protozoa, and nematodes and low levels of plant pathogens (such as root rot fungi, bacterial and fungal wilt organisms, soft rot bacteria, and plant parasitic nematodes). In a healthy soil, vegetable crop root systems explore a large portion of the soil volume, crops are under reduced stress, and pest problems are minimal. A healthy soil will also support mineralization of organic matter by soil microorganisms at levels appropriate to the climate.

From a chemical standpoint, healthy vegetable soils will be at a proper pH (6.0-6.8 in most soils); have a high cation exchange capacity; have optimal levels of calcium, magnesium, and potassium held on exchange sites; contain optimal but not excessive levels of other mineral nutrients needed by crops, have high levels of organic matter in various levels of decomposition and high levels of stable humus; support aerobic mineralization processes; and be free of toxic minerals from natural sources (such as high free aluminum levels) or from toxic chemical contaminants.

From a physical standpoint, healthy soils will have high levels of stable aggregates in the topsoil (creating a stable granular structure); an optimal mix of pore sizes (macropores and micropores) so that it is well aerated in the root zone, well drained, but also has a high available water holding capacity; and a low bulk density relative to the soil texture. They will be free of compaction, which limits root growth. Healthy soils are highly permeable to water and not prone to crusting.

From a management standpoint, vegetable growers have several tools at their disposal to maintain and improve soil quality including:

Crop Rotations
It is critical to choose crop rotations that minimize soil born diseases and at the same time can help to improve or maintain good soil physical and chemical characteristics. Mixing in deep rooted crops, crops with extensive root systems, and crops with high residue in the rotation will add organic matter, leave root channels which benefit future crops, break up compaction, and recycle nutrients from deeper in the soil. Crops that have similar pest profiles should not being planted consecutively, especially those vegetable and field crops that are susceptible to the same soil born diseases. Crop diversity in rotations is a key to maintaining or improving soil quality health.

Cover Crops and Green Manures
These are crops that are specifically used to recycle nutrients and to add organic matter to the soil. They occupy land and time periods in the rotation when grain and feed crops are not being grown. It is important to always have something growing on the land, even when not in production, to maintain soil health. Including cover crops and green manures in rotations increases crop diversity and provides the benefits associated with that diversity. For example, certain cover crops and green manure crops have been found to have benefits in reducing soil born diseases.

Reduced Tillage
It is important to reduce the levels of tillage in soils to maintain soil health. The more that soils are tilled the more soil aggregates are broken down and the more quickly soil organic matter is oxidized (decomposed). Soils that are excessively tilled generally have lower organic matter levels and often have poor physical characteristics. While some vegetables and vegetable cropping systems are not well adapted to no-till planting, there have been some great successes with vegetable no-till, such as pumpkins. Reduced tillage tools may be appropriate for other vegetable cropping systems. Zone tillage, vertical tillage (such as turbo till), and soil aeration are all examples of approaches that may be used successfully in vegetables. Other field crops in the rotation should be planted using no-till or reduced tillage tools as much as possible and attempts should be made to conserve crop residue (as long as it does not interfere with the vegetable portion of the rotation).

Compost, Manures, and Other Organic Matter Additions
Compost, manures, and other organic matter sources can be added to vegetable soils to improve soil quality. This approach is most appropriate where heavy tillage must be used, such as in plasticulture. By adding these organic matter sources you can counteract the effect of the heavy tillage and maintain soil health. These materials offer all of the benefits associated with increased organic matter in the soil: increased microbial diversity, reduced disease pressure, increased nutrient holding capacity, slow release of mineral nutrients, increased water holding capacity, improved aeration, and reduced bulk density.

Traffic Management
Managing traffic in vegetable crops is another soil health key. By reducing trips across a field with heavy equipment and trucks, soil compaction is reduced and soil health is maintained. Limiting traffic to designated areas, driveways, drive lines, or tram lines is another way to achieve this because areas in between are conserved and remain uncompacted. These heavy traffic areas can then be targeted with a subsoiler or other tillage equipment to break up compaction. While it is not always possible, reducing trips across vegetable fields when wet is also important. One pass by heavy equipment over wet soils can destroy the productivity of that area for a long period of time.

In 2009, the University of Delaware Cooperative Extension is launching a soil health education initiative specifically aimed at vegetable growers. In this initiative we will provide vegetable growers with information on soil health and vegetable production, soil health testing methods, how to evaluate soil health on farms, and how soil health testing can fit into an integrated pest management plan. We will be working with growers on how to create healthy rotations for vegetable crops specific to their farms. We will be doing demonstrations and field trainings on the use of different cover crops and green manure crops in vegetable rotations and demonstrations on the use of different types of composted materials and their the effects on soil health and subsequent vegetable production. For more information on this initiative, contact Gordon Johnson or Joanne Whalen.