Case Study 1: Deep Zone-Tillage (DZT)

Cecarelli Farm, Northford, CT, – New Haven County

Farmer: Nelson Cecarelli

Farm size: 121 acres (half owed, half rented)

Crops: sweet corn and mixed vegetables

Climate: Located about 10 miles from the Long Island Sound and from New Haven, the farm enjoys some on-shore breezes during the summer months and a slightly warmer fall than most of Connecticut.

Farm History & Markets

The Cecarelli Farm was purchased by Nelson’s grandfather in 1912, and was farmed as a vegetable farm by his grandfather, his dad and his seven uncles. Nelson inherited the property in 1996, and has produced sweet corn and mixed vegetables for the wholesale market and for other farm stands ever since. In 2009, he started retailing at his own farm stand and at local farmers markets in New Haven and Durham. Nelson grew up farming with his uncles, and has also worked in the computer field and owned his own insurance agency.

Soils and identified soil health issues:

  • Main farm – Cheshire fine, sandy, loams (extremely stony).
  • Across River – Cheshire fine, sandy, loams and Branford silt, loams (extremely stony).
  • Anderson‘s (rented) – Cheshire fine, sandy, loams (extremely stony).
  • Cellar‘s (rented) – Wethersfield loam and Ludlow silt, loams (slightly stony).
  • Wallingford (rented) – Cheshire fine, sandy loams (extremely stony).

Prior to adopting reduced-tillage, Soil Health Tests identified consistent problems in most fields with subsurface hardness (plow pans), low total organic matter and low active carbon, while some fields were rated poorly in soil surface hardness and potentially mineralizable nitrogen. Other fields were rated mediocre or below optimum in aggregate stability, root health and/or had excess levels of phosphorus. Plow pans ranged in depth from 9 to 13 inches.

Crop mix

  • sweet corn 60 acres
  • tomatoes 9 acres
  • peppers 7 acres
  • eggplant 3 acres
  • summer squash 6 acres
  • cucumbers 2 acres
  • winter squash 4 acres
  • cabbage 5 acres
  • snap beans 5 acres
  • fava beans 2 acres
  • lettuce & greens 4 acres
  • peas 2 acres
  • herbs 0.5 acre
  • hay 12 acres.

They raise all their own transplants in 2 greenhouses.

Rational for Adopting Deep Zone-tillage & Early Experiences

In 2006, Nelson rented some nice corn land from the Cella‘s Farm in the nearby town of Wallingford, some of which was rather steeply sloped and had experienced some erosion problems in the past. There were 4 precipitation events that dropped between 4 and 6 inches of rain that first season on the land, the first of which produced 3 to 4-foot-deep erosion ditches that ran perpendicular to his corn and drive rows. He had to fill the ditches with stones just to spray the sweet corn for insect control. Another gully-washer came along and washed out the temporary bridges he had built for his sprayer, and he had to rebuild the stone bridges to keep his corn worm-free. Nelson decided that if he was going to survive farming, he was going to have to farm smarter. During the following fall and winter he read an article written by a grower in upstate New York and contacted several growers for more information about a form of reduced-tillage known as vertical-tillage or deep zone-tillage.

After early penetrometer testing (push rod with pressure gauge) confirmed that his fields had a firm plow pan, Nelson decided to purchase an Underferth 2-row Zone Builder, which arrived during mid-May the following season. The Zone Builder comes with a front coulter to cut through the killed cover crop, a narrow sub-soiling shank to break up plow pans below the crop row (down to 21 inches), two larger opposing wavy coulters in the rear to produce a narrow seedbed or cleared strip for planting, and finally, a rolling basket to break up any large clods in the soil.

The first couple of days were spent learning how to adjust the rear coulters to produce a narrow (5 to 8-inch wide) seedbed through his killed cover crop of winter rye. Early attempts looked more like no-till rather than like strip- or zone- tillage. There were also problems with large clumps of rye roots accumulating between the coulters and piling up in the seedbed, which would have caused the seeds from the planter to bounce off and not enter the soil and germinate. The solution to this clump clogging problem was a combination of coulter adjustments, and more importantly, making sure that the rye cover crop was completely dead before zone building. Rye that is more than 4 inches tall must be killed at least 3 weeks prior to preparing the land for planting, to allow time for the roots of the cover crop to soften or break down to the point where they no longer build up between the rear coulters.

Due to early adjustment difficulties, Nelson ended up preparing half of his next corn field using conventional tillage (plow and disk harrow) and the second half with his Zone-Builder. It took the better part of a week to prepare the half where conventional tillage was used, while the zone-tilled half was prepared in the morning and planted in the same after-noon. Both halves were planted two days apart with the same varieties of sweet corn. Because there had been an early spring drought and it had not rained for over 4 weeks, germination in the conventionally-tilled half was reduced to 70-80% because the topsoil had dried out during the week of preparation, while the germination in the zone-tilled half exceeded 90% because all the moisture had been preserved in the topsoil prior to planting. Nelson had the highest sweet corn yields (50 bags/acre higher) he had ever experience in 2007 and was hooked on DZT.

When Nelson first stood back and looked at the narrow, dark, DZT strips across the steep hillside in Cella‘s field, the field that had erosion problems the previous year, he was convinced that some land should only be farmed using reduced-till methods. It was easy to see that with the majority of the soil surface protected by the killed cover crop residue, rainwater would be unable to build up enough speed to cause an erosion problem anymore. In the two wet years that followed, these steep grades have not suffered any erosion, even in the biggest storms.

Nelson admits that it took him a bit of time to get used to the way a DZT field looks at planting compared to a field prepared using conventional tillage. At first Nelson would make a double pass (both up and back on the same rows) with the Zone Builder to make sure that he had a clear enough seedbed for planting. It took a year and a half before he convinced himself that a single pass was all that was needed to get a great planting every time, no matter how much cover crop residue he was dealing with.

Nelson did have one unpleasant experience with the frame of his Zone Builder. New England fields tend to be smaller than fields father west, and Nelson uses a 2-row planter on his farm. This had been the first 2-row Zone-Builder made by the equipment company he bought it from, and the frame was cut down to size from a 4-row machine. After using it for a while, the welds on the two cross-braces between the two main tool bars let go and he left half the machine behind during a pass across the field. A neighbor re-welded the cross-braces and reinforced the joints, and also adding end plates to the tool bars that same afternoon and he was back Zone Building the next morning. When I caught up to him the next day, he told me about the mishaps, and swore he would never go back to conventional tillage because there are far too many advantages with the DZT system. The equipment dealer has since solved the problem on the latest 2-row machines that they have shipped by welding heavy metal end plates on to the end of the tool bars to produce a reinforced frame that will never separate.

Nelson’s Procedure and Techniques using DZT

A Soil Health Test was conducted on each of Nelson’s fields to provide preliminary data on chemical, physical and biological attributes, so that he can re-test them in 5 or 10 years to see if DZT has helped improve his soil health (see ‘Measuring Soil Health Before Converting to DZT’). This test includes an extensive check of surface hardness and subsurface (plow pan) depth and firmness with the penetrometer.

All of Nelson‘s fields are planted to winter rye for a cover crop. His equipment has traditionally been set up to plant and maintain rows 38 inches apart, so the Zone Builder was set to this same spacing. He uses DZT for all his large-seeded crops: sweet corn, winter squash, pumpkins and beans. Winter squash is planted in every other strip so that the rows are over 6 feet apart.

With the exception of the earliest sweet corn fields, the cover crop is killed with glyphosate (i.e. Roundup) and crop oil, when it is 8 to 24-inches tall, and/or at least 3 weeks prior to preparing each field for planting. The rye is killed on Nelson‘s earliest April sweet corn field, as soon as possible in the spring and before it exceeds 4-inches in height. Killing the cover crop well ahead of time, or when it is still small, prevents roots from clumping up in the seedbeds and reducing plant stands.

The narrow sub-soiling shank on the Zone Builder is set to a depth 2 to 3 inches below the hardpan, as measured with the penetrometer. In Nelson‘s fields, it is usually set to a depth of 15 to 17 inches to be sure to put a slit all the way through the plow pan and allow crop roots to fully explore the soil profile. The following year, he tries to zone build between the rows from the previous year, to continue the process of breaking up the plow pan throughout the field. Eventually, when the plow pan has been destroyed, he will raise the sub-soiling shank up to about 5 inches to conserve fuel.

The Zone Builder is pulled with a John Deere 6420 Tractor (90 hp), with 800 pounds of added weight on the front, at 6-8 mph. Fields are planted later the same day or the very next day using a Monosem 2-row planter. Yetter (brand) residue managers, attached immediately in front of each planting shoe, helps clear away any remaining cover crop residue or stones that the Zone Builder fails to remove from the seedbed. Nelson also added white, plastic “seed depth gauges” behind each planting shoe to help assure uniform emergence of the seed.

Normal pre-emergence herbicides are used at planting. For the Cecarelli Farm, this usually means 5-6 ounces of Callisto, 1 pint of Duel II Magnum and ½ to 1 pint of Attrax for sweet corn weed control or a combination of a light rate of Strategy and Sandea for winter squash and pumpkins. For sweet corn fields planted in early summer, where weeds may have re-emerged before planting, a post-emergence application of Impact (3/4 oz/acre, with MSO and ammonium sulfate) may be substituted for the Callisto to control both broadleaf weeds and annual grasses. Fields are spread with lime and potash in the fall. Phosphorus and nitrogen are banded at planting and urea is side-dressed when the corn is 8 to 12 inches tall, using a 2-row side-dresser, equipped with a no-till disk in front of the drop tube. Custom blends are used at planting, with the rates dictated by soil tests. Nelson‘s fields tend to test high in phosphorus, so it is usually only needed in small amounts for early spring plantings when the soil is cold.

In 2007 and 2008, Nelson planted his cover crop by harrowing down the corn stalks, broadcasting the rye seed, and passing a light disk to insure good seed-to-soil contact to help assure seed emergence. In 2009, he used a rotary mower to shred the corn stalks, before spreading his rye seed at a rate of 2 bushels per acre. He feels that this change, recommended by New York growers, will further reduce the amount of compaction his fields are exposed to by eliminating one or two passes with the harrow. In the future, Nelson hopes to purchase a no-till drill to plant his cover crop to help assure good plant stands and eliminate that last disking for good seed-to-soil contact.

Notable Changes in the Field Preparation Process

In order to prevent hard pans from reforming in fields, it is necessary to reduce the traffic from heavy equipment, especially when the soil is wet. DZT accomplishes this by eliminating passes with a moldboard plow, several passes with a disk-harrow, and possibly one with a cultipacker to smooth the field. With DZT there is one additional pass to kill the cover crop with an herbicide. Over time, the numbers of annual weeds decrease, and perennial weeds increase with reduced-tillage, which may also add a fall herbicide application in some years. To compensate for these extra herbicide passes, some farms fertilize, Zone Build, and plant in a single pass to further reduce traffic. Nelson’s fields have not experienced an increase in perennial weeds yet and he is still preparing the field with his Zone Builder and planting in two separate operations. Field preparation is notably faster with DZT, saving both time and fuel, and dramatically reducing both dust and noise.

Nelson (and other DZT converts) found that the wet soil conditions in June and July of 2009 did not interfere with planting sweet corn. Fields that are moldboard plowed or harrowed absorb rain like a sponge and quickly turn into a quagmire that can result in stuck tractors, wasted time, delayed plantings and compacted soils. Fields that have a heavy rye cover can usually be prepared with DZT and planted on time without putting a rut in the field. Even fields that never get planted in wet years can usually be planted using DZT without tearing up the field, resulting in increased yields compared with conventionally tilled farms.

Far fewer rocks are pulled to the surface using DZT, almost eliminating the back-breaking chore of picking rocks before planting. Occasionally a large rock will get hooked by two or more sub-soiling shanks and get pulled to the surface. These large rocks are easily removed from the field with a front loader or bucket.
Weights are needed on the front of the tractor to counterbalance the Zone Builder. A 2-row Zone-Builder requires at least a 55 hp 4-wheel-drive or 70 hp 2-wheel-drive tractor with rear tires that are at least 30 inches in diameter. Residue managers that attach to the planter are required to adequately clear the seedbed strip for planting.

Nelson‘s original light-weight side-dresser did not track straight enough across a field, especially on a hillside, to assure that he placed the nitrogen 4 inches to the side and 4 inches deep. To accomplish the proper fertilizer placement, he purchased a new, heaver model that tracks straighter and is equipped with a no-till disk in front of the drop tube, so that he can open the soil through the killed cover crop outside of the prepared seedbed.

Nelson’s DZT Equipment and Modifications 

  • Unverferth 2-row Zone Builder, equipped with reset springs for the sub-soiling shank, 8-inch wavy front coulter, two 13-inch back coulters, rolling basket and narrow wheels.
  • 2 Yetter (brand) Residue Managers (for planter)
  • 2 plastic seed firmers (for uniform seed depth and emergence)
  • 1 Mechanical Transplanter brand side-dresser modified with no-till discs in front of drop tube
  • 1 Monosem planter
  • Brushhog rotary mower (to prepare field for seeding cover crop)

DZT Benefits and Drawbacks

Nelson has found that the benefits of DZT fall into several distinct categories and include things he has experienced first-hand and others he expects to see in the near future.

How DZT saves money

  • Preparing fields for planting require far fewer passes, which makes it much faster than conventional tillage, resulting in savings for labor, ma-chine hours/maintenance, and fuel. Nelson claims it takes him less than 30 minutes per acre to prepare the ground for planting.
  • In 2009, Nelson‘s fuel deliveryman actually complained that he wasn‘t using near as much diesel as he once did. Now that‘s a problem we‘d all love to have!
  • Improves plant stands, yield and crop quality.
  • Far fewer rocks to pick
  • There should be fewer annual weed seeds over time and less weed competition. This happened due to less tillage to turn up new weed seeds and by banding most fertilizers, which feeds the plants and not the weeds.

Improvements in Fields, Soil Health and Environment

  • Reduces/stops soil water erosion and thus limits the amount of soil, nutrients and pesticides that leave the fields to pollute nearby surface or ground water.
  • Reduces wind erosion and eliminates “dust devils.”
  • Soil warms faster in spring than with no-till or conventional-tillage.
  • Nelson is watching for an increase in soil organic matter over time.
  • Should result in an increase of biological activity in the soil, such as earthworms and beneficial fungi, that help hold soil clods together to improve soil structure, porosity (air spaces in soil), and provide deep channels for drainage and extended root growth.
  • Eliminates soil crusting, which can inhibit seed germination
  • Eliminates plow pans over time (see below)
  • Preserves soil moisture during droughts
  • Improves soil drainage during wet periods

Improvements in Plant Growth and Crop Quality

  • Roots of corn plants in DZT fields now reach down over 2 feet into the soil instead of stopping at the plow pan (9-13 inches deep).
  • Since switching to DZT, Nelson harvests the cleanest winter squash and pumpkins ever, because the fruit are separated from the soil by a layer of rye mulch.
  • In a severe drought (2007), Nelson‘s sweet corn did not share the “dry tip” problems that were prevalent throughout the state and in previous dry years on his own farm.

Improvements in crop yields

When researchers do small plot work, even on commercial farms, they often find DZT and conventional tillage produce similar yields, but Nelson claims he has witnessed several ways that yields increase on a whole-farm basis using DZT, that are hard to measure in small-plot work.

  • One of Nelson‘s rented fields (Anderson‘s) has always had a large, low area or wet hole that floods in the spring and after heavy rains. Over the three years he has been using DZT, Nelson has watched this low spot turn from an unproductive piece of ground, where his corn was always stunted and produced unmarketable ears, to an area that is hard to distinguish from the rest of the field with full-sized, productive corn plants. Nelson attributes this change to the slow destruction of the plow pan, which no longer holds water and causes the area to flood for extended periods.
  • Nelson expects that since surface flooding is usually a necessary ingredient to start a Phytophthora epidemic in susceptible host crops, that his yields for tomatoes, peppers, squash and cucumbers will increase as he continues to eliminate plow pans on his farm and rotate these crops to corn ground. He thinks he experienced less destruction from Phytophthora in highly infested fields on tomatoes in 2008 and summer squash in 2009.
  • As mentioned earlier, DZT preserves soil moisture during spring droughts and allows for timely plantings and better seed emergence and plant stands in dry years than conventional tillage.
  • Also mentioned earlier, DZT allows Nelson to plant in a timely fashion during wet years, like 2008 and 2009, when other growers are getting their tractors mired. He can even plant fields that are traditionally left unplanted during wet years, without putting a rut in them.

Miscellaneous improvements

  • Land is hard to come by in Connecticut, and municipalities and land trusts are often reluctant to rent open space to vegetable growers who use conventional tillage, because they fear soil/land degradation over time. Nelson has succeeded in convincing the land manager of the neighboring town to rent municipal land to him that is not available for conventional tillage.
  • Faster field preparation means less tractor noise and dust for urban neighbors and better neighbor relations. Many of Nelson‘s neighbors are his relatives, so it pays to get along with them!

Drawbacks of DZT

  • Increased use of herbicides (glyphosate to kill cover crop and possibly perennial weeds).
  • 2008 fuel and steel price increases almost doubled the cost of a Zone Builder (now approximately $9,100 for a 2-row machine). However, medium and large farms will recover this investment in just 1 or 2 years with the savings listed above.
  • Nelson‘s “chopped-down,” 2-row machine required some modifications that have been incorporated into newer machines before delivery. Machines are also available in 4-row or even larger models.
  • May require special equipment to side-dress crops or to use liquid N sources.
  • Neighboring farmers may refer to DZT as “ugly farming” because newly prepared and planted fields don‘t look as neat and tidy as conventional till. By knee-high it is hard to tell a DZT field from any other.
  • There is a small learning curve with coulter adjustments and managing cover crops.

Art of DZT (What has Nelson learned?)

Nelson found that it took him a while to adjust his comfort zone to DZT. At first he was afraid that plantings in fields with a heavy rye mulch would not germinate properly unless he made two passes over the seedbeds. Over time, he has come to realize that one pass is all that is ever needed, and that planting with DZT is a much more dependable way to achieve great plant stands than with conventional tillage.

Nelson recommends that you get off your tractor often to check or adjust your planter. He thinks it is too easy to blame poor plant stands on bad seed or other factors, when most of the time they can be avoided by making sure your planter is working properly.

Nelson also found that part of the art of zone tillage is learning how to manage the cover crop. When cover crops are planted early (August), grow a lot due to a warm fall, or if heavy seed rates are used (4 bushels/A instead of 2), then he has to kill them at a younger stage in the spring.

He also learned the hard way that for most fields, you must kill the cover crop a full three weeks before Zone Building and planting. Glyphosate sometimes works faster than that in the right weather conditions, but you can‘t count on that happening.

Nelson’s Advice to Farmers Interested in DZT

“Don‘t wait any longer to transition to DZT, the system pays off in so many ways that I will never even consider returning to conventional tillage again. Buy from a knowledgeable dealer who will service your machine and help you with initial adjustments. If I hadn‘t used the dealer I did, the transition may have been a lot tougher.

Talk to other growers who are already using DZT before making the plunge and consult state or regional Extension specialists with experience in reduced-tillage for helpful hints. Talking with people who have experience with DZT can make your transition much easier.”

What’s next?

Nelson hopes to eventually pick up a no-till planter for his cover crop and hopes to learn how to use his Zone Builder to prepare the ground before making raised, plastic-mulched beds for his transplanted crops. He also plans to continue to help other growers make the transition to DZT and will be speaking at the 2009 New England Vegetable & Fruit Conference at the Radisson Hotel in Manchester, NH on December 16th.

Deep Zone Tillage Posters 2010

T. Jude Boucher, Agricultural Educator-Commercial Vegetable Crops, UConn Cooperative Extension, Vernon, CT. December 2009. Reprinted from Croptalk v.5.3

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