Deep Zone Tillage for Small Organic Farms

Jude Boucher, UConn Extension, Commercial Vegetable Crops

Ever since we launched the deep zone tillage (DZT) educational program in CT, the question I hear most frequently is “How can I DZT on a small organic farm without spending $10,000 on a zone builder and without a 70-hp tractor?”   The biggest hurdle to overcome on an organic farm is not the machinery, but rather trying to figure out how to DZT without herbicides to kill the cover crop and suppress annual weeds throughout the spring and summer. Of course, the best organic growers have worked all or most of the weed seeds out of their soil over time with a combination of summer and winter cover crops, crop rotations, and summer fallow and cultivation, so it may not be as challenging to adopt this technology if you have reached this stage of evolution. But even if you do not have a weed-free seed bank and are determined to try some form of DZT, if you are willing to experiment and fine tune a system, then here are a few ideas I have thought about, seen, or heard about over the years to get you started.

DZT through Turf:   This is my favorite and I have seen it work for pumpkins and winter squash, but it could work for any crop.  Start by sowing your field down to turf grass in the fall, just as you would if you were renovating the lawn around your house.  In the spring, remove the outside tines of a rototiller and prepare 6”-wide strips or seed beds in the lawn at the row spacing you wish to plant at.  Then rip through that prepared strip with a subsoil shank or something that will penetrate at least 15-17” to put a slit through the plow pan.  Re-smooth the soil (i.e. with compost) and simply plant or place transplants into the strip and mow between the rows with a standard lawn mower.  You could also mulch between the plants in the row to eliminate weeding the row or you could flame emerging weeds between the crop plants.  To maximize yields, you would want to find a way to kill the turf for about a foot on each side of the prepared strip to reduce competition for fertilizer and water (living mulches can be very competitive).  They didn’t kill the turf on either side of the row for the pumpkin/winter squash field that I mentioned and still had great results.  At the end of the season, simply fill the strip with compost and seed it back to turf.  For the next crop simply move mid-way between the previously prepared rows and switch crops to complete your crop rotation.  The nice part about this system is your field looks as neat as one of those organic magazine covers.

Substitute tillage radishes for a zone builder:  This idea was mentioned at the RC&D Healthy Soils workshop last fall in E. Windsor.  In the fall, using GPS, plant or drill tillage radishes at the row-spacing you intend to use for planting your cash crop the next spring (i.e. 20”, 30” or 36”).  Then sow oats between the rows of radish.  Both crops will winter kill.  In the spring, again using GPS, plant the cash crop in the same rows that the radish was in and mulch, cultivate or flame between rows to control weeds.  The 15” radish roots completely decompose by the spring leaving holes 2-3 inches in diameter and punching holes through the plow pan 12” down.  You may need to smooth the field in the spring before planting to fill the holes left by the tillage radish roots.  Maybe that’s why you need the GPS – to find the rows – they didn’t mention anything about filling the holes at the workshop!).

Oats for spring crops, harvested winter rye for summer crops: For vegetable crops that must be planted in the spring, use a winter cover crop, such as oats, that will winter kill.  For summer vegetable plantings, leave the rye until it is shedding pollen, then cut, bail and harvest it (or just windrow and create seedbeds between).  Use a subsoiler to break the plow pan at the row spacing you wish to plant at.  Smooth the subsoiled strip to make a seedbed for planting.  Plant or transplant your cash crop in the bed and mulch or flame between rows for weed control.  Remember that organic matter will still accumulate in the soil over time because the roots of the cover crop are undisturbed throughout most of the field.  In other words, by reducing the tillage, you reduce the amount of aeration in the soil and thus less organic matter leaves as CO2.  One VT grower uses a roller-crimper to roll down and mostly kill the mature rye at pollen shed before using DZT.  Unfortunately, the roller-crimper does not kill all the rye (usually kills 70-80%), but this grower has found this system still suitable for competitive crops like pumpkins.

Just improve the root zone  One CT fruit grower has 2-3 acres of vegetables and figures he can’t justify the cost of a zone builder.  He uses conventional tillage to prepare his field (not reduced-tillage), then runs a subsoiler across the field at his desired row spacing.  He then plants or transplants right over the subsoiled path and controls weeds with black plastic or cultivation. Why is this still worth doing?  In 2010, during the severe drought, he tried to keep his plants alive by running a piece of T-tape out of his orchard sprayer to water because he lacked an irrigation system for the vegetables.  With this small amount of water, all the plants in the first 10 feet of each row, where the subsoiler had not yet penetrated through the plow pan, died from dehydration.  However, the plants in the rest of the row survived because the roots were able to grow deeply through the plow pan and utilize the whole soil profile to search for water.  It was a striking example of what subsoiling immediately beneath the crop row can do.  In wet years subsoiling beneath the row obviously helps drain excess water, and you don’t risk re-compacting the soil with field traffic as you would if the subsoiler was used to make random passes over the field before plowing.

Hobby-farmer zone tiller:   Unverferth also sells a small hobby-farmer version of the zone builder for DZT under the name of Frontier.  This miniature version of the larger machine uses shear bolts instead of spring resets so it is not fit for stony or rocky ground.  The hinged-frame on the larger machine allow the subsoiling shank to pop straight up out of the ground when it hits large rocks or ledge and then the spring resets shove the shanks right back down into the soil so that you don’t have to stop when preparing a rocky field.  Obviously, if you brake a shear bolt on the smaller machine you would need to stop and put in a new shear bolt like with a snow blower that jams.  This makes the small machine impractical for most rocky New England fields.  However, if you are lucky enough to have stone-free bottom land, you can still DZT with a small tractor and a much cheaper zone builder.  After Cornell brought the Frontier machine down to a twilight meeting at URI in a mini-van, the research farm manager copied the design and made himself one from mostly spare parts he had lying around on the farm.  Some of you may be as handy as him or you just might want to purchase one.  Then you could DZT small fields with a miniature machine using oats for spring crops and harvested or rolled rye for summer crops, or you could DZT through turf.  I’ll just leave you with this warning: you wouldn’t farm with a garden tractor, so don’t buy a hobby-machine for large fields or rocky fields.  You’ll just end up parking it in frustration.