The following excerpt is adapted from Bryan O’Hara’s new book No-Till Intensive Vegetable Culture: Pesticide-Free Methods for Restoring Soil and Growing Nutrient-Rich, High-Yielding Crops (Chelsea Green Publishing, February 2020) and is reprinted with permission from the publisher.
Converting the vegetation of an area of land from the more natural conditions of perennial plant coverage to that of selected annual crops is often a necessary part of starting a new vegetable farm or garden, or expanding an existing one. This process, and the continuing work of maintaining production areas from year to year, has often employed extensive tillage in order to fit the land into a state that is acceptable for seeding and planting. Tillage has become both excessively utilized and extreme in its damage to soil functions, especially with the development of more powerful equipment. Many growers are now seeking to limit this damage by being much more careful and judicious in their use of tillage equipment. This is often referred to as reduced tillage. When systems are developed that require essentially no disturbance of the soil, no-till has been achieved.
In terms of soil health, it is best to reduce tillage as much as possible, but conditions may dictate the need for occasional tillage, as in the case of initial conversion of an area to vegetable growing, or to incorporate soil amendments thoroughly into severely depleted soils, or to control particularly noxious perennial weeds. For purposes of my book No-Till Intensive Vegetable Culture, no-till means that tillage is not utilized for seedbed preparation. However, soils may still be slightly disturbed at some times, such as when opening a furrow to set transplants in, hoeing to cut weed roots, or harvesting root vegetables.
Pros and Cons of Tillage
Tillage, though inherently detrimental, can also provide some benefits to the vegetable grower. The natural state of agriculturally suitable land is a cover of perennial vegetation such as grasses, shrubs, and trees. Tillage is the traditional method to convert such land to vegetable production. Most vegetables are fast-growing annuals, and annual plants are nature’s response to disturbance.
Thus vegetables, to some degree, are a reasonable plant to cover a tilled soil. Tilling not only quickly converts land out of its natural perennial growth but also creates a surface that is appropriate for seeding or planting. Tillage destroys weeds and mixes fertilizers and organic materials into the soil profile and can break up plow pans and surface crusts. Thus tillage may have beneficial results in terms of air and water movement, soil temperature, and residue decay. The need for many of these improvements, however, may actually arise from inappropriate past tillage events. To some degree tillage may lead to conditions where more tillage is needed, a sort of tillage treadmill effect.
For growers to best utilize tillage for potential benefits and avoid perpetuating the need for tillage, they must first identify a clear purpose for tilling and understand the damage that tillage events may cause. This provides the best chance that they will achieve their goal and inflict the least possible damage. Though nature is forgiving, over time repeated disturbance by tillage can wear down a soil’s ability to effectively recover. The deterioration of soil structure leading to soil crusting and subsurface plow pans, increased erosion of soil, destruction of soil life, and the dramatic impact on the soil temperature and imbalance of soil air:water biology and nutrients are just a short list of the detrimental impacts of tillage. The ramifications of these conditions on crop health can be extensive. Weeds respond to the disturbance with rampant growth. Damage and imbalance to the soil biology lead to nutrient imbalances that if unmanaged by growers quickly lead to disease and insect assault as well as poor growth with all manner of production difficulties, leading to lack of profitability. Fortunately, there is a better way.
The transition from tillage systems to reduced tillage and finally to no-till is often gradual. As well, no-till may not be a permanent field condition, and some form of tillage may be reintroduced in order to achieve a specific goal such as eliminating an infestation of aggressive perennial weeds, with an eventual return to no-till when that goal is achieved.
Growers whose systems presently incorporate tillage may need to approach the conversion to reduced and no-tillage carefully, because it may take time to learn the intricacies of a new system. Experimentation with various methods on smaller areas as opposed to going cold turkey with tillage may well be more financially stable.
Below is a brief overview of field conversion methods and choices of tillage equipment, but these techniques and equipment are presented primarily as the means to achieve an eventual no-till system.
Clearing Woody Growth
Clearing existing perennial vegetation is an essential first step in preparing a field for annual vegetable production of any sort. This may be as simple as plowing in a sod, but in many regions, sod is mixed with scrub and tree regrowth. Some growers even face the daunting task of converting forest to cropland. When clearing trees and other woody vegetation, the general formula is chainsaw, remove the firewood, and haul off the tops and brush. Piled brush can be crushed with a tractor after a few years; this process greatly enhances the soil underneath. A heavy-duty mower serves well to reduce any residual vegetation after the clearing. If there is time to spare before the area must be brought into production, it’s beneficial to then seed a cover crop of a perennial nature and mow it for a period of time; this allows stumps to begin to decay. A partially decayed stump pulls out with much less disturbance and more ease than a fresh-cut live stump.
Destumping can be very disturbing to the soil profile, so it is best to approach it as carefully as possible. Backhoes, excavators, tractors and chain, or ax and mattock can be used to remove stumps. Moldboard plowing of root-ridden, stumpy soil is very difficult. In fields with only small stumps, we have had success with not destumping upon clearing. Instead we used a combination of chisel plow and disk harrow to fit the field for vegetable crop seeding for a few years. Over time, the chisel plowing acted to pull out the roots and stumps. Of course there’s the stones and boulders that needed to be removed, too . . .
When land is being converted to field for vegetable production, it is also the opportune time to address any major drainage projects. Before beginning the conversion process, it’s ideal to observe the general water condition of a future growing area over a period of time—the longer the better, because groundwater characteristics can change dramatically over the course of a year. Drainage characteristics of a soil do improve in tandem with the general soil improvement, such as soil aggregation that the grower will facilitate. With careful observations, though, it often becomes obvious that a soil will need additional drainage efforts—for instance, soils in areas with seasonal high water tables. Drainage can be in the form of surface ditches or swales around the field area or subsurface drainage via stone-filled French drains or perforated pipe buried with stone. All drainage channels must discharge outside the field area, of course. When a backhoe or excavator is in the field digging drainage ditches, it is a prime time for a little careful destumping and boulder removal as well, if needed.
Tillage Tools and Techniques
Tillage tools range from plows and harrows down to hand shovels. Some are meant to work the soil very deeply, others to work only the surface. Tools that work the soil below a depth of about 10 inches (25 cm) are often called subsoiling tools. Tools for working the soil from a depth of a few inches to about 10 inches are primary tillage tools. Tools that penetrate the surface only a few inches are the secondary tillage tools. A traditional tillage routine is subsoiling and primary tillage in the fall if necessary, followed by spring secondary tillage. This allows the soil to recover its structure and biology to some degree through the winter months, with only surface disturbance occurring during spring seedbed preparation. Regardless of time of year, tillage is best done when soils are relatively dry; this lessens compaction and soil structure deterioration in comparison with working wet soil. It is often said that when tilling, seeing a little dust flying off the soil surface is a desirable sign. This is especially the case with subsoiling and primary tillage and thus an additional reason to take advantage of any fall dry periods for primary tillage. Spring may not offer any such conditions in a timely manner.