Minimum Till Cultivation: What? Don’t Turn over the Garden Soil?
I remember, as a boy, what a big event it was every spring when we all grabbed shovels and “turned over” the soil to prepare the vegetable garden for the coming growing season. There was something really satisfying about digging deeply into the garden soil, burying the weeds, breaking up the clods and smoothing the surface. And, honestly, it is hard to give that thinking up. But current wisdom says that this isn’t the best way to build soil or improve garden production.
The change in thinking started in commercial agriculture as several related problems with 20th century farming practices became evident:
- Reliance on synthetic fertilizers, rather than following nature’s practice of regularly adding organic matter to the soil, was actually depleting soil health
- The loss of organic matter, and addition of chemical fertilizers reduced pathogen-controlling soil organisms, forcing dependence on chemical pesticides
- Deep tilling speeded up the reduction of organic matter and soil organisms, released soil-sequestered carbon into the atmosphere and destroyed soil structure by pulverizing it
- Exposing bare soil to the elements during winters and fallow periods caused erosion and nutrient leaching that further depleted soils and polluted streams and natural drainage systems.
This recognition has led to the evolving practice of “minimum tillage cultivation” — a practice that is often referred to as no till. This has come to mean keeping “live” roots in the soil year-round by utilizing cover crops over winter and during fallow periods, using their roots to improve soil structure and in some cases “fix” nitrogen in the soil, while reducing erosion, nutrient loss and related pollution. The green parts of the crops become mulches or soil amendments, to build valuable organic matter levels. Allied with this, instead of tilling soil deeply and turning it over, tilling is minimized. By using different shallow tillage tools and techniques, natural amendments are added to the top few inches of soil by loosening rather than inverting it. Meanwhile, a healthy community of organisms in the top layer carry organic nutrients to and improve the texture and structure of deeper layers.
A Leap of Faith
Really? It’s easy to understand the negative aspects of leaving soils unprotected. Ditto with the alliance between cover cropping and using organic matter as the key soil amendment rather than relying on synthetic chemicals for nutrients and pest control. But abandoning deep tilling is harder to accept. What about compaction? Doesn’t looser soil allow deeper root growth? Apparently not. Many research trials over the past twenty years indicate that the benefits of regularly-added organic matter, roots in the soil, and a healthy population of soil organisms can equal or surpass conventional production levels, while reducing the need for synthetic fertilizers and pesticides.
History and Evolution of No Till
There has been growing recognition of the problems of deep cultivation, chemical additives and fallow fields for 100 years. Certainly the depression era dustbowl provides a vivid example. Unfortunately the growing dependence on these methods, related production increases and corporate influences have trumped concerns about soil depletion and environmental damage. By the late 20th century, experiments with cover cropping and light tilling were showing encouraging results. The main concern of commercial growers had to do with weed control during the germination and early growing stages when competition does the most harm to crop growth. The first solution was the use of glyphosate to kill the cover crop. The dead matter was then left on the soil surface as a mulch to stifle weed growth, using shallow till cultivation tools, like chisel plows, to cut narrow furrows for transplant insertion or seed drill operation.
Happily, in recent years, more organic methods have been developed and proven to be effective. The next advance was to flail mow the above ground portion of the cover crop, chopping it into small pieces and using it as a mulch. A more recent advance is to use a roller crimper on the back of a tractor to kill the cover crop plants while laying the green portion down more or less linearly on top of the soil. This orderly arrangement makes establishing rows for planting between stalks more convenient.
The no-till technique has been and continues to be tested in the US and many countries around the world. The results are very encouraging in terms of maintaining or increasing crop yields while reducing chemical use, pest problems and erosion/pollution issues. There is often a 2 or 3 year ramp up of crop production to reach or surpass prior levels, but the long term success of the practice seems clear. Smaller organic growers and the related agro-ecology movement are the main drivers of the practice. Big farms, with a large investment in the mechanized practices and heavy dependence on chemicals face bigger obstacles to changing. The good news for home gardeners is that there are techniques that are practical and economical to aid our transition.
Minimum Tillage Techniques for Backyard Gardens
As noted, minimum tillage has evolved to encompass the practices of not only minimum disruption of soil structure, but also cover cropping and incorporation of organic matter into the upper soil levels. While the Cooperative Extension focuses mostly on commercial agriculture, there is a wealth of consistent information available from committed organic market gardeners, small plot farmers and supporting organizations. You’ll find detailed information to help you choose and get started with cover cropping in “Cover Crops” The Garden Shed, Sept. 2015 and “Forage Radishes — a hard-working cover crop, The Garden Shed, Aug. 2017.
It makes sense to start with cover crops because their nature and hardiness affects spring planting requirements:
- Winter kill cover crops germinate and grow in fall and are killed by frost, leaving a mat of dead vegetation that becomes a mulch that protects soil from temperature variation and erosion through winter. Legume crops like field peas fix soil nitrogen prior to dying. Forage radishes, with a strong tap root are good for building soil structure. Oats are another popular choice that provide a nice mat.
- Over-wintering crops will continue to grow until spring planting requires action to deal with their vegetation:
- If the crop is relatively immature and small, it can be incorporated directly into the soil. It should be allowed to decompose for at least 3-4 weeks prior to planting.
- Taller crops should be cut:
- If you want to leave intact stalks on the soil surface as a mulch, as some commercial growers do, a scythe can be used to cut them in an orderly way and lay them out along your eventual planting rows. They will be easy to separate for seeding or transplanting.
The alternative is to mow or weed-whack them, chopping the material up. It can then be used as a mulch, composted or worked into the upper 4-6 inches of the soil and allowed to decompose prior to planting.
Minimum Tilling options:
- If immature cover crop greens are directly incorporated into the soil, let them age for 3-4 weeks and simply smooth the soil surface for planting. Mature compost can also be added to the top 4-6 inches of soil at this time.
- If you cut your cover crop and leave the plant base in the soil, there are a couple of options:
- Chop the roots manually and mix them into the top few inches, smoothing the planting surface and leaving some decomposition time prior to planting.
- Or, for a less invasive practice, use a stirrup hoe to cut the roots an inch or so below the soil surface, collecting and composting the cut residue. The surface can then be smoothed and planted.
Aerating and reducing compaction:
Even faithfully following minimum till methods doesn’t completely avoid soil compaction over time, especially if equipment is driven over the garden. A good method for loosening naturally-maintained soils with minimum disruption to soil structure, at least in small gardens, is with a broadfork. Insert the fork into the soil as deeply as possible and gently rock it back and forth. Do this every few inches in the garden to loosen and aerate the garden soil while leaving structure relatively intact.
Feed the Soil Not the Plants
Once the planting surface is prepared, whichever tilling practice is followed, be as organic as possible during the growing season. Use organic matter and organic fertilizers to amend your soil, feed soil organisms and minimize your need for synthetic additives and pesticides. Mulch around plants and between rows to protect soil during the growing season and add organic matter as it breaks down. Rotate crops and interplant to encourage bio-diversity.
Practices are Evolving but the Principle is Clear
Exposing bare soil to the elements for long periods, deep tilling, reliance on chemicals to feed plants and kill pests is not the best long term approach to maintaining productive soils. Protecting the soil surface, maintaining soil structure, regularly adding organic matter and building a diverse population of soil organisms to release nutrients to plants is a more natural and superior long term approach.
Specific techniques and available equipment used to achieve this conversion will undoubtedly continue to develop and improve. But the concepts are pretty simple and are within the capability of most gardeners. Let’s join the movement and be part of the solution, rather than the problem.
Teaming with Microbes, Lowenfels and Lewis (Timber Press, rev.ed. 2010).
“Environmental Horticulture: Guide to Nutrient Management,” Va.Coop.Ext. Pub. No.426-613
“Managing Soil Health: Concepts and Practices,” Pa.State Ext.
“Managing Cover Crops in Conservation Tillage Systems,” Sustainable Agriculture Research&Education, sare.org
“HOW TO: No-Till spring bed prep,” The Urban Farmer, www.youtube.com/