The Dirt Issue 40 – Till vs. No Till

Posted on June 24, 2019
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Till? Or No-Till?
SPF’s fervor to protect Skagit County farmlands starts with the soil itself. The remarkable characteristics and high nutritive value of native soils has been well known and celebrated for decades. Interest in preserving and enhancing the soil is a constant preoccupation of both farmers and researchers. As the latter learn and share more and more about the intricacies of various soils, that new knowledge has brought revision and even revolution to soil management.

One such area of concern is tillage. 

First, a bit of background
Tillage is, in the most straightforward definition, the preparation of soil for agriculture. As most of us imagine it, it is that clean, smooth surface that is left after soil is turned and churned to create a fine seedbed. The pristine surface gives seeds a more than fighting chance at germination and, at least temporarily, forestalls competition from weeds. With good seed-to-soil contact, a crop is established and produces a better yield as the loosened soil allows unrestricted root growth. Modern science has shown it also stimulates mineralization of organic nitrogen into forms that are accessible to plants. Sounds good, doesn’t it?

But, something else is happening, something bad. In time, and without mitigation, crops begin to decline or even out-and-out fail. From the first days of agriculture some 10,000 years ago, lands have been cleared for crops and, in all too brief a time, have been depleted of their value as farmland. Some have never been reclaimed.  Figuring out what had happened and how to prevent it continues to be an issue to this day.

One of the problems is tillage.
Tillage of the type we’ve been discussing—full-field tillage—so loosens the soil, and reduces it to small aggregates, that wind and rain easily erode it. This process strips layer after layer of the most fertile soil, the topsoil. According to Building Soils for Better Crops: Sustainable Soil Management, “Most of the properties we associate with topsoil—good nutrient supply, tilth, drainage, aeration, water storage, etc.—are there because topsoil is rich in organic matter and contains a huge diversity of life. A typical agricultural soil has 1% to 6% organic matter. It consists of three distinctly different parts—living organisms, fresh residues, and well-decomposed residues. As soil organic matter decreases, it becomes increasingly difficult to grow plants, because problems with fertility, water availability, compaction, erosion, parasites, diseases, and insects become more common. Ever higher levels of inputs—fertilizers, irrigation water, pesticides and machinery—are required to maintain yields in the face of organic matter depletion.”

This depletion, this soil degradation is, in part, related to tillage practices. When soil is thoroughly turned, its structure is broken down. Fresh residues will decompose too rapidly and as they do they collapse. What will also collapse are the natural channels in the soil, everything from spaces between soil aggregates to earthworm burrows, which allow water and air to infiltrate into the soil, just where roots need them. The soil disturbance caused by full-field tillage disrupts the natural balance between soil components.

Methods of Tillage
These days, depending on the specific characteristics of the soil, types of amendments required, and the crop to be grown, farmers have many choices in the types of tillage to use.

Full-field tillage, where the soil is left bare before planting, is achieved through such implements as a moldboard plow (invented 2,500 years ago by the Chinese, but brought into “modern” form in England in the 1700s), a chisel plow or a disk harrow. The moldboard plow is the most destructive of natural soil structure, but it does have its uses under certain circumstances. Chisel plows and disk harrows are less harmful.  Under full-field tillage, multiple passes are often required to achieve the desired result, although the implement used is usually not the same.

In contrast to full-field tillage is reduced tillage, a term which covers a range from minimal disturbance to no-till. Quoting again from Better Soils for Better Crops, “These systems are based on the idea that tillage can be limited to the area around the plant and does not have to disturb the entire field.” 

In a no-till system, a conservation planter or seed drill is used to loosen the soil in a narrow and shallow band, just the right dimensions for a seedbed. Because that’s the only area disturbed, previous crop residues are left in the field. As they naturally decompose they refresh and build up soil organic matter while greatly reducing erosion. No-till is the obvious opposite to full-field, or conventional, tillage, but there are a number of methods such as zone, strip and ridge tillage that, although clearly in the camp of reduced tillage, are appropriate for certain crop rotations or as transitional methods.

When there’s no choice but full-field tillage
Considering the benefits of maintaining soil in its most healthful, well-structured state, you may wonder why any farmer would still use full-field tillage. In Skagit County the answer to that is compaction.

Many of the soils around here have a high proportion of clays and fine silts. They feature very small, easily compacted particles. Heavy rains over long periods compact such soils and can form a hardpan layer so dense that air and water cannot penetrate it, nor can roots grow into it. Under circumstances like these, full-field tillage to break up such compaction may well be the only solution.

What works best? Well, it depends.
Tillage methods are just one of many decisions a farmer faces when working to enhance soil. What works within one application, or even in one field, may not apply in another. But, in general, reduced tillage is a good thing. Even better is to incorporate cover crops along with the reduced tillage. As long as at least 30% of the soil’s surface is covered with a previous crop’s residue—a definition of conservation tillage—erosion is measurably and effectively reduced and soil organic matter can deliver on its potential.