Understanding Tillage: Why a clean field leads to dirty water

Written by Mark Ludwig

Of the many topics in agriculture today, tillage of the soil is both a source of controversy and confusion for farmers and other citizens. Tillage is the disturbance of the soil in an effort to achieve certain goals. These include burying crop residues like corn stalks, smoothing soil to make planting seeds easier, incorporating fertilizer or manure, killing weeds, and breaking up compacted layers that can limit root growth.

Primary Tillage of the Past: The Moldboard Plow
In the past, the moldboard plow was a common tool for primary tillage. This tool completely inverts about eight inches of soil, totally burying crop residue. Burying residue was considered essential in the past because it was difficult to plant seeds through residue using older machines. The moldboard plow fell out of favor because bare soil erodes very readily, and other soil quality factors like organic matter content decrease with use of the plow.

The Disk or Disk Harrow: A replacement?

Edward Faulkner’s 1943 book, Plowman’s Folly, is an early work critical of the moldboard plow and remains one of the most iconic books on soil management to come from the Dust Bowl era. Faulkner suggested using the disk (sometimes called a disk harrow), which stirs the soil shallowly while cutting up residues. Today, the disk remains a common tool on farms. The moldboard plow, however, was largely displaced by the chisel plow, a tool that still mixes the soil but does not bury as much crop residue.

The Chisel Plow Takes Over

Chisel plows can be fitted with different kinds of shovels that vary in the amount of residue they bury and the roughness of the field after tillage. Rough fields are generally less susceptible to erosion, especially if the furrows that result are perpendicular to the slope of the field. Though the chisel plow was an improvement, it still buries most of the crop residue in a field.

Surface Residue Builds the Soil

Surface residue is desirable as a source of nutrients for soil biology and growing plants, plus it covers the soil. This cover reduces the impacts of rain drops that detach soil particles and start the process of erosion. The energy of raindrop impacts loosens much more soil than water simply flowing over the land, so the more cover a soil has, the less likely that soil is to erode. Residue cover is critical for preventing soil loss during months when there is no growing crop to intercept raindrop energy. For this reason, any type of tillage that buries substantial residue in the fall is very likely to lead to soil loss.

Emerging Conservation Tillage Tools

Though the chisel plow is still a mainstay of soil management on many farms, new tools have emerged that leave more residue in place. These tools are referred to as “conservation tillage” tools. In general, they disturb only a few inches of soil and leave a good cover of residue on the surface. When combined with tools called sub soilers that provide deep fracturing of the soil without inverting the soil profile, many of the benefits of chisel plowing can be achieved while preserving good residue cover.

Vertical Tillage Tools

An emerging class of tools called vertical tillage, aggressively chop residues to make them more manageable while leaving them in place near the surface. Many resemble disk harrows, but the disks are sharper and not as aggressive when stirring the soil. These tools are expensive and require high horsepower tractors since they are pulled quickly through the field, so adoption by smaller farms may be difficult.

The Best of Conservation Tillage: No-till Farming

Some farmers have eliminated tillage all together. Called no-till farming, these producers rely on herbicides to control weeds and planting tools capable of planting through heavy crop residues. Not only do these farms experience much less erosion, they frequently build a more resilient soil over time as organic matter builds up. When a soil is tilled, air rushes into the root zone and oxidizes (burns) some of the organic matter that is present. Unless measures are taken to balance these losses, organic matter content tends to decline over time.

Wonderful Organic Matter and Benefits of No-till

Organic matter is a wonderful material; it makes soils more productive and increasing the soils capacity to hold water and nutrients. Populations of soil micro organisms and earth worms substantially increase under no-till and conservation tillage systems. These creatures help process residues, cycle critical plant nutrients and excrete natural glues that help soils hold together during rain events. Some specialized fungi even assist plant roots in extracting water and nutrients from the soil. When the soil is undisturbed, these fungi form large networks of hyphae (fungal roots) that can quickly colonize crop roots and boost yield. Undisturbed soils also form more pores.

Healthy Soil Requires Pores

Pores are critical for soil health as they allow water to drain through the soil profile and allow some air into the root zone. A healthy soil has a balance of mineral soil, organic matter, water, and air. Tillage temporarily adds more air, but also breaks the pore spaces built by worms and insects. It also shatters micropores that develop over time. Micropores take significant time to develop, especially in soils with substantial clay content (the smallest type of soil particles), but can be broken down with one pass of a tillage tool or compacted away by heavy equipment traversing a wet field.

Transitioning to No-till

No-till takes several seasons to fully develop these pores, build micro organism populations and increase organic matter. This lag time can make for a difficult transition for farmers, as can difficulties setting up equipment and dealing with ruts and other issues typically handled with tillage. Another issue with using no-till is manure application. The nutrients in manure may be lost if it is not injected below the soil surface or incorporated into the soil after spreading, which means disturbing the soil. Neighbors may also be upset if manure is left on the surface as odors are more likely to be noticed. The pores that worms create also can be a problem on land with subsurface drain tile, since the pores can transport liquids directly to the tiles and then to water bodies. All these issues can be managed in a no-till system, but they add more difficulty to an already tough job.

No-till on the Organic Farm

Though organic farms represent a small fraction of producers, many people are interested in how they get their job done. Organic farms are highly reliant on tillage as they cannot use chemical weed control methods. Some kind of tillage is often needed to kill weeds: some of it very shallow like tine weeders or rotary hoes, some deep like the chisel plow. However, there have been some systems developed that rely on growing vigorous cover crops like cereal rye and hairy vetch over the winter, and then rolling the crop with a tool that crimps the stalks to kill the plants. The resulting mulch suppresses weeds and crops can be planted through it.

Many people have a romantic view of the farm. Our visions of what a farm “ought to be” may include gable roofed red barns, cleanly tilled fields, and moldboard plows rolling over a rich, black soil. While these images make nice calendars, they neither reflect the economic realities of making a living on a farm nor what makes a farm’s soil management sound. As you drive around the Macatawa basin and elsewhere in the Midwest, try to appreciate those big farms with “trashy” looking fields. The smooth, cleanly tilled field is an iconic image that ought to be relegated to history.

Further Reading:

Conservation Tillage GuideNo Till Farmer Magazine<>/em
For 40 years No Till Farmer Magazine has been providing farmers real world information on how to get no till farming done. Many of their articles can be found online at www.no-tillfarmer.com

Plowman's FollyPlowman’s Folly, Edward Faulkner, 1943: The breakthrough work that shook the agricultural world by challenging the supremacy of the moldboard plow.

From the introduction,” We have equipped our farmers with a greater tonnage of machinery per man than any other nation. Our agricultural population has proceeded to use that machinery to the end of destroying the soil in less time than any other people has been known to do it in recorded history.”

No Tillage – the Relationship between no tillage, crop residues, plants and soil nutrition. Carlos C.Crovetto Lamarca, 2006: South America has a very high rate of not till adoption, and a lot of the credit for that goes to Sr. Crovetto. This is his second book, written with great passion and a firm grounding in science and practical agronomic practices. Available from the Conservation Technology Information Center, find them on line at www.ctic.purdue.edu.

From the introduction,”I believe that my soil, enriched year after year by the way I tend it, is my wealth and legitimate inheritance for those who follow me.”

The Biological FarmerThe Biological Farmer –A Complete Guide to the Sustainable and Profitable Biological System of Farming. Gary F. Zimmer, 2000: Gary is a leader in the organic and biological farming movement. His theme of “tillage with a purpose” fits well with organic and conservation tillage systems. This book is a comprehensive look at soil management from a biological viewpoint. Find it at www.midwesternbioag.com

From the Introduction, “Biological Farming improves the environment, reduces erosion, reduces disease and insect pressure, alters weed pressure, and it accomplishes this while working in harmony with nature.”

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