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Upper Midwest Tillage Guide

A brief history of tillage and tillage research

Aaron Daigh, North Dakota State University, and Jodi DeJong-Hughes, University of Minnesota Extension

Why do we till soil?

Knowledge of "what produces a good crop" has been passed down, generation to generation, for centuries. Farmers gained this knowledge the long and hard way . . . by experience through trial and error. Before we dig in too deep, it is of benefit to ask the question:

Why do we till the soil?

Most farmers and researchers alike will answer, "to prepare a good seedbed". However, this does not answer the question, nor does it place it in any historical perspective. Instead, it only causes us to rephrase the question:

Why do we want a good seedbed?

Coming up with a clean, short answer is not easy. The following sections and chapters will provide information and results from local research on the various modern tillage implements available and how these implements prepare a good seedbed.

For now, addressing a slightly different question is perhaps more convenient and easier:

What happens if we do not prepare a good seedbed?

The historical answer is competition. Since human's first use of "digging sticks" to grow a crop thousands of years ago, the main objective has been to provide the crop with the best chance to compete against weeds (Photo 1). Disturbing the soil kills the weeds that compete for space, water, sunlight, and nutrients with our seedlings. The disturbed soil also gives the seed a safe place without being eaten by birds and rodents. As the seed sprouts and the plant grows, farmers continue to thin out the competition with cultivation, thus giving the seed the advantage.

Over the centuries, farmers have recognized other benefits of tillage than just weed management. These include the drying and warming of soils during the wet, cool spring months, breakdown of the previous crop’s residue, removing ruts and compaction, and incorporation of broadcasted manures and fertilizers. The invention of herbicides replaced tillage as the primary tool for removing the weedy competition. Therefore, these other benefits have now become what contemporary tillage implements are based on. In the last 150 years, the advancement of science and technology has moved forward our farming practices at an astounding rate, resulting in the need for up-to-date information for producers to stay informed of their management options.

To gain perspective of the current state of modern tillage technologies and the variety of implement options available, let us start with a brief history of tilling the soil.

A global perspective

In ancient times, the difference between a good and a bad crop determined if families had to rely solely on hunting and gathering to survive the upcoming months. Around the world today, many people still rely on handheld or draft animal-pulled implements to give them the best chance for maintaining their health and nutrition and even gain some wealth. In other societies with strong economies and appropriate landscapes, farmers rely on tractor-pulled and automated implements to grow crops on thousands of acres each year. Regardless of where they live or how sophisticated their tools, the primary goal of all farmers has been to produce a plentiful crop by giving each plant a competitive advantage.

Digging sticks and draft-animal-powered agriculture

puddling-rice-soils

Photo: Dr. Jill Motschenbacher

Photo 2. Puddling of rice soils in Los Banos, Philippines.

The methods and strategies for obtaining a plentiful crop differ from farmer to farmer based on their region, soil, and crop of interest. For instance, a soil preparation strategy called “puddling” is vastly popular across the world for rice farmers (Photo 2). This strategy contradicts any strategy used on corn or soybean fields in the Midwestern United States. To puddle the soil, farmers plow and harrow the ground while it is flooded, often with the use of draft animals. The goal of puddling is to destroy soil aggregates so that the ground becomes nearly impervious to water and can be flooded. This is the exact opposite of what is desired for corn and soybean fields in the Midwestern United States. This method would almost certainly cause failed corn and soybean stands. However, rice is a wetland plant and the puddling of soil helps to maintain and conserve water levels. This helps to drown out competing plants and makes it much easier to transplant rice seedlings by hand, giving the rice a competitive advantage.

The Ifugao people in the Philippines have puddled the famous Banaue rice terraces using handheld and then draft-animal-pulled tools for over 2,000 years (Photo 3). The mechanization of rice production in Banaue with large, modern equipment is nearly impossible due to the small size of the terraces and the topography. This is a similar scene across Asia and South America on terraced, steeply sloped landscapes. In other regions, the economy is the primary restriction for agricultural mechanization. However, this is changing for some areas. In Kirinyaga, Kenya, the mechanization of rice production with tractors and combines is on the rise for the Mwea Irrigation Scheme (Photo 4). These efforts and many others around the world are largely made possible through international aid and the generous voluntary contributions of agricultural experts from around the world.

rice-terraces

Photo: Dr. Jill Motschenbacher

Photo 3. Two thousand-year-old rice terraces in Banaue, Philippines.

rice-mechanization

Photo: Dr. Jill Motschenbacher

Photo 4. Puddling of rice soils in Wanguru, Kenya for the Mwea Irrigation Scheme.

tillage-hand-tools

Photo: Dr. Jill Motschenbacher

Photo 5. Tillage using hand tools (digging sticks, hoes, etc.).

Many grain (corn, beans, etc.) and root-crop growers in rural regions of the world rely solely on hoeing the soil by hand using digging sticks (Photo 5). Farmers in the high mountainous regions, such as the Himalayans and Andes, are generally inaccessible for large equipment. Their soils may also be too rocky for tools pulled by draft-animals. Whereas other farmers in sub-regions of Uganda, Sudan, and Ethiopia rely on digging stick and other hand-held tools largely due to severe poverty after years of armed conflict.

Mechanization

Agricultural mechanization and technology has helped to enhance farmers’ productivity, particularly in industrialized countries with large farms that require timely field operations during the fall and spring seasons. Such countries include the United States, Canada, Australia, New Zealand, and South Africa, which all have an average farm size of over 250 acres. The arrival of mechanization in the early 1900s and its progression through the 2000s relieved the food pressures of these countries’ booming populations as they endured a dwindling workforce of field laborers.

farm-statistics

Figure 1. Farm statistics of industrialized and unindustrialized regions as of the year 2000.
Source: Pawlak, J., G. Pellizzi, and M. Fiala. 2002. On the development of agricultural mechanization to ensure a long-term world food supply. Agricultural Engineering International: The CIGR Journal of Scientific Research and Development.

The trends among corn yields, number of tractors, and hours of labor per acres give evidence to the importance of mechanization (Figure 1). In general, mechanization is an important step in agricultural areas that have a dwindling workforce and require timely field operations due to weather constraints. However, many regions are not conducive to mechanization either due to the shape of the landscape, the region’s economy, or tradition. Mechanization is also not always beneficial to a farmer’s bottom line if the region’s seasonal weather shifts are relatively mild and a substantial portion of the population rely directly on labor jobs in the field. In these areas, the use of digging sticks and draft-animal-pulled implements remain the best economic options.

Philosophy and knowledge of soil

In the United States, farmers, engineers, and researchers have played a vital role in shaping the history and progression of tillage implements available today. Tillage tools used here have varied as much or more than most other regions of the world. Although much of the early activities were heavily influenced by Europe, substantial breakthroughs in soil management have been the product of work in the United States.

Pre-1850s

jethro-tull

Hulton Archive / Getty Images

Photo 6. English scientist Jethro Tull.

The European settlers brought over and deployed soil management practices from their western European homes. Until the early 1900s, after World War I, most American scientists continued to look to Europe for new philosophies and knowledge. In these early days, many American scientists traveled to Europe for their advanced education and scientific training. During this time, European scientists attempted to uncover the sole “principle” or the one, single item that plants consumed in order to grow.

In the 1500’s, Bernard Palissy of France proposed that plants took up salts from the earth. Crop residues and animal excrement would then return those salts to the soil for use by the plants to follow. In general, he was somewhat correct, but not all salts are the same nor are all salts beneficial to plants. In the 1600’s, Jan Baptista van Helmont of the Netherlands proposed water as the "principle" item that plants consumed after conducting his famous willow tree experiment. Other scientists proposed that air or even heat was the “principle” item. Later, John Woodward of England as well as many others proposed that the pulverized earth itself (individual soil particles) or the particulate decay of plants was the "principle." In the early 1700s, Jethro Tull of England also proposed that plants consumed the small, pulverized power of the earth (Photo 6). In other words, he thought plants actually took in pieces of the earth such as silts and clays.

Earth. That which nourishes and augments a plant is the true food of it. Every plant is Earth, and the growth and true increase of a plant is the addition of more Earth. . . . Suppose water, air, and heat, could be taken away, would it not remain to be a plant, tho’ a dead one? But suppose the earth of it taken away, what would then become of the plant?
tull-cultivator

Photo 7. Tull cultivator.
Source: inventors.findthebest.com

Mr. Tull had a wide influence on agriculture across the world, since he was the inventor of the cultivator (referred to as a horse hoe in those days) and the seed drill (Photo 7). In his book Horse-Hoeing Husbandry: An Essay on the Principles of Vegetation and Tillage, first printed in 1731, Jethro Tull emphasized a need to pulverize the soil to a fine power so that plants could access the fine pieces of earth that were otherwise bound up in clods of soil.

The first and second plowings with common ploughs scarce deserve the name of tillage; they rather serve to ;prepare the land for tillage. The third, fourth, and every subsequent plowing, may be of more benefit, and less expense, then any of the preceding ones. But the last plowings will be more advantageously performed by way of hoeing. For the finer land is made by tillage, the richer will it become, and the more plants it will maintain.

... I am in no doubt, that any soil (be it rich or poor) can ever be made too fine by tillage.

Through the late 1700s to the mid-1800s, scientists, such as Antoine Lavoisier and J.B. Boussingault of France and Justus von Liebig of Germany, discovered that no single "principle" was the source of the plant's growth; instead many chemicals (nutrients, oxygen, water, and carbon) were responsible and required for plants to grow. However, the soil was still not recognized as a physical media that hosts a tremendous activity of biological life, which is responsible for cycling these nutrients. In the book, Soil: The 1957 Yearbook of Agriculture, the famous Dr. Charles Kellogg** states in his chapter We Seek; We Learn:

The seemingly simple reasonableness of (these) views… swept away all the alchemistic theories of plant growth. … however, was based on the assumption that soils were static, lifeless storage bins filled with pulverized rocks, which held the water and nutrients and which farmers stirred in tillage.

**Dr. Kellogg was a professor of soil science at North Dakota State University and served as Chief of the Bureau of Chemistry and Soils within the Soil Conservation Service (now the National Resource Conservation Service) implementing a vital role in the National Cooperative Soil Survey Program.

1850s to the early 1900s

Since the 1850’s, scientists have made enormous advances in discovering plant nutrient requirements and in laboratory analyses for determining the amount of nutrients within soil, manures, and plant tissues. Although much of the earlier science was done in or with the heavy influence of Europe, American scientists and engineers made huge strides forward with testing management practices with practical field experiments. In the year 1919, Dr. M.C. Sewell at the Kansas Agricultural Experiment Station published Tillage: A Review of the Literature in the Agronomy Journal. The Agronomy Journal is the official journal of the American Society of Agronomy, which to this day remains the nation’s strongest collection of professional agricultural researchers and scientists. Dr. Sewell's article was the journals first publication on soil tillage. In the opening sentences of Sewell's article, he stated:

The prevailing opinions are so conflicting regarding plowing and cultivation that a review of the literature seems desirable

Photo: Dorian Gatchell

Photo 8. Mechanized corn production in 2015.

Back in those days, corn yields exceeding a couple dozen bushels per acre meant you had a good year. In farmers' fields today, producers raise ten times as much grain due to advances in technology, seeds, and varieties.

Dr. Sewell's review included reference to 70 manuscripts, books, experimental station bulletins, and state board of agriculture reports from as far back as the year 1790. These documents reported on a number of field studies across the United States concerning mixed results of whether soil tillage did or did not benefit crop yields and noting the consequences of tillage to the soil. A couple noteworthy references in Dr. Sewell's paper include Dr. D. Lee’s 1849 article, The Philosophy of Tillage, and Dr. H.J. Water's 1888 report, Relation of Tillage to Soil Conservation. Dr. Water's report noted observations concerning the ease of "soil washing" (water erosion in today's terminology) following tillage and the subsequent decline in crop yield. This report, and many more to follow over the next century, began the first concerns about soil and water conservation and the notion that soil lost to erosion is nonrenewable within our lifetimes. In Dr. Lee's article, he concluded:

Crop yields decline over time due to the oxidation and loss of soil organic matter.

Producers were also observing yield declines in their fields after years of continuous tillage and cultivation. Mr. David Rankin (whose farm inventory was valued at $3.2 million in 1908; most of which was in land) wrote a marvelous short book on this farming experiences, titled Modern Agricultural Methods Compared with Primitive Methods by the Life History of a Plain Farmer, first printed in the year 1909. In his recommendations "to raise a good corn crop," he advised others to invert the soil with the moldboard plow, pulverize the soil by harrowing or disking, and then cultivate as soon as possible in the year. He then went on to advise at least weekly cultivations thereafter through the crop season. However, Mr. Rankin immediately followed with this statement:

Then when I raise four, five or more crops, just as the land will stand, I sow my corn field down to clover and timothy, and begin to pasture and feed on the land three to five years, and get good rich soil.

By putting his corn fields to pasture for several years, Mr. Rankin was unknowingly building back soil organic matter and creating soil aggregates.

"Dirty Thirties"

dust-bowl

Photo courtesy of USDA Natural Resources Conservation Service.

Photo 9. Dust bowl.

During the early 1900's, the "dirty thirties" or "dust bowl" emphasized the need for soil conservation and the adoption of reduced tillage strategies (Photo 9). Although the dust storms tended to lessen, soils continued to erode in many regions. New strategies were developed to reduce tillage even more and leave more of the soil protected from wind and water erosion. New research on the physical and biological properties of the soils emerged and the complex nature of soil began to be revealed. The most profound findings have stemmed from our new understanding of the beneficial role soil aggregation and structure has on the soil environment and crop production (Photo 10). These findings sharply contrast with the previous eras when producers and scientists alike believed a fine, pulverized power was essential for a good seedbed. Through modern research, we now know the following benefits emerge from a well-aggregated and structured soil:

Jodi DeJong-Hughes

Photo 10. Photo of a well-structured soil in Minnesota.

All of these benefits are based on building and preserving good soil structure. Tillage breaks apart soil aggregates, damaging the existing soil structure. The deeper and more aggressive the tillage, the less structure the soil will have. In some production systems, such as in rice, this may be actually desirable. However, for nearly all other crops, a well-structured soil is essential for sustainable crop production.

Producers are still faced with the challenge of how to manage crop residues. Since the 1940’s, advances in plant breeding, use of herbicides, and technology has produced high yielding crops that also leave large quantities of crop residues. These advances shifted the use of tillage from a primary means to manage weeds to now a primary means to manage crop residues. Therefore, the question, "Should I till the soil and how deep or aggressive should I till?" remains vital to most producers.

In the following chapters, we aim to present an overview of our current knowledge regarding the benefits, challenges, and options farmer have when reducing their tillage operations. However, before we get to these chapters, the remaining sections briefly detail the history of soil tillage tools in the United States from the Native Americans up to the new implements for reducing soil tillage.

Tillage tools

precision-technology

Photo: Dorian Gatchell

Photo 11. Monitors in tractor cab precisely deliver nutrients, seed and location within the field.

Before European settlement, Native Americans developed an array of handheld digging sticks using their natural resources. Later, settlers and Native Americans began to integrate the use of horse- and oxen-drawn implements made initially from wood and then iron and steel in following decades. Mechanization replaced the use of draft animals and paralleled the development of the oil and gas industry. Today, mechanized implements are becoming "wired up" with sensors, circuits, and screens coupled with hydraulics so producers can monitor progress in real time without leaving the tractor's cab, except for the initial adjustments to the field's current soil moisture conditions (Photo 11).

Native Americans and Colonists

scapula-hoe

Photo: Aaron Daigh, NDSU

Photo 12. Bone hoe used for tilling the ground.

From the beginning, many of the digging sticks used by Native Americans and the early settlers had wooden handles tethered to a strong shovel-like object to work the soil. In the Great Plains, bison shoulder blades were sometimes tethered to the wooden handle (Photo 12). In the Ozarks, a flat, sharp-edged stone and or even a thick mollusk shell was used. Although made primarily for farming, these tools were likely used to make foundations for buildings. In the desert regions of the west, Native Americans would also dig up and remove the soil above the caliche hardpans. This caliche layer (sometimes called petrocalic soil horizon or Kankar) consists of soil particles cemented together by the accumulation of calcium carbonate (also called lime). Native Americans would sometimes use this layer as the foundation and flooring for their buildings.

draft-horse

Photo: USDA Natural Resources Conservation Service

Photo 13. Draft horse-pulled plow.

Most European settlers managed their soils by using the same methods they implemented back in Western Europe. They cleared forests, applied fertilizers and lime to the acidic soils, and plowed, harrowed, and cultivated by hand or draft animal-pulled implements in the colony regions of what are now the eastern United States (Photo 13). These sloped soils began to lose their fertility and eroded in the humid, rain-abundant climate. In the century between the American Revolution and the Civil War, the nation’s youth progressively moved westward to richer Midwestern and Great Plain soils, the prairies, leaving nearly all the northeastern farms to grow back to forest.

wood-plow

Photo: Jodi DeJong-Hughes

Photo 14. Wood plows

The move to the prairies

Farmers broke sod and cultivated the American prairies using horse- and oxen-drawn moldboard plows (Photo 14). They then used the moldboard plows, shovel plows, discs, harrows, and rolling baskets to prepare seedbeds on the rich, black soils. At this time, the moldboard plows had a wooden moldboard with an iron share and coulter. The coulter would vertically slice open the soil in front of the horizontal-cutting iron share. The moldboard would then lift and invert the soil off to the side. David Rankin reminisced on purchasing his first plow around the year 1840 in his book Modern Agricultural Methods Compared with Primitive Methods by the Life History of a Plain Farmer. He stated:

With these plows (wooden moldboards) you had to carry a paddle and clean the plow about every twenty rods. A good team of oxen would plow about an acre each day.
horse-drawn-moldboard-plow

Photo: USDA

Photo 15. Horse-drawn moldboard plow used to till the prairies.

tractor-with-moldboard-plow

Photo: Jodi DeJong-Hughes

Photo 16. Tractor pulling a moldboard plow through the field.

In the 1830s, John Deere fabricated the first steel moldboard plow. The polished steel had the advantage of cutting easier through the soil and the benefit of the soil easily sliding off the moldboard without sticking. This timesaving modification gave way to the end of the walking plows in the United States. Although horse or oxen already drew plows, a plowman needed to walk behind the plow to steer and control the depth of tillage with a set of handles. Horses needed resting regularly throughout the day to maintain strength for timely operation. The easier plowing with the steel implement allowed plowmen to ride on a seat framed onto the plow with adjustable wheels to control a steady plow depth. Even with the added weight of the seat, wheels, and a plowman, the steel moldboard plow could turn two to three acres per day when its wooden predecessor could turn only one acre (Photo 15).

Figure 2. Trends in U.S. agricultural mechanization
Source: United States Department of Agriculture National Agricultural Statistics Service, 2016. https://www.nass.usda.gov/Publications/Trends_in_U.S._Agriculture/Mechanization/

Soon after the invention of the steel plow, farmers and engineers began to build implements with two, three, and sometimes four rows of plows or cultivators to work the soil between plant rows (called gang plows and straddle-row cultivators). The use of the single plow implement (called a Sulky plow) was now starting to diminish. In David Rankin's book, he claims to have been the first to design and build a straddle-row cultivator in 1853. In these days, a single person could cultivate four acres per day by hand with a single shovel and eight acres per day with a single-row cultivator drawn by a horse. By attaching a second row of shovels to the cultivator, the same person could now cultivate both sides of a plant row at the same time, doubling their efficiently to sixteen acres per day. As for the moldboard plow, double-sided steel moldboards (called lister plows or furrow plows among many other names internationally) began to be fabricated more often. These lister plows moved soil to both sides of the plow creating a furrow and ridge. As technology advanced, more rows of plows, shovels, and harrows were added in series to implements as steam-engine tractors and then diesel-powered tractors were invented. By the late 1950s, the average farmer had more tractors than draft animals and could pull several gangs of plows and cultivators in a single pass (Figure 2).

Post "Dirty Thirties"

After the "dirty thirties" or "dust bowl," emphasis was shifted from the moldboard plow method of inverting the soil to the need for soil conservation and the adoption of reduced tillage strategies. The chisel plow replaced the moldboard plow on many fields as the primary tillage pass. Chisel plow fractures and tills the soil while leaving approximately 30 percent cover of the soil surface with the previous crop's residue. Secondary tillage passes stayed relatively the same with discs, harrows, and cultivators with or without rolling baskets. As soils continued to erode in many regions, new strategies were developed to reduce tillage even further and leave more of the soil protected from wind and water erosion.

As modern use of herbicides developed, weeds were more easily controlled. Therefore, soil tillage was no longer the primary means for weed control, but only served to prepare a "good seedbed." Recalling the previous question, "Why do we want a good seedbed?" there was not yet a clean, short answer.

Photo: Jodi DeJong-Hughes

Photo 17. Soybeans grow in a no-till field in western Minnesota.

In the 1970s, no-till practices gained in popularity. By definition, no-till fields receive no primary or secondary tillage operations; the only disturbance to the soil occurs during planting. Engineering innovations of the no-till drill have helped producers obtain good crop stands in the presence of high crop residue quantities. However, no-tilled fields were difficult to manage in wet, clayey soils and in frigid regions. A number of other intermediate tillage implements** have been developed since then. These implements have the option of countless configurations and designs of shanks, coulters, disks and harrows with adjustable depths and pitches. These modern implements provide producers the ability to control the aggressiveness of their primary tillage and how much residue remains on the soil surface.

The following chapter aims to describe some of the more popular of these implements, common tillage depths and number of passes to prepare a seedbed. Discussion on the expectations for crop residues during the following spring months and the benefits to the soil among these various tillage implements is also made. The chapter includes emerging technological advances, environmental factors, as well as how fuel use relates to tillage intensity.

**Many vague categorical terms are used throughout the literature when discussing these new tillage strategies that purposefully leave some portion of the previous crop residue on the soil surface to reduce soil erosion. Terms such as conservation tillage, minimal tillage, reduced tillage, no tillage, etc., are found throughout the internet as well as in textbooks and the scientific literature. Although some government agencies and scientific societies clearly define specific criteria for each of these terms (typically a range of percent soil cover by crop residue), their actual use in any level of literature or personal discussions is inconsistent. Therefore, in the proceeding chapters, we avoid these terms (with the exception of "no-till" in its literal sense of the phrase) and use only the names of the tillage implements themselves in hopes to reduce any confusion.

Credits

Upper Midwest Tillage Guide is a collaboration between University of Minnesota and North Dakota State University

Peer review provided by Richard Wolkowski, Extension Soil Scientist, Emeritus, University of Wisconsin-Madison

2017

Next: Tillage implements

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