16.1: Introduction

... the crying need is for a soil surface similar to that which we find in nature ... [and] the way to attain it is to use an implement that is incapable of burying the trash it encounters; in other words, any implement except the plow.

—E.H. Faulkner, 1943

Although tillage is an ancient practice, the question of which tillage system is most appropriate for any particular field or farm is still difficult to answer. But we know that soil disturbance is generally bad for long-term soil health. Before we discuss different tillage systems, let’s consider why people started tilling ground in the first place. If we know that tillage is damaging to soils, why has it been so widely practiced?

Tillage was first done by farmers who grew small-grain crops, such as wheat, rye and barley, primarily in western Asia (the Fertile Crescent), Europe and northern Africa. The primary reason was to create a fine, clean seedbed, thereby greatly improving germination over broadcasting seed on untilled ground. It also gave the crop a head start against a new flush of weeds and stimulated mineralization of organic nutrients to forms that plants could use. In the early days of agriculture soil was loosened by a simple ard (scratch plow) in several directions. The loosened soil also tended to provide a more favorable rooting environment, facilitating seedling survival and plant growth. Animal traction (oxen, horses, etc.) was generally employed to accomplish this arduous task because the power and energy requirements for tilling entire fields are generally beyond human capabilities.

At the end of the growing season, the entire crop was harvested because the straw also had considerable economic value for animal bedding, roofing thatch, brick making and fuel. Sometimes, fields were burned after crop harvest to remove remaining crop residues and to control pests. Although this cropping system lasted for many centuries, it resulted in excessive erosion, organic matter loss and nutrient depletion, especially in the Mediterranean region, where it caused extensive soil degradation. Eventually deserts spread as the climate became drier.

Jethro Tull And Tillage: A Mixed Legacy And An Important Lesson

Jethro Tull (1674–1741) was an early English agricultural experimentalist whose book The New Horse Hoeing Husbandry: An Essay on the Principles of Tillage and Vegetation was published in 1731. It was the first textbook on the subject and set the standard for soil and crop management for the next century. (It is now available online as part of core historical digital archives; see “Sources” at the end of the chapter). In a way, Tull’s publication was a predecessor to this book, as it discussed manure, rotations, roots, weed control, legumes, tillage, ridges and seeding.

Tull noticed that traditional broadcast sowing methods for cereal crops provided low germination rates and made weed control difficult. He designed a drill with a rotating grooved cylinder (now referred to as a coulter) that directed seeds to a furrow and subsequently covered them to provide good seed-soil contact. Such row seeding also allowed for mechanical cultivation of weeds, hence the title of the book. This was a historically significant invention, as seed drills and planters are now key components of conservation agriculture and building soils. But the concept of growing crops in rows is attributed to the Chinese, who used it as early as the 6th century B.C.E.

Tull believed that intensive tillage was needed not only for good seed-soil contact but also for plant nutrition, which he believed was provided by small soil particles. He grew wheat for 13 consecutive years without adding manure; he basically accomplished this by mining the soil of nutrients that were released from repeated soil pulverization. He therefore promoted intensive tillage, which we now know has long-term negative consequences. Perhaps this was an important lesson for farmers and agronomists: Practices that may appear beneficial in the short term may turn out detrimental over long time periods.

Conversely, ancient agricultural systems in the Americas did not have oxen or horses to perform the arduous tillage work. So, interestingly, in the context of current interests in reduced tillage, Pre-Columbian American farmers did not use full-field tillage for crop production. They instead used mostly direct seeding with planting sticks (Figure 16.1), or manual hoes that created small mounds (“hills”). These practices were well adapted to the staple crops of corn, beans and squash, which have large seeds and require lower plant densities than the cereal crops of the Old World. In temperate or wet regions the hills were elevated to provide a temperature and moisture advantage to the crop. In contrast with the cereal-based systems (wheat, rye, barley, rice) of growing only one crop in a monoculture, these fields often included the intercropping of two or three plant species growing at the same time, like the corn, beans and squash (“Three Sisters”) system in North America. Therefore, early American farmers were early adopters of both no-till and intercropping while the European invaders brought “improved” technologies that damaged the land in the long run (Figure 16.1).

Figure 16.1.Artist rendering of Pre-Columbian American farmers using a planting stick (left) and plowing after the European invasion (right). Painting by Diego Rivera, Palacio Nacional, Mexico City.

Technologies That Have Lessened The Need For Tillage

• herbicides
• new tillage tools that provide targeted decompaction within the crop row
• new planters and transplanters
• new methods for cover crop management

A third ancient tillage system was practiced as part of the rice-growing cultures in southern and eastern Asia. There, paddies were tilled to control weeds and puddle the soil to create a dense layer that limited downward losses of water through the soil. The puddling process occurs when the soil is worked while wet—in the plastic or liquid consistency state (see Chapter 6)—and is specifically aimed at destroying soil aggregates. This system was designed to benefit rice plants, which thrive under flooded conditions, especially relative to competing weeds. There is little soil erosion because paddy rice must be grown either on flat or terraced lands, and runoff is controlled as part of the process of growing the crop. Recent research efforts have focused on less puddling and ponding to conserve soil health and water.

Figure 16.2. Soil erosion dramatically decreases with increasing surface cover. Note: FP = fall plow, FC = fall chisel, NT = no-till; circles = corn, no circles = soybeans. Modified from Manuring (1979).

Full-field tillage systems became more widespread because they are adapted to mechanized agriculture, and over time traditional hill crops like corn and beans became row crops. The moldboard plow was invented by the Chinese 2,500 years ago but was redesigned into a more effective tool in England in the 1700s and improved for American land development by blacksmith John Deere. It provided better weed control by fully turning under crop residues, growing weeds and weed seeds. Its benefits were compelling at first: it allowed for a more stable food supply and also facilitated the breaking of virgin lands. The development of increasingly powerful tractors made tillage an easier task (some say a recreational activity) and resulted in more intensive soil disturbance, ultimately contributing to the degradation of soils. The exposed plowed fields were more susceptible to erosion, higher organic matter decomposition, and reduction in the soil reservoir of nutrients and carbon that are critical to soil health.

Increased tillage and erosion have degraded many agricultural soils to such an extent that people think tillage is required to provide temporary relief from compaction. As aggregates are destroyed, crusting and compaction create a soil “addicted” to tillage. But new technologies have lessened the need for tillage. The development of herbicides reduced the need for soil plowing as a weed control method. Cover crops help to suppress weed growth, as do rotations that alternate annual and perennial crops. And new planters achieve better seed placement, even in a suppressed cover crop, without preparing a seedbed beforehand. Amendments, such as fertilizers and liquid manures, can be directly injected or band-applied. Now there are even vegetable transplanters that provide good soil-root contact in no-till systems. Except perhaps for most organic production systems, in which tillage is often needed because herbicides aren’t used, a crop produced with limited or no tillage can generate better economic returns than one produced with conventional tillage systems.

Table 16.1 Tillage System Benefits and Limitations

Tillage system	Agronomic benefits	Agronomic limitations	Economics and environment
Full-width tillage
Moldboard plow	Allows easy incorporation of fertilizers and amendments Buries surface weed seeds Allows soil to dry out fast Temporarily reduces compaction Leaves soil bare and easy for seeding	Destroys natural aggregation and enhances organic matter loss Commonly leads to surface crusting and accelerated erosion Causes compacted “plow pans” Requires secondary tillage	Highest cost for labor and fuel High energy consumption High equipment wear High off-site impacts for water quality and quantity, and carbon dioxide emissions
Chisel plow	Same as above, but leaves some surface residues Flexible tillage depth and residue retention	Same as above, but less aggressively destroys soil structure; leads to less erosion, less crusting, no plow pans	Lower energy use, costs and environmental impacts than moldboard plowing, but more than restricted tillage practices
Disk harrow	Same as above, but with repeated passes has limited benefits over plowing	Same as above, but restricted pan layer may develop at depth of harrowing	Same as above
Restricted tillage
No-till	Leaves little soil disturbance Requires few trips over field Provides the most surface residue cover and runoff/ erosion protection Higher yields after initial conversion period	Makes it more difficult to incorporate fertilizers and amendments without specialized equipment Requires specialized planters to deal with firm soil and residues Wet soils dry and warm up slowly in spring Can’t alleviate compaction except through cover cropping Steep learning curve for adopters, especially with fine-textured soils Possible yield reductions in early years after conversion	Low energy use Labor savings More economical than full-width tillage systems in long run Carbon capture and nutrient buildup stimulated Promotes soil biological activity Conserves water Low off-site impacts for water quality and quantity, although concerns may exist with higher preferential flow of nutrients and pesticides to tile lines
Strip-till (zone-till)	Same as above Generally good alternative to no-till on compacted and fine-textured soils Allows for deeper fertilizer placement Flexible depth of soil loosening	Same as above, but compaction is alleviated in the seed zone, allowing for better rooting and seed germination	Same as above, but somewhat higher cost and energy use compared to no-till
Ridge-till and bedding	Allows easy incorporation of fertilizers and amendments Provides some weed control as ridges are built Allows seed zone on ridge/bed to dry and warm more quickly Reduces soil saturation after excessive rainfall Fixed travel lanes reduce overall compaction	Is hard to use with sod-type or narrow-row crop in rotation Requires fixed travel lanes and wheel spacing to be adjusted to travel between ridges	Cost and energy use vary depending on intensity level of ridging and bedding Environmental impacts generally between plowing and no-till