Horizontal Movement of Soil

There are some tillage operations that are carried out with the specific intent of moving soil horizontally. These operations are carried out to enhance soil environmental conditions for crop growth, to retain surface water, to shed surface water, or to facilitate subsequent field operations.

Practices such as bedding, ridging, and hilling improve soil environmental conditions for the growth of some crops under some climatic conditions. Raised beds are formed by pushing soil into rows and forming it into ridges or beds in which crops can be planted. This is done to provide a deeper, drier, and warmer seedbed and rooting zone. This practice is carried out for crops such as carrots. A less dramatic form of this practice is called ridge-till and occurs when soil is pushed from the inter-row area of a crop to the row area to create low ridges on which the subsequent crop is planted. Ridge-till can be found in regions such as the Great Lakes Region of North America that are dominated by row crops such as corn and soybeans. Hilling is carried out to ensure that root crops such as potatoes are covered with soil. This practice is carried out during the growing season, once the crop is established.

Although soil is moved horizontally for these practices, it is commonly assumed that any soil that is moved laterally and will simply be moved back over the course of a crop year (i.e., no long-term horizontal soil movement), and, that if there is any long-term horizontal soil movement, it is of little consequence. However, some of these practices can result in considerable horizontal movement. For example, hilling and harvesting of potatoes can cause some soil to move several meters in the direction of tillage, with soil moved much further during tillage downslope than tillage upslope.

Soil is also moved horizontally to smooth out ruts and ridges or fill in rills and small gullies caused by water erosion. These practices are necessary in order to carry out subsequent field operations. Ruts and ridges are created when heavy equipment is operated under wet conditions and during some primary tillage operations (Box 2). They can be smoothed out with an extra pass of tillage using a disk or another heavy tillage implement or a blade. An example of this is when dead furrows (ruts between passes where furrows are thrown in opposing directions) and back furrows (ridges between passes where two furrows are thrown together and overlap) are created by traditional moldboard plowing. The creation of dead furrows and back furrows can be minimized by using a two-way or rollover moldboard plow rather than a traditional one-way moldboard plow. A two-way mold-board plow allows the placement of the dead furrows and back furrows at the edges of a field.

In general, it is desirable to minimize surface roughness caused by tillage, reducing the need for subsequent tillage operations. However, tillage implements can be operated to maximize surface roughness for the purpose of retaining rainfall and maximizing soil moisture. This practice is used in regions where rainfall is deficient during the growing season. The most extreme form of this is achieved by plowing along the slope contour using a moldboard plow, throwing the furrow upslope so that it stands on its edge and creates a small dyke to capture rainfall. When the furrow is thrown downslope, it tends to lie flat with much less capacity for surface water retention. When tillage is carried out up and down the slope, the surface roughness is oriented up- and downslope, encouraging water to flow down-slope. This may be done to intentionally shed excess surface water, but in doing so, it can also lead to serious soil erosion.

Box 2 Tillage operations

Tillage operations used to prepare the seedbed can be divided into two categories: primary and secondary tillage. Primary tillage can include the use of the moldboard plow, chisel plow, or disk plow. It is often the most intensive form of tillage. For example, moldboard plowing inverts the soil over the entire field. Primary tillage marks the end of one cropping season and the beginning of the next and creates a dramatic visible change on the landscape. Subsequent tillage operations used to prepare the seedbed are referred to as secondary tillage. These operations can include the use of tandem or off-set disks, field cultivator, harrows, packers. Operations that disturb the soil during seeding, management, or harvesting the crop are referred to as tertiary tillage.

There are also implements that are designed specifically to increase the retention of rainwater. These implements create small, shallow pits and ridges in the furrows between the rows of a crop. This practice is called furrow dyking. The added benefit of retaining rainfall is that it reduces surface runoff and, therefore, reduces water erosion.

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