Tillage

Primary tillage loosens the soil and mixes in fertilizer or plant material, resulting in soil with a rough texture. Secondary tillage produces finer soil and sometimes shapes the rows, preparing the seed bed. It also provides weed control throughout the growing season during the maturation of the crop plants, unless such weed control is instead achieved with low-till or no-till methods involving herbicides. • The seedbed preparation can be done with harrows (of which there are many types and subtypes), dibbles, hoes, shovels, rotary tillers, subsoilers, ridge- or bed-forming tillers, rollers, or cultivators. • The weed control, to the extent that it is done via tillage, is usually achieved with cultivators or hoes, which disturb the top few centimeters of soil around the crop plants but with minimal disturbance of the crop plants themselves. The tillage kills the weeds via two mechanisms: uprooting them, burying their leaves (cutting off their photosynthesis), or a combination of both. Weed control both prevents the crop plants from being outcompeted by the weeds (for water and sunlight) and prevents the weeds from reaching their seed stage, thus reducing future weed population aggressiveness. ==History==

Tilling was first performed via human labor, sometimes involving slaves. Hoofed animals could also be used to till soil by trampling, in addition to pigs, whose natural instincts are to root the ground regularly if allowed to. The wooden plow was then invented. (It is difficult to pinpoint the exact date of its invention. However, the earliest evidence of plow usage dates back to around 4000 BCE in Mesopotamia (modern-day Iraq) . It could be pulled with human labor, or by mule, ox, elephant, water buffalo, or a similar sturdy animal. Horses are generally unsuitable, though breeds such as the Clydesdale were bred as draft animals. Tilling could at times be very labor-intensive. This aspect is discussed in the 16th-century French agronomic text written by Charles Estienne: The popularity of tillage as an agricultural technique in early modern times had to do with theories about plant biology proposed by European thinkers. In 1731, English writer Jethro Tull published the book "Horse-Hoeing Husbandry: An Essay on the Principles of Vegetation and Tillage," which argued that soil needed to be pulverized into fine powder for plants to make use of it. Tull believed that, since water, air, and heat were clearly not the primary substance of a plant, plants were made of earth, and thus had to consume very small pieces of earth as food. Tull wrote that each subsequent tillage of the soil would increase its fertility, and that it was impossible to till the soil too much. However, scientific observation has shown that the opposite is true; tillage causes soil to lose structural qualities that allow plant roots, water, and nutrients to penetrate it, accelerates soil loss by erosion, and results in soil compaction. The steel plow allowed farming in the American Midwest, where tough prairie grasses and rocks caused trouble. Soon after 1900, the farm tractor was introduced, which made modern large-scale agriculture possible. However, the destruction of the prairie grasses and tillage of the fertile topsoil of the American Midwest caused the Dust Bowl, in which the soil was blown away and stirred up into dust storms that blackened the sky. This prompted re-consideration of tillage techniques, In the mid-1930s Frank and Herbert Petty of Doncaster, Victoria, Australia developed the Petty Plough. This steerable plough could be pulled by either two horses or a tractor and the disc wheels could be steered in unison, or separately allowing the operator to plough the center of rows as well as between and around orchard trees. ==Types==

Primary and secondary tillage Primary tillage is usually conducted after the last harvest, when the soil is wet enough to allow plowing but also allows good traction. Some soil types can be plowed dry. The objective of primary tillage is to attain a reasonable depth of soft soil, incorporate crop residues, kill weeds, and to aerate the soil. Secondary tillage is any subsequent tillage, to incorporate fertilizers, reduce the soil to a finer tilth, level the surface, or control weeds. Reduced tillage Reduced tillage it is often not appropriate to refer to this type of tillage as conventional. Intensive tillage often involves multiple operations with implements such as a mold board, disk, or chisel plow. After this, a finisher with a harrow, rolling basket, and cutter can be used to prepare the seed bed. There are many variations. Conservation tillage Conservation tillage Conservation tillage also benefits farmers by reducing fuel consumption and soil compaction. By reducing the number of times the farmer travels over the field, significant savings in fuel and labor are made. Conservation tillage is used on over 370 million acres, mostly in South America, Oceania and North America. In most years since 1997, conservation tillage was used in US cropland more than intensive or reduced tillage. • No-till – plows, disks, et cetera are not used. Aims for 100% ground cover. • Strip-till – Narrow strips are tilled where seeds will be planted, leaving the soil in between the rows untilled. • Mulch-till - Soil is covered with mulch to conserve heat and moisture. 100% soil disturbance. • Rotational tillage – Tilling the soil every two years or less often (every other year, or every third year, etc.). It is designed to only disrupt the soil in a narrow strip directly below the crop row. In comparison to no-till, which relies on the previous year's plant residue to protect the soil and aids in postponement of the warming of the soil and crop growth in Northern climates, zone tillage produces a strip approximately five inches wide that simultaneously breaks up plow pans, assists in warming the soil and helps to prepare a seedbed. When combined with cover crops, zone tillage helps replace lost organic matter, slows the deterioration of the soil, improves soil drainage, increases soil water and nutrient holding capacity, and allows necessary soil organisms to survive. It has been successfully used on farms in the Midwest and West of the US for over 40 years, and is currently used on more than 36% of the U.S. farmland. Some specific states where zone tillage is currently in practice are Pennsylvania, Connecticut, Minnesota, Indiana, Wisconsin, and Illinois. Its use in the USA's Northern Corn Belt states lacks consistent yield results; however, there is still interest in deep tillage within agriculture. In areas that are not well-drained, deep tillage may be used as an alternative to installing more expensive tile drainage. ==Effects==

tillage. Valencian Museum of Ethnology. Positive Plowing: • Loosens and aerates the top layer of soil or horizon A, which facilitates planting the crop. • Helps mix harvest residue, organic matter (humus), and nutrients evenly into the soil. as the soil absorbs water more slowly than before) • Destroys soil aggregates. ==General comments==

• The type of implement makes the most difference, although other factors can have an effect. • Tilling in absolute darkness (night tillage) might reduce the number of weeds that sprout following the tilling operation by half. Light is necessary to break the dormancy of some weed species' seed, so if fewer seeds are exposed to light during the tilling process, fewer will sprout. This may help reduce the amount of herbicides needed for weed control. • Greater speeds, when using certain tillage implements (disks and chisel plows), lead to more intensive tillage (i.e., less residue is on the soil surface). • Increasing the angle of disks causes residues to be buried more deeply. Increasing their concavity makes them more aggressive. • Chisel plows can have spikes or sweeps. Spikes are more aggressive. • Percentage residue is used to compare tillage systems because the amount of crop residue affects the soil loss due to erosion. ==Alternatives==

Modern agricultural science has greatly reduced the use of tillage. Crops can be grown for several years without any tillage through the use of herbicides to control weeds, crop varieties that tolerate packed soil, and equipment that can plant seeds or fumigate the soil without really digging it up. This practice, called no-till farming, reduces costs and environmental change by reducing soil erosion and diesel fuel usage. ==Site preparation of forest land==

Site preparation is any of the various treatments applied to a site to ready it for seeding or planting. The purpose is to facilitate the regeneration of that site by the chosen method. Site preparation may be designed to achieve, singly or in any combination, improved access by reducing or rearranging slash and ameliorating adverse forest floor, soil, vegetation, or other biotic factors. Site preparation is undertaken to ameliorate one or more constraints that would otherwise be likely to thwart management objectives. A valuable bibliography on the effects of soil temperature and site preparation on subalpine and boreal tree species has been prepared by McKinnon et al. (2002). Site preparation is the work that is done before a forest area is regenerated. Some types of site preparation are burning. Burning Broadcast burning is commonly used to prepare clearcut sites for planting, e.g., in central British Columbia, and in the temperate region of North America generally. Prescribed burning is carried out primarily for slash hazard reduction and to improve site conditions for regeneration; all or some of the following benefits may accrue: :a) Reduction of logging slash, plant competition, and humus prior to direct seeding, planting, scarifying or in anticipation of natural seeding in partially cut stands or in connection with seed-tree systems. :b) Reduction or elimination of unwanted forest cover prior to planting or seeding, or prior to preliminary scarification thereto. :c) Reduction of humus on cold, moist sites to favour regeneration. :d) Reduction or elimination of slash, grass, or brush fuels from strategic areas around forested land to reduce the chances of damage by wildfire. Prescribed burning for preparing sites for direct seeding was tried on a few occasions in Ontario, but none of the burns was hot enough to produce a seedbed that was adequate without supplementary mechanical site preparation. Changes in soil chemical properties associated with burning include significantly increased pH, which Macadam (1987) Deficiencies of copper and iron in the foliage of white spruce on burned clearcuts in central British Columbia might be attributable to elevated pH levels. Even a broadcast slash fire in a clearcut does not give a uniform burn over the whole area. Tarrant (1954), for instance, found only 4% of a 140-ha slash burn had burned severely, 47% had burned lightly, and 49% was unburned. Burning after windrowing obviously accentuates the subsequent heterogeneity. Marked increases in exchangeable calcium also correlated with the amount of slash at least 7 cm in diameter consumed. in the same Sub-boreal Spruce Zone found that although it increased immediately after the burn, phosphorus availability had dropped to below pre-burn levels within 9 months. Nitrogen will be lost from the site by burning, though concentrations in remaining forest floor were found by Macadam (1987) describe experiments to test prescribed burning as a means of seedbed preparation and site amelioration on representative clear-felled Picea/Abies areas. Results showed that, in general, prescribed burning did not reduce organic layers satisfactorily, nor did it increase soil temperature, on the sites tested. Increases in seedling establishment, survival, and growth on the burned sites were probably the result of slight reductions in the depth of the organic layer, minor increases in soil temperature, and marked improvements in the efficiency of the planting crews. Results also suggested that the process of site deterioration has not been reversed by the burning treatments applied. Ameliorative intervention Slash weight (the oven-dry weight of the entire crown and that portion of the stem less than four inches in diameter) and size distribution are major factors influencing the forest fire hazard on harvested sites. Forest managers interested in the application of prescribed burning for hazard reduction and silviculture, were shown a method for quantifying the slash load by Kiil (1968). In west-central Alberta, he felled, measured, and weighed 60 white spruce, graphed (a) slash weight per merchantable unit volume against diameter at breast height (dbh), and (b) weight of fine slash (3) compared with black spruce sheltered (210 cm3), as well as white spruce open (175 cm3) and sheltered (229 cm3) plantations. White spruce open plantations also had smaller volume than white spruce sheltered plantations. For transplant stock, strip plantations had a significantly higher volume (329 cm3) than open plantations (204 cm3). Wang et al. (2000) but the need for more efficacious and versatile equipment was increasingly recognized. By this time, improvements were being made to equipment originally developed by field staff, and field testing of equipment from other sources was increasing. According to J. Hall (1970), for instance, documented this as well as the effect it had on root growth of outplants (Table 30). The mounds warmed up quickest, and at soil depths of 0.5 cm and 10 cm averaged 10 and 7 °C higher, respectively, than in the control. On sunny days, daytime surface temperature maxima on the mound and organic mat reached 25 °C to 60 °C, depending on soil wetness and shading. Mounds reached mean soil temperatures of 10 °C at 10 cm depth 5 days after planting, but the control did not reach that temperature until 58 days after planting. During the first growing season, mounds had 3 times as many days with a mean soil temperature greater than 10 °C than did the control microsites. Draper et al.'s (1985) Tenth-year stem volumes of trees on south-, east-, and west-facing microsites were significantly greater than those of trees on north-facing and untreated microsites. However, planting spot selection was seen to be more important overall than trench orientation. In a Minnesota study, the N–S strips accumulated more snow but snow melted faster than on E–W strips in the first year after felling. Snow-melt was faster on strips near the centre of the strip-felled area than on border strips adjoining the intact stand. The strips, 50 feet (15.24 m) wide, alternating with uncut strips 16 feet (4.88 m) wide, were felled in a Pinus resinosa stand, aged 90 to 100 years. ==See also==