The Mouldboard Plough (US spelling moldboard plow) is a form of plough consisting of a share (blade) and hitch attached to either a tractor or livestock. The share digs into the earth 14-20+ inches and overturns the soil, burying organic matter from the previous harvest and bringing fresh but organically starved soil to the surface. It was originally designed for "sod busting": the reclaiming of raw land and creation of farmland. However, until the past two decades it was routinely used even on previously tilled land, in the Midwest of the United States and elsewhere. Awareness of the potential for soil damage has led to reduced use in favour of shallower ploughing and other less invasive tillage techniques.

The Moldboard Plow was first developed in the 9th century in Northern Europe. It was heavier than previous plows so it could get into deeper soil

Use

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In modern use, the mouldboard was used for three reasons. First and foremost was the control of weeds. In this function, mouldboard ploughing is very successful, a farmer can control weed growth with far fewer herbicides by using this technique than is otherwise possible with any other method, aside from hand weeding, which is labor-intensive and not practical for large operations. The second use was to break up the soil for planting. The third reason for mouldboard ploughing was to warm the soil for planting. Only the first reason for mouldboard ploughing really paid off. Most plants require little soil agitation to germinate, so breaking up soil is unnecessary beyond what a planting implement accomplishes on its own. Soil warming is also unnecessary beyond two or three inches below the surface, therefore bringing black fresh soil which heats more quickly and more deeply after the final frost of the year in unneeded.

Problems with Mouldboard Ploughing

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Mouldboard ploughing has become increasingly recognized as a highly destructive farming practice with the possibility of rapidly depleting soil resources. In the short term, however, it can be successful, hence the reason it was practised for such a long time. A field that is mouldboarded once will generally have an extraordinary one time yield as the larvae of pests and seed from weeds are buried too deeply to survive. After the first harvest, however, continued mouldboarding will diminish yields greatly.

The diminishing returns of mouldboard ploughing can be attributed to a number of side effects of the practice. Foremost is the formation of hardpan, or the calcification of the sub layer of soil. In some areas, hardpan could once be found so thick it could not be broken up with a pickaxe. The only effective means of removing hardpan is using a "ripper", or chisel plow, which is pulled through the hardpan by an extremely powerful and costly tractor. Obviously, this layer eventually becomes impenetrable to the roots of plants and restricts growth and yields. This layer also becomes impenetrable to water, leading to flooding and the drowning of crops.

Also, mouldboarding rapidly depletes the organic matter content of soil and promotes erosion; these two problems go hand in hand. As soil is brought to the surface, the root structure of the previous harvest is broken up, and the natural adhesion of soil particles is also lost; though loose soil appears good for plan germination (and it is), this loose soil without cohesion is highly susceptible to erosion, multiplying the rate of erosion by several factors compared to a non-mouldboarded plot. This increased rate of erosion will not only outpace the rate of soil genesis but also the replacement rate for organics in the soil, thus depleting the soil more rapidly than normal.

Finally, mouldboard ploughing leads to increased soil compaction and loss of pore space within the soil. Soil is a bit like a bucket full of balls filled with sand. Each ball represents a cohesive particle of soil, and when stacked the balls leave a great deal of air space, required for healthy root growth and proper drainage. Mouldboarding so disturbs the soil that it breaks these balls and releases their contents. When this happens, the much smaller particles that are within the larger particles are released and pore space diminishes, leading to hard compacted soil that floods easily and restricts root growth.