There are a large number of more or less well defined tillage systems for soil preparation and crop establishment. A common approach is to group these according to whether or not they involve ploughing, giving two main groups; ploughed and ploughless tillage. A third main group that is generally recognised is direct drilling, where the seed drill is the only tillage implement used.
Ploughed system (Conventional tillage)
A well-executed ploughing, irrespective of ploughing depth, produces a soil surface that is in principle free of harvest residues, due to the inverted furrows left by the plough. Disc cultivators also have a certain inverting action on the soil, but all implements apart from the plough work mainly by mixing the tilled soil. This gives the ploughed system a number of unique advantages. Ploughing works well on most soil types and in most climates, although the greatest advantages are observed in wetter conditions and on lighter soils that require loosening.
Ploughed systems cope better with a poor crop rotation than ploughless systems, although a good rotation brings major advantages even when the plough is used.
Ploughless system (Reduced tillage)
Ploughless systems are commonly categorised according to tillage depth into either shallow or deep tillage. In general, ploughless systems have a higher capacity than ploughed systems and are more common on large farms, where time is a limiting factor. Ploughless tillage places great demands on the crop rotation in dealing with straw-borne diseases and volunteer seeds. The timing of tillage is also more critical in ploughless systems.
Ploughless tillage works well for most soils and climates, although the greatest advantages are achieved on heavier soils and in drier conditions.
As the name indicates, direct drilling refers to systems where the first and only soil tillage operation is performed by the seed drill. Direct drilling systems are usually sub-divided according to the soil cultivating action of the seed drill. Seed drills that cultivate most of the soil surface actually have more characteristics in common with ploughless or reduced tillage than with systems in which more specialised seed drills are used.
Pure direct drilling (No-till) systems often use special seed drills that concentrate on placing the seed with minimal soil disruption. Direct drilling is most competitive in dry areas.
Most farmers do not use a single tillage system but combine several different systems on the farm or at field level in the crop rotation. The advantage of this is that tillage can be more freely adjusted to a particular season, crop and field. The disadvantage is of course the need for a larger number of machines and thus higher fixed costs. However, technological development has resulted in the creation of machines that can operate effectively in different systems, making it easier to combine e.g. ploughing and reduced tillage.