2.2. Equipment Used for Soil Preparation

Tractor - a traction machine that provides mechanical, hydraulic, and/or electrical power to implements to perform a wide range of crop production and handling operations. Tractors are most often used to perform drawbar work (pulling equipment through the field) and PTO (power take-off) (power to rotate equipment components) work. Tractors can be equipped with rubber tires, rubber belts, or steel tracks. A modern farm tractor is almost always equipped with a diesel engine and tractor size is measured by the amount of power that the tractor can produce at the PTO. Tractor sizes range from those with less than 40 PTO horsepower to ones that produce more than 500 horsepower.

Plow - an implement used to perform primary tillage. A number of types of plows are in common use including the moldboard plow, the chisel plow, and the disk plow.

The moldboard plow has a large frame that is equipped with a series of "bottoms," each of which consists of a steel coulter to slice through residue followed closely by a steel share that cuts the soil and an attached moldboard that is used to raise and turn over the cut "slice" of soil.

Disk plows work in a similar manner to laterally displace and invert soil through the use of concave steel disk blades.

Chisel plows use curved shanks to penetrate and "stir" the soil without inverting a soil layer. Chisel plows cause less residue disturbance than moldboard plows and are often used in conservation tillage systems.

Disk Harrows (or Disk) - are implements that uses steel blades to slice through crop residues and soil. Disk blades are mounted in groups or gangs that rotate as they move forward through the soil. Front gangs move soil toward the outside of the disk while rear gangs move soil back toward the center of the disk. A disk can be used for primary or secondary tillage.

Field Cultivator -an implement used to perform secondary tillage operations such as seedbed preparation and weed eradication. Field cultivators are equipped with steel shanks that are typically spring mounted to permit the shank to move within the soil and shatter clods. Field cultivators are constructed similarly to chisel plows, but are more lightly built. Large chisel plows can exceed 50 feet in width in the field. 

3. Primary tillage

Primary tillage is the first soil tillage after the last harvest. It is normally conducted when the soil is wet enough to allow plowing and strong enough to give reasonable levels of traction. This can be immediately after the crop harvest or at the beginning of the next wet season. When there is sufficient power available some soil types are ploughed dry.

 The objectives of primary tillage are:

• to attain a reasonable depth (10-15 cm) of soft soil with varying clod sizes;

• kill weeds by burying or cutting and exposing the roots

• soil aeration and water accumulation; depending on the soil type and the plough the soil will normally be inverted aerating the deep layers and trapping water during a rainfall event

• chop and incorporate crop residues.

The implement most commonly used with an animal powered system is the moldboard plows. In clay soils, the fields often have to be fully saturated before tillage can be undertaken. In lighter texture soils such as loam or sand, tillage can be undertaken at moisture levels below field capacity.

In a 4-wheel tractor system, three-disc, seven-disc and offset ploughs are the most common. Tined plows are preferable in the upland systems but as yet not widely available in Asia.

Primary tillage is the deepest process in the tillage system, aimed to create a physical state within the soil’s regularly cultivated layer to meet crops requirements and to protect the soil.

Attention should be paid to the following:

• Quality expectations: e.g. cloddiness, workability, looseness, inverting or mixing stubble residues in the soil.

• The site features: determining depth of tillage and implements to be used.

• The stubble residues from the previous crop (mass of stalks and roots) and weed infestation; whether or not there is a need for ploughing.

• Soil protection tasks: the best method should be chosen for the given circumstances or any inevitable damage should be minimised.

• The wide range of the available machinery or implements.

The methods and tools of primary tillage. Primary tillage may be shallow, mid-deep and deep, while in terms of implements:

• ploughing,

• ploughless methods as

- shallow loosening with the aid of disk, cultivator or rotavator,

- deeper loosening with the aid of subsoiler or deep ripper implements.

• combined method: in one tillage operation, using plough combined with subsoiler shank, or loosening and ploughing separately.

Frequently encountered defects in primary tillage

Wrongly chosen interventions creating unfavourable conditions – or making them even worse – entailing excessive energy input should be regarded as ‘wrong practice’. Such cases may include excesses or shortcomings in terms of depth and quality of primary tillage.

Primary tillage is too deep if it exceeds the depth required by the condition of the soil, the mode of production or the need for environmental protection, if its depth is not warranted by agronomical considerations or if it entails a waste of energy. The depth and mode of primary tillage can be adapted to the condition of the soil at the time of the intervention. Failure to provide for such adaptation may result in excess energy input without improving the soil condition, just like any primary tillage when it is not necessary

Too shallow primary tillage on compacted top soil is a highly risky intervention from the aspect both of cropping (lower yields) and of environmental protection (water-logging on compacted layer, the whole of the shallow tilled layer being drifted down the slope). In this case the energy saving that may be achieved in comparison to deeper soil condition improving tillage will result in more loss and damage than the benefits of saving on fuel costs. Shallow tillage should also be carefully considered on pest- or weed-infested fields.

Disregarding soil parameters affecting the quality of primary tillage. In addition to the soil natural parameters (clay content, plasticity, stratification, humus content etc.) the quality of tillage is also affected by moisture content and compaction. If compaction has appeared in the top 10-20 cm layer and the implement gently loosens the soil (cultivator) or if work carried out with the aid of the implement is not heavily affected by the compaction of the top soil (disk), the two factors have identical impacts on quality.

The compactness of deeper layers has a stronger impact on clodding caused by loosening than had soil moisture. The higher clay content (heavier soils) has the greater impact on soil compaction.

The quality of deep ploughing is also affected more by compaction than by soil moisture. The unfavourable impacts of compaction are greater in heavier soils.

The quality of tillage using cultivator is affected more strongly by soil moisture content and the compaction of the top soil. In the case of disks – resulting in a stronger disturbance of the cultivated layer – the quality of the operation was similarly affected by the compact layers.

The quality of loosening is affected by soil moisture in light and in heavy soils. The compaction of the top layer was the second most important factor in light and medium heavy soils. In heavy soils compaction of deeper layers was found to be more unfavourable.

Soil moisture does have an important impact on the quality of loosening but this technique is judged more in terms of the loosening effect than in terms of clodding.

Compaction of the top soil layer is the primary factor determining the cloddiness of the soil after ploughing. At the higher content of the clay the impact of soil moisture is also stronger.

Assessments have confirmed the assumption soil’s current condition (moisture, compaction, the depth of compact layers) determines the best possible quality of the soil after primary tillage. Adaptation is an essential prerequisite for optimising quality. The possible quality of the soil after primary tillage and the required energy input can be planned more precisely and any damage to soil structure can be best avoided by taking soil condition into account.