Soil loosening. Requirements, implements and techniques

ABSTRACT

This review aims to improve the efficiency of soil loosening operations by presenting to the practitioner, in a readily usable form, information on the many factors which influence the success of these operations.

Background information is provided on the soil conditions required to ensure that all the factors influencing effective crop production are met, namely the needs of the crop and mechanisation operations. Crops need appropriate levels of heat, air, water and nutrients, which can be satisfied with air filled pores of the correct diameter, through which the roots can develop. Achieving these conditions requires good soil structure and drainage. Tractor access, support and traction can best be met by strong compact soils, where water drains from the wheelings. To best meet crop and mechanization requirements, a well structured soil condition is needed comprising a network of continuous drainable pores, in a soil that is not too compact.

Compaction resulting from prolonged wetting, high vehicle loads or wheel slip, or a combination of these factors, causes the essential larger drainable pores to disappear first and if very severe the structural aggregates to break down. Loosening in these situations can create larger fissures to replace the lost drainable pores enabling water, air and root movement to be re-established. Loosening will only be beneficial to the crop and to the timeliness of operations if a soil compaction problem actually exists and providing there is good sub-surface drainage. Loosening in the absence of these criteria may make conditions worse and excessive loosening should also be avoided, since this not only wastes energy but is detrimental to the support of equipment and traction.

The results of agronomic experiments assessing soil loosening effects show that positive yield benefits from soil loosening are by no means guaranteed. There have been many situations where the response has been zero and a few where it has been negative. Crop response depends on the severity of the compaction problem, the effectiveness of the loosening operation, the weather pattern in the crop growth period, and the subsequent management practices.

The following guidelines should be considered when contemplating and executing loosening operations:

Check to ensure a real compaction problem exists and its location. If the problem is marginal there is unlikely to be any benefit for loosening, hence only loosen if problem is likely to become rapidly worse. Compaction problems usually taken one of three forms:

Compaction in upper layers - resulting from weak top soils unable to support heavy surface loads.
Pans - discreet layers of dense soil near equipment working depth.
Compaction at depth, often from natural causes such as glacial action.

Subsurface pipe or mole drainage should be adequate.

Check to ensure the desired degree of loosening is being achieved; adjust equipment accordingly.

Loosening to improve drainage has highest priority on heavy soils and to improve rooting depth on lighter soils.

Minimise traffic on loosened soil to avoid rapid recompaction.

The most effective method of identifying problems is to observe the soil and growing crop in the late May to early July period in areas of good and poor crop development. A soil profile pit in these areas will enable soil structure and root development problems to be identified from which, loosening needs and depths can be decided.

The loosening action of the range of soil loosening implements available is reviewed in relation to the ratio of depth of work to width of the implement tip, which is the critical factor governing the effectiveness of the operation. Depth/width ratios of less than five are usually satisfactory, whereas implements with depth/width ratios greater than five tend to form slots or square moles at depth. The attachment of wings or leading shallow tines greatly enhances the ability of an implement to produce effective loosening at greater depths. The correct tine spacing for these operations is specified in relation to the depth of work of the tool. From this review the most suitable equipment to alleviate the various compaction problems is suggested based upon:

• The working depth range needed;
• Degree and extent of loosening required;
• Surface conditions required;
• Power unit available

Details are provided allowing implement working depth and number of tines to be matched to tractor size. Operational methods for achieving the desired result with reduced tractor power are also considered by correct tine positioning and depth in relation to tractor wheel spacing. The sequencing of operations where additional surface tillage is required is critical, since a subsequent operations, following deep loosening, can immediately recompact the subsoil. Wherever possible deeper loosening operations should be carried out as late in the sequence as possible.

To maximize the benefits from a loosening operation, the loosened soil needs careful handling to ensure that:

The surface layers are not excessively loosened so as to inhibit germination and growth particularly on the light soils. Excessive recompaction does not occur as a result of high tractor and equipment loadings. If these objectives can be achieved the benefits will be relatively long lasting.

These risks can be minimized by:

• keeping the degree of loosening and its depth to the minimum required;
• consolidating loosened soil at the time of loosening with crumblers/presses;
• Carefully planning the sequence of operations through to crop establishment, to minimize the traffic;
• Keeping loads and pressures to a minimum when working on the loosened soil;
• Concentrating traffic to local traffic lanes;
• Maintaining an adequate subsurface drainage system.

This review completed in February 1990 has 52 pages in the full article.