- Effect of compaction in wheeltracks
- Recognising and limiting compaction damage
- Extent of the problem
- Impact on farming
Orchard and Berry Fruit Soils
The traditional management of orchard soils was clean cultivation in which the orchard soil was cultivated several times a year to keep the surface weed-free. Under such management, soil structural breakdown was common, resulting in reduced water infiltration and impeded aeration. Most crops are now grown with a grassed-down alley and a herbicide strip down the tree row. The soil in the herbicide strip area undergoes natural consolidation and can be denser than that out in the grassed alley. This can sometimes limit infiltration after heavy rainfall and irrigation events. On the other hand, extensive cracking can occur in the herbicide strip area, which can greatly increase infiltration of water. In the grassed alley region, some degree of compaction is inevitable below wheel tracks since tractors, trailers and heavy spray equipment frequently pass up and down. In some situations such compaction can be a problem.
Effect of compaction in wheeltracks
The extent of wheeltrack compaction and whether it is a problem will depend on soil conditions, the frequency and weight of traffic and the type of crop grown.
- Compaction is particularly severe where heavy equipment (e.g. sprayers) drives over the orchard surface when the soil is wet and in a plastic, malleable condition.
- For crops with a fibrous root system that extends only to about the width of the tree canopy (e.g. pipfruit, stonefruit and citrus), this compaction is of little consequence. That is, the tree roots do not normally extend out to the compacted zone to any great extent.
- For crops with shallow, but extensive roots that run laterally into the alley (e.g. kiwifruit and most berry fruit) this is a potential problem. That is, their roots would normally spread into the alley area and grow below wheeltrack areas. Severe compaction below wheeltracks may restrict root growth to the row area. However, in most kiwifruit orchards, root activity is more-or-less evenly distributed below the orchard floor (i.e. in rows and alleys) so compaction is not an important issue.
- The problem of wheeltrack compaction is worsened by over-irrigation. Water can pond in wheeltrack areas and anaerobic conditions can develop in the compacted zone. This further restricts root growth through the zone.
Recognising and limiting compaction damage
Compaction can be identified by digging several holes in the wheeltrack area and examining the soil for compaction. Digging holes on either side of the wheeltrack will identify if roots have grown under the wheeltrack or whether compaction has restricted roots to the row area.
One practical way of minimising compaction effects in wheeltracks where this is a problem is to manage and control irrigation carefully. This is particularly important when vines are young and their water-use is small. Over-irrigation is not only wasteful, but can also maintain the alley area in a wet state thus encouraging compaction to occur in wheeltracks.
Where wheeltrack compaction is a problem, there is probably little that can be done to either prevent or alleviate the problem. Deep ripping along the wheeltracks has sometimes been tried. However, any roots in the vicinity are severed and, following passes of heavy traffic, the soil soon compacts down to its former density or to an even greater density. Careful soil management of the row area where the bulk of the roots are restricted is the practical answer. This is routine practice for berry fruit. Fertilisers and irrigation are carefully managed in the row area and organic mulches are sometimes applied to the soil surface.
Extent of the problem
In most kiwifruit orchards compaction in wheeltracks is of little, if any, consequence and roots grow vigorously in the alley area. In some localities, such as parts of Nelson/Motueka, compaction in wheeltracks has been identified as a factor restricting root growth to the row area. This can result in poor vine performance. Over-irrigation early in the orchard’s life, sometimes in combination with poor initial soil structure, were probably the major causes of the problem. In such cases, careful management of fertiliser and irrigation applications to the row areas is essential to provide optimum conditions for growth and activity of the restricted root system.
Wheeled traffic can be frequent on berry fruit orchards and can often occur under wet conditions (e.g. spraying for fruit rot diseases). As a result, wheeltrack compaction is relatively common and, for cane fruits with laterally spreading roots, it can tend to restrict root activity to the row area. As noted above, the appropriate action is to manage fertiliser and irrigation additions and soil conditions carefully in the row area.
Impact on farming
Susceptible Manawatu soils can also become compacted under orchards, if they are cultivated between rows or if there is frequent wheeled traffic on them when wet. Measured effects include:
- retarded growth rates in young trees and vines due to root damage,
- delays in onset of fruiting, and
- reduced fruit yields.
These effects are more severe in vines such as kiwifruit, with their extensive shallow lateral root networks, than under pip or stone fruits, which have deeper roots, closer to the trunks.
Similar effects have also been noted elsewhere in the country, notably Nelson.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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