A soil that can house a well distributed root system and healthy root zone – physically, chemically and biologically – is determinative to the lifetime of a vineyard and grape quality.
Before vineyards are established, the effective removal of physical and chemical limitations is central to ideal vine and root growth over the long term. Deep soil preparation with the correct implement choice at the right time before establishment is the only stage at which these upliftments/corrections can be effectively applied. Recompaction of the prepared soil before establishment is however unavoidable due to normal soil processes, management practices and cultivation practices in the vineyard. It impedes root distribution throughout the soil profile, as well as the effective supply and distribution of water and oxygen, and thus impairs healthy soil biology and the efficiency of all root functions.
Visual vigour above the soil surface is a direct reflection of the performance of the roots below the soil surface. The maintenance of a healthy root zone and good root distribution is thus imperative (Photo 1).
PHOTO 1. Example of good root distribution.
In this article, the most common compaction problems in vineyards are briefly discussed, namely:
- Plant hole compaction.
- Recompaction due to cultivation after soil preparation.
- Surface compaction/crust formation.
- Tractor wheel compaction.
- Root pruning.
Plant hole compaction
Plant hole compaction (Photo 2) is a serious yet widespread problem in vineyards and is caused by incorrect planting methods and timing. Unfortunately poor planning and contractor teams racing against time are often the main cause of this problem.
In such cases the young vines are planted when the soils are too wet and the smearing action of a spade results in smooth plant hole walls through which roots cannot penetrate. It is compounded by the lever action of a spade to scoop soil out of the plant hole, which leads to compaction of the side walls in the plant hole.
PHOTO 2. Vine roots confined in the plant hole.
Furthermore the young vines are sometimes positioned against the side of the (smeared/compacted) plant hole and tamped down (Photos 3 and 4) instead of placing the vine in the middle of the plant hole on heaped loose soil (the so-called mole-hill method).
The plant holes are then simply filled with soil, while the best practice is rather to use a fork to break in the compacted side walls around the young vine. The result of this incorrect planting technique is that grapevine roots remain confined in the plant holes and are unable to grow out and utilise the soil volume optimally. The growth of such young vines is severely impeded and the vines cannot perform as desired.
To alleviate this compaction problem, a cultivation action must take place between the tractor wheel and vines. The soil should be dry enough to enable loosening of compacted plant hole walls, but not so dry that clods form, and the toe length of the implement should be at least 40 – 60 cm long. A paraplough (Photos 5 and 6) or toe ripper with swing wings on the back is the designated implement choice in this case if the soil properties allow.
PHOTOS 3 and 4. A shallow developed root system which occurred because the roots could not penetrate through the compacted bank, caused by cultivation after soil preparation. Also note that the roots only developed to one side of the vine because the young vine was planted against the wall of the plant hole and not in the middle of the hole.
PHOTO 5. A paraplough in action in the work row. Note that the toes move between the vine row and the tractor wheel. This crawler tractor can only cultivate blocks with rows of 2.5 m and wider (Photo: JNG Earthworks, 2023).
PHOTO 6. A paraplough can easily reach a depth of 60 or 70 cm (Photo: JNG Earthworks, 2023).
Depending on the severity of the compaction and growth of the vines, the action should be performed on both sides of the vine row (Photo 7). If the problem was only identified two or three seasons after establishment, cultivation should only take place on one side of the vine row. The other side of the vine row can then be cultivated in the next season.
The ideal time for this action is probably late summer or early autumn when the soil’s water status is optimal (relatively dry) to obtain the desired breaking-up action. Vineyards have a root flush in the post-harvest period which can be utilised. Fertilisation and irrigation should also be applied after the cultivation action to further stimulate root growth.
PHOTO 7. The paraplough and the result of the cultivation between the vine row and the tractor wheel. Note the large volume of loose soil that can now be colonised by the roots.
Plant hole compaction causes stress conditions for young vines and gives rise to secondary problems which will further impact negatively on the vines. Photos 8, 9 and 10 below compare plant hole compaction at adjacent vines. Chemical and biological soil analyses in the root zones were requested. The analyses did not show any chemical differences between the two samples, but the plant-parasitic nematode analyses differed drastically. At the vigorously growing vine where the roots were not confined, parasitic nematodes only constituted 30% of the population. However at the weak growing vine where roots were confined in the plant hole, 70% of the population was parasitic nematodes and a chemical treatment was subsequently recommended. The secondary negative effects and costs of performing corrections should never be ignored.
PHOTO 8. Two adjacent plant holes with weak growing (left) and vigorously growing (right) vines next to each other (top view).
PHOTO 9. Side view of the weak growing vine on the left, with plant hole compaction and parasitic nematodes comprising 70% of the population.
PHOTO 10. Side view of the vigorously growing vine on the right, with minimal plant hole compaction and good root distribution. Only 30% of the population is parasitic nematodes.
Recompaction due to cultivation after soil preparation
The levelling of soil after soil preparation to ease the planting process, remove rocks, drive in material, or establish a cover crop, is common practice. While no heavy traffic is preferred in the first two years after establishment of the vineyard, such wheel and implement traffic will lead to severe recompaction in the topsoil (Photo 11). These cultivation actions are sometimes unavoidable however, thus the following guidelines can be applied:
- Avoid wheel traffic on the vine row after soil preparation. The vine rows must be clearly marked out to ensure that no wheel traffic occurs across or on the vine row.
- If there is a possibility of traffic on the vine row, loosening with a toe implement to a depth of 50 – 60 cm should take place on the row before planting. For this action, the moisture status of the soil is very important. If the soil is too dry, clods can form (Photo 12), while soil that is too wet can cause a smearing action which can severely restrict root growth.
- Make the plant holes slightly deeper to ensure that the vine roots can grow into the loose soil beneath the compacted layer.
PHOTO 11. Soil that has been rolled with a heavy-drag roller to break up clods after soil preparation. This can lead to severe recompaction and crust formation, and is thus an undesirable action.
PHOTO 12. Clods have broken in the subsoil and roots grow around this area. This is a result of overly dry conditions during soil preparation.
Surface compaction/crust formation
Crust formation is a common yet subtle problem in vineyard soils and can occur due to physical and/or chemical causes. Crust formation is more common on bare soils than on soils with a cover crop, and the intensity thereof can vary depending on the mother material of the soil.
The primary physical cause of this phenomenon is excessive or incorrect cultivation which destroys the soil structure. It results in densification of soil particles, reduced porosity and the formation of a crust on the surface which restricts movement of water and air to the deeper soil layers. Runoff of irrigation water subsequently occurs on the berm, which in turn leads to impaired infiltration to the subsoil.
Soil chemical factors also have a significant impact on the carbon content (organic material) and concentration of soluble salts (especially sodium and magnesium) in the topsoil. A decrease in carbon and increase in the sodium and magnesium concentrations cause dispersion of clay particles, and to such an extent that the soil’s surface structure disintegrates, and clay seals the surface with a layer restricting water and air movement. The effective utilisation of rainfall and irrigation water to supplement the ground water, is thus negatively impacted. Furthermore, gas exchange and the balance of aerobic microbial activity (essential for healthy root growth) are also impeded.
Cultivation to uplift crust formation will improve water infiltration, but it has to be performed at the right rime and with the correct implement. To ensure a long-term benefit, the action has to be supported by chemical additions (gypsum/lime), the establishment of cover crops or laying out a mulch which will ensure that there are no bare areas where crust formation can reoccur. Cover crop practices may vary depending on several factors and the correct practice choice and management are crucial.
Gypsum (CaSO4) can also be applied to inhibit crust formation (Photos 13 and 14). The calcium cations displace sodium and magnesium on the clay particles and help the soil to maintain its structure so that the clay particles don’t disintegrate and crusting of the soil is avoided. The amount of gypsum applied must be determined by a chemical soil analysis. Gypsum and laying a mulch or establishing a cover crop are a good combination to fight crust formation.
PHOTOS 13 and 14. A soil crust is a microscopically fine layer of crust which seals the surface of the soil.
Tractor wheel compaction
Trying to alleviate tractor wheel compaction is a futile exercise because the soil will just recompact again with the first wheel traffic on the loosened soil. The intensity and depth of the compaction can vary greatly and factors like ground water and stone percentage play an important role. Soils with a higher stone percentage are not prone to compaction. Contrary to general belief, sandy soils compact just as easily as soils with a high clay or silt content (Photo 15).
Recompaction occurs varyingly in zones where the most wheel traffic takes place and can stretch between 15 – 50 cm deep. It is a function of the type of implement used.
Tractor wheel traffic is therefore a given. Correct soil preparation and establishment practices allow roots to utilise the soil volume optimally so that tractor wheel traffic does not impact negatively on the vine.
PHOTO 15. Recompaction (30 cm deep) on sandy soil after a single movement of a tractor wheel.
Root pruning
Although root pruning is not necessarily involved in the alleviation of compaction, the two actions are mostly unavoidably linked. The appropriate timing for both actions is therefore of utmost importance. Timing is determined by the groundwater content around autumn so pruning can coincide with root flush. Untimely root pruning is detrimental for shoot growth and can affect yields as the carbohydrate reserves which are stored in the roots can possibly be cut off.
The degree of loss brought about by the action will thus determine whether the roots have to be pruned on both sides of the vine, or only on one side. In most cases, it is recommended to spread out the action over at least two seasons. Wheel traffic in the cultivated rows also has to be limited to a minimum for a season in order to allow the new roots to colonise the loosened soil. This has implications for the management of cover crops and the vineyard’s chemical programme.
Summary
Recompaction is unavoidable over the lifetime of a vineyard due to the mechanised nature of grapevine cultivation. The causes of compaction are not always obvious however, and deep tillage is not always the answer to all problems. It is important to do a thorough investigation into the cause of the problem prior to performing any cultivation. To this end the advice of an expert is required, who can perform and evaluate the following actions:
- Dig holes to determine where the compaction is located and also the intensity thereof.
- Determine where the roots are concentrated and what the effect of the cultivation action will be on the roots.
- Take soil samples to investigate the possibility of chemical and biological problems.
- Plan corrective actions in order to perform these actions at the optimal time and with the correct implements.
- Adapt your management practices to ensure the long-term success of the correction and avoid reoccurence of the problem.
Optimal deep soil preparation and controlled wheel traffic before establishment, the correct approach to making plant holes during establishment, and the establishment and management of cover crops are non-negotiable basic practices which serve as a basis for long-term soil health and vine production. If these actions are performed correctly from the outset, it will significantly contribute to the maintenance of well aerated soil profiles, good water infiltration, healthy soil biology, optimal conditions for root development and satisfactory yields.
Contact Johan de Jager (Vinpro) at johan@vinpro.co.za or Bennie Diedericks (Soilution) at bennie@resalt.co.za if you want to find out more about practical approaches to uplift recompaction and improve root growth, as discussed in this article.
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