Site preparation for olives and vines

18/07/2007 8:21:09 PM

Phil Barnett

The first step in preparing a site for planting is to conduct a thorough soil survey to identify the soil types present including the subsoils.

A physical examination of the soil profile will identify the depth of topsoil, the depth to the water table, and any potential barriers to healthy root growth.

Soil chemical analysis

Samples of all topsoil and subsoil types present should be sent to APAL for a comprehensive analysis of nutrient levels and balance.

The time before planting is the only chance you will have to improve the condition of the subsoil in particular by deep ripping amendments into the profile. After planting, nutrients can only be applied to the surface and will have limited effect on the lower layers.

An APAL test and recommendations will specify exactly what needs to be applied pre-planting, to set up your orchard or vineyard soils for optimum health and production in the future.

The full program is specific for the soil tested and includes recommendations for:

• Lime dolomite and gypsum
• Solid fertilisers
• Organic matter—compost, mulches, manures, pelleted manures.
• Foliar fertilisers

Proper soil chemical balance will improve soil structure and drainage, provide nutrients at the right rates to your crop, and establish soil conditions for healthy biological activity.

In less than ideal conditions, soil structure and effective topsoil depth can also be improved physically by deep ripping, mounding, or bed forming along the tree/vine row and the use of mulches and other organic matter.

Deep ripping

The site can be ripped well into the subsoil layers to a depth of 60cm or deeper if possible. This should be combined with the lime or gypsum application to increase the effectiveness of the operation. Make several passes along the planting line to a width of 2 to 3 metres. Rip down the slope for best drainage.

The purpose of deep ripping is to create a continuous system of soil pores from the surface to the lower depths to allow water infiltration, gas exchange, and drainage.  Ripping will also reduce soil strength and facilitate root extension. To be successful the soil should crumble and the majority of soil particles in the ripped subsoil should be less than 20mm in size. This can only be achieved if the soil conditions are right at the time of ripping, and the operation is carried out in the correct way:

• The water content of the clay at ripping is critical and should be drier than field capacity but above the wilting point water content. Usually these conditions will be found in late spring or late autumn.
• To gauge the correct moisture content, mould some clay in your hand till you form a ball—then break it open and take a pinch of soil from the centre and then roll this into a thread. If you can't roll a thread, the soil is too dry, if it crumbles before it reaches 3mm in diameter it is ideal, but if it rolls thinner than 3mm it is too wet.
• The soil should break down to a friable mass and crumble up—not just smear or deform.
• The ripping rate must be low—less than 5km/h.
• Avoid tractor wheel or track slip as this will damage the surface soil.
• The job may require several passes at gradually increasing depth to achieve the desired result. It is essential that the ripping process brings the minimum amount of subsoil to the surface because this will reduce the free draining nature of the topsoil.

With a clay subsoil use a ripper with a rake angle 20 degrees from horizontal and wings attached to the tine having a sweep angle of 90 degrees and a width of  0.7 of the working depth. During ripping, check on the effectiveness of the operation by digging a trench behind the ripper and look at the soil profile to see if:

• there is enough lateral fracturing and loosening,
• there is no compaction,
• and the clods are less than 20mm diameter.

After ripping be careful to avoid any re-compaction by keeping all vehicles off the rip lines, including the tractor.  Don’t track roll to level the ground, instead drag a heavy bar over the rip line to smooth it off.

When working use tined implements (at up to 30cm deep) rather than disc ploughs or rotary hoes.

Bed forming

After deep ripping, the topsoil can be formed into beds along the tree rows to maximise its depth and create an area where soil structure can be maintained at an optimum level to ensure the trees or vines have adequate water, aeration, and drainage.

As with ripping, the moisture content of the soil should be right  before starting—a good indicator is when the topsoil can be moulded into a ball which then crumbles readily when pressure is applied.

The top of the ridge should not be higher than 500mm and can be flattened off to prevent water run-off by dragging a piece of pipe along the top. The sides should be gently sloped at less than 45 degrees. Offset discs or a grader can be used for the job but the wheel tracks of heavy equipment should be ripped between passes. The beds should then be protected from machinery traffic and not cultivated in order to avoid compaction and loss of structure. This would have to be considered when planning the orchard to allow sufficient space between beds for machinery.

Organic matter

    Additional organic matter can be applied along the planting lines in the form of  manure, compost or humates.

A general rate for manure is 1 cubic metre spread along 50 metres of planting row 2 to 3 metres wide. Make sure that manures are not too fresh—it is ideal if they have been composted to kill weed seeds and pathogens.

Mulching

Using mulches of various materials can be an advantage because mulching

• reduces losses through evaporation and can therefore lower water use dramatically.
• reduces surface salt accumulation,
• improves surface porosity and water infiltration, so allowing better leaching of salts,
• reduces weed growth,
• protects the soil surface from rain and irrigation impact and so preserves soil structure and prevents crusting,
• reduces soil temperature in summer,
• and promotes soil biological activity.

Some negative aspects to be considered are that mulching can make poorly drained soils excessively wet, and mulched soils take longer to warm up in spring and may delay early spring growth. Materials used will depend on availability and cost but could include:

• Straw—cereal straw in round bales can be spread along the rows mechanically using machines designed for feeding livestock.  Use about 5kg per metre of tree row 2 metres wide.  This should last for up to three years.
• Commercial mulches—eg Jeffries Composted Forest Mulch at recommended rates, a layer of at least 50mm deep.  This material has been composted to eliminate pathogens and weed seeds.
• Living mulches—various varieties of ryegrass are suitable for this purpose especially those that produce early bulk and then set seed early in the spring.

As soon as the grass begins to compete with your trees for water it can be sprayed out leaving a surface cover which can be allowed to regenerate in the following autumn. The roots of the grass will also help to maintain soil structure.

In areas where there is some doubt about the drainage, test holes can be used to assess the suitability of the site for olives. Late winter would be a good time to see soils when the potential for water-logging is greatest.

Dig holes approx 300mm by 300mm and 600mm deep or at least into the lower subsoil layers.

Leave for 24 hours—

• if  water rises in the hole it means the water-table is too high and the soil is unsuitable,
• if the hole is empty, fill completely with water.

Leave for another 24 hours—

• if there is still water in the hole then drainage is poor,
• if the hole is empty fill it completely with water again.

Leave for another 24 hours—

• if the hole is empty for the second time then the drainage is OK and the site should be satisfactory.
• if water rises in the holes or fails to drain after the addition of water, the drainage is unsatisfactory and will affect root growth unless it can be improved.

References : 

Cass A.,Cockroft B. & Tisdall J.M   New Approaches to Orchard Soil Preparation & Management

O’Conner G., Strawhorn J. & Orr K.  Soil Management for Orchards and Vineyards

McLaren R.G. & Cameron K.C.  Soil Science – Sustainable Production and Environmental Protection

Clark J. & Birch P.  Site Selection for Olive Orchards