Establishing the High Density Supported Apple Orchard

Part 1: Site Selection and Preparation

Table of Contents 

1. Foreward
2. Introduction to High Density Apple Orchards
3. Orchard Location
4. Soil Drainage
5. Soil Type and Depth
6. Organic Matter
7. Soil Nutrient Levels and pH
8. Nematodes
9. Irrigation
10. Frost Protection
11. Fertigation

Foreward

There are many different systems and approaches that could be used successfully to establish a new apple orchard. This report summarizes the main process required to establish a High Density Supported Apple Orchard. This document will evolve as new knowledge and experience with these systems is gained in Ontario. Be sure to consult the most recent issue.

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Introduction to High Density Apple Orchards 

The decision to plant a high density supported apple orchard requires a total commitment to this approach. The grower must be prepared to acquire new skills and to do what needs to be done exactly when it needs to be done. With higher density plantings, the impact of a mistake is potentially much greater than with lower density plantings. Add to this the high cost of establishment and one can knowingly say the risks are high. The rewards have the potential to be high in terms of yield and quality of apples. Done properly, a grower should realize a marketable yield from a mature planting of 2000 - 2500 bushels per hectare (800 - 1000 bushels per acre) or more depending on cultivar. Unless these levels of yields are achieved there is probably little advantage to a high density supported system over a well managed, free standing system of lower density.  

There are several variations available in the type of support system that can be used. Recent studies suggest that density of planting (trees/acre), cultivar selected, and grower management is a bigger factor in the success of a new planting than the exact support system used.

High-density apple orchards cost more to establish than lower-density orchards. The cost to establish a high density supported orchard at 600 tress/acre could be over $12,000 per acre. Increased costs for a new high-density apple orchard are justified only if returns are generated early to offset these costs. To pay off higher initial costs rapidly, the new orchard must come into production very quickly. The cultivar selected must produce fruit of adequate market value to quickly recover the cost of establishment. To plant a cultivar on a high density supported system that has minimal market value will be a costly mistake.  

Success in the apple business in the future is going to require long range planning. Conversion to higher density supported systems has to be slow, slow enough that the grower and nurseryman can stay abreast of the latest technology and changes, and slow enough that the costs of conversion do not exceed the grower's ability to finance successfully.

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Orchard Location

Site considerations are crucial; so is the time spent in proper preparation. Every attempt must be made to select a site where dwarfing rootstocks with limited root systems will perform well.  It is important to choose a site for an apple orchard close to the moderating effect of a large body of water. In Ontario, all successful apple areas are in proximity to one of the Great Lakes and benefit from the climate moderation provided by these large deep bodies of water. Because large bodies of water take a long time to change in temperature, temperature extremes are reduced in both the summer and winter. Their cooling effect in the spring delays the onset of bloom, lessening the risk of damage from spring frosts. In the fall their effect reduces the onset of cold temperatures and the damaging effect these can have on unharvested apples and on trees before they completely harden off.  

The topographical elevation of an orchard is important for avoiding spring frosts. A higher elevation relative to the surrounding countryside is desirable because heavier cold air, in the spring, will flow into the lower areas. This makes low areas frost prone resulting in poor tree performance with crop loss and/or damaged fruit. Avoid any obstructions to downward flow of air such as woods, a hedgerow, buildings or even a heavily travelled highway. Woods or hedgerows can be opened to allow airflow by creating 25 m openings every 100 m.  

A gentle slope is most desirable. Steep slopes make orchard activities more difficult and are susceptible to soil erosion. Northern slopes are most desirable because they tend to result in delayed bud development in the spring; however, other factors may be important such as reducing exposure to the prevailing wind.  

Wind is another consideration. Windy sites should be avoided. Strong winds can reduce the growth rate of trees, increase fruit bruising and fruit drop at harvest, reduce bee activity during pollination and make effective spraying more difficult. Windbreaks can help but excessive snow build up, increased shading and slower drying in the orchard resulting in an increase in fruit and leaf diseases, are drawbacks. 

Availability of water for irrigation is another important consideration when selecting a planting location. Dwarfing rootstocks have a limited root volume. Most of the roots that feed are located in the top 30 centimeters of soil profile. The M9 rootstock is much less tolerant of hot dry soils than the MM106 or a standard rootstock. A dependable supply of good quality water for irrigation is needed. The taking of this water must not have any long term implications to the local environment or short term regards concerning interference with other users. You should have an estimate of how much water might be needed. The location of the water supply (horizontal distance and vertical lift) will impact on the cost and design of the irrigation system. A moisture equivalent of 2.5 cm of water per week from rain and/or irrigation is usually adequate to avoid drought stress. A source of water nearby that would be adequate for a growing season may well be necessary to grow dwarfing rootstocks successfully. For more information on irrigation and water requirements consult the publication entitled, "Best Management Practices - Irrigation Management", at an OMAF field office. 

The range of soil and climate conditions that are acceptable for high density orchards is narrower than for lower density orchards. Even if a low density planting grew successfully on a location it may not be a good location for higher density plantings. A thorough knowledge of any previous orchard or other crop problems is a vital first step in assessing the suitability of your chosen site. With the considerable investment in a high density orchard, you must be able to bring the site up to the exacting requirements of a high density orchard, or seek an alternate site.

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Soil Drainage

The removal of excess water from the soil profile is the form of drainage often forgotten by apple growers. Under no conditions should apple trees stand in water for more than one or two days. Root suffocation will occur under such circumstances resulting in tree injury and/or death. For trees to produce well on the dwarfing rootstocks used in high density plantings, the drainage must be nearly perfect. Improving drainage is most effectively done by tiling. Additional drainage from pockets of wet areas may be handled using raised beds after tiling is installed. Usually it is the heavier clay soils that require drainage improvement, but problems have also been encountered in orchards on sandy soils where the water table is high. Wet spots may be effectively drained using irregular patterns. Generally, a systematic drainage pattern is often required and on some sites the distance between tile lines may need to be as close as every tree row. Tile drainage should be installed before planting by a qualified contractor. 

Poor water drainage down through the profile may be a result of the existence of a hard pan or a compacted layer in the sub-soil. This can be readily detected by close observation of inspection holes that are hand dug 1 m deep in different areas of the planting site. A hard layer within 50 - 60 cm of the surface will adversely affect root penetration and water movement. In these situations chisel ploughing or sub-soiling is required to break up these compacted areas. Sub-soiling is most effective when the soil is dry so that it will shatter, usually during August. Do it in the year before planting and do it in both directions if possible.

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 Soil Type and Depth

 There is no exact soil type for best apple production. It would be safe to assume that the soil should be at least 1 m deep with few surface stones or hidden boulders. Successful orchard soils may range from sand to clay types. There are advantages and disadvantages of all soil types. Avoid droughty soils and eroded soils with no distinct horizons between topsoil and subsoil.

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 Organic Matter 

Organic matter (o.m.) is the material left behind after crop residue is broken down by microbial or chemical action. It is important for: improving soil structure, workability, a home for beneficial microbes, improving water holding capacity, improving nutrient supply within the soil. Organic matter determination is available as part of soil analysis upon request. If organic matter is low (less than 2.0 %) it should be improved by ploughing down organic matter such as manure or planting a crop to produce organic matter. Choose a crop that is not a host for nematodes such as those listed below.

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Soil Nutrient Levels and pH

 A soil sample should be taken well in advance of planting so that nutrient and pH adjustments can be made and incorporated before planting. Fertilizer application rates recommended pre-plant should only be determined from a thorough and complete soil analysis. A list of accredited soil testing labs is available at all OMAF Field Offices.For additional reading on soil nutrition, consult Best Management Practices manual - "Nutrient Management". 

To take a soil sample, scrape away the surface 2 cm of soil. Using a soil probe or shovel, collect a sample from 2.5 - 30 cm (1 - 12 inch) depth. In a 4 hectare orchard, a minimum of 15 subsamples should be mixed together and a handful of soil sent to the lab for analysis. Restrict the area sampled to a uniform soil type or condition within the orchard. If several distinctly different soil types, soil textures, drainage conditions, or crop histories, exist in the orchard, they should be sampled separately.

To avoid micronutrient contamination of samples, do not use galvanized tools or containers for sampling.

The pH of a soil is a measure of its acidity. The target pH before establishing a new apple orchard is 6.5 on sandy soil and 6.0 on clay soils. If pH is below that range, lime is required. The type and amount of lime required will be determined on the soil report. Prior to planting is the only time elements such as phosphorus, boron and lime for pH adjustment can efficiently be worked into the soil. Nutrient levels in the topsoil considered to be adequate for orchard establishment are: 

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Nematodes

Whether in a replant situation or planting new ground, a soil diagnostic sample to detect the presence of nematodes (microscopic threadlike worms that live in the water film in the soil) should always be taken the year before planting. Nematodes in the soil feed on plant roots and have the capability of setting root and tree growth back significantly. Often the trees do not recover. Nematodes are of greatest concern in sand and sandy loam soils and may not be a problem on heavier clays. Information on sampling procedures and diagnostic services is available from all OMAF field offices. Instructions for taking and submitting a soil sample for nematode analysis can be found in OMAF Factsheet, "Soil and Root Sampling for Nematode Analysis", Agdex 628. 

In Ontario, the nematode of concern when establishing a new apple orchard is the Root Lesio (Pratylenchus penetrans). If the number of root lesion nematodes are over 1000/kg of soil control is required.

Other nematode species such as Spiral, Stunt, and Pin feed mostly on grass roots and do not significantly affect tree growth. The Dagger nematode can be a problem if viruses are present. Populations over 50/kg of soil deserve consideration. For more details on nematodes and their control consult factsheet, "Nematode Management for Ontario Orchards", Agdex 206/628.

Where required, fumigation should be done the fall before planting. Many growers are now making use of a deep shank fumigator and fumigating only tree planting strips. Your local chemical supplier will have information on the availability of fumigation services. Where nematode populations are moderately high, keeping the site fallow and free from all weeds and grass cover for one growing season with repeated cultivation often drops the nematode levels to below the need for chemical control. If you are fumigating, correct preparation of the soil to break up clods and sods is important to ensure satisfactory dispersion of the nematicide. Soil that is not in fine enough division will allow populations of nematodes to escape control. The result is less than satisfactory control for the money spent.

Because proper site preparation is so important there should be no hurry to plant an orchard on a replant site or any other site. Take the time to properly condition the soil before planting.

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Nematode Suppressing Cover Crops - See discussion in Publication 360, Fruit Production Recommendations. Examples of nematode suppressing cover crops include oilseed radish, certain mustards, specific sorghum x sudan grass hybrids, African marigold, and Canadian Forage Pearl Millet 101.

 Irrigation 

Tree establishment and development early in the life of the orchard is highly dependent on available soil moisture. Different soils vary in their ability to store water. A well structured clay loam soil can store more water available for tree growth than a sandy soil. Soils that have adequate moisture available throughout the growing season are likely to establish better trees, grow more fruit bearing shoots, initiate more and healthier fruit buds and produce larger, better keeping apples.  

Each mature apple tree on fully dwarfing rootstock may require up to 36 litres of water per day in July and August applied with a trickle irrigation system. Irrigation can influence the individual sizes of fruit in the orchard, and have a positive effect on return bloom the following year. Both of these crop characteristics can translate into more bins filled and better dollar return on an annual basis to the grower. 

Timely irrigation which maintains adequate soil moisture will delay the formation of terminal buds towards the end of the season. This allows enough time for new growth to mature and harden off properly for the coming winter. Trees suffering from drought stress will form terminal buds earlier at the expense of extension growth and proper winter hardiness. Under drought stress phytosynthesis becomes the primary function. Water will move from the bark and fruit into the leaves. A tree is out of available moisture long before its leaves wilt. 

Available Soil Moisture

The ideal situation is to have a continual adequate supply available all through the season so growth is not interrupted and the tree is not stressed. A level of 40 - 50% available soil moisture (A.S.M.) is considered adequate for all soil types. With trickle irrigation system the A.S.M. under the emitters is maintained at 85 - 90%. With sprinkler systems the A.S.M. can drop to 50% without affecting yield. This level will be easy to maintain at some times and not at others. In some soil types it will require constant monitoring and careful application.

Monitoring Available Soil Moisture

Available soil moisture can be determined by feel. Fine textured soils (silt and clay loams), which can be cupped in the hand and gently squeezed into a ball that holds together, probably contains up to 50% A.S.M. A ball which is somewhat crumbly, although holds together with pressure, may contain only 30 to 40% A.S.M. or less. 

A device called a tensiometer can also be useful. This instrument measures the "pull" of water out of a sealed tube through a porous ceramic tip planted at a specific depth. A vacuum gauge measures the vacuum created as the soil draws water out of the tube. A chart will compare dial readings to the available soil moisture for each soil type.

Particle Film Technology - The use of particle films like 'Surround^WP Crop Protectant' on young trees can help with both tree establishment and crop volume by relieving tree stress symptoms during the hottest part of the growing season. See Publication 360, Ontario Fruit Production Recommendations for details.

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Frost Protection

By choosing an irrigation system that sprinkles water onto the crop canopy, a grower may be able to control frost in the spring. Frost control can be achieved by continually watering until the threat of freezing injury is over the following morning. As water freezes it liberates heat, even though blossoms may be covered in ice, as long as the ice is kept wet by water, heat is available to protect the blossoms. A system which is set up to apply 4 mm of water per hour is usually sufficient to frost protect apple blossoms down to about -6°C.  

Care must be taken to adequately protect from diseases such as apple scab and fireblight where water is used for frost protection.

  Fertigation

The benefits of fertigation may not justify the extra cost and management required.

The use of trickle irrigation systems to apply prescribed amounts of the macronutrients, nitrogen (N) and potassium (K) is commonly called fertigation. This approach to fertilizing is being cautiously investigated by some growers. For more information on the principles and practises of fertigation consult, "Best Management Practices - Irrigation Management". 

With fertigation, instead of applying the required amount of N as a single banded application around the drip line of each tree or in the herbicide strip, 1/3 of the N requirement per tree is injected as a single dose in early April before the trees leaf out. This is done to stimulate early vegetative growth in the spring. Active root growth starts before any obvious bud development in the tree canopy. Total recommended rates of N and K applied as dry fertilizer can be reduced by about 50% with fertigation. This method of feeding orchard trees should be carefully monitored by leaf analysis. 

Soil acidification occurs rapidly below the emitters where ammonium nitrate is used as the nitrogen source. The remaining 2/3 of the N requirement is applied in equal amounts with subsequent irrigation in May and June, but not thereafter. Termination of N application in June is required to slow vegetative growth and promote hardening off for winter. Calcium nitrate is the preferred N source for fertigation of tree fruits because soil acidification occurs more slowly.  

When applying potassium (K) using fertigation, instead of applying the total requirement per tree as a single banded application in the spring, K is injected in equal amounts with each irrigation in July and August. The delayed application of K relative to N is to enhance fruit colour, winter hardiness, tree growth and disease resistance during the latter half of the growing season. 

Fertigation is not used for:

Phosphorous (P): Ontario orchard soils usually have sufficient levels of phosphorous and apple trees normally do not have any trouble extracting adequate amounts.

Magnesium (Mg) and Calcium (Ca): Where needed, are best applied as soil amendments or as foliar sprays.

Micronutrients (e.g. boron, manganese, iron, zinc): Where needed, are best applied as soil amendments or as foliar sprays.

Each fertigation application should be part of a scheduled irrigation, and is best conducted near the end of each irrigation cycle to avoid leaching of nutrients below the main rooting zone. The lines must be flushed immediately after each fertigation to prevent plugging of the emitters. 

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