Agronomic Principles

soil for planting apple tree

Soil and Water Requirements

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Apples trees can thrive in a wide range of soils, from medium-textured clays to gravelly sands. However, it’s important to note that poor soils will yield poor results. For the best crops, fertile sandy soils and loams are ideal.

Well-drained soils are essential as wet soils can lead to poor aeration and increased crown rot incidence in apple trees. Shallow rooting is common in apples, so wet soils can hinder development, resulting in weak tree anchorage and limited nutrient extraction.

Soils rich in organic matter are typically better structured and promote healthy rooting. In dry soils, especially during the establishment and growth of young orchards, irrigation is necessary. Trickle irrigation and fertigation are increasingly popular methods. Fertigation, in particular, aids early tree growth and accelerates fruit-bearing. Sprinkler irrigation can also be utilized to protect tree buds and fruitlets from frost damage.

A common practice is to sow a grass mulch between tree rows. This, along with clippings, helps increase water holding capacity, infiltration rate, soil aggregation, and nutrient recycling.

Apples prefer slightly acidic to neutral soil with a pH between 5.8 and 7.0. Extreme pH values can result in nutrient tie-up or toxicity, negatively affecting tree and fruit development. It’s crucial to amend acidic soils by incorporating lime before planting.

Rootstock

Choosing the right rootstock is crucial as it determines tree size and nutrient uptake efficiency. Optimum planting density depends on the cultivar, rootstock, and pruning strategy.

There are four general categories of rootstock: vigorous, semi-vigorous, semi-dwarf, and dwarf. The choice of rootstock should match the soil conditions (pH, structure, humidity) and local factors such as frost hardiness, pest and disease resistance, and more.

For apple trees, the dominant rootstocks used are the Malling types (M. and MM. series).

Orchard Systems

Various planting systems are employed for apple orchards. The goal is to produce high-quality, early-yielding crops while ensuring ease of harvesting and management.

Modern systems utilize higher densities compared to older orchards. Normal densities today range from 400 to 2,500 trees per acre, whereas several decades ago, 28 to 41 trees per acre were more common. In fertile soils and favorable sites, growers can even plant up to 4,000 trees per acre and expect high yields.

This increase in density became possible with the introduction of dwarf rootstocks, which enable higher yields in the first decade of production.

Four basic tree shapes are commonly manipulated in orchards: spherical canopies, conical canopies, flat fan shapes, and Y, A, or V shapes.

Spherical shapes were traditionally used in European and North American orchards, allowing the natural shape of the tree to develop. However, conical shapes have become more prevalent because they allow better light penetration, limit the width of the tree’s canopy, and require minimal manipulation.

Flat fan systems are increasingly popular in high-density orchards as they encourage early bearing, increase yield, and simplify harvesting.

V-shaped or angled canopies, typically trained on trellises like the Tatura system, maximize light penetration and yield. They are most effective in producing high yields at maturity and allow efficient cropping of alleyways.

Tree Manipulation

Pruning is essential for newly planted trees and continues during full production. The exact pruning techniques depend on the desired tree shape.

To achieve an optimum leaf to flower/fruit ratio and improve fruit quality and size, pruning and thinning of fruits are necessary. Pruning also ensures that water and nutrients are available to a sufficient number of well-positioned fruits.

Major pruning is typically performed while trees are still dormant in late winter. Summer pruning targets weak-bearing water sprouts and allows light to penetrate dense canopies. Late summer pruning is not recommended as it can delay dormancy and make trees more susceptible to winter damage.

It’s generally better to prune trees in smaller increments rather than performing severe pruning in one session. Severe pruning stimulates vigorous vegetative growth, which diverts nutrients and water away from fruit production, ultimately affecting fruit quality and bud differentiation.

In many years, reducing the crop load is crucial. Allowing too many fruits to remain on the tree reduces fruit size, weakens the tree, and can lead to biennial bearing (fruiting every other year).

Apple trees typically have five to six flowers blooming on each bud. To ensure optimal fruit size and tree health, thinning the crop is necessary, leaving about one fruit for every 3 to 5 buds.

Crop Protection

To achieve top-quality fruit production, effective disease, pest, and weed control measures are vital.

Apple trees are vulnerable to over 50 types of pathogens, including fungi, bacteria, viruses, and nematodes. These diseases can directly damage the fruit, making it unattractive or inedible. Additionally, they can weaken the tree by invading leaves, trunk, and branches. Reduced productivity, increased susceptibility to winter injury, and further pest attacks can result from such damage.

Insects pose another threat to apple trees, with some directly damaging the fruit. Examples include apple maggot, caterpillars (such as leafrollers, fruitworms, and codling moth), plum curculio, and rosy apple aphid. Other insects and mites feed on foliage or branches, weakening trees and inhibiting growth, bloom, and fruit set.

It’s important to ensure that grass or other competing vegetation does not grow within at least 15-20 inches of the tree trunk. Netting is also utilized to protect developing fruit from hail damage.

Harvesting

Fruit should be harvested before it reaches full ripeness but after it has matured. The timing varies depending on the cultivar, and different apple varieties ripen at different times over a three-month period.

As the fruit matures, starch converts to sugar, and the aroma and flavor develop. Sugar content (referred to as ┬░Brix) is often used as an estimate of fruit sweetness, as sugars are the major soluble solids in fruit juice.

Immature fruit has a starchy taste, undeveloped aroma, and a very hard and crisp texture. Mature fruits are firm but not hard.

Determining the best harvest date requires practical experience due to variations in quality parameters each year.

Storage

Proper storage conditions are essential for maintaining long-term fruit quality and shelf life. Harvested fruit should be handled carefully to minimize bruising, cooled rapidly, and stored in controlled atmosphere conditions to prevent further physiological changes.

High relative humidity (90-95%) is necessary to minimize moisture loss. Controlled atmosphere conditions, with lower oxygen and higher carbon dioxide levels, slow down metabolism and reduce fruit breakdown.

Leaving picked fruit in high temperatures for extended periods accelerates deterioration in quality.

Earlier maturing apples (summer and autumn varieties) produce higher levels of ethylene in storage and are more prone to breakdown compared to later maturing cultivars (winter apples). As a result, their storage potential is reduced.

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