Soil Management for Orchards

Damon Boynton and John R. Magness.

Orchard trees grow and produce in one place for 15 to 50 years or more. By the time they are in bearing, they have extensive root systems that extend outward from the trunk and downward several feet if the soil has an open texture and is well drained.

The roots can take up nutrients throughout a long season probably all year in mild climates. The nutrients may be stored in the roots and trunks until they are used in new growth of leaves, stems, and fruits.

The ideal soil for orchard trees is deep, well drained, free of impervious layers that restrict development of the roots, good in water-holding ability, and slightly acid--pH 5.5 to 6.5.

The danger of injury by low temperatures exists in nearly all deciduous orchard regions of the United States, especially in spring during the early growth period. Sites selected for orchards therefore are protected from spring frost as much as possible. They may be to the south and east of large bodies of water or in elevated locations, where air drainage is good. Low areas, in which cold air tends to settle, are avoided.

Often the elevated and sloping sites that are most nearly frost free do not have the deepest and best soil. The problem of preventing soil erosion on them is serious, particularly if the orchard has to be cultivated during the season when heavy rains are likely. Planting the trees on the contour may be a solution.

Good soil-management practices in orchards require that soil fertility is maintained; that water from rain or irrigation penetrates the soil readily and is not lost by runoff; that soil structure is not unduly injured, despite the hauling of heavy equipment through the orchard; and that conditions favor the growth and fruitfulness of the trees from decade to decade.

Practices that give such results vary with the kind of orchard and the part of the country.

THE APPLE is a deep-rooted, long-lived, slow-growing deciduous tree of the Temperate Zone.

The production of its leaf surface, most of its vegetative growth, its flowering, the early development of the crop, and the initiation of buds for the bloom of the following year all take place in about 9 weeks of the spring and early summer.

In the summer and early fall until harvest, the fruit grows, and the leaves continue to make foods, which may be used at once or stored for the spring growth of the next year. The tree increases its resistance to winter cold in the late autumn after harvest.

These facts have a bearing on the systems of soil management in apple orchards.

The main climatic problems in the regions where apples are an important crop are the hazards of frost during the early growing season, the possibility of freezing in winter, and too little rain or too much rain during the growing season.

The location of the orchard determines the degree of frost hazard. The two natural protections against frost hazard are bodies of water large enough to reduce daily variations in temperature and hillsides or valley slopes that permit the coldest air to move to lower elevations. Most apple orchards are on sloping lands.

The hardiest varieties of apples can stand temperatures down to 30 F. below zero in midwinter without injury. The least hardy may show injuries at 20 below zero.

All varieties are more susceptible to winter injury if they bore a heavy crop the preceding season, if their leaf surface was poor, and if late vegetative growth caused the trees to go into winter lacking hardiness.

The prevailing climate in a region determines the hazard of killing winter temperatures. The location of the site offers only a slight degree of protection, except when it is near a large body of water that does not freeze over.

Soil management that fosters a healthy leaf surface and permits hardening of the trees for winter helps to reduce losses from winter injury.

The average rainfall, its distribution during the year, the ability of the soil to hold water, and the intensity of evaporation of water from leaf and soil surfaces determine the probabilities of water deficiency in apple orchards.

In sites where soils are shallow or in areas where the annual rainfall is below 30 inches and where less than 15 inches of rain falls during the growing season and transpiration is relatively rapid, the moisture may be deficient often enough to justify supplementary irrigation. Irrigation is necessary if the yearly rainfall is less than 20 inches, less than 10 inches falls during the growing season, and transpiration is high. Practices to conserve moisture are valuable in places where rainfall is marginal. They may involve special modifications of soil management.

In areas where spring rainfall may be excessive, control of fungus diseases becomes a matter of primary importance at the same time that accumulation of excess water in the soil may make it difficult to move heavy spray equipment through the orchard.

APPLE ORCHARDS grow on many different kinds of soils, which vary in texture from heavy clay to light, sandy loam and in nutrient content from low to high fertility.

The soil-management practices that are best for a particular soil situation depend on the depth of rooting of the trees and the fertility in the zone of rooting.

If the soil in a humid climate is well aerated and of medium texture and permits rooting to a depth of 4 feet or more, it has a large enough reservoir ,for available moisture so that special practices to conserve moisture are unnecessary. They would be needed, however, if rooting is restricted to a zone less than 3 feet deep.

Soil-management practices that promote fertility and supplementary applications of fertilizer likewise are most significant on soils of low fertility. They may give little benefit in places where the initial soil fertility was high.

Anyone who plans to plant an apple orchard should give special attention first to contouring, tile drainage, and orchard roads.

Contour planting may be desirable even though erosion is to be controlled by permanent sod management on hillside locations. It is often the best way to provide orchard roads for sprayers and other equipment.

As there may be a good deal of traffic in apple orchards during the spraying season, the roadways need special protection against gullying.

Although a tile drainage will not change a poor orchard soil into a first-rate one, the use of tile lines to drain out the wet spots often pays big dividends by reducing the difficulties of spraying and other practices during wet weather or in the early spring after a winter of water accumulation.

Special problems of fertility and management arise because apple trees remain in the same positions many years.

Acidifying fungicides and fertilizers that enter the soil mainly under the trees may cause the leaching of replaceable calcium, magnesium, and potassium at a much faster rate and to a greater depth under the trees than between them a reason for magnesium deficiency in apple orchards planted on soils that initially were acid. The resulting loss of fertility has been a major cause of the disappearance of grass cover under the trees in mature apple orchards. Fungicide or insecticide spray materials may accumulate in the soil and harm plants under the trees.

THE SOIL-MANAGEMENT systems that are available for use in apple orchards include systems based on annual tillage or cultivation and systems based on permanent sod. Supplementary practices that may be combined with either or both systems include irrigation, mulching with organic residues or plant materials, fertilization with nitrogen and other inorganic nutrients, liming, and the use of cover crops.

Many variations of the basic systems and their combination with supplementary practices have been used successfully in apple orchards.

During the early life of an apple orchard, cultivation at least in the tree rows during the first half of the growing season is an almost universal practice. In the first 3 to 5 years, when the trees are small, intense competition for nutrients and water can develop between the small tree and the grass and weeds around it.

Cultivation reduces the competition easily and economically. The branches are short enough in the early years to make possible the use of harrows and other tillage tools to eliminate the plants close to the trunks. Since the terminal growth of the young tree is completed by the end of July, cultivation is needed particularly from April until August.

Thereafter it is customary to allow annual grass and weeds to form a cover during the fall and winter. The cover crop reduces or prevents erosion and permits the trees to harden their tissues against the coldest winter temperatures. If the volunteer cover growth is sparse, cover crops may be seeded in late summer on a rough seedbed in the orchard.

Many grasses and legumes have been used as cover crops in apple orchards. Because of the shade and low fertility in many orchards, strong-growing winter annual grains or grasses usually have been found to be superior to legumes for this purpose.

Among those that have been used are rye and domestic ryegrass. They are seeded on a rough seedbed in August or September and disked down the following spring.

Of the leguminous plants that can furnish satisfactory annual cover, sweetclover has been successful. Both ryegrass and sweetclover are sometimes carried over from one year to the next by permitting some of the plants to survive in the spring as a source of natural seeding in midsummer.

Several implements may be used for cultivation. The disk and spring-tooth harrows are commonly used. Newer tools that cut and shred the cover crop and stir the soil to a shallow depth have been tried in orchards.

Many orchardists no longer cultivate mature orchards annually except to prepare furrows for irrigation in and regions or to conserve moisture. Even in irrigated regions, the tendency has been away from cultivation as sprinklers have supplanted the use of furrows for distributing water.