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Fertilization

All plants require certain chemical elements for normal growth. There are 16 elements, each of which is essential: the plant cannot complete its life cycle without them; and, no element can completely substitute for another.

Certain elements are permanently removed from soil over time. Some are removed each season, but ultimately returned in the form of fruit dropped and thinned, leaves and pruning. For example, 14-year old peaches producing 30 tons of fruit per hectare have been shown to permanently remove: 30.8 kg of nitrogen, 5 kg of phosphorous, 39 kg of potassium, 6.3 kg of calcium, and 1.8 kg of magnesium.

Fertilizers are classified into two broad groups: organic and non-organic. Organics are typically plant, animal or naturally occurring in origin. Non-organics are manufactured or formulated from many sources and processes.

Historically, both commercial and backyard orchards were established without pre-plant fertilization. Maintenance fertilizers, usually nitrogen (N), were applied after establishment. Greater reliance on soil tests prior to planting and use of organic supplements has accelerated in recent years.

Fertilization should be considered as:

  • What can be done at planting and during the first year
  • Maintenance applications from second year on to full tree maturity

Nitrogen (N)

Nitrogen is necessary for many tree functions, including growth, fruit bud formation, fruit set and fruit size. Because of the complexity 

of nitrogen interactions with quality and production, the best guide for nitrogen rates is leaf analysis.

Identification

Usually first appears on older leaves,

Leaves turn light green or yellow as nitrogen is relocated from older, less productive leaves to the newest growth,

The bark of shoots and twigs may become reddish in colour and shoot growth is spindly,

Nitrogen deficiency symptom

  • If the deficiency is prolonged, older leaves become orange to reddish in colour and may drop prematurely,
  • Fruit bud formation and fruit set may be restricted, 
  • Fruit is small and highly coloured and yields will be reduced.
  • Terminal shoot growth of less than 20 cm on bearing trees and less than 40 cm on non-bearing trees may indicate a nitrogen deficiency.

Nitrogen effect at growth stages

Stage

Nitrogen effect

Bud Burst – Start of Flowering

Promote strong early growth of new plant tissues and maximum tree productivity

Fruit Set to Fruitlet at 30mm

In reduced amounts to maintain fruit fill

Fruit Fill – Maturity

In reduced amounts to maintain fruit fill and high sugars – excess can lead to rots and quality deterioration

Post Harvest

Boost reserves for next season’s early growth

Often Confused With

Chemical:

  • spray damage yellowing and browning of leaf margins and interveinal areas,
  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil, amitrole.

Diseases:

  • canker diseases along trunks and branches,
  • anthracnose,
  • leaf blotch.

Insects:

  • aphids,
  • leafhoppers,
  • mites,
  • plant bugs,
  • wood boring insects,
  • root feeders.

Mechanical: 

  • damage to tree bark,
  • leaf scorch, 
  • root injury,
  • ozone.

Soil & planting conditions:

  • decomposition  of organic materials with high carbon/nitrogen (C/N) ratios,
  • leaching of nitrates from sandy soils or soils with low organic matter,
  • waterlogged soil conditions,
  • dry soil conditions,
  • soil compaction,
  • weed  competition,
  • too little fertilizer applied.

Weather:

  • low temperatures and frost.

Scouting Notes

Cool growing conditions in early spring often cause plants to develop a temporary nitrogen deficiency. This is usually due to poor growing conditions, and not necessarily a lack of nitrogen in the soil. Nitrogen deficiency often occurs when a permanent grass is seeded in the orchard or when a large amount of organic matter which is low in nitrogen, such as straw, is worked in to the soil.  Deficiency symptoms may also occur when fertilizer is leached by heavy rains. 

Potassium (K)

Potassium deficiency symptom

 
Potassium is important for fruit colour, winter hardiness, tree growth and disease resistance.

Identification

  • Usually first appears on older leaves.
  • Interveinal purpling start at leaf margin and working into the centre of the leaf.
  • Leaf margins become brown.
  • Necrotic spots develop between leaf veins and may drop out.
  • Fruit will ripen unevenly and have poor/variable colour development.

Potassium effect at growth stages

Stage

Potassium effect

Bud Burst – Start of Flowering

Promote strong early growth of new plant tissues and maximum tree productivity

Fruit Set to Fruitlet at 30mm

Minimize fruit disorders

Fruit Fill – Maturity

Maximize fruit weight, TSS levels in the fruit and minimize disorders and sunscald, but at levels that don’t compete with calcium

Post Harvest

Boost reserves for next season’s early growth

Often Confused With 

Chemical:

  • spray damage yellowing and browning of leaf margins and interveinal areas,
  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil,

Diseases:

  • canker diseases along trunks and branches
  • anthracnose

Insects:

  • aphids
  • leafhoppers

Mechanical: 

  • damage to tree bark,
  • leaf scorch
  • root injury

Soil & planting conditions:

  • leaching from sandy soils
  • waterlogged soil conditions
  • dry soil conditions
  • soil compaction
  • High levels of calcium, magnesium, sodium, nitrogen or phosphorus can affect uptake, especially if potassium  deficient

Weather:

  • Late spring or summer frosts
  • High winds at high temperatures on succulent spring growth
  • Drying and shriveling of leaf margins from wind

Phosphorous (P)

 

 

.Phosphorus deficiency

symptoms​

Deficiency is not often found except on red foothill and mountain soils. Available P comes from the breakdown of soil minerals or organic matter, and it is quite mobile in plants. Mature fruit trees rarely show deficiency symptoms or respond to phosphorus fertilizers in tree growth or in cropping. However, growers commonly apply superphosphate to stimulate clover growth in the ground cover or sod. This in turn can boost nitrogen to the tree and increase organic matter return to the soil, improving its structure. Foliage of deciduous or evergreen trees deficient in P becomes dull and bronzed (even purplish) in late summer

Phosphorus is involved in energy transfer and the maintenance of cell membranes. It has a direct effect on yield and tree health, but it is also important in determining fruit size, firmness, color and storage potential.

Phosphorus effect at growth stages

Stage

Phosphorus effect

Bud Burst – Start of Flowering

Maximize root development and flower cluster formation

Fruit Set to Fruitlet at 30mm

Fruit set and development

Post Harvest

Maximize bud development and early rooting and new tissue growth in the following spring

There are other trace elements that are essential for growth and the production of fruit crops

Their deficiency symptoms can occur late in the season after plant growth or the crop has already been affected.

Foliar sprays may be an effective way of correcting some trace element deficiencies. Sprays are best applied in early to mid-summer, with three to four applications required each year. The rate and number of applications will depend on the product specifications and the degree of deficiency of the trace element to be corrected.

Boron (B)

Of the micronutrients, boron is needed in greatest amounts both in the fruit and leaf, but there is a relatively narrow margin between deficiency and toxicity.​

Boron plays an important role in the structure of cell walls, fruit set and seed development. It is also a component of protein and carbohydrate metabolism.

Boron effect at growth stages

Stage

Boron effect

Bud Burst - Start of Flowering

Maximize pollination and strong flower development

Fruit Set to Fruitlet at 30mm

Improve fruit set

Post Harvest

Replenish reserves and strengthen new buds

Identification

  • Boron deficiency develops also as a fruit disorder,
  • Apples may exhibit internal breakdown and premature drop of highly coloured fruit.

Scouting Notes

Boron deficiency is most likely to be found on alkaline soils or sandy knolls. Boron deficiency is common in dry weather and in soils with a high pH.

 
Boron Deficiency in apple

Calcium (Ca)

Calcium is a vital component in cell walls and is involved in the movement of sugars and starches within the plant.

Identification

  • Calcium deficiency does not usually cause foliar symptoms but does show as fruit disorders,
  • Bitter pit of certain apple varieties have been related to a lack of calcium,
  • A shortage of calcium in the developing fruit causes these disorders, 
  • There may be ample in the soil and leaves but it does not move to the expanding fruit since calcium is immobile in the plant 

Bitter pit:

  • The physiological breakdown of cells under the skin, causing slight depressions generally concentrated at the calyx end of the fruit,
  • The tissue in these depressed areas is darkened, dry and spongy with a bitter taste,
  • In some instances the symptoms may not be apparent on the fruit surface but appear under the skin,
  • Large fruit from trees with light crops are more likely to have bitter pit.
  • Spy is frequently affected by this disorder,
  • With the right conditions, bitter pit can occur on Delicious, Idared, Crispin, Cortland, Empire, Honeycrisp and other varieties,
  • Bitter pit may not be evident at harvest but develops in stored fruit and can result in extensive loss from storage.

Calcium effect at growth stages

Stage

Calcium effect

Bud Burst – Start of Flowering

Boost root and leaf growth and high yields

Fruit Set to Fruitlet at 30mm

Maintain good fruit quality and minimize fruit disorders

Fruit Fill – Maturity

Maintain good fruit firmness and storage quality

Post Harvest

Maintain high levels in the tree

 

Bitter pit on apple - University of Georgia

Plant Pathology: bugwood.org

Young leaf showing discoloration and necrosis (top)

Nearly mature leaf with extensive areas of dead tissue (bottom)

Iron (Fn)

ron deficiency symptom

 Iron is needed for chlorophyll formation, plant respiration and the formation of some proteins.

Deficiency leads to characteristic chlorotic yellowing, and sometimes bleaching, of new leaf growth. In severe cases, leaves become scorched in summer months.

Soil applications with chelates are used early season in calcareous soils, or alternatively in season foliar programs targeting the growing shoots are used to meet iron needs. Care has to be taken with foliar applications to minimize phytotoxicity risks. 

Identification

  • Symptoms are very similar to manganese deficiency,
  • Deficiency occurs more frequently when pH is high and can be caused by high levels of lime (lime-induced chlorosis),
  • Symptoms appear on the young leaves first,
  • Leaves turn yellow between the veins, but the veins will remain green except in extreme cases,
  • Often symptoms are seen in only one area of the plant,
  • Shoots may die back if iron deficiency is not corrected.

Often Confused With 

Chemical:

  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil, paraquat, fluazifop-butyl, oxadiazon,
  • high -very levels of phosphorus may reduce iron uptake,
  • excessive soil liming.

Disease:

Insects:

Mechanical:

Weather:

virus diseases

  • aphids,
  • leafhoppers,
  • mites,
  • plant bugs.

damaged stem or trunk.

  • excessive soil moisture and cold, wet spring,
  • hot, dry summer.


Soil & planting conditions:

  • calcareous soils, mineral soil pH > 6.5,
  • excessive levels of phosphorus, copper, zinc or manganese may induce deficiency,
  • over fertilization or salt damage,
  • cool, wet or compacted soils resulting in reduced root growth and poor uptake,
  • waterlogging,
  • poor soil aeration.

Scouting Notes

Factors associated with iron deficiency include soils with high lime content (and therefore high pH), and gross imbalances with other micronutrients like molybdenum, copper or manganese. 

Magnesium (Mg)

Magnesium is an essential part of chlorophyll and aids in the formation of sugars, oils and fats. Magnesium is a part of the chlorophyll molecule, magnesium deficient trees have older leaves that are pale in colour. Leaf analysis is the best way to evaluate magnesium requirements.

    
                                  
Magnesium deficiency - Three successive stages of blotching     www.agric.wa.gov.au

Identification

  • Magnesium is mobile within the plant and therefore deficiency usually appears first on the older leaves as it translocates to the growing tissue
  • The leaf tissue between the veins turns yellow, while the veins remain green
  • Severe deficiencies will cause the leaf margins to curl
  • Necrotic spots develop later and eventually the leaves drop prematurely 
  • If deficiency is prolonged, only a few pale leaves are left at the growing tip
  • Fruit matures early, is highly coloured and drops prematurely
  • Fruit bud formation may be limited

Magnesium effect at growth stages

Stage

Magnesium effect

Bud Burst – Start of Flowering

Promote strong early growth of new plant tissues and maximum tree productivity

Fruit Set to Fruitlet at 30mm

For reduced fruit drop

Post Harvest

Replenish reserves and strengthen new buds

Often Confused With 

Chemical:

  • pesticide spray damage yellowing and browning of leaf margins and interveinal areas,
  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil, paraquat, fluazifop-butyl, oxadiazon.

Mechanical:

  • mechanical damage to tree bark,
  • leaf scorch root injury.

Soil & planting conditions:

  • availability is reduced when potassium levels are excessive,
  • conditions which limit root growth such as wet, dry, or cold soils can reduce magnesium availability,
  • excessive boron also causes interveinal and marginal leaf scorch.

Scouting Notes 

Symptoms are most pronounced at the end of the growing season and are more severe in wet years.

Manganese (Mn)

Manganese is involved in photosynthesis and chlorophyll production. It helps activate enzymes involved in the distribution of growth regulators within the plant.

Somewhat faint intervenal chlorosis beginning near margins.

Manganese effect at growth stages

Stage

Manganese effect

Bud Burst - Start of Flowering

To maximize tissue growth

Fruit Fill - Maturity

Along side with phosphorus will promote fruit coloration

Identification

  • Deficiency causes yellowing between veins of young leaves,
  • Leaves gradually turn pale-green with darker green next to the veins,
  • Shows first at the growing tip on the young developing leaves which become bright yellow between the veins,
  • Veins remain green and the contrast between the dark-green veins and yellow interveinal area is striking,
  • If the deficiency is prolonged, the entire leaf assumes a dull-yellow appearance followed by premature leaf drop.

Manganese toxicity:

  • Manganese toxicity can occur on soils with a low pH (pH 5.5 or lower)
  • It causes brown spots or yellow mottled areas near leaf tips and along the leaf margins and usually develops on older leaves,
  • Brown spots may also develop on veins, petioles and stems,
  • The bark of new shoots becomes necrotic, developing “measles”,
  • Growth is stunted.

Often Confused With 

Chemical:

  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil, paraquat, fluazifop-butyl, oxadiazon,
  • high-very high phosphorus,
  • excessive magnesium on low manganese soils.

 

Disease:

Soil & planting conditions:

Weather:

virus

  • cold soils, dry soils
  • excessive liming
  • may be more severe in spring than later in summer
  • cold, wet weather

Scouting Notes

Manganese deficiency may appear early in the season under excessive moisture conditions and later disappear. It is more common when the soil pH is high.

Zinc (Zn)

Zinc is important in early plant growth and in seed formation. It also plays a role in chlorophyll and carbohydrate production. (Zn)

www.agric.wa.gov.au

Symptoms occur in the spring and include chlorosis of the youngest shoot leaves, which are stunted and narrower than normal – ‘little leaf’.

Yellowing occurs between leaf veins and is less symmetrical than, for example manganese deficiency. The leaves may show a wavy margin. Blind bud and rosetting can also occur. Leaf symptoms are not strong in apples compared to other fruit trees.

Extreme deficiency results in shoot defoliation and the production of misshapen and poorly colored apples.

Zinc effect at growth stages

Stage

Zinc effect

Bud Burst – Start of Flowering

To optimize bud burst and early leaf development

Post Harvest

Replenish reserves and strengthen new buds

 

Identification

  • Zinc is relatively immobile within the plant,
  • Deficiency symptoms appear first on younger leaves,
  • Young leaves become mottled and show interveinal chlorosis, striping or banding,
  • In advanced stages in tree fruits, small, narrow terminal leaves are arranged in whorls or “rosettes”,
  • Defoliation may occur early, starting with older leaves.

Often Confused With

Chemical:

  • herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil);  dichlobenil; gylphosate.

Insects:

  • sucking insects (aphids, leafhoppers, mites, plant bugs).

Soil & planting conditions:

  • alkaline soils or overliming may cause deficiency,
  • soil pH > 7.0,
  • soils high in natural phosphates or over applications of fertilizers high in phosphates reduce zinc absorption and translocation,
  • may result on course sandy soils,
  • liberal applications of nitrogen or high levels or iron may induce deficiency.

Weather:

  • may be induced by cool, wet spring weather,
  • low soil temperatures

Scouting Notes

Zinc deficiencies are most often seen on sandy soils with high pH levels. Heavily eroded knolls may also have deficiency problems. Large applications of phosphorus may aggravate zinc deficiencies.

Deficiencies of the other essential nutrient elements: phosphorus, sulphur, copper, molybdenum and chloride have not caused problems in fruits.  Soils are normally supplied with sufficient quantities these nutrients.

Source for the materials:  

Crown copyright©  http://www.omafra.gov.on.ca

Yara copyright© http://www.yara.us/agriculture/crops/apple/