Tree Fruit: Horticulture

Orchard Nutrition

Good orchard fertilizer practices and proper tree nutrition are extremely important for satisfactory yields and quality apples. Soil and foliar analysis plus orchard observation should be used to determine the nutritional status of the tree. One of the most effective nutrient management practices in an apple orchard is the maintenance of the soil pH in the range of 6.0 for the subsoil to 6.5 for the topsoil because the pH influences the availability of the various elements to the plant. Figure 1 shows the availability of some essential nutrient elements as influenced by the soil pH. For example, as the soil pH becomes acidic (pH <5.5), the phosphorous in the soil becomes unavailable to the plant. It does not matter if there is an adequate amount of phosphorous in the soil; the roots are unable to uptake it.

Under common orchard practices, the soil tends to become more acidic over time, and a regular liming program is required to maintain the soil at the proper pH. Table 1 lists the commonly used nitrogen fertilizers and their residual effect on pH. Soil pH and texture are commonly used to determine the lime requirements. Leaf tissue analyses indicate the amounts of the various elements that have been taken by the tree and translocated to the foliage. In other words, soil analysis tests gives you an assessment of acidity and fertility of the soil before the growing season, and leaf analysis gives you the nutritional status of the plant during the growing season. Soil and leaf testing is available through UVM Agricultural and Environmental Testing Laboratory.

Knowing the leaf analysis standards for apple, your soil and leaf analysis results, and personal, visual observations should help you make decisions in determining what nutrients are causing an unwanted response, and what treatments are necessary to change or enhance the response. Due to the many variables involved, such as cultivar, rootstock, soil pH and type, age of tree, the grower is the only person should make the final call on tree fertilization. Table 2, with minor modifications, was compiled by D. Schmitt and J. Clements, under the supervision of Dr. Costante in 1993. It is an attempt to familiarize you with information regarding the role of macro and micro nutrients, nutrient disorder symptoms, and corrective measures. This information has been adapted from several publications, particularly useful was the Orchard Nutrition Management by W. C. Stiles and W. S. Reed from Cornell Cooperative Extension. Tables 3 and 4 are the leaf analysis standards and the fertilizer chart recommendations, respectively, for young- nonbearing trees. These tables are intended only as general guides to maintain tree nutrition at an optimum level rather than correcting severe deficiencies

Nutrition pointers

Adding too much fertilizer is not only a waste of money, but it can have a negative impact on the plant and fruit. In apples, too much nitrogen results in soft fruit with poor color. Too much potassium can cause Bitter Pit.
The amount of nitrogen applied is more important to fruit quality than its form. Use the cheapest source available.
The relationship between nitrogen and potassium is very important. A ratio on N/K of about 1.25 is about where the balance of these two elements results in optimum fruit size, color, sugar content and firmness.
Foliar sprays should be considered as supplemental treatments. They add usually no more than 15% of the tree's nutritional needs. If you have had Bitter Pit or Cork Spot, regular applications of calcium chloride are recommended.
Apply ground fertilizers early in the spring, one or two weeks before bloom.

Care of young trees

Special attention should be given to phosphorous fertilization at pre-plant site preparations. Surface applications of phosphates in established orchards are likely to contribute to surface water contamination.
Young trees can be fertilized by a split application in early April and early June.
Try to band in a circle 12 to 18 inches from the trunk. A leaf analysis program should begin a year before the trees will produce a commercial crop.

Fig. 1. Availability of some essential nutrient elements as influenced by soil acidity or alkalinity

Table 1. Nitrogen FERTILIZERS, their COMPOSITION, and RESIDUAL EFFECT on pH

Inorganic	%Nitrogen	% Other elements	Residual effect
Anhydrous ammonia	82	----	acid
Urea	45	----	acid
Ammonium nitrate	33.5	----	acid
Calcium nitrate	15.5	19 Ca	basic
Potassium nitrate	13	44 K₂O	basic
Organic
Dried blood	15	1.30 P₂O₅;0.70 K₂O	acid
Activated sludge	5.00	3.00 P₂O₅	acid
Cottonseed meal	3.15	1.25 P₂O₅;1.15 K₂O	acid

Table 2. 1998 Apple Team Mineral Nutrition Bearing Orchard Fertilization Summary

NUTRIENT	PHYSIOLOGY	IDEAL FOLIAGE RANGE	DEFICIENCY
Capitalized nutrients- the 'big five', are of particular importance for tree maintenance and fruit quality	An appreciation for the complex physiological role played by mineral nutrients helps explain their importance in orchard nutrition	Leaf analysis results in this range should be considered ideal for maintaining tree health, adequate vigor, and fruit quality	Deficiency symptoms are important indicators of a nutrient deficiency or imbalance
NITROGEN (N)	Primary building block for all plant parts- leaves, shoots, roots, fruit buds etc.	Young, non-bearing trees 2.4 to 2.6%; young, bearing 2.2-2.4%; mature, soft fruit 1.8 to 2.2%; mature, hard and processing 2.2-2.4%	Older leaves affected first. Leaves are small, uniformly light green or yellowish. Tips and margins may show necrosis. Bark is yellowish orange. Shoots/spurs-short, thin and spindly. Fruit set may be reduced. Current season's growth <4"
POTASSIUM (K)	Enzyme activator, necessary for the formation and translocation of sugars, proteins, plant growth hormones	1.35 to 1.85%	Older leaves affected first, necrosis advancing from margins toward mid-rib; slender shoots and weak spurs; more susceptible to winter injury; smaller, poorly colored, low acidity fruit
CALCIUM (Ca)	Component of cell wall; regulates nutrient uptake and movement in plant	1.3 to 2.0 %	Deficiency symptoms difficult to identify in leaves. Shoot and root growth inhibited; storage disorders-bitter pit, cork spot, internal breakdown
MAGNESIUM (Mg)	Molecular component of chlorophyll ; enzyme activator	0.35 to 0.50	Older and mid-shoot leaves, and those on spurs bearing fruit are affected first. yellow-brown necrotic areas; shoots and spurs are thin, weak, and brittle; blind wood and premature fruit drop
BORON (B)	Aids in formation of pollen tube and feeder roots, and translocation of Ca, sugars, plant hormones	27 to 45 ppm	Flower development and fruit set decreased; young leaves often small, misshapen; corkiness in fruit flesh, wrinkled skin
Phosphorous (P)	Cellular energy transfer and storage; nucleic acid component or regulator cofactor	0.13 to 0.33%	Deficiencies generally not seen in fruit trees. New leaves are small, bluish green, margins or main veins or undersides of leaves having purple pigmentation. Older leaves drop early. Flowering is reduced. Affects fruit quality
Zinc (Zn)	Component or regulator cofactor of enzymes, plant hormones proteins (i.e.. aids in normal growth and fruiting)	35 to 50 ppm	Leaves at shoot tip are stunted and misshapen with mottled necrosis; little leaf disease; leaf rosettes may be confused with winter injury; reduced fruit set and, quality, and size
Manganese (Mn)	Aids in chlorophyll synthesis; involved in photosynthetic oxygen evolution	50 to 150 ppm	Older and mid-shoot leaves affected first. ' Herringbone' chlorosis between main veins. Shoot dieback may occur. Flowering and fruit set are reduced
Iron (Fe)	Required for chlorophyll formation; a chlorplast enzyme component	50+ ppm	Chlorosis of tip leaves while veins remain green. Shoot growth is stunted and may die back.
Copper (Cu)	Important enzyme component	7 to 12 ppm	Younger leaves are affected first. Leaves are stunted or misshapen with irregular margins. Whitish, mottled chlorosis between veins. Fruit color, quality, and size are affected

Table 2. (cont.)1998 Apple Team Mineral Nutrition Bearing Orchard Fertilization Summary

NUTRIENT	EXCESS	FOLIAR APPLICATION	GROUND APPLICATION	COMMENTS
Capitalized nutrients- the 'big five', are of particular importance for tree maintenance and fruit quality	If an element is in excess in soil or plant tissues, expect to see the following- often debilitating, toxicity symptoms	Most/foliar sprays are 'quick-fix' solutions to nutrient deficiencies that supplement ground applications	The preventive approach to orchard nutrition- a ground fertilization program based on soil and leaf analysis results	Be sure to consult an orchard nutrition reference or your extension fruit specialist for more detail
NITROGEN (N)	Excessive shoot growth; soft, green fruit (poor CA storage candidate); more susceptible to winter injury and diseases such as fireblight	Urea @ 9#/acre, IX-3X; apply at pink and 1st cover; boosts spur vigor; do not apply with oil	Ammonium nitrate (34-0-0) @ 0-75#/acre (see comments)	See Table 1 for N fertilizer details. In bearing trees, a rule of thumb for applying actual N on a per tree basis would be: 8-15 bushels: 0.66 lb; 15-25bushels :0.66-1.0 lb; >25bushels: 1.33-2.0 lb;
POTASSIUM (K)	Mg, and Ca deficiencies become pronounced w/ excess K	None	Muriate of potash (0-0-60) @ app. l50-200 #/Ac annually; if Mg low use Sul-Po-Mg	Potassium deficiencies are more common with heavy crop loads, high N and inadequate water supply; annual fertilization advisable
CALCIUM (Ca)	No distinctive symptoms	CaCl @ 1-4 # / 100 gal, in 4-6 sprays 14 days apart, begin 7-10 days after petal fall	lime 4 tons/Ac every 4-5 years or as indicated by soil test; if low in Mg use dolomitic lime	Sprays necessary to offset fruit quality problems, however, maintain soil calcium supply via liming. Fluctuations in soil moisture increase severity of deficiency symptoms
MAGNESIUM (Mg)	Can hinder Ca uptake (Ca deficiency symptoms become more prevalent) when soil Ca supply is low	Epsom salts @ 15 # /Ac @ PF, 1st and 2nd covers; generally tank-mix compatible	Dolomitic (high Mg lime) @ 4 tons /Ac every 4-5 years	Supplement ground application w/foliar sprays; if K high, Mg requirement increases. Deficiencies more pronounced in young trees or trees with heavy crop loads.
BORON (B)	Chlorosis of leaf tissue along the midrib. Premature defoliation from shoot tip toward base. Fruit drop likely; fruit cracking. Excess symptoms similar to deficiency.	Prebloom to bloom (if leaf sample< 35ppm)- Solubor @0.5-1.0/100 gal; at PF or 1st-3rd cover sprays Solubor at 1lb/100 gal not compatible with oils, EC's	Granular Borate 2-3# (young trees) up to 7-8 # (older trees)/Ac often blended w/ other fertilizers	Foliar and ground applications should be used to supplement one another. Deficiencies more pronounced in trees with heavy crop loads or under dry weather conditions
Phosphorous (P)	Zn and Cu deficiencies exacerbated	No application necessary	Superphosphate (0-20-0)or triple superphosphate (0-45-0) to maintain soil levels at 300-400 # / Ac	P fertilization of bearing orchards usually not necessary; pre-plant P in root zone very desirable
Zinc (Zn)	Cu deficiency symptoms induced	Zn sulfate @(22-36 % Zn); apply 3-5 # actual Zn/ 100 gal. Dilute only, up to silver tip	Trees generally unresponsive to ground applications	Maintain pH of 6.0-6.5 to reduce likelihood of Zn deficiency
Manganese (Mn)	Necrotic bark tissue (measles on Delicious; otherwise not evident	Mn sulfate @ 2-4 # / 100 gal. 1 week before PF; EDBC fungicides also contain Mn	None	Delicious most sensitive to excess Mn; toxicity symptoms commonly associated w/Ca deficiency
Iron (Fe)	None	None	None	Maintain soil pH at 6-6.5 to avoid Fe deficiency problems
Copper (Cu)	Root death; other micronutrients likely to become exaggerated	Choose bordeaux mixture or other Cu containing fungicide for disease control (i.e.. Fireblight, scab if warranted	None for bearing orchards; pre-plant incorporation of Cu sulfate (90-120# Cu /Ac)	Treat foliar application of Cu with caution, as fruit russeting and/or foliage injury likely

Table 3. LEAF ANALYSIS STANDARDS FOR YOUNG, NON BEARING APPLE TREES

Element Optimum (Within)	Excess (More than)	Optimum (Within)	Excess (More than)
Nitrogen(N)	2.00 %	2.00-2.50 %	2.50%
Potassium (K)	1.00 %	1.20-1.50 %	1.50 %
Calcium (Ca)	1.00 %	1.25-1.80 %	?
Magnesium (Mg)	0.20 %	0.25-0.40 %	0.50 %
Manganese (Mn)	20 ppm	25-100 ppm	110 ppm
Boron (B)	25 ppm	30-45 ppm	70 ppm
Copper (Cu)	4 ppm	7-12 ppm	12 ppm
Zinc (Zn)	15 ppm	25-50 ppm	50 ppm

Table 4. YOUNG TREE FERTILIZER RECOMMENDATION CHART

Pounds applied per tree in early spring and 6 to 7 weeks later
Age (yrs)	Calcium nitrate (15%)		Ammonium nitrate (34%)		Urea (44%)		20-20-20		Muriate/Potash (60%)
	Spring	6wks	Spring	6wks	Spring	6wks	Spring	6wks	Spring	6wks
1	1.33	1.33	----	----	----	----	0.50	0.50	----	----
2	1.75	1.75	1.00	1.00	0.75	0.75	1.66	1.66	0.50	0.50
3	2.66	2.66	1.25	1.25	1.00	1.00	2.25	2.25	0.50	0.50
4	3.75	3.75	1.66	1.66	1.25	1.25	3.0	3.0	0.75	0.75
5	4.00	4.00	1.75	1.75	1.33	1.33	3.0	3.0	0.75	0.75