Fruit Tree Nutrition

Monitoring and Assessing the Nutrient Needs of the Orchard

Proper balanced nutrition is important in all crops; however, knowing what the right nutrient needed at the right time for the right reasons with the right product can be very different between commodities, orchards, and seasons. There are several different sampling methods that can be utilized to assess the nutrient status of a block and help aid in nutrient management decisions. The main assessment methods are leaf, fruitlet, and soil analysis. There are some other techniques, such as sap analysis, that are being tested and may be more available in the future.

Leaf Analysis

Leaf analysis is currently the best available method of determining nutrient status of most minerals in fruit trees. The limitation of leaf sampling is the possible contamination that season by foliar sprays. To reduce contamination, most foliar sprays, except calcium, are finished in orchards by June with leaf samples collected later in the growing season (see sampling methods below). The exception to this would be spring zinc sprays that do not wash off the leaves easily. Calcium levels for fruit quality are not monitored with leaf samples. Maintaining a consistent nutrient program and sampling timing, year to year, allows annual results to be used despite the contamination issue to better monitor nutrient trends in the orchard.

Caution: a few pesticides contain nutrients (e.g. ziram contains zinc or Kumulus is sulphur). If one of these pesticides has been applied to the leaves collected for leaf analysis, results for that nutrient could be invalid.

Leaf Sampling Methods for Orchards

What to sample: A sample is a composite sample of leaves from multiple trees within a similarly comparable block within the orchard and should not represent more than 10 acres. Take each sample from the SAME VARIETY and the SAME AGE group on the SAME ROOTSTOCK and of the SAME VIGOUR of trees in similar soil and management conditions.

When to sample: Samples should be taken from late July to early August to compare to the standard values for tree fruits. Samples can be taken at other times during the growing season but, in this case, comparative samples should be obtained from the area of concern and one from a “good” area to assess results.

Where to sample: Take leaves from the middle third of the terminal growth (this year’s growth). Select terminal growth which is growing upward and outward in an angle between 30° and 60° degrees. If the block to be sampled has a large number of trees, randomly select 50 leaves in a cross-section of the orchard (1 -2 leaves per tree); if the block is small, select 2 - 3 leaves from each tree for a total of 50 leaves.

Follow a pattern suitable for the block of trees. Use the X-pattern wherever possible. Do not take leaves from the outside trees on the border of a block or from trees within two rows of any roads. Never sample damaged leaves.

Fruitlet Mineral Analysis

Like soil and leaf analysis, fruitlet analysis can be a valuable tool when making decisions about feeding programs in apple orchards. Because the concentrations of certain minerals in apple fruit are correlated with fruit various aspects of quality, fruitlet analysis results can be used as a guide to produce higher quality fruit. Table 1 indicates fruit and tree problems associated with either excessive or deficient fruitlet mineral concentrations in BC apple orchards. Unlike leaf analysis, there are no standard sampling methods for fruitlet analysis. Optimum fruitlet mineral levels differ by variety, timing of sample collection and methods of preparation and analysis. Optimum values for Ambrosia fruitlets sampled six weeks before anticipated harvest are shown in Table 2 expressed on a fresh weight basis. See your Field Service or Crop Advisor for recommended fruitlet sampling methods.

Table 1. Potential fruit and tree problems when fruitlet mineral concentrations are in excessive or deficient ranges.

Mineral

Status

Fruit/Orchard Problems

Excess

Storage rots, breakdown, bitter pit, soft fruit, poor colour

Deficit

Small fruit, biennial bearing, premature ripening, increased susceptibility to winter injury

Deficit

Soft fruit, low temperature breakdown in some varieties

Excess

Bitter pit, breakdown

Deficit

Poor colour, poor flavour, increased susceptibility to winter injury and spring frosts (when leaf K < 1%)

Deficit

Storage rots, breakdown, bitter pit, fruit easily damaged, early ripening, poor visual appearance

Excess

Bitter pit, soft scald in some varieties

Deficit

Small fruit, premature ripening, preharvest drop

Excess

Early ripening, preharvest drop, breakdown, bud damage, blossom blast

Deficit

Small, misshapen fruit, drought spot, fruit cracking, early ripening, preharvest drop

Table 2. Optimum 'Ambrosia' fruitlet mineral values and ratios for samples collected six weeks before anticipated harvest.

Mineral	Optimum Value¹
N	38-44
N/Ca	<5.0
N/K	<0.35
P	11.0-14.0
P/N	>0.26
K	120-130
K/Ca	<15
Ca	>8.5
Mg	6.0-6.5
Mg/Ca	<0.8
B	0.28-0.35
B/Ca	0.03-0.04
Zn	>0.04

¹Values are for whole fruit analysis less seeds and stems expressed as mg/100 g Fresh Weight.

Soil Analysis

Soil analysis is mostly used to determine the soil acidity or alkalinity (pH), the level of soil salts as electrical conductivity (EC), and boron. Soil analysis at the end of a season that shows high nitrogen can be an indication of excess nitrogen fertilizer applications. However, soil analysis is not a reliable guide to the other mineral requirements of fruit trees. The presence of a nutrient in the soil, such as phosphorus or calcium, does not always mean it is available for the tree.

Soil Sampling Methods for Orchards

When to sample: Soil sampling is typically done in the fall or spring. If replanting, it is best to collect a soil sample in the fall preceding planting. Such analyses can reveal unsuitable soil conditions that may be rectified before planting. Lime, for example, can be incorporated into the soil by cultivation if the pH is found by analysis to be low. Incorporation of any materials by cultivation is more difficult once an orchard is established and roots begin to grow.

Where to Sample: There can be significant differences in the soil in a block. Natural land variations, irrigation, and orchard practices can result in changes to the nutrient content of the soil, thus where you sample can make a difference in the results. Common land variations can be areas of high calcium carbonate from runoff of nearby hills. Irrigation can impact soil nutrient content by reducing the presence of soluble nutrients through leaching and will impact where the majority of roots will be growing. Orchard practices such as the use of mulch, fertilizer placement, and herbicide strips can result in changes of soil in the root zones compared to the alley ways of orchards. Soil samples should be collected as a composite sample (single sample resulting from the combination of several smaller samples) from similar parts of the acreage and composite samples collected separately when land contours or soil types obviously vary.

For replant: When the planting is an old orchard that is going to be replanted, at least 2 composite samples should be taken and kept separately. One composite sample from the sites of removed trees where fertilizer applications have been heavy and one on sites between tree rows that have received little or no fertilizer.

Trees planted >13’ between rows: Select five to ten trees for sampling in an orchard block where the soils are similar (see diagram below.) For large areas of similar soil, a minimum of 30 trees per ha (12 trees per acre) should be used. Take one sample beneath each tree at 1 m from the tree trunk and make a composite sample for analysis.

For Young Trees: Select young trees which are similar in growth characteristics and height in an orchard block where the soils are similar, e.g., less than 0.5 m, 0.5-1 m, more than 1 m, etc.

Obtain individual samples from within 60 cm from the trunk beside four to eight young trees with similar growth and height and make a composite sample for analysis. Obtain a composite sample for analysis from two or more locations with comparable growth and height.

How To Sample

Lime recommendations are based on lime requirement analysis of composite samples taken from the 0-30 cm (0-12”) depth.

How to sample:

(a) Soil probes (see below), augers, or shovels can be used to take samples. Be sure all tools and containers are clean.

(b) If a shovel is used, clear away the surface litter and dig a U-shaped hole in the soil.

(d) Trim both sides of this slice to leave a 2.5 cm width of soil. This is an individual sample which should be mixed in a clean pail or plastic sample bag to make a composite sample.

(e) Samples can also be taken from 30-45 cm in order to analyse the subsoil for soil acidity. Samples taken from these depths are obtained in a similar manner to the 0-30 cm method described above.

(f) After the individual soil samples are mixed together well, fill the soil sample box with soil and label the box with date of sample and sample identification (name of orchard, block id, location of sample, etc).

(g) Fill out a soil information sheet for each sample.

(h) Draw a rough sketch of the orchard indicating the various sampling locations.

Soil and Tissue Testing Laboratories

A&L Canada Laboratories Inc
2136 Jetstream Road
London ON N5V 3P5
ph. 519-457-2575
Fax 519-457-2664
Web: www.alcanada.com

BC Tree Fruits Cooperative Quality Development Lab
Winfield, BC
Can test soil pH and conduct replant bioassays (bioassay tests require minimum 4 months for results).
www.oktreefruits.com
phone 766-2527 ext. 205

Exova
104-19575 55A Avenue
Surrey, B.C. V3A 8P8
ph. 604-514-3322
Fax 604-514-3323
Web: www.exova.com

MB Laboratores Ltd.
By courier: 4-2062 West Henry Ave, Sidney BC V8L 5Y1
By mail: PO Box 2103, Sidney BC V8L 3S6
ph. 250-656-1334
Fax 250-656-0443
Email: [email protected]
Web: www.mblabs.com

Pacific Soil Analysis Inc.
#5 - 11720 Voyager Way, Richmond, BC, V6X 3G9
ph. 604-272-8226
email: [email protected]

Apple Leaf Drop

Apple leaf drop is sometimes diagnosed as a disease or sometimes as a nutrient deficiency. In fact, it is neither.

Application Methods of Mineral Elements

All fruit trees in the British Columbia Interior require applications of mineral elements in addition to nitrogen. These minerals can be applied directly to the soil as a granular fertilizer, sprayed onto the leaves (foliar), or delivered to the soil through irrigation system (fertigation). How much of each element and the best way to apply it will vary between orchards and growers due to differences in soil type, topography, and management practices. A balanced nutrient program is a part of good horticultural practices. A nutrient program is never a replacement for proper pruning, crop load management, and pest control.

Soil applied nutrients, either granular or fertigated, is the ideal means of supplying the bulk of a trees needs for such nutrients as nitrogen, phosphorus, potassium, and sometimes calcium. Other micro-nutrients that should be checked and sometimes balanced every few years are boron and magnesium. Boron is highly soluble in the soil, which can result in large differences in boron levels under drip irrigation systems vs the alley ways in an orchard. Magnesium, while usually applied as a spray, will also be supplemented whenever Sul-po-mag or dolomite lime is added to acid soil. There are some soil amendments that are used to help manipulate the chemical or structural make-up of the soil to improve conditions for nutrient uptake. Such soil amendments are various lime products, peat, compost, sulphur, gypsum, compost, and various mulch materials.

Foliar sprays are an efficient way to deliver some nutrients when they are required more at a specific growth period or when there are limitations to soil uptake by the tree. However, foliar fertilizers are very limited in the total amount of minerals they can deliver to the tree and thus, are most effective for minerals required in lesser amounts (micronutrients). In most orchards, foliar sprays of boron, zinc, and magnesium should be applied regularly to prevent the development of deficiencies of these elements. Multiple calcium sprays are applied annually as a means to aid fruit quality. If needed, manganese, and iron must be applied as sprays. The best time of day for foliar sprays is the early morning when temperature favour slow evapotranspiration. Morning is when the stomata (pores in the leaves) are open and the nutrients are taken up best when wet.

With over-tree irrigation, apply mineral sprays as soon as possible following an irrigation to allow maximum time for absorption before the next irrigation. The elapsed time between spray and the next irrigation must be not less than 24 hours but the longer the time the better.

Fertigation is the addition of fertilizers with irrigation water. Information is growing with this technique as local experience is gained with research and grower interest. Equipment specific to fertigation includes a back flow prevention device and equipment for injecting fertilizer into the system. A list of certified testers for backflow prevention devices is available at BC Ministry Agriculture offices.

Fertigation has several advantages:

Transport of nutrients directly to the root zone so that fertilizer amounts and timing can be precise.
Reductions in the amount of fertilizer applied relative to standard broadcast application.
Less excess nutrients will therefore be available to be leached and pollute the groundwater.

Fertigation cautions:

Drip irrigation system must be well designed to provide uniform water distribution
System must be maintained regularly to prevent plugged emitters.
Only soluble fertilizers can be applied and rates of fertilizers can be adjusted only by irrigation zone, not to suit individual trees.
To ensure that fertilizer is uniformly distributed regardless of the irrigation system layout:
- Begin fertilizer injections after the system operating pressure has stabilized following turn-on; and
- Allow 30 minutes of flushing with water after injection has been completed prior to switching to the next zone or turning the system off.

Such procedures are especially important if injections are infrequently made (i.e. weekly).

Soluble fertilizers which have been successfully applied include urea, ammonium nitrate and calcium nitrate as sources of N. There is an advantage to using the more expensive calcium nitrate (15.5-0-0) when soil pH is low and manganese toxicity is a problem. Ammonium polyphosphate (10-34-0), monoammonium phosphate (10-52-10), and phosphoric acid (0-68-0) have been successfully applied as a soluble replacement for first year planting hole granular P applications. Fertigation of phosphorus (P) is physically easier than the application of P to the planting hole. When using fertigation, lower amounts of P can be applied to achieve similar improvement in tree vigour and P nutrition. Most soluble P forms can react with Ca or Mg dissolved in irrigation water to form precipitates which may block emitters, especially when Ca and Mg concentrations exceed 300 mg/L (a mixing test can be done to check for potential precipitation problems). Although chelates or sulphates of most minor elements can be safely fertigated, such nutrients, if required, are more efficiently applied via foliar sprays.

Mineral Nutrients

Boron (B)

Boron is important for pollen tube growth and thus, is needed at bloom to aid fruit set. It is also needed for movement of plant sugars, and new cell formation in shoots and roots. Fruit trees grown in the British Columbia interior often require ground and foliar applications of boron at some point. However, excess boron is toxic to fruit trees, especially peaches, prunes and apricots. Leaf symptoms of boron deficiency and toxicity are similar in appearance. Therefore, where symptoms occur, leaf and soil testing must be done to determine which problem is present. Periods of drought or water-logging of soils can artificially result in a boron deficiency in the tree due to poor root uptake from the soil.

Soil and leaf analysis can be helpful in determining where boron should be applied and at what rate. Leaves showing suspicious symptoms can be collected in May for analysis compared to regular leaf analysis done in July. Leaf analysis cannot be used to test boron levels after post-bloom sprays have been applied to foliage. To avoid this problem, boron can be applied effectively in the fall before leaves start to senesce. In these cases and where boron toxicity is suspected, soil analysis is useful. High boron levels in the soil can be an indication of a potential soil drainage issue. Issues could be a hard pan that is not allowing proper drainage or there is a problem of leaching or seepage from a higher property. Applying boron without testing could aggravate tree damage where boron levels are already high. High boron levels in fruit are associated with early maturity and storage problems.

Where required in the soil, boron ideally should be applied in August. Dry or spray applications to soil should be distributed evenly over the main root zone areas and should not be made within one month of liming. Boron is normally applied to the soil at very small rates that can be difficult to apply uniformly and thus has started to be incorporated as a coating on fertilizer mixes to allow easier even distribution. Soil boron levels should be balanced with a soil application once every three years on fine and medium textured soils or annually on coarse soils. The best boron application methods to the soil are through a blended fertilizer mix or as Solubor dissolved in water and applied with the herbicide sprayer. Care should be taken not to exceed recommended rates with use of multiple products that contain boron.

Foliar boron sprays can be combined with sprays of chelated zinc, magnesium, manganese and urea. Boron sprays may also be combined with some pesticides. This may include a supplemental boron spray of solubor (20.3% B) at 2.8 kg/ha. Boron can be applied in the fall with other nutrients on all crops. In apples and Anjou pears, boron can be applied with the tight cluster stage dormant oil spray or at the pink-bud stage if not used the previous fall. Consult the container label to determine mineral-pesticide compatibility. Foliar boron sprays are not to be considered as substitutes for soil application in all years.

Soil boron (B) values less than 0.4 ppm (ug/g) are considered low. Soil values should not exceed 1.0 ppm for peaches, prunes and apricots or exceed 1.25 ppm for apples, cherries, and pears.

SUGGESTED RANGE OF LEAF LEVELS FOR BORON (Boron - ppm)
Leaf Type	Very Low	Low	Optimum	Moderately High	High
All	0 - 20	21-30	31-40	41-50	50+

Boron Applications for all Fruit Trees

Method of Application	Frequency of Application	Type of Material	Rate of Application
Method of Application	Frequency of Application	Type of Material	Per hectare	Per Acre
Broadcast over orchard soil.	Apply only when soil or leaf levels of boron are low.	Granubor Fertilizer Borate Granular (14.3% B) Various Orchard Mixes	20 - 34 kg Follow label	8 - 13.8 kg Follow label
Spray over orchard soil (coarse soils)	Preferably in August	Solubor (20.3%)	10 kg	4 kg
Air-Blast Sprayer (Foliar Spray)	When deficiency becomes apparent	Solubor (20.3%)	5.5 kg (Dilute 100 g/100 L)	2.2 kg (Dilute 454 g/100 gal)
Air-Blast Sprayer (Foliar Spray)	When deficiency becomes apparent	Bortrac 10.9%	1 L	400 mL

Possible Fertigation Boron Applications

It is relatively easy to increase leaf and fruit boron concentrations via fertigation of modest rates of 0.34g B per tree per year at any time in the growing season. The preferred time for fertigation applications though is within 4 weeks of bud break when leaf boron concentrations have been chronically low. Like nitrogen, boron is very soluble and can be leached from the soil with excessive irrigation, especially for sandy soils. As boron has a narrow range of suitability for most fruit trees it is not advisable to exceed recommended application rates or else toxicity and growth reduction will occur.

Calcium (Ca)

Calcium is very important for the building of strong cells in the fruit, new shoots, and roots. Calcium deficiencies contribute to certain fruit disorders including bitter pit, internal breakdown, storage rots, cork spot (Anjou pit), and alfalfa greening. Honeycrisp and large sized apples are particularly sensitive to bitter pit development. Fruitlet samples are the best method to determine if there are adequate amounts of calcium reaching the fruit. Leaf samples are the next best choice for monitoring calcium levels in the tree. Soil samples are not useful for determining the amount of calcium needed by the tree; however the use of lime to correct pH can add calcium to the soil (see Liming below).

Unfortunately, calcium is not highly mobile in the plant and can be limited in uptake from the soil in cool weather. The competition within the plant between leaves and fruit for limited calcium results in a need to supplement calcium through foliar sprays in season to the fruit every year. Calcium sprays are most effective when applications start during the period of fruit cell division (petal-fall) when demand and interplant competition is high. The next good timing is later in the season when the fruit is larger and acts as a bigger target. Calcium sprays alone cannot be expected to eliminate calcium related fruit disorders. There are several cultural factors that impact the amount of calcium in the fruit (see cultural and chemical controls below).

Bitter Pit of Apple, Cork Spot (Anjou Pit) and Alfalfa Greening of Pears

Bitter pit on apples shows as small pits that resemble miniature bruises. The skin within the pit is grey, brown or black and the flesh beneath is dry, brown and spongy. Bitter pit is most common on vigorous trees bearing light crops and is especially common on large fruit in the upper part of the tree. The symptoms may show in the orchard but more frequently they become apparent in storage. Bitter pit is a disorder that results from an inadequate supply of calcium to developing fruit.

Cork spot, often called Anjou pit, affects only Anjou pears. Pears develop a bumpy, uneven surface as they approach maturity. Affected areas turn yellow and soften prematurely. The flesh beneath the depressions is soft and turns brown or grey. Anjou pit occurs most seriously in seasons when hot, dry weather precedes picking. Cork spot is a disorder that results from inadequate supply of calcium to developing fruit.

Alfalfa greening (Green stain) affects only the Anjou variety of pears. Fruits develop dark green, slightly sunken areas on the skin shortly before picking. Alfalfa greening is a physiological disorder, most likely caused by a nutritional imbalance between calcium and nitrogen, and excessive irrigation.

Suggested Range of Leaf Levels for Calcium
Leaf Type	Low	Adequate	High
Apples	1.0	1.3	1.5
Cherries	1.5	1.8	2.1
Peaches	1.6	2.2	2.8
Pears	1.0	1.3	1.5

Control of Calcium Related Disorders

Cultural

1. Reduce nitrogen application to moderate tree vigour.

2. Avoid dormant pruning practices that stimulate excessive growing points and growth in tree.

3. Do not over or under irrigate in the spring.

4. Lime when soil pH is low.

5. Use bees to ensure good pollination for crop load and full seed set for drawing calcium to fruit

6. Practice summer pruning in vigorous trees mid-July to expose fruit to calcium sprays.

7. Do not apply excessive amounts of potassium in the spring.

Chemical

For Apples – There are several foliar calcium products to choose from. Some calcium products should not be tank mixed with other nutrients or pesticides, such as Calcium Chloride (see warning below). Apply choice product at 10 day intervals beginning at petal-fall. See warning below for when to use highly caustic products such as Briner’s Choice. Most orchards should aim for a total application rate of 10 kg/ha (4 kg/acre) actual calcium per orchard per year, however, more may be required in bitter pit prone varieties or cold wet springs.

Calcium Chloride WARNINGS– Application of unbuffered calcium chloride almost always causes non-serious burn of leaf edges but severe leaf and fruit injury is possible under some conditions. To reduce the chance of severe injury, be careful not to exceed recommended rates. Do not apply the spray under wet, humid, or slow drying conditions. Spraying when temperatures are high may also produce injury. Although the safe upper temperature limit is not known, it is suggested that damage may occur at about 27°C. In hot weather, growers should apply the spray during the coolest part of the day.

Compatibility of Calcium Chloride with Pesticides

1. Compatible with wettable powder formulations of Imidan.

2. Do not mix with spray oils or emulsifiable concentrate formulations of pesticides.

3. Do not add spreaders, stickers or emulsifiers unless specific instructions for their use are given.

4. Sprays should be applied promptly and not left in the spray tank longer than necessary.

5. Not compatible with magnesium, zinc or other plant nutrient minerals.

6. Not compatible with captan, carbaryl (Sevin), thiophanate-methyl (Senator).

For specific recommendations, consult your fieldman or Horticultural consultant. In general, the following table may be used as a guide.

For Pears – Do not apply at the apple rate as this may result in leaf and/or fruit burn. Apply three or more sprays at 2-week intervals beginning mid-May. Apply Briner’s Choice (34.5% calcium). For dilute applications use 0.4 kg/450L of water. Apply Briner’s Choice at up to 4.5 kg/ha (1.8 kg/acre).

For Stone Fruit – Some calcium products, such as Caltrac, can cause visible residue issues on many stone fruit that don’t go through a vigorous washing process before market. Early applications at the petal-fall or husk-fall stages are also beneficial for fruit quality in all stone fruit. See chart for application rates of various products.

Ca Sprays in Rain to Prevent Cherry Cracking

This application may not always work and is based on research using overhead irrigation application. Calcium sprays to prevent rain splitting go on during the rain event.

First spray: 3.2 kg CaCl₂/100 gal + 200 mL Agral 90

Subsequent sprays: 1.6 kg CaCl₂ /100 gal + 200 mL Agral 90

Can be applied every two hours during continuous rain showers. Potential problems – reduced fruit size if applied too often. The high concentration of salts can cause some leaf burning.

Copper (Cu)

Low leaf copper concentrations have been observed in a few Interior orchards, especially in young high density plantings. Leaf copper concentrations in all crops less than 4 ppm, especially if accompanied by symptoms involving sudden withering of leaf tips and die-back of the terminal portion of apparently normally growing shoots in summer, may indicate copper deficiency. Copper sulphate applied at 500 g product per 100 L of water using a gun sprayer should correct symptoms of copper deficiency.

WARNING – Do not apply to fruit during the growing season, especially Anjou pears, as fruit russeting is likely to occur. In other areas copper sprays have been applied at green tip or as a post-harvest foliar spray when there is no risk of spray injury. Post-harvest foliar sprays may also be applied as chelates or other copper containing compounds at recommended label rates.

Iron (Fe)

Iron chlorosis can occur with high pH soils (lime-induced chlorosis), such as seepage sites where salts have accumulated in the soils, or in water logged soils. Peaches and nectarines on peach seedling rootstocks are extremely susceptible to iron chlorosis. The use of peach/almond hybrid rootstocks can sometime help the situation if the lime layer is below the shallow roots in the soil profile.

Foliage may be made greener by foliar application of iron chelate products. This is a provisional measure and does not correct the basic cause, thus yearly application may need to be part of the orchard spray program if the underlying problem is a difficult to correct high soil pH condition. Although a temporary measure, it still can make an improvement in stem quality of cherries where iron deficiency is causing a problem. When iron deficiency is severe, repeat once or twice at 10-day intervals. It is best to apply early in the spring, under cooler temperature due to burning risk to plant tissue. Iron sprays may not be combined with sprays of pesticides or other minerals. Applied alone, they have occasionally injured sweet cherry and pear foliage and fruit. Dilute application is not recommended.

Suggested Range of Levels for Leaf Iron in all Fruit Crops

Adequate level = 45 ppm for all varieties of tree fruits.

Moderately high level-100 ppm.

Less than 45 ppm - Increase level by applying as per table below.

Foliar Iron Applications
Type of Treatment	Frequency of Application	Type of material	Rate of Application
			Air-blast sprayer
			per ha	per acre
Spray	Annually as soon as leaves well developed	Iron Chelate Ferleaf	1.1-2.25 kg 1 L	0.4-0.9 kg 400 mL

Magnesium (Mg)

Magnesium is a critical component of photosynthesis. Unless leaf magnesium is high, most orchards require at least one annual spray. Some orchards have become seriously deficient requiring 2 - 3 magnesium sprays annually. Magnesium deficiency symptoms (brown dead tissue and/or yellowing between leaf veins) are usually noted first on the basal leaves of the new shoot growth. It can show up on McIntosh and Spartan basal leaves in a heavy crop year. High levels of potassium (K) or low levels of available phosphorus (P) in the soil can also result in poor uptake of magnesium in the tree.

Magnesium sprays may be combined with sprays of boron, manganese or urea.

Foliar Magnesium Applications
Type of Treatment	Frequency of Application	Type of Material	Rate of Application
			Air-blast		Dilute
			per ha	per acre	per 100 L
Preventative spray	Annually as soon as leaves well developed OR Petal Fall	Magnesium sulphate 16% (Epsom salts) Hydromag	45 kg 4 L	18 kg 1.6 L	2 kg n/a
Curative spray	Repeat preventative spray two or three times, at 2-3 week intervals depending on the severity of the deficiency.

*Suggested Range of leaf Levels for Magnesium (Magnesium - %)*
Leaf Type	Low	Adequate	High
Apples	0 - 0.26	0.27 - 0.36	0.37+
Cherries	0 - 0.36	0.37 - 0.46	0.47+
Prune	0 - 0.26	0.27 - 0.36	0.37+
Peaches	0 - 0.36	0.37 - 0.46	0.47+
Pears	0 - 0.26	0.27 - 0.26	0.37+
Apricots	0 - 0.26	0.27 - 0.36	0.37+

Manganese (Mn)

Manganese deficiency occurs in only a few orchards, usually on alluvial fans near the lakes. Frequently, deficiencies are associated with a high soil pH together with the accumulation of soluble salts in the soil. Other orchards may suffer from manganese toxicity. Red Delicious and Fuji may show manganese toxicity in the form of bark measles. Apply manganese only if foliar analyses indicate that a deficiency exists.

Foliar Manganese Applications
Type of Treatement	Frequency of Application	Type of Material	Rate of Application
			Air-blast sprayer		Dilute
			per ha	per acre	per 100 L
Curative spray	Annually as soon as leaves well developed	Manganese sulphate Mantrac (27.4% Mn	9 kg 1 L	3.6 kg 400 mL	200 g n/a

Manganese sprays may be combined with sprays of boron, zinc chelate, magnesium or urea. Dilute application is not recommended.

Suggested Range of Levels for Manganese *(Manganese - ppm)*
Leaf Type	Low	Adequate	High
Apples, pears	0 - 25	26 - 60	60+
Cherries, Peaches	0 - 20	21 - 300	300+
Apricots	0 - 25	26 - 200	200+
Prunes	0 - 20	21 - 60	60+

Nitrogen (N)

Nitrogen Soil Application

Nitrogen is the primary mineral used in tree fruit nutrition. It is essential for tree growth, fruit sizing, and fruit set. However, too much nitrogen can lead to poor fruit colour and storage qualities, increased bitter pit, increased crown and root rot of apples, excess tree growth ( susceptibility to fire blight, increased pruning costs, mildew, increased populations of aphids, leafhoppers and pear psylla), and alfalfa greening and Anjou pit of pears. When trees do not respond to increasing amounts of nitrogen, the cause is frequently a deficiency of some other nutrient, most often zinc. Nitrogen applications can be wasted with excessive irrigation sets that drive the nutrients down past the rooting zone. Over irrigating and excessive nitrogen applications can be toxic in the environment due to leaching into ground or surface water.

Nitrogen is best applied as a soil application very early in spring. The nitrogen is then available very early to help the tree during critical growth and fruit development stages. Nitrogen applications to the soil should not exceed end of May in all fruit bearing blocks. It is especially important in apples so that soil nitrogen levels are low by the time the fruit is colouring in late summer. In young nurseries and new plantings, soil applied nitrogen should not be applied after mid-July (clay) or mid-August (sand) depending on soil type.

Determining how much nitrogen to use is not always easy. The nitrogen needs of an orchard will be higher with young trees filling space, large crop years, and stone fruits. Any suggested rates in this chapter are just starting points and will need to be modified through observations and data from your own orchard blocks.

All nitrogen fertilizers must convert to the nitrate form of nitrogen in the soil for the majority of uptake by the tree. Some ammonium can be taken up directly by the tree. Thus, the different choices of fertilizers can vary in how long they take after application to be available to the tree. The most commonly recommended ground nitrogen fertilizers used are urea (46-0-0) and ammonium sulphate (21-0-0) that can take up to 3 weeks to convert for tree uptake, especially in cool springs. Ammonium sulphate is more acidifying than the other fertilizers. Ammonium nitrate (34-0-0) is the old standard, but only available through limited controlled locations, requires ID, and is an expensive form of nitrogen. Ammonia urea sulphate (34.5-0-0) is now a common replacement, but acts differently than ammonium nitrate (34-0-0) due to the absence of nitrate. Calcium nitrate (15.5-0-0) though expensive, has quick uptake and may also be used with no acidifying effect and can be used with drip emitters on sandy soils. Calcium ammonium nitrate (CAN 27-0-0) is half calcium nitrate (quick uptake) and half ammonium (can take 3 weeks to convert) with no acidifying effect. Nitrate and urea forms of nitrogen are more easily leached out of the soil than ammonium forms however, ammonium will readily convert to nitrate under optimum pH and aerobic conditions.

Commonly Available N Fertilizers in BC (*available in soil and foliar form)

Source	Analysis %
Source	Nitrogen	Calcium	Sulphur
Ammonium Sulfate 21-0-0	21.0		24.0
Ammonium Urea Sulphate 34.5-0-0	33.0-34.5		11.0
Calcium Nitrate 15.5-0-0*	5.0	34.0
Urea 46-0-0*	45.0 - 46.0
Calcium Ammonium Nitrate 27-0-0	27.0	4.0
Liquid Blend 32-0-0	32.0
Liquid Blend 12-0-0-26S	12.0		26.0

Due to the various options, it is helpful to record your applications as ‘actual N’ applied by acre or hectare so you are using comparable rates properly.
For example:     100 lbs of 21-0-0 would be 100 lbs x 21% = 21 lbs actual N.
                          100 lbs of 46-0-0 would be 100 lbs x 46% = 46 lbs actual N
Thus, the same quantity of each fertilizer results in half the amount of nitrogen being applied as calcium nitrate relative to urea.

Fertilizer should be spread evenly within the clear “herbicide strip” around the tree trunks to target the main root zone. It may be spread evenly over the orchard floor in orchards with closer-spaced smaller trees, however, fertilizer rates should be adjusted to match the total area of application. Do not concentrate acidifying fertilizers in piles or narrow bands as this will cause “hot spots” of low pH. Spread fertilizer a day or two after a full irrigation set, then irrigate for only 2 hours following application to help move the fertilizer just into the root zone of the trees. Urea fertilizer left sitting on the surface of the ground in warm weather can lose nitrogen to the air through volatilization.

First Year Non-Cropping

Possible Broadcast Nitrogen Application Rates

Rates and Frequencies of First-Year N Soil Broadcast Applications
	Sandy Soils	Loamy Solis	Heavy Soil
Actual N/ha	120 kg	90 kg	60 kg
Actual N/10 m²	120 g	75 g	60 g
Number of Applications	Split into 3 applications		1

Fertilizer rate = (actual N rate) x 100

% N in fertilizer

Example (for urea on a sandy soil): Fertilizer rate = 120 kg N/ha x 100 = 260 kg urea (46-0-0)/ha

First soil application recommended soon after planting. Most nitrogen fertilizers (especially Nitrate forms) are highly soluble and are washed from the root zone with frequent and over irrigation.

Possible Fertigation N Applications

Fertigation Rates and Timings for First-Year Plantings
Growth Period Post-bloom	Amount (g/tree/season)
	Sandy Soil	Loamy Soil	Heavy Soil
1 - 4 weeks	20	15	10
5 - 8 weeks	30	22	15
8 -12 weeks	10	5	5
Total	60	42	30

Commence applications at post-bloom when finished phosphorus applications. These fertilizer rates compensate for the inefficiency of nitrogen uptake from sandy soils where irrigation can leach nitrogen below the root zone. It will be possible to reduce the amount of nitrogen applied by as much as 50% by avoiding excessive leaching loss of nitrogen by, for example, atmometer scheduled irrigation. Recent research has indicated in an orchard with a sandy loam soil and irrigation controlled by atmometer based scheduling that production and quality of apples could be sustained by application of a total of 12-15 g nitrogen per tree, applied during any 4 week period.

Second Year (Transition to Fruiting Trees)

If high density planted trees have failed to adequately fruit after first year, continue first year nutrition program. If vigour has been low, also investigate possibility of another nutrient deficiency (leaf analysis) or inadequate first year irrigation. If vegetative vigour is excessive, reduce nitrogen application rates by to ½.

Mature Bearing Trees

Broadcast

Mature producing trees are considered to be those capable, due to size, of carrying 30 to 50 bins of fruit per acre. Reduce the suggested nutrient schedule if mature trees that are capable of carrying a full crop, have experienced a frost or event that results in a significantly lighter crop. Smaller trees that must still grow to achieve a structure that fills the tree spacing and are older than 3 to 4 years may be carrying too heavy a crop for the tree size. These weaker trees should receive the start of their nutrient schedule after bloom and should not have rates cut with the removal of crop load.

In all apples, too much nitrogen can lead to poor fruit colour (especially in heavy crop years), soft fruit, poor storage quality, increased bitter pit issues, crown and root rot of apples. There can be varietal differences in nitrogen requirements. For example, Honeycrisp is especially sensitive to balance tree needs compared to fruit needs. The fruit requires low levels of nitrogen as long as growth is adequate (pruning and crop load management seems to encourage adequate growth) as fruit size and quality is easily negatively affected.

Factors such as fruit size, block colouring, crop load, susceptibility to bitter pit and maturity dates may influence the amount of nitrogen needed in a given block. Growers should plan to make adjustments to their nitrogen rates based upon these and other influencing factors. Higher crop loads have higher nutrient requirements, thus more total nitrogen is required to produce a 45 bin/acre crop compared to a 20 bin/acre crop. Some of the rich silt soils may require very little, if any, nitrogen for mature producing trees for a number of years in a row. Vegetative growth, leaf nitrogen analysis, fruit size and fruit colour development must be used to adjust rates of application.

These nitrogen recommendations are guidelines only! There is no substitute for careful observation. In late dormant period, usually late March to early April, nitrogen applications can have a broad range of 30-140 kg actual N/ha. As mentioned above, the rate will depend upon tree growth, commodity, and fruit quality. The lower rates are for apples growing in good soil compared to the higher rates for peaches growing in sandy soil.

Vegetative/Fruit Balance

As a good balance between cropping and vegetative growth is achieved, less nitrogen per kg of fruit is used. Good consistently cropped trees have proportionately less vegetative extension growth. There is less demand for calcium, i.e. a better leaf to fruit ratio. High leaf to fruit ratios, that is lots of vegetative growth and a light crop, particularly under low humidity, creates a stronger leaf demand for calcium away from the fruit. Large fruit size with a small crop will also contribute to a calcium dilution in the fruit.

To determine if you are using a good amount of nitrogen for mature trees, measure the length of current season’s terminal growth. Too much or too little growth, as well as leaf analysis results provides the information needed to help adjust the required nitrogen rates for the following season. Measure leading terminals growing outwards at an angle of 45 degrees around the outside of the tree and take an average of these measurements. Increase, reduce or eliminate the quantity of nitrogen fertilizer to achieve the correct amount of terminal growth as shown in the following table:

Correct Amount of Terminal Growth¹
Mature spur Red Delicious apples (Gala, Ambrosia)	25-30 cm
Mature non spur Red Delicious apples (Granny Smith, Fuji, Pink Lady	30-40 cm
Other mature apples and prunes	25-30 cm
Mature pears and cherries	30-35 cm
Mature peaches and apricots	40-45 cm

¹ For apple trees on size controlling rootstocks (M.9, M.26, G.41), the lower values should be used.

Nitrogen must be in good supply as reserves in the tree for developing flowers and fruitlets. In apples, excess nitrogen is one of the main contributors to poor fruit colour and poor fruit quality. In cherries, it has been suggested in studies from Michigan that a ratio of 5 leaves: 1 cherry is ideal for sizing quality fruit. Previous season nutrient applications can have a big impact on spring reserves in the current season. Nitrogen applied over the winter and spring up to flowering encourages strong vegetative growth. If there are concerns, nitrogen applications can be delayed until immediately after bloom to allow for adjustments to match crop load. In all fruit trees, heavy cropped trees may also need additional nitrogen foliar spray after harvest, or before harvest in late maturing apple varieties. Regular leaf analysis is strongly recommended to assist in determining nitrogen requirements.

The relationship between tree spacing and actual nitrogen fertilizer application rate (kgN/ha) and amount of nitrogen supplied is indicated in Table below.

Common per ha Soil Nitrogen Application Rates in Actual g N/tree for Established Trees for Various Spacings
	50 kg/h	100 kg/ha	150 kg/ha	200 kg/ha	250 kg/ha	300 kg/ha
4.5 x 12	25 g	50 g	75 g	100 g	125 g	150 g
4 x 11	20 g	40 g	60 g	80 g	100 g	120 g
3 x 11	15 g	30 g	45 g	60 g	75 g	90 g
3 x 10.5	15 g	25 g	35 g	50 g	65 g	75 g
2.5 x 10.5	15 g	25 g	35 g	50 g	65 g	75 g
2.5 x 10	15 g	25 g	35 g	50 g	60 g	70 g
2 x 10	10 g	15 g	25 g	35 g	45 g	55 g
1.5 x 9	10 g	15 g	25 g	30 g	35 g	40 g

* Fertilizer rate = (actual N rate) x 100

% N in fertilizer

Fertigation

N Fertigation Timing for Established Trees
Growth Period	Feeding
1-4 weeks before & during bloom	No N applied by fertigation (assuming good N nutrition status in previous years)
Post Bloom (1^st week of June)	Start fertigating 40 bin/acre and heavier crops
Mid-June	Start feeding 20, 25 & 30 bin/acre crops
Beginning of July	Start feeding 10 & 15 bin/acre crops. Do not feed N to crops on mature trees that have less than 10 bins/acre
Finish feeding N by end of July for all trees	40 bin/acre crops and larger- feed late N just before or after harvest, applying approximately 15-20% of the total N.

Nitrogen Foliar Application (Urea)

IMPORTANT: None of the foliar mineral element sprays should be applied with emulsions or oils.

Foliar applications of urea: To avoid delayed maturity of fruit, do not apply urea later than 45 days before harvest on apples or pears or later than 21 days on stone fruit. Use of foliar urea on pears may aggravate fire blight. A fall spray (September) of 20 – 40 lbs /acre of urea on sweet cherries has been found to be very effective at helping with first leaf sizing the following season when nitrogen in the tree is low.

Ammonium thiosulphate (ATS) is a liquid fertilizer containing 12% nitrogen and 26% sulphur. A dilute spray (see page 14-15), at rates ranging from 1.2 L per 100 L to 1.6 L per 100 L, applied to the point of run-off when 80% of the blossoms are open has resulted in larger fruit size and increased return bloom of several apple cultivars. Caution is necessary, however, as foliage injury and excessive fruit removal can occur when this material is applied. Some growers concentrate spray more at the tops of trees where the nutrient is needed more. Apply under good drying conditions. Cultivars differ in their sensitivity to ATS. Application of ATS is not suggested for varieties such as Braeburn and Sunrise that have low fruit set tendencies as excessive fruit removal may occur. Jonagold, Gala, and Empire are sensitive to rates above 1.2 L per l00 L. Spartan, Fuji, Delicious, Golden Delicious, and McIntosh have benefited from rates up to 1.6 L per 100 L.

When applying, use eye protection, a respirator, rubber gloves and protective clothing.

UREA (46-0-0) SPRAY FOR ALL TREES
Time of Application		Rate of Application
		air blast sprayer		dilute
		per hectare	per acre	per 100 L
1. Young non-bearing trees with poor growth 2 sprays 2 weeks apart.	June - July	11 kg	4.4 kg	1.0 kg
2. Bearing trees more than one spray may be required.	Petal fall - June	13 kg	5.3 kg	0.5 kg

*Suggested Range of Leaf Levels for Nitrogen (Nitrogen %)*
Tree Fruit	Tree Age	Low	Adequate	High
McIntosh apple	Mature	1.6	1.9 - 2.3	2.5
McIntosh apple	Young	1.6	1.9 - 2.6	2.8
Spartan apple	Mature	1.5	1.8 - 2.2	2.4
Spartan apple	Young	1.5	1.8 - 2.5	2.7
Ambrosia, Gala, other apples		1.6	1.9 - 2.4	2.6
Cherries	Mature	1.6	1.9 - 2.7	3.3
Cherries	Young	1.6	1.9 - 3.0	3.6
Plum/Prune	Mature	1.6	1.9 - 2.5	3.0
Plum/Prune	Young	1.6	1.9 - 2.8	3.3
Peach	Mature	2.0	2.6 - 3.2	3.8
Peach	Young	2.0	2.6 - 3.5	4.1
Pear	Mature	1.6	1.9 - 2.3	2.5
Pear	Young	1.6	1.9 - 2.5	2.7
Apricot	Mature	2.0	2.6 - 3.2	3.8
Apricot	Young	2.0	2.6 - 3.5	4.1

Phosphorous (P)

Soil sampling is not a reliable method for assessing available phosphorus levels for application decisions. Plant tissue samples are a more accurate method to assess phosphorus needs by the trees. The adequate level in leaves of mature apple and stone fruit trees is 0.15%. A leaf phosphorus concentration range of 0.20 to 0.30% is recommended for 1- to 2-year-old apple trees. Recent research has indicated that early flowering in apples is promoted by high phosphorus nutrition in the first year. High leaf P in year 1 increases the number of flower clusters the second year for apples on M.26 and M.9 rootstocks.

Foliar phosphorus applications are used during the cell division period of the fruit following petal-fall to help with fruit quality and sizing potential. A few studies found Phosphorus used within 6-weeks of apple harvest may help boost apples already developing colour, however, results can be variable. Fruit exposure to the sun will still give the highest colour results compared to any fertilizer treatment.

Most newly transplanted trees benefit from the addition of a soil phosphorus treatment to ensure available phosphorus in the soil for improved root development. Years of replant bioassays in apples by Dr. John Slykhuis, showed phosphorus and then fumigation treatments as having the most consistent significant effect on positive root growth. Phosphorus is more efficiently utilized when applications are incorporated near the developing roots by mixing into the soil of the planting hole or percolated into the main root zone as dissolved phosphorus in irrigation water.

Common P fertilizer sources in B.C. are shown in the table below.

Ammonium phosphate fertilizers are the most common choices for phosphorus fertilizers with replants because high phosphorus availability has been observed when they are applied in the root zone. The most used ammonium phosphates are the granular monoammonium phosphate (11-52-0) or the soluble 10-52-10. Rock phosphate and triple superphosphate (0-45-0) are granular forms, which are less soluble and are less available to trees when surface broadcast. Liquid formulations suitable for fertigation include ammonium polyphosphate (10-34-0) or phosphoric acid (0-54-0). Organic waste materials, such as composts, with known high phosphorus (near or exceeding 1 %), can be applied at rates of 4-5 tonnes/ha rototilled into the planting row. With any incorporated granulars or composts, make sure the fertilizer is mixed well with planting hole soil or peat mixtures. Reduce rate by half on extremely coarse textured gravelly soils to avoid root burning.

NOTE: Prior to planting new trees in old orchard soils, read the last paragraph under LIME and the section on APPLE REPLANT PROBLEM

WARNING: Phosphite based fertilizers are NOT a source of phosphorus to the tree. Phosphites are used to help move whichever nutrient is attached to it into the plant.

Phosphorous Applications for all Tree Fruit
Type of Treatment	Frequency of Application	Material Choices	Rate of Application			Notes
Type of Treatment	Frequency of Application	Material Choices	per tree	per ha	per acre	Notes
Ground for new planting	Incorporated into soil pre-planting	11-52-0 Mono Ammonium Phosphate 0-45-0 Triple Super Phosphate	0.8-1.5/L soil (gravel-clay)	23-41 kg	9-16.5 kg	Can seriously burn roots and must be well mixed into the planting hole or trench. Approximate guidelines: 5 L soil high density to 30 L soil low density*
Ground for new planting	Dissolved in planting water	10-52-10 Mono ammonium phosphate	2.5 kg /375 L applied @ 1 L /tree high density to 6.5 L /tree low density*	37.5 kg	15 kg (1 -2 apps)	Do not do a full irrigation for a week after application to avoid washing nutrients past root zone. Very low burn risk.
Ground for new planting	Fertigation	10-52-10 0-55-0 10-34-0	See fertigation chart			Fertigation depends on many factors. Consult supplier of fertigation system.
Foliar spray	Petal fall	Hydrophos Deniphos Nutraphos 10-51-10		10 L 10 L 6.25 - 12.5 kg 6.25 kg	4 L 4 L 2.5 - 5 kg 2.5 kg

* Based on high density = 2' x 10' trench planting (2178 trees per acre) and low density = 8' x 16' auger planting (340 trees per acre)

Commonly Available Soil P Fertilizers in BC
Material	Frequently used Abbreviations	Analysis (%)			Form of P	% Total P Available	Formula of Main P Compounds
Material	Frequently used Abbreviations	N	P₂0₅	S	Form of P	% Total P Available	Formula of Main P Compounds
Rock phosphate	RP		25-40		Orthophosphate	14-65	(Ca₃(PO₄)₂)₃.CaF_x. (CaCO₃)_x.(Ca(OH)₂)_x
Wet Process phosphoric acid			48-53		Orthophosphate	100	H₃PO₄
Triple superphosphate	TSP or CSP		44-53	1-1.5	Orthophosphate	97 - 100	Ca(H₂PO₄)
Monoammonium phosphate	MAP	11-13	48-62	0-2	Orthophosphate	100	NH₄H₂PO₄
Diammonium phosphate	DAP	18-21	46-53	0-2	Orthophosphate	100	(NH₄)₂HPO
Ammonium polyphosphate	APP	10-15	35-62		Ortho & poly	100	(NH₄)₂HP₂O₇+other
Soluble High Phosphorus Blend	NPK	10	52		Orthophosphate

Possible Fertigation P Applications

Phosphorus is an important element in root growth. The use of liquid and soluble granular products are generally more efficient than granular recommendations used in the planting hole, therefore rates are lower for phosphorus than those for planting hole application. Use caution if mixing more than one nutrient in fertigation as phosphate fertilizers can be incompatible with some magnesium or calcium fertilizers resulting in precipitates that plug emitters. Check irrigation water calcium (Ca), magnesium (Mg) and bicarbonate (HCO₃) concentrations. According to information from Ontario, to avoid phosphate precipitates, Ca and Mg combined levels should be less than 50 ppm and HCO₃ less than 150 ppm.

P Fertigation Rates
Growing Period (start at bud break)	Phosphate (P₂O₅/tree)*	Phosphate (P₂O₅/ha)	Phosphate (P₂O₅/acre)
1^st 4 week period	20 g	29.1 kg	11.8 kg
2^nd4 week period	5 g	7.3 kg	2.9 kg
3^rd 4 week period	5 g	7.3 kg	2.9 kg
4^th 4 week period	5 g	7.3 kg	2.9 kg
Total	35 g of P₂O₅/tree/season	51 kg of P₂O₅/ha/season	20.5 kg of P₂O₅/acre/season

*If planting is high density reduce the amount/tree so that 80 kg/ha or 32 kg/acre is not exceeded.

Second Year (Transition to fruiting trees)

Continue P fertilizer regime if trees have failed to grow adequately.

Mature Fruiting Trees

Phosphorus demands of mature fruiting trees usually declines so annual soil phosphorus fertilizer may not be required. Monitor leaf and fruit concentrations to ensure adequate phosphorus nutrition. Recent research has indicated that applications of 20 g P₂O₅per tree as ammonium polyphosphate annually at bloom would be advantageous for apples receiving adequate applications of nitrogen, potassium and boron.

Potassium (K)

Potassium is an important major element in tree growth and function, however, deficiency is not a common disorder in British Columbia. Potassium deficiency has been shown to be more common in high density fertigated orchards, especially when drip irrigated. The deficiencies usually develop in sandy, coarse textured soils and show up as trees begin heavy fruit production (usually third year. It is characterized by reddish brown leaf scorch symptoms. Symptoms appear when leaf potassium is below 0.70%. The majority of orchards in British Columbia show leaf tests above the adequate level of 1.3 – 1.6% for apples, cherries, prunes and pears and 1.2% for apricots and peaches. Potassium deficiency is less common in lower density orchards with sprinkler irrigation but has been reported when soil potassium levels are low. Potassium deficiency can be corrected by surface application of 100-200 kg of potassium /ha as KCl (0-0-60) applied every 3 years.

Some studies have shown an improvement of fruit colour when potassium nutrition moves from deficient to adequate levels (See production guide leaf analysis levels), but too much potassium can be a problem. Unnecessary application of potassium to tree fruits may interfere with uptake of calcium and magnesium. Calcium is especially important for the prevention of bitter pit and breakdown in apples and preventing Anjou pit in pears. Magnesium is important in preventing leaf scorch and premature dropping in apples.

Fertilizer Potassium

Commonly Available K Fertilizers in BC
Material	Analysis (%)
	N	P₂0₅	K₂0	S	M
Potassium chloride			60-62
Potassium sulfate			50-52	17
Potassium magnesium sulfate			22	22	11
Potassium nitrate	13		44

Possible Broadcast K Applications

Apply 200 kg K/ha when soil and leaf K levels are low.

Possible K Fertigation Applications

N-K fertigation should be considered for high density orchards on sandy soil especially when drip irrigated. The following rates can commence in the first year and then be adjusted upwards or downwards depending on K concentration in subsequent years.

K Fertigation Rates
1^st 4 week period	1.5 - 4.5 g*	8.3 kg	3.3 kg
2^nd4 week period	1.5 - 4.5 g*	8.3 kg	3.3 kg
3^rd 4 week period	3 - 8 g*	16.6 kg	6.7 kg
4^th 4 week period	3 - 8 g*	16.6 kg	6.7 kg
Total	9 - 25 g K₂O/ tree/season*	50 kg/ha/ season	20 kg/acre/ season

*If planting is high density reduce the amount of K₂O/tree so that 50 kg/ha or 20 kg/acre is not exceeded.

**It is also important to monitor leaf Mg and fruit Ca to avoid any negative antagonism with K.

Soil Sulphur (S)

A sulphur fertilization recommendation is issued by some laboratories when the soil sulphur level is 25ug S/mL soil or less. This soil test level is used to ensure sulphur adequacy for all crops grown in British Columbia. Ensuring immediate adequacy can be realized at little or no cost by using a fertilizer that contains sulphate-sulphur as a secondary nutrient; for example, ammonium sulphate (21-0-0); Epsom salts (magnesium sulphate); potassium sulphate (0-0-50); gypsum (calcium sulphate) and other fertilizers. On calcareous soils (those with a pH above 7) using 21-0-0 when applying nitrogen fertilizer will ensure sulphate adequacy. However, this fertilizer should not be used on acid soils (See Soil Acidification).

Zinc (Zn)

Zinc is important in trees for the formation and function of chlorophyll, several enzymes, and the growth hormone auxin. Foliar analysis results indicate low zinc levels in interior orchards, particularly in apples, cherries, and pears. This is due to sandy soils with pH levels above 7.5 or below 4.5 where even if soil sample levels show high amounts of zinc, it is not available to the trees. Zinc does not move readily within the plant due to translocation problems. It is common for leaf zinc concentrations to remain low, even after application of recommended dormant zinc sprays. However, zinc does not easily wash off leaves and the use of chelated zinc products in the spring/summer or Ziram will contaminate leaf sampling for subsequent nutrient analysis. Use the early dormant spray timing if planning on using leaf analysis in the summer to monitor zinc levels. Zinc deficiency symptoms such as chlorosis, blind bud, rosetting and little leaf can, however, be reduced by such applications.

For apples it is recommended that zinc sulphate be applied annually at silver tip to green tip stage of bud development (stages 2 and 3), supplemented by one or more sprays of chelated foliar formulations of zinc during the growing season. It is not recommended to use chelated products, such as Zintrac, mixed in with the dormant oil sprays as a replacement to zinc sulphate applications. Chelated products are designed for best absorption when applied directly to leaves.

Two zinc sulphate sprays are recommended for cherries; the first during the late dormant period up to bud swell stage (stage 2). Do not mix with the dormant oil spray. The second spray can be applied within 2 weeks after harvest. Chelated zinc products can also be used during the growing season to help supplement zinc, but should never fully replace the dormant zinc sulphate spray.

For pears, an annual application of zinc sulphate is usually adequate. Apply at green tip stage (stage 3) before dormant oil.

For other kinds of fruit trees showing low zinc levels, a zinc sulphate application at late dormant stage should be applied annually.

*Suggested Range of Leaf Leels for Zinc (Zinc - ppm)*
Leaf type	Low	Adequate	High
Apple	0 -20	21 - 25	26+
Cherry	0 - 16	17 - 26	27+
Prune	0 - 16	17 - 26	27+
Peach	0 - 16	17 - 26	27+
Pear	0 - 14	15 - 24	25+
Apricot	0 -16	17 - 26	27+

Foliar Zinc Applications
Type of Treatment	Time of Application	Type of Material	Rate of Application
			Air-blast sprayer		Dilute
			per ha	per ac	per 100 L
Zinc sulphate spray for all tree fruits - to be used when foliar analysis indicates low zinc levels	Stone Fruits late dormant Apples & Pears silver tip. Causes injury if applied in summer	zinc sulphate (36% Zn)	40 kg	16.2 kg	1.25 kg
		OR liquid zinc sulphate (1.5 kg a.i. zinc per 10 L, or, 1.5 lb a.i. zinc per gal)	95 L	38.5 L	2.5 L
Zinc products* that may be used to supple- ment but not replace zinc sulphate treatment	From tight cluster until end of June	Powdered zinc chelates	Follow label recommendations
		OR Zinc Oxide (Zintrac 40%)	1 L	400 mL
Zinc sulphate spray for cherries only+	Within 2 weeks after harvest only	zinc sulphate dry (36% Zn)	up to 12 kg	up to 4.9 kg	up to 1000 g
		OR liquid zinc sulphate	7 L	2.8 L	625 mL

* May be applied with sprays of boron, manganese, magnesium or urea.

+ WARNING – Do not apply at air temperatures above 30°C, do not mix with other chemicals and do not allow drift to other crops.

Other Soil Amendments Affecting Soil and Plant Nutrition

Soil Acidification and Changes in Nutrient Content

Soil acidification can occur in orchards from the use of nitrogen fertilizers. Soil acidification can be accelerated by applying acidifying fertilizers through drip irrigation (see table below). The rate at which a soil becomes acidified depends on the type of soil. A sandy soil becomes acid more quickly than a clay soil. High lime or organic matter content in a soil slows the acidification process. Sensitivity to soil potential acidification can be identified through a quick test that determines the Acidification Resistance Index (ARI). This index is calculated from standard soil test data (soil pH and exchangeable Ca, Mg, K, Na). The results of the quick test and recommendations are available from your soil test laboratory. There are three categories of soils:

ARI 0-5 very sensitive

ARI 6-25 moderately sensitive

ARI >25 not sensitive

Acidification can be prevented by using fertilizers that do not contain either ammonium or urea. Soils that are already acidified should be limed to at least pH 6.5 before planting.

After several years of drip irrigation, the nutrient content of soil beneath drip irrigation emitters may change. Soil sampling to determine soil boron, potassium and salinity is a desirable strategy to prevent nutrient deficiencies or excesses from developing. Comparison of a composite soil sample (see soil sampling section) collected directly beneath emitters to samples collected from alleyways would provide a measure of changes which may have occurred in specific orchards or orchard blocks.

Recent research indicated that orchards frequently have very low leaf boron and zinc concentrations and occasionally low leaf magnesium and potassium levels. Regular leaf sampling and analysis will alert the grower to emerging problems and is an excellent strategy to track the nutritional health of orchard blocks.

Equivalent Acidity of Commonly Applied Fertilizers
Fertilizer	Content	*Equivalent Acidity (in kg CaCO₃)**	Or Basidity
Urea	45-46% N	71
Calcium nitrate	15.5% N		20
Phosphoric acid	52-54% P₂O₅	110
Monoammonium phosphate	11% N, 48% P₂O₅	58
Diammonium phosphate	16-18% N, 46-48% P₂O₅	70
Ammonium sulphate	21% N, 24% S	110
Anhydrous ammonia	82% N	148
Triple superphosphate	45-46% P₂O₅, 1% S	Neutral
Potassium chloride	60-62% K₂O	Neutral
Potassium nitrate	13-14% N, 44-46% K₂O		26
Sulphate of potash magnesium	22% K₂O, 22% S	Neutral

* Per 100 kg of fertilizer, amount of lime required (acidity) or applied (basicity). From Western

Fertilizer Handbook.

Note: There are also various N sources containing multiple nutrients. These forms of N are usually more expensive sources of N but are advantageous under situations where other nutrient deficiencies occur as indicated by leaf, soil or fruit analysis.

Lime (Calcium carbonate, Dolomite and calcium hydroxide)

Soil Application

Where soils have become acidic (below pH 6), poor tree growth and certain disorders, such as bark measles on Red Delicious or Fuji, may result. Lime may be applied to raise soil pH levels. Most virgin soils in the British Columbia Interior are neutral or alkaline (i.e. pH 7.0 or higher). However, the use of most nitrogen fertilizers and continued irrigation in orchards for many years favours the development of acidic conditions which are caused by the leaching of calcium and magnesium. Low pH levels are most likely to appear in coarser soils and are often restricted to areas within the driplines of trees, where fertilizers have been applied.

The need for liming must be determined by measuring soil pH. The quantities of limestone to be applied to achieve pH 6.0 or 6.5 can be determined with a lime requirement test.

The lime prescribed by a soil test is assumed to have a neutralizing value of 100 calcium carbonate equivalent. Rates for other materials must be adjusted according to their calcium carbonate equivalent. For example, calcium hydroxide (hydrated lime) as used fresh has a calcium carbonate equivalent of 135, and therefore, only 76% as much of this material needs to be applied. Lime which has been used in CA storage and dolomite lime may be applied at the liming rate recommended for calcium carbonate. However, CA lime must be applied in a pulverized (fine) condition to obtain effectiveness equal to ground limestone. Dolomite lime, in addition to alleviating soil acidity, is valuable for supplying magnesium which is commonly deficient to McIntosh, Spartan and Newtown apples.

Lime can be applied at any time of year, except that one month should be allowed between application of fertilizer and application of lime to avoid loss of ammonia nitrogen to the air. Also, one month should be allowed between soil-applied boron and application of lime. Spring and summer applications of hydrated lime require care be taken to avoid deposits on foliage and fruit, which can suffer burning.

Lime must be broadcast evenly over areas in which the pH is low (pH 6.0 or lower). These will usually be areas where fertilizer has been spread year after year. Areas of an orchard in which soil tests show pH levels above 6.5 should not be limed. Shallow cultivation after application will aid in the absorption of lime. However, shallow cultivation can also damage tree roots, outweighing any advantage to cultivating in the lime.

Limed soils begin to re-acidify from the surface upon reapplication of the commonly used nitrogen fertilizers (urea, ammonium nitrate and ammonium sulphate). Regular pH monitoring of the surface layer (10 cm) will indicate when there is a need to reapply.

Before planting trees, soil samples should be taken at 0-30cm depth. If the soil pH is below 6.0, lime should be thoroughly worked into at least the top 15 cm of soil or deeper if warranted and machinery will permit. Lime should be applied at a rate to bring the soil pH to 6.5. Otherwise the pH could drop below 5.5 before the trees become established, especially in sandy soil, and cause bark measles, slow growth, and other damage to the trees.

Compost and Other Soil Amendments

This chapter has been prepared in the spirit of encouraging effective use of high quality compost to improve the long term sustainability of fruit production in interior BC. Not all compost is the same, and raw manure is not compost.

Overview

Enhancing soil organic matter is critical for sustaining orchard productivity, particularly for orchards on coarse-textured soils with low organic matter contents. Enhancing soil organic matter has multiple benefits that all contribute to improved root growth. These benefits include improved soil structure or “tilth”, increased storage of soil nutrients in relatively “slow release” forms and reduced need for supplemental fertilizers, improved pH buffering, and improved water-holding capacity; enhancing soil organic matter may also cause specific changes in soil biology that translate to reduced activity of root pathogens.

For orchardists, the most effective means of enhancing soil organic matter is through the addition of compost to the root zone, either through incorporation into trenches or planting holes before replanting, or through surface application to established plantings.

Composts are distinct from manures and other organic wastes: It is very difficult to use manures and some other non-composted organic wastes as soil amendments without injuring crops and having negative impacts on environmental quality. Such materials can burn roots (salt stress, ammonia, organic acids), and surface application can increase the prevalence of fecal bacterial contaminants in the orchard environment which in-turn increases the probability of fruit contamination. Due to risk of fecal bacterial contamination, Canada GAP certification does not allow application of manure within 120 days of harvest whereas finished compost can be applied at any time of the year (http://www.canadagap.ca).

How is compost distinct? Compost is stabilized earthy matter having the properties and structure of humus or native soil organic matter that is beneficial to plant growth when used as a soil amendment. Compost is produced by actively managing the decomposition of large quantities of fresh organic matter. The first phase of composting involves intense microbial activity as the most easily decomposed parts of the organic matter (sugars, starches, proteins) are quickly metabolized. In most cases, this phase generates heat and the material reaches temperatures in excess of 50 C, which kills fecal bacteria, plant pathogens, insects and most weed seeds. After the most easily decomposed material has been utilized by the microbes, the rate of activity drops off and the material is considered to be “stable”. This property of stability is important because the application of non-composted organic materials to soil in relatively large quantities can stimulate undesirable flushes in soil microbial activity resulting in the immobilization of nutrients and production of organic acids that are detrimental to root health. In the case of organic wastes with high nitrogen contents, such as poultry manure, high application rates can also generate toxic levels of ammonia in the soil.

Sources of Compost

Compost can be produced from a wide variety of initial feedstocks, including manures, prunings, municipal yard trimming, kitchen wastes from municipal greenbin collection programs, food processing wastes, old or spoiled hay, and wood wastes. Growers can obtain finished compost from commercial and municipal composting operations. Composts can also be made on-farm.

Commercially available composts: Composts produced for sale to the public by commercial and municipal operations must meet requirements of the BC Organic Matter Recycling Regulation (OMRR) [http://www.env.gov.bc.ca/epd/mun-waste/regs/omrr/]. The requirements of OMRR ensure that the material has passed through a thermal phase adequate to kill-off fecal bacteria, and that the finished compost is stable, i.e. that it is sufficiently decomposed with a final C/N ratio between 15 and 35 so that it will not cause drastic negative changes in soil nutrient availability. The requirements of OMRR also include limits for heavy metals that are set to prevent their accumulation to problematic levels with long-term repeated compost application. Collectively, the requirements of OMRR ensure that the compost is generally safe for the environment and stable. Growers should nonetheless obtain an analysis of the compost (usually available from the producer), as information on properties of agronomic interest - N, P and K contents, C/N ratio, pH and salts(EC) - need to be considered before application (see sections below on testing and utilization).

Some municipal composts include biosolids or municipal sewage sludge as a feedstock.
Such composts can be very high quality and meet OMRR specifications for environmental safety. It should be noted, however, that guidelines for organic production and some food safety certification programs such as CanadaGAP prohibit the use of compost made with biosolids as a feedstock.

On-farm production of compost: For growers in the Okanagan and Similkameen, poultry manure from the Fraser Valley is a common source of feedstock for making compost. Using inadequately or improperly composted poultry manure is not substantially different from using fresh poultry manure. As described above, such materials can burn roots (salt stress, ammonia, organic acids), and surface application can increase the prevalence of fecal bacterial contaminants in the orchard environment. Due to risk of fecal bacterial contamination, Canada GAP certification does not allow application of manure within 120 days of harvest whereas finished compost can be applied at any time of the year (http://www.canadagap.ca). Growers attempting to produce on-farm compost from poultry manure should be familiar with how to compost properly. On-farm composting of manures and other agricultural wastes must adhere to regulations described in the Code of Agricultural Practice for Waste Management (AWCR) (http://www.env.gov.bc.ca/epd/industrial/regs/ag_waste_control/index.htm). Excellent descriptions of how to produce stable compost on-farm at a small scale can be found at: http://www.certifiedorganic.bc.ca/programs/osdp/I-050%20Compost%20Factsheet.pdf, http://www.agf.gov.bc.ca/resmgmt/publist/300Series/382500-2.pdf and http://www.rdosmaps.bc.ca/min_bylaws/ES/solid_waste/BCAgCompostHandbook1998.pdf.

A list of suppliers of composts and manures for composting:

1. Bighorn Contracting Ltd., 3815 McLean Creek Road, Okanagan Falls. Phone 250-486-3552

2. GlenGrow, City of Kelowna. Wholesale quantities of GlenGrow are available at the Glenmore landfill, 2105 North Glenmore Road. Phone compost info line 250-469-8868.

3. Ogogrow (contains biosolids), City of Kelowna. Wholesale quantities of Ogogrow are available at the Regional Compost Facility, 551 Commonage Road. Phone compost info line 250-469-8868.

4. Superior Peat Inc. (includes bark mulches and composts), 1700 Carmi Avenue, Penticton Phone 250-493-5410.

5. Classic Compost, Kelowna BC, phone 250-470-1323, website http://classiccompost.com/

6. Corfe Farm. Wholesale quantities of poultry manure compost, delivery available. 3950 Wood Ave, Armstrong BC. Phone 250-546-9732.

7. Southern Plus Feed Lot. 6975 Sibco Landfill, Oliver BC. 250-498-3077

Compost Testing

It is important to note that chemical properties can vary substantially between composts made with the same feedstocks, and even among batches of compost made at the same place out of the same feedstocks. Regardless of whether composts are obtained from commercial suppliers or made on-farm, they should be analyzed before use. The influences that composts have on soil and tree growth are affected by how they are applied as well as their properties. See Soil and Tissue Testing Labs page 9.

Basic properties to test:

1. Nitrogen content and carbon-to-nitrogen (C/N) ratio: The N content of stable, high quality composts typically varies from about 1% to about 2.0% of dry weight. Typically, very little of this N is immediately available to the crop as occurs with chemical fertilizers, but becomes available in the long term as the organic material decomposes and interacts with soil N. Consequently, composts should be considered as soil amendments rather than N fertilizers. Nonetheless, they will affect soil N availability. Many factors can influence how rapidly the organic N is released or “mineralized”, but C/N ratio of the compost has a stronger influence on how rapidly the N is released than any other factor. When incorporating composts into planting holes or trenches before replanting, composts with C/N ratios exceeding 15 can temporarily reduce N availability, and application of supplemental N fertilizer would be advisable, particularly if the compost has a C/N ratio greater than 20. This can occur for composted dairy solids. Composts with C/N ratios less than 12 may release between 10 and 20% of their total N in the first growing season and, depending on application rate, may supply N in excess of crop needs and warrant reduced fertilizer inputs. By contrast, non-composted poultry manure, is often characterized by a high N content (about 5%) and low C/N ratio, and may release as much as 40-50 % of its N in the year of application.

2. Total P and K contents: As with N, the P and K in compost is not as readily available as it is in fertilizers. In contrast to N, however, less is known about factors governing the availability of P and K in composts.

3. Electroconductivity (EC): The EC of compost is a critical property reflecting the salinity of applied materials. For example, many composts derived from manures have EC values in excess of 20 mS/cm. Fruit trees are relatively salt sensitive, suffering decreased growth and yield when EC values in the rooting zone exceed 1-2 mS/cm. It is possible to utilize high EC amendments, but care must be taken to avoid direct contact with roots or the material must be sufficiently diluted with low EC soil to prevent root burn. In contrast, low EC composts (1-2 mS/cm) can be applied directly in the rooting zone, as, for example planting-hole additions for establishing trees. In general, surface application is safer than mixing compost into root zone soil when EC is a concern.

Utilization of Compost

Composts are generally mixed into soil in planting holes or trenches before replanting or surface-applied as a mulch.

Rates: The “best” rate will vary with the soil and the problem being addressed. The following are general guidelines for commonly used rates.

1. Maintenance rate - 4 tons per acre covered (4 tonnes per hectare) or approximately 10 yards.

2. In response to trees showing decline – 12 tons per acre covered (12 tonnes per hectare).

Root examination before and after application is recommended and may indicate when additional applications are necessary.

Application:

Compost is generally spread by shovel off a trailer. In this case the compost should be spread evenly in the herbicide strip. The application rate can be estimated by weighing a 20 litre bucket, spreading the contents evenly in a 10 sq. ft. area. This gives a visual indication of the rate. For example, a 20 litre bucket full of compost (zinc sulphate container) should cover the 4 ft. herbicide strip of 2 ½ trees on a 1 ft. spacing.

Commercial spreaders are also available.

Specialty amendments

Biochar: Biochar is an amendment which has received recent publicity due to its perceived environmental benefits which include the potential to stabilize and elevate the carbon content of soil at the same time providing the benefits associated with increasing organic matter content. It is produced by the incomplete combustion of organic material such as forestry waste wood under low oxygen conditions and is often a by-product of its use for energy production. There are several BC companies actively researching its production. At present there is considerable variability in its composition and limited research on its benefits for use in perennial horticultural production systems.

Humic materials: Commercial formulations of humic acid or humate (solid form of humic acid) are being marketed as growth-promoting soil amendments. These materials are extracted from ancient decomposed plant material in the form of leonardite or lignite (soft forms of coal). Their nutrient contents can be low but formulations can be supplemented by the addition of nutrients. They also have high cation-exchange capacities. The effects of these materials on fruit tree growth have not been studied adequately to support any recommendations. A phosphorus amended humic material improved initial growth of grape in half the plantings when tested in local vineyards.

Liquid organics: There are several liquid organics available and suitable for application with irrigation water, but there have been few comparisons of their effectiveness. Compost teas are from the leachate produced by aerated or anaerobic (no oxygen) digestion of manures and have been advocated for insect and disease control and as nutrient supplements. There is limited documentation of their effectiveness under field conditions.

Vermicomposts: Composting carried out via earthworms does not include a high temperature incubation period since temperatures above 35 C kill earthworms. Furthermore vermicomposting requires a moisture content of 70 to 90 % compared to the normal composting carried out between 40 to 60 %. Commercially available vermicomposts will have had to meet requirements of OMRR with respect to pathogen reduction. Acceptance of vermicomposts can be greater than that of composts because of better visual aspect, high nutrient content and microbiologic activity but there is limited documented proof of superior performance relative to other composts from replicated field trials.

Local experience

Pros

Over the past 20 years a wide range of field experiments have been conducted in grower and government research station orchards to test the effectiveness of increased application of organic matter applied either as surface mulches or amendments incorporated into the soil profile. The experiments have been conducted in high-density apple orchards on dwarfing rootstocks and involved randomized and replicated comparisons of treatments carried out for 3-5 years. The number of sites where increased use of organic matter improved orchard performance (primarily increased tree yield) is summarized in Table 1. It is important to note that about half of the trials with incorporated amendments were with compost. In one orchard it was found that surface mulching and amendment incorporation buffered against water stress and associated reductions in fruit size which occurred from accidental failure in the irrigation system.

Table 1. Summary of number of orchards exhibiting improved performance in multi-year experiments conducted over the past 20 years by PARC-Summerland in grower and research high density apple orchards on dwarfing rootstocks.

Experiment Type	Number of Sites	Sites with Improved Performance²	Success Ration
Surface mulch	12	8	0.667
Incorporated amendment	16	5	0.313

²Increased yield and frequently larger tree size.

From this data it can be concluded that use of surface mulches has generally been more effective than incorporation of amendments and that benefits have not always been observed.

Cons

In the course of experimentation it was discovered that organic amendments may not result in improved growth of trees on sites with fertile soils or with strong fertigation programs suggesting that for these sites there was no measurable effect on tree performance by the addition of compost. However, as previously noted, compost can be used to promote long term improvements in soil quality and nutrient reserves. Although use of composts can improve soil moisture regimes this is not a substitute for proper and timely irrigation. For example high frequency irrigation (four times daily with small volumes of water) could be more effective than surface mulching on a very coarse loamy sand soil. Also over-irrigation resulting in excessive leaching of nitrogen mineralized from compost could negate the benefits of using composts.

Compost is not a substitute for fertilizer programs. Routine soil and leaf analysis are still recommended in order to maintain nutrient balance in tree fruit blocks. Growers are encouraged to discuss their plans for composting with their field person or with the BC Ministry Extension Service.

Organic application could be ineffective when an important limitation such as replant disease or a nutrient deficiency such as potassium was unaffected by the treatment. Although beneficial, the grower should not rely on composts to overcome severe replant disease or nutrient deficiency which can often be diagnosed by soil analyses or a plant pot test at the time of planting. As previously indicated compost with a high salt content can inhibit plant growth particularly if concentrated around bare roots.