There are various sources and application methods for mineral nutrients and other amendments beneficial to fruit trees.  There are 3 main application methods used for fruit trees:  direct as a broadcast application across top of soil, delivery to the soil through an irrigation system (fertigation) and spray onto the leaves (foliar spray). 

Applying nutrients to the soil, either by broadcast or fertigation, is the ideal means of supplying the bulk of a tree’s needs for macronutrients such as N, P, K and sometimes Ca.  Foliar sprays are commonly used for micronutrients and some macronutrients.  Since fertigation and foliar spray require some special considerations, general information on these applications methods will be given.

Fertigation

Fertigation use is growing as local experience is gained through research and grower interest.  The advantages of fertigation are:

1)  transport of nutrients directly to the root zone so that fertilizer amounts and timing can be precise,

2)  reductions in the amount of fertilizer applied relative to standard broadcast application, for example, lower amounts of P can be applied to achieve similar improvement in tree vigour and P nutrition, and

3)  less excess nutrients available to be leached and pollute the groundwater.

The disadvantages of fertigation are:

1)  drip irrigation system must be well designed to provide uniform water distribution,

2)  system must be maintained regularly to prevent plugged emitters, and

3)  only soluble fertilizers can be applied and rates of fertilizers can only be adjusted by irrigation zone, not for individual trees.  

Equipment specific to fertigation includes a back flow prevention device and equipment for injecting fertilizer into the irrigation system.  A list of certified testers for backflow prevention devices is available at BC Ministry of Agriculture offices.  To ensure that fertilizer is uniformly distributed regardless of the irrigation system layout, first 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 with fertigation include urea, ammonium nitrate and calcium nitrate as sources of N.  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 granular P in first year planting hole applications. Fertigation of P is physically easier than the application of granular P in planting holes. 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.

Foliar Spray Applications

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 B, Zn and Mn should be applied regularly to prevent the development of deficiencies of these elements.  Multiple Ca sprays are applied annually as a means to aid fruit quality.  If needed, Mn and Fe are applied as sprays.  None of the foliar mineral element sprays should be applied with emulsions or oils. When applying, use eye protection, a respirator, rubber gloves and protective clothing.

The best time of day for foliar sprays is the early morning when lower temperature favours 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, mineral sprays should be applied 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 at least 24 hours, but the longer the time the better. When, how much and how to apply mineral elements will vary among orchards and growers due to differences in soil type, topography and management practices.  A balanced nutrient program is part of good horticultural practices.  A nutrient program is never a replacement for proper pruning, crop load management and pest control.

Soil Inorganic and Organic Amendments 

Along with chemical fertilizers, there are other soil amendments that are used to help manipulate the chemical or structural make-up of the soil to improve conditions for nutrient uptake.  Maintain a soil in the proper pH range is critical for nutrient availability and improving things like soil organic matter (OM) are important for enhanced retention and availability of various nutrients in the soil.  Examples of soil amendments are various lime products, peat, compost, sulphur, gypsum and various mulch materials. 

Most virgin soils in the British Columbia Interior are neutral or alkaline (i.e. pH 7.0 or higher).  The use of most N fertilizers and continued irrigation in orchards for many years can favour the development of acidic conditions by the leaching of calcium and magnesium.  However, choosing an acidifying fertilizer product can be beneficial in an orchard with high pH due to calcareous soils (soils with high calcium carbonate).  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.  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.  The need for liming must be determined by measuring soil pH and there are various lime products to choose from that also have other attributes for soil health to consider when choosing what to use. 

The acidifying properties of a fertilizer can be detrimental or beneficial over time depending on your soil.  Table 27 presented the equivalent acidity or basicity of some fertilizers.  After several years of drip irrigation, the nutrient content of soil beneath drip irrigation emitters may change.  Soil sampling to determine soil B, potassium and salinity is a desirable strategy to prevent nutrient deficiencies or excesses from developing.  Comparison of a composite soil sample 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.

Table 1. Equivalent acidity/basicity of commonly applied fertilizers

Fertilizer	Content	Equivalent Aciditya(kg CaCO3)	Basicity
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

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

   Fertilizer Handbook (Western Plant Health Association, 2002).

 

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 a soil test laboratory.  There are three categories of soils:

ARI      0-5       very sensitive

ARI      6-25     moderately sensitive

ARI      >25      not sensitive

Lime (Calcium Carbonate, Dolomite and Calcium Hydroxide)

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 pulverized (fine) to obtain effectiveness equal to ground limestone.  Dolomite lime, in addition to alleviating soil acidity, is valuable for supplying magnesium which is commonly deficient in McIntosh, Spartan and Newtown apples.

Lime can be applied at any time of year, except one month should be allowed between application of fertilizer and application of lime to avoid loss of ammonia-N to the air.  In addition, one month should be allowed between soil-applied B and application of lime. Spring and summer applications of hydrated lime require care be taken to avoid deposits on foliage and fruit, which can cause 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 N 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 0-30 cm 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.  This pH drop can cause bark measles, slow growth and other damage to the trees.

Compost 

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).

Compost is distinct because it 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 N contents, such as poultry manure, high application rates can also generate toxic levels of ammonia in the soil.

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 so 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.

Source 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 produced for sale to the public by commercial and municipal operations must meet requirements of the BC Organic Matter Recycling Regulation (OMRR) https://www2.gov.bc.ca/gov/content/environment/waste-management/food-and-organic-waste/regulations-guidelines/

  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.  The compost should have 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) for information on properties of agronomic interest (N, P and K contents, C/N ratio, pH and salts (EC) to be considered before application (See Compost Testing section below).

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.

For growers in the Okanagan and Similkameen, poultry manure from the Fraser Valley is a common source of feedstock for making on-farm 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, increase the prevalence of fecal bacterial contaminants and Canada GAP certification does not allow application of manure within 120 days of harvest.  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 Agricultural Environmental Management Code of Practice (AEM CoP) https://www2.gov.bc.ca/gov/content/environment/waste-management/industrial-waste\agriculture

 

An excellent description on how to produce stable compost on-farm can be found at: https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/agricultural-land-and-environment/waste-management/manure-management/composting_guide.pdf

 

Suppliers of composts and manures for composting include those in the list below.

 

1)  Bighorn Contracting Ltd., 3815 McLean Creek Road, Okanagan Falls, BC.  Phone 250-497-5942

2)  GlenGrow, City of Kelowna, BC. Wholesale quantities of GlenGrow are available at the Glenmore landfill, 2720 John Hindle Drive. 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, BC. Phone 250-493-5410.

5)  Classic Compost, 2424 Mayer Road, Kelowna, BC.  Phone 250-470-1323. 

6)  Corfe’s Farms, 3950 Wood Avenue, Armstrong, BC.  Phone 250-540-4320.  Wholesale quantities of poultry manure compost, delivery available.

7)  Southern Plus Feedlots, 6975 Sibco Landfill, Oliver BC.  Phone 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.

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% 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.  In 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.

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. More information is available at Chapter 6 of “Soil Fertility Handbook, Publication 611” by OMAFRA that can be accessed from http://www.omafra.gov.on.ca/english/crops/pub611/p611order.htm .

Electrical conductivity (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, for example as 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 Rates of Compost

Composts are generally mixed into soil in planting holes or trenches before replanting or surface-applied as a mulch.  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 – up to 12 tons per acre covered (12 tonnes per hectare) might be needed.

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

Compost is generally spread by shovel off a trailer.  In this case the compost should be spread evenly in the herbicide strip.  A visual estimation of the application rate can be determined by weighing a 20 litre bucket and spreading the contents evenly in a 10 square feet area. In a typical 10' x 2' apple planting, a 20 L bucket full of compost should cover the 4 feet herbicide strip of 2 ½ trees on a 1 foot spacing.  Commercial spreaders are also available.

Liquid Organics (Compost Tea)

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 are several liquid organics available and suitable for application with irrigation water, but there have been few comparisons of their effectiveness.  There is limited documentation of the effectiveness of compost teas under field conditions.

Vermicomposts

Composting carried out using 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 have to meet requirements of the OMRR with respect to pathogen reduction.  Acceptance of vermicomposts can be greater than that of composts because of their 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.

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 Material

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 P amended humic material improved initial growth of grapes in half of plantings when tested in local vineyards.

Seaweed Extract

Seaweed extracts have been applied as a foliar spray to promote growth, prevent pest and diseases, and improve quality in various plants (Vekleij, 1992).  The extracts contain plant hormones and trace nutrients.  The limited number of studies using seaweed extract on fruit trees suggest that the extracts can improve fruit quality.  Further studies will help determine the usefulness of these extracts for fruit trees.  

Canola Meal

Turffix is a natural fertilizer that is a by-product of Canola oil production with added corn gluten.  Its analysis is 6-1-1.25-0.25 NPKS and usually applied at 1 ton per acre (The rate will vary with the condition of the trees and should be determined with the advice of your advisor).  Turffix is a pelletized product that is usually topically applied along the herbicide strip.  This rate would add 120 lb. of nitrogen to the trees.  Like the canola plant itself, Turffix has some biological activity which have been used to suppress a number of soil pathogens.    Timing for application to established orchards is best in the spring.

Local Experience With Application of Organic Amendments

In the past, 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 2.  It is important to note that about half of the trials with incorporated amendments used compost. In one orchard, it was found that surface mulching and amendment incorporation buffered against water stress and associated reductions in fruit size when there was an accidental failure in the irrigation system.  From this data, it can be concluded that use of surface mulches has generally been more effective than incorporation of amendments, where benefits have not always been observed.

Table 2. Summary of the number of grower and research high density apple orchards on dwarfing rootstocks exhibiting improved performance in multi-year experiments conducted over the past 20 years by the Summerland Research and Development Centre

Experiment type	Number of sites	Sites with improved performance*	Success ratio
Surface mulch	12	8	0.667
Incorporated amendment	16	5	0.313

*Increased yield and frequently larger tree size.

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 sandy soil.  In addition, over irrigation resulting in excessive leaching of N mineralized from compost could negate the benefits of using composts.

Although beneficial, the grower should not rely on composts to overcome severe replant disease or nutrient deficiency.  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 representative or horticultural consultant.