Forest Fertilization Guidebook Table of Contents]

Fertilizing method and application

Type of fertilizer

There are two general classes of fertilizer: organic (e.g., sewage biosolids, fish morts, secondary pulpmill effluents) and inorganic. Most operational fertilization has focused on the application of inorganic fertilizers because of their known chemical and physical properties and their cost-effective means of application.

Organic fertilizers

Biosolids are treated waste water sludge that meet quality criteria for beneficial land application. They can act as an excellent slow-release fertilizer. Although biosolids are not currently used operationally for forest fertilization they will likely play an increasingly important role in the rehabilitation of roads, landings, and other degraded sites, as well as enhancing forest growth. A regulation is in place for the use of municipal solid waste compost. A regulation for the use of biosolids will soon be in place. Compliance with regulations is required when applying those organic fertilizers. A waste management permit must be acquired from a Ministry of Environment, Lands and Parks office prior to application of any organic fertilizer not covered by regulation. Information on environmental protection, site suitability, and application methods can be obtained from Silviculture Practices Branch, B.C. Ministry of Forests.

Inorganic fertilizers

Only four elements are currently operationally applied through use of inorganic fertilizers on forests in British Columbia. These are N (nitrogen), S (sulphur), P (phosphorus), and B (boron). Nitrogen is applied in the largest amount with S, P, and B being added to ensure the benefits of the nitrogen fertilizer are not limited by deficiencies of other elements.

Supplements of nitrogen frequently improve growth of coastal Douglas-fir, lodgepole pine, and sometimes western hemlock. Urea ((NH2)2 CO) is currently the only fertilizer widely used by the B.C. Forest Service for operational applications. This is due to its good response history, ease of storage, availability, environmental effects, and high nitrogen content (46%) which minimizes application costs per unit area.

“Forestry grade” fertilizer (approximately 3–5 mm prill diameter) should be used rather than “agricultural grade” (approximately 2–3 mm prill diameter). Aerial distribution of forestry grade prills is more uniform and the larger particles penetrate the canopy more easily.

On the coast, urea (46-0-0) is generally the only fertilizer operationally applied to Douglas-fir forests. Fertilization with N + P has been effective in young western hemlock stands growing on substrates rich in decaying wood in the CWHvh subzone and salal prone sites at low elevations in the CWHvm subzone.

In the interior, S deficiencies may limit the responsiveness of lodgepole pine to N fertilization over fairly extensive portions of the Sub-boreal Spruce and Sub-boreal Pine–Spruce biogeoclimatic zones within the central and northern portions of the interior plateau. It is recommended that S be combined with N in the operational fertilizer mix when pre-fertilization foliar sulphate-S levels are <60 ppm. A forest grade blended fertilizer (35-0-0-10S) consisting of 58% urea (46-0-0) and 42% ammonium sulphate (21-0-0-24S) is currently used in the B.C. Interior.


The type of fertilizer (organic/inorganic) and the amount (kg/ha) of each elemental component should be identified in the silviculture prescription or stand management prescription for the site.

Rates and timing for nitrogen application

The following information only applies to forest grade urea fertilizer unless otherwise stated.

Application rates

Application rate refers to the amount of the element applied, not to the total weight of the fertilizer.

Although growth increments may improve as dosage of fertilizer increases, response per unit of nitrogen is generally most cost effective for coastal areas when treatments use 200–225 kg N/ha. This rate is therefore recommended. The equivalent dose of urea prills is 435–490 kg/ha.

In the interior, it is recommended to use a urea-ammonium sulphate fertilizer blended to deliver 175–200 kg N/ha and 50–60 kg S/ha.


Frequency of application

A single application of fertilizer will generally increase the growth of a treated stand for more than six years. To ensure maximum benefit from each application, and to attain the highest N efficiency (m3/kg N), treatments should not normally be repeated until at least six years have elapsed. However, more frequent applications (e.g., every 3–4 years) will be necessary if the objective is to maintain growth rates at, or near, optimal levels.

Season of application

The season is not as important as the weather conditions under which urea fertilizer is applied. The ideal season of application is when roots are actively growing, temperatures are low, soils are wet, and precipitation is frequent. Under such conditions losses due to volatilization are greatly reduced.

In community watersheds with lakes or reservoirs, do not apply fertilizer during times of rising water temperatures. Generally, do not apply fertilizer during the following periods:


Effects on growth are generally similar for urea applications in spring compared with treatments during fall, but late fall operations (October and November) are preferred since weather is fairly predictable. For the interior, fall applications will be earlier in the north and later in the south. In the spring, temperature, time of snow melt, and consequent accessibility can vary considerably, and other tasks (e.g., planting, planning for summer work) have significant priority. Therefore, whenever possible, plan the fertilization project for the fall.


Cost is the primary reason for contractor selection. This criteria has led to helicopter application being the main delivery system in B.C. Fixed wing aircraft require an air-strip and have limited use in British Columbia’s rugged topography.

Heliport details should be worked out with the contractor. The heliports must allow for safe and efficient loading of helicopters. Remove danger trees near the heliport which jeopardize the safe operation of the helicopter. In addition, personnel involved in the operations should be briefed on working around helicopters and spectators kept at a safe distance.

When a heliport is located on a main logging road, arrangements must be made to accommodate local traffic in a manner which ensures safety for the general public as well as the application crew. Signs must be posted far enough back to give truckers plenty of warning. When large highway trucks are used to haul the fertilizer they require a turn around or loop past the heliport for the return trip. These trucks will require radio communication on active logging roads and, in some cases, pilot vehicles to escort them to the heliport.

Heliport distance from treatment area is one of the most important factors in determining cost of application. Heliports should optimally be within 1 or 2 kilometres of treatment area and if possible, at equal or higher elevation than the stands. Because of the extra concentrations of fertilizer present at a loading site and the potential for spills, all heliports should be located in dry areas, well removed from ditches or natural water bodies. Any drainage through heliports must be directed away from ditches or streams.


Pre-fertilization block layout

Block layout is important to ensure an efficient operation while protecting other resources. Clearly marked blocks with suitable heliports close to treatment areas will minimize application time and reduce the risk of affecting other resources.

Block boundaries, water bodies, buffer zones, and hazards should be clearly marked on aerial photographs and/or project maps for use by the pilot.

On some blocks minor boundary amendments may result in leftover fertilizer. Each grouping of blocks should include an extra area to use up excess fertilizer thus reducing the cost of transporting to another project. An approved prescription and suitable map is required for the additional area.


No fertilizer application zone

A 10-metre “no fertilizer application zone” or buffer zone should be left around the following water bodies:

* Riparian classes are defined in Part 10 of the Operational Planning Regulation.

A typical swath width for helicopter aerial fertilization is approximately 60 m. Fertilizer is spread 30 m on each side of the helicopter. In this case a flight parallel to the water body should have the helicopter 40 m away to maintain a 10-metre buffer strip (see Figures 1 and 2).

In community watersheds the following buffers are required:

Any research trials in the area should be protected from treatment. Check up-to-date district maps and the Sx trial registry for any research trials. It is also wise to check with district staff for local knowledge of any existing research trials. Ensure the organization responsible for the trial is contacted and a buffer suitable to the researcher is left.

With the encroachment of residential and farmland areas on the forest land base, suitable buffers must be established to protect the rights of the private land owner. Check the Forest Cover Atlas maps for private land in the area. Leave at least a 60-metre buffer strip around residences and a 30-metre buffer strip adjacent to lands used for agriculture. This can be modified if the residence or farmland is owned by the forest landowner or the aerial application is acceptable to the resident or landowner.


Private land, water bodies visible from the air, and other sensitive areas should be protected as follows:

Contact the organization responsible for any silviculture trial or research installations to determine the size of buffer strip required.

Air operations

Aircraft and hopper must be properly equipped to ensure safety and an acceptable level of application.

Figure 1. Strategy for laying out a buffer zone to protect a stream flowing through an area proposed for fertilization.

Figure 2. Strategy for laying out a 10-metre buffer zone for no fertilizer application along a creek.


In addition to proper equipment, pilots must have demonstrated ability and experience in applying fertilizer to forest land.

Fertilizer application operations should be restricted to times of adequate daylight and visibility to ensure a safe, efficient application. The applicator must stop operations when there is inadequate daylight or weather conditions arise which could adversely affect treatment effectiveness, maintenance of buffer zones (no fertilization application), or safety of application.


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