Fertilizing method and application

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 occasionally being added to ensure the benefits of the nitrogen fertilizer are not limited by deficiencies of other elements.

Urea ((NH₂)₂ CO) (agriculture grade) is currently the only nitrogen fertilizer widely used in B.C. 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.

Rates for nitrogen application Although growth increments may improve as dosage of fertilizer increases, response per unit of nitrogen is generally most cost effective when treatments use 200 kg N/ha. This rate is therefore recommended. The equivalent dose of urea prills is 435 kg/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 financial benefit from each application, and to attain the highest N efficiency (m³/kg N), treatments should not normally be repeated until ten years have elapsed.

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.

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. In the spring, temperature, time of snow melt, breakup 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. Fertilizing over snow to a depth of at least 50 cm has provided good tree response.

Heliports

Cost is the primary reason for contractor selection. This criteria has led to helicopter application being the main delivery system in B.C.

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.

Heliport distance from treatment area is one of the most important factors in determining cost of application. Heliports should optimally be within 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 identified 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 identified for the pilot. The pilot applying the fertilizer should be present on a pre-treatment reconnaissance flight to become familiar with the treatment units. Important locations can be positioned on the pilot's GPS.

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.

No fertilizer application zone

See Environmental protection.

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 30-metre adjacent to lands used agriculture. This can be modified if residence or farmland is owned by forest landowner aerial application acceptable resident landowner.

Air operations

Aircraft and hopper must be properly equipped to ensure safety and an acceptable level of application. Aircraft must have electronic guidance instruments capable of ensuring even and accurate application of fertilizer over the treatment units and the avoidance of non-target areas. The guidance system can log the treated locations and be used for reporting.

Hoppers must be equipped with a calibration system or loading equipment must be equipped with an accurate metering device to provide an accurate measure of the fertilizer.
Hoppers must have a leak proof system with a positive shut-off device easily controlled by the pilot.

Suitable equipment must be present to enable constant ground to air communications.

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.

Monitoring

A fertilizing project should be monitored for compliance with any treatment standards set. Application rate should be within 15% of target application rate.

Monitoring aerial application

The major points to be considered when monitoring contractor performance:

Check that loading sites are cleaned daily.
Observe flight paths, flying procedures, and fertilizer spread from the bucket.
Ensure that weather and visibility conditions do not adversely affect treatment effectiveness.
Keep track of the cumulative weight of fertilizer spread on the block of known area. This should normally be done by the contractor. By calculating the cumulative load weight for a given block and dividing by the known area of the block, you can determine the application rate. This calculation lets you know if the block received the correct amount of fertilizer.

A fertilization contract should detail start and finish dates, obligations of both parties, scheduling, standards of performance, payment, suspension and cancellation, fire prevention, liabilities, and operational specifications including provisions for environmental protection.

Monitoring procedures

On site monitoring can normally be done by one person. Good communication with the contractor is a necessity. Monitoring must begin right away. Any necessary modifications to the application can then be worked out early with the contractor.

The uniformity of the fertilizer application is dependent on the spreader output rate, ground speed, swath width and swath overlap. The contractor should calibrate the spreader output rate and ground speed to obtain the desired coverage based on the swath width and target overlap. Monitoring procedures to check these factors are listed below.

Spreader output rate

The spreader output rate can be determined by timing how long the hopper takes to empty with a known weight of fertilizer. The drop rate can vary with the fertilizer grade, type of equipment, and equipment wear. The spreader mechanism can be calibrated to obtain the desired spreader output rate.

Swath width

This width will vary with the spreader mechanism and grade of fertilizer. Within the range of altitudes flown during fertilization, swath width can be considered independent of altitude. Swath width must be measured at the start of treatment to ensure proper application along buffers. Swath width can be easily measured by having the helicopter apply a swath across a logging road. With forestry grade pellets, some will be flung outside the swath. The edge of the swath is where the uniform distribution of pellets rapidly tails off to a few scattered pellets.

Ground speed

A constant ground speed is obtained by adjusting air speed to compensate for wind. An accurate reading of ground speed is possible with aircraft equipped with a global positioning satellite system (GPS).

Calibration

The contractor can modify the spreader output rate and/or the speed of the aircraft to ensure that the target application rate is being obtained. This calibration should be done at the beginning of the contract. To check calibration:

Calculate the distance over which a known weight of fertilizer should be spread to obtain the target application rate for a single swath.
Measure out this known distance and clearly mark the start and end points so the pilot can see them.
Have the pilot fly the line and spread the known weight of fertilizer.
Check that the actual distance obtained provides an application rate within 10% of the target rate.

Example:

The target application rate and the swath overlap should be listed in contract specifications. The swath width can be measured as previously described.

Known:

For this example, the actual distance flown can be between 303 and 370 metres. This will provide an application rate within 10% (plus or minus) of the target application rate for a single swath width.

If the application rate varies by more than 10% from the target, then the contractor should be responsible for further calibration. If the calibration is within 10%, then proceed with the application. During the operation, the area should be walked to check for even coverage (see Monitoring aerial applications) and the swath overlap should be measured.

Swath overlap

The pilot lays down fertilizer in parallel swaths. The second swath of fertilizer will overlap the first so that part of the ground is fertilized twice.

The aircraft must first be in the right place to deliver an accurate and consistent swath overlap. Variation from the target is likely if the flying is being done without the use of electronic guidance (e.g., transponders). The use of electronic guidance, to provide for line flying guidance should be a contract requirement.

With less than 50% overlap (double coverage), strips having double coverage alternate with strips having single coverage. To get even fertilizer distribution, there must at least double coverage over the entire area.

Measurement of coverage can be done by standing under the aircraft during active fertilization, or checking the recorded flight lines..

During application, stand directly under the helicopter as it passes overhead. The fertilizer pellets will hit the ground and bounce like hailstones. Wear suitable clothing and eye protection. After they have stopped bouncing and before the aircraft returns, walk across the fertilized swath to the new outside edge where the unfertilized ground begins. Mark this edge with flagging tape. Some will be flung outside the swath. The edge of the swath is where the uniform distribution of pellets rapidly tails off to a few scattered pellets.

On the next flight path, the aircraft will lay down another swath. As before, once the pellets stop bouncing, walk across to the new outside edge and mark it with a second piece of flagging tape.

Measure the horizontal distance between the two pieces of tape. Repeat this process for six consecutive flight lines to get five horizontal distance measurements. For slopes greater than 10% use a clinometer and slope tables to convert slope distance to horizontal distance. For slopes less than 10% hold the tape horizontally.

This procedure may be repeated until six consecutive edges have been identified and five consecutive horizontal distances measured. Then another location in the block should be chosen and a second sequence of six consecutive edges identified and five consecutive horizontal distances measured.

Average the overlap from the measurements. A variation of 10% or greater from the target overlap should be discussed with the contractor so further flight lines can be corrected.

Final application rate

The final check is a calculation of application rate based on the total weight of fertilizer applied and the area of the treatment unit. This check relies on the accuracy of the weighing scale used by the loader. If a check against this scale is desired, the cumulative loads for a given truck load can be checked against the Bill of Lading from the fertilizer manufacturer. The total application rate should be within 10%, plus or minus of the target application rate. Greater than 15% variation from the target application rate is considered unacceptable.