[Forest Fertilization Guidebook Table of Contents]

Monitoring and reporting

A fertilizing project should be monitored for compliance with any treatment standards set out in the silviculture prescription or stand mangement prescription. The following methodology is suggested for monitoring of aerial fertilizer applications. Application rate must be within 15% of target application rate.

Monitoring aerial application

To be effective, monitoring plans and procedures must be identified prior to initiating the contract. This section reviews the major points to be considered.

When monitoring contractor performance:

Monitoring a contractor’s performance is easier if the application contract clearly identifies the standards required. 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

Monitoring can normally be done by one person. If problems arise an extra person can be brought in so one person is in the landing and another in the treatment unit. 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. This should be done periodically throughout the application. 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. For a given spreader output rate and swath width, the weight of fertilizer per area decreases with increasing ground speed. An accurate reading of ground speed is possible with aircraft equipped with a global positioning satellite system (GPS). However, using the following techniques it is not necessary for the personnel monitoring the fertilizer operation to know ground speed.


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


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


Target application rate: 450 kg/ha
Swath width: 66 m
Swath overlap: double coverage (50% overlap)
Weight of fertilizer in hopper: 500 kg

Each swath provides half the target application rate (i.e., 450 kg/ha / 2 = 225 kg/ha). The 500 kg of fertilizer in the hopper should therefore cover 2.22 ha.

500 kg divided by 225 kg/ha = 2.22 ha or 22 222 m2 (1 ha = 10 000 m2)

With a 66-metre swath, the distance necessary to provide the target application rate can be calculated.

66 m swath width ´ swath length = 22 222 m2
swath length = 22 222 m2 divided by 66 m
swath length = 336.7 m

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 only be done by standing under the aircraft during active fertilization.

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. 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.

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. This distance is shown on Figure 3.

Figure 3. Fertilization overlap after two swaths.

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 should 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.



Application rate must be within 15% of target application rate.

Monitoring water quality

When fertilization projects encroach on streams or water bodies, or occur in community watersheds, special precautions must be taken.

Water quality sampling

Water quality sampling is required in community watersheds and should be done when fertilizing near fisheries-sensitive zones. Samples should be taken before, during, and after treatment. Guidelines for sampling and analysis are provided in Appendix 4.


Water quality sampling is required in community watersheds and should be done when fertilizing near fisheries-sensitive zones.

Reporting of accomplishments under SMPs

Reporting of stand management prescription accomplishments on free growing stands is required for major licence holders.

The Silviculture Practices Regulation requires that a treatment report is submitted quarterly to the district manager. This report must:

The submission dates are April 15, July 31, October 31, and January 15.

Fertilizing done by the Small Business Forest Enterprise Program should be reported following ministry procedures.

[Return to top of document]