LandWISE 2015 Presenter, Dan Bloomer

The SFF “On-Farm Fertiliser Applicator Calibration” project arose from repeated requests by farmers for a quick and simple way to check performance of fertiliser spreading by themselves or contractors.  They wanted to know that spreading was acceptable.

A calibration check includes assessment and correcting of both application rate (kg/ha) and uniformity (CV). Farmers indicate determining the rate is reasonably easy and commonly done. Very few report completing any form of uniformity assessment.

There are many protocols internationally relating to the spreading of fertiliser products. Lawrence (2007) compared six test methods.

Most used 0.5 m trays organised in a single transverse row to capture the spread pattern of the spreader. No account is taken of the longitudinal variation between individual rows when multiple tests are carried out.

The results of the test are given as the bout width where the coefficient of variation (CV) does not exceed a specified level. In all cases the maximum allowable CV is 15% for nitrogenous fertilisers and 25% for low analysis fertilisers.

An On-Farm Protocol

There is no set method dor assessing uniformity. On-farm testing could use a set number of collectors per swath (spacing changes with swath width) or a set spacing between containers (container number varies with swath width). Farmers can decide.

There are however some important principles:

• Uniformity requires collection of samples from a spreading event and calculation of a uniformity value.
• Set equipment up correctly according to manufacturer’s instructions
• Ensure the spreader is horizontal, and at the correct height off the ground
• Use standard test trays, given the need for baffling to stop fertiliser bouncing out
• Ensure the spreader is driven well past the trays to capture all fertiliser
• If a larger sample is wanted, two or more runs at the chosen application rate should be made rather than applying a higher rate.

Weighing samples is complicated by the very small quantities involved – often a single prill in the outer containers. Scales weighing to 0.01g are required, but satisfactory options are readily available at reasonable price.

An alternative is to assess the volume of fertiliser captured in each tray. Disposable syringe bodies make good measuring cylinders.

Determining a field uniformity will involve either physical or theoretical over-lapping of adjacent swaths.

On-line software is being developed to process data and generate statistical reports. Key outputs will be measured application rate, the CV at the specified bout width and the bout width range at which CV is within accepted limits.

Test spread-pattern checks performed to date show there is a need for wider testing by farmers. Unacceptable CVs and incorrect application rates are not unusual.

 

There remains some question about the percentage of fertiliser caught in some types of tray

The SFF project is co-funded by the Foundation for Arable Research and the Fertiliser Association