Features Agronomy
Granular materials: They’re only as good as their application

By Sean Jordan, T.Ag.

In the July/August 2010 issue of Turf & Recreation, Ryan Beauchamp
of Syngenta Crop Protection Canada wrote an article entitled, “The fine
art of spray application” which brought to light often overlooked
points related to the efficacy of sprayed products.

The following article is meant to complement Mr. Beauchamp’s piece, but with respect to granular materials and their application.

According to IPM regulations, sprayers must be calibrated several times per season. Why is this not the case with spreaders? Granted, spreaders are rarely used for pesticide application, but don’t the fertilizers and amendments that they apply directly contribute to the overall vigor of a turfgrass stand and its ability to resist stress and disease? The efficacy of any application—liquid or granular—is limited by how well it is applied. If the sprayer or spreader is not calibrated and/or if there are operator errors, the performance of application is limited from the start.

With respect to sprayers, the initial setup is a detailed task requiring the technician to consider all of the products to be applied and where they should come to rest. After this setup which involves nozzle selection, setting the boom height and speed/pressure adjustment, subsequent rate checks are straightforward and relatively painless. A sprayable material may be applied without major changes to the equipment because the rate of the spray solution has already been determined at the time of setup and the amounts of the chemicals or fertilizers in that solution are dependant on the area to be covered. Granular spreaders, on the other hand, require calibration with each product as differences in particle sizing, uniformity, density and shape all affect how the material is distributed, even if the applied rate is the same as another granular product.

So why calibrate? Big picture, the reasons are environmental. Products and their breakdown components that aren’t taken up by the plant, bound up in the soil, or have an effect on the target pest(s), as is the case with pesticides, can end up either in groundwater, surface water or the atmosphere. 

Speaking in more perceptible terms, misapplied fertilizers are a waste of money. This includes not just the price of the product, but also labour, equipment costs and expenditures to manage turf that is not performing as well as it can.

So how do you justify the extra time and expense to calibrate spreader(s) for each material? Consider the following: It is not uncommon to calibrate just before applying, if calibrating at all.  Many times it is a rushed process that ends up with only a slightly better result than not having calibrated. A simple calibration protocol can be easily implemented with respect to spreader calibration. Most managers stock fertilizers and granular pesticides ahead of time and also have the spreaders and personnel in place well in advance, so why not utilize rainy days to calibrate walking spreaders in a shop or equipment shed?

Rainy days in many operations can consist of a quick cutting if conditions allow, equipment washing and shop sweeping before the crew is sent home early. While the equipment is out and the floors are clean, take advantage of the space. If you are worried about the mess that can be made, using a calibration catch will reduce the amount of product strewn around the floor. The following are key points to remember when calibrating:

Have each operator walk at a pace that they can maintain throughout the entire spreading process. Too often, operators will jog through the calibration process only to end up walking much slower during the actual spreading job. This results in a much higher applied rate due to a narrower effective width and greater flow of material through the hopper gate relative to the ground speed.

The spreaders should be identifiable (numbered or lettered) so the operators can use the spreader that they calibrated. The reasoning behind this is that even though two spreaders may be of identical make and model, the applied rate can be affected by wear, age and handling.

Calibrate as close as possible to the calculated application rate as there are many variables in the field that cause inaccuracy such as wind, terrain, obstacles, operator error or a lack of product uniformity.

So how does this relate to cost savings? Everything above requires labour hours, correct? Follow this example for the cost recovery of calibration: If a calibration takes approximately one hour of labour, including setup, measurement and cleanup, and one bag of fertilizer (typically costing the equivalent of two to three hours of labour) is saved, the calibration essentially paid for itself. 

Also, keep in mind that operators who calibrate often will become more proficient and eventually take less time to perform a proper calibration. This model can also be applied to calibrating vehicle-mounted spreaders outdoors during calm periods of both wind and workload.

Taking the time to properly calibrate may lead to finding problems with materials and equipment prior to going out in the field. A simple procedure such as pan testing for effective width can reveal biases in spread patterns. Understanding how granular products are distributed by a spreader can help determine the most efficient overlap. 

A large influence on the distribution of a granular product and the contained nutrients is particle size. When comparing two products of differing particle sizes applied at the same rate, as the size of the particles decrease, the number of particles per unit area increases. This is an important point to remember as cutting heights continue to be reduced. Fewer larger particles, rather than more smaller particles, on a low-cut turf decreases the uniformity of the nutrient distribution and increases the chances of uneven growth and colour, especially with nitrogen or iron containing particles.

The key point to remember is that calibration is necessary to apply the calculated rate of a product and to improve the chances of the granular material reaching its target and performing up to its potential.