A Change of Winds in Spray Technology

OF ALL AG EQUIPMENT, the sprayer has emerged as the most-used piece on the prairie farm. It runs nearly every week of the growing season, starting with pre-seed burnoff, continuing through insecticide, herbicide, and fungicide applications, perhaps some nutrient topdressing, and ending with pre-harvest weed control, and increasingly, desiccation and late fall residuals. The average farmer covers each field four to five times per season with the sprayer.

With the growing importance of the sprayer, an interesting new issue has come into focus. In the past five years, we’ve moved away from obsessing about nozzle technology and instead are taking on the task of improving time management. Why time management? Because with greater workloads and more constraints regarding when we can spray, we need to make better use of every spray hour available. Remember, good agronomy is doing the right thing at the right time – that includes spraying at the right time.

The basis for better time management is analyses of how sprayers use their engine hours. It turns out that for an average user, about one third of engine hours are idle time. Another quarter or so is spent transporting. And less than half (sometimes as little as a third) of the time is spent actually spraying.

That begs the question: How is idle time spent? And the follow-up: If idle time is reduced, how will it impact sprayer productivity?

Dozens of important tasks happen on a spray day while the sprayer is idling. These range from routine servicing to fuelling to entering data in the monitor. But the biggest time hogs on a spray day are filling and cleaning. And that’s where we find the most interesting innovations in spraying.

The best thing someone can do to improve their spray operation is to conduct an audit of their time use and invest in better tendering and cleaning procedures. Reducing fill time from 30 minutes to 10 or even five minutes can add 30 to 50 acres per engine hour (Figure 1). This is especially true in pulse crops where higher water volumes for herbicides, fungicides, and desiccants are common. Improving cleaning efficiency can add another 10 to 20 acres per hour. You can’t get those kinds of improvements with a new sprayer purchase.

The value of increased productivity is two-fold. We obviously need to cover ground efficiently with bad weather approaching. But we also recognize that simply driving faster has many negatives – more dust, more fuel consumption, more wear and tear on equipment, more drift, and lower spray deposit uniformity. If we can get more done and do a better job, it’s a win-win.

Let’s take a closer look at the tendering system. At the heart of it is a three-inch plumbing system mated to an efficient pump that can deliver about 400 gallons per minute. That will fill an average sprayer tank in three to four minutes. Of course you need to allow for a throttle- back to induct the product, but the whole process can be completed in seven minutes or so. Don’t forget to include the time to reach the tender truck, or to swing the heavy three-inch hose over; it makes sense to minimize that too.

And don’t forget about filling the tender itself. A 5000-gallon tank requires more than one hour of pumping time through three-inch plumbing. Upgrading to a faster fill rate for that operation alone can add significant capacity to a busy day. I’ve visited farms with five-inch electric pumps that deliver 1000 gallons per minute. Or others that install bulk water tanks at a remote location for faster access.

Cleaning is another time thief. As pulse crops can be very sensitive to many of our cereal herbicides, it’s important to ensure complete removal of residues from the spray tank and plumbing. As a result, we often add rinses as insurance. A thorough cleaning can take 90 minutes, often because there are no real indicators when the task is done (we might find out in a week or two, though).

Cleaning can be improved with some simple plumbing changes. My favourite is the continuous rinsing system we learned about from some German colleagues.

It involves the installation of a second pump – one dedicated to the clean water tank (Figure 2). It works as follows: An operator finishes a field and sprays out any remainder. When the tank is empty and the pressure gauge becomes erratic, she simply turns on that second pump to introduce clean water to the tank via the washdown nozzles. Carefully watching the pressure gauge to keep the sump volume low, she continues to spray out the tank as the water rapidly dilutes the spray mix. When the clean water tank is empty, the plumbing will contain mostly water. And the elapsed time will be five minutes. She still needs to look after screens and boom ends, but the most time consuming part is done.

Boom ends are another problem area. Clearing them of residue involves opening both ends on each section and allowing the material to spill on the ground – a messy operation. When the next spray mix is added, boom ends should be cleared of air or water to prime the boom. A recirculating boom takes care of both issues (Figure 3). To create such a system, the individual sections are strung together to form a continuous line on each wing. Spray mix is fed to the end of each boom wing and centre section, and it runs along the entire boom back to the tank where there is a shutoff valve. When this valve is open, the spray tank contents simply recirculate through the boom and back to the tank. When the valve is closed, normal spraying occurs. Sectional control is achieved through individual nozzle shutoffs, either solenoids via PWM, or air- activated for less cost.

Recirculating booms avoid residue build up in boom ends. They also allow the boom to be primed without spraying anything on the ground, minimizing waste. The feature is standard on European sprayers and is being added to many North American brands. Retrofit kits are also available.

A clever invention that I have come to appreciate is the Accu-Volume System tank level indicator. It’s a load cell plumbed into the tank sump that measures the weight of the liquid and reports the tank remainder to the closest gallon at any slope position. It’s more accurate than the level reporting from traditional floats or sight gauges, particularly when that level is low. Knowing the exact volume of the tank is powerful – it allows continuous rinsing, for example, to work optimally by informing the operator if the clean water flow into the tank matches the spray outflow so that water accumulation in the sump can be prevented. It also eliminates the uncertainty of filling the last tank, making sure there’s enough without creating waste. That knowledge saves stress and time.

It’s been interesting to watch and nurture this change of winds in spraying. Ten years ago, most of my inquiries were about selecting the right nozzle. Today, I field many calls on how to improve spray efficiency. With sprayers costing a sobering amount of money, it’s well worth looking at getting the most from what you already have before opening the wallet. Having completed all your scheduled spraying, a confident calm can descend on you as you watch the rain approach.