Sprayer Productivity for Smaller Scales

Travel is an amazing teacher. It exposes assumptions and replaces them with real life experiences.

On a recent trip to New Zealand, I learned a valuable lesson in sprayer productivity. I had long talked about wider booms being a key factor, being an easy change that allowed more area to be covered per pass. I had assumed large fields, large tanks, and fast fills as part of that system, and validated it with calculations and observations.

During a recent trip to New Zealand, I learned that things look really different when the landscape dictates certain limitations. In places like New Zealand, fields tend to be smaller, as expected, with the longest run averaging 300 m or so. Sprayers are also smaller capacity, with trailed sprayers typically fitted with a 24 m boom and a 3000 L tank. Mounted sprayers, commonplace on the North Island, may have smaller tanks and booms, with 2000 L and 18 m width a reasonable average. Self propelled sprayers are not common on farms, but custom applicators use them.

Tender systems (called bowsers) are also rare. Most applicators return to the farm yard, or another nearby water source, to fill. A single filled sprayer can often do that entire field, so moving to a new field and re-filling are part of the same workflow.

Some very interesting things happen when such a scenario is analyzed.

We used a newly re-vamped Productivity Calculator (below) to make the calculations.

Some basic configurations were assumed. All sprayers travelled 15 km/h when spraying, and turned in one headland at 8 km/h. The tank remainder that necessitated a re-fill was set at 5% of tank volume. Tank cleaning was assumed to be required every four tanks, taking 60 minutes. Sprayers were typically refilled in the farm yard or a nearby water source, requiring a ferry (transport) time of 15 minutes each way.

The first scenario was the base configuration, from which one factor was changed in each iteration to examine the magnitude of the change. With the 24 m boom, 3000 L tank, 200 L/ha application volume, a field length of 300 m, a loading time of 30 minutes, and a loading location that required a 30 minute round trip, net productivity was 8.0 ha/h. 22% of engine hours were spent spraying, the remainder was lost to turning at the end of a run, driving to the loading location, loading the sprayer, and cleaning it. We will call that the spraying efficiency.

Because wider booms are successful in improving productivity in western Canada, we examined the practice for smaller farms. Increasing the boom width from an average 24 m to 36 m yielded the first surprise. Productivity only increased to 8.5 ha/h (7%), and spraying efficiency was reduced to 16%.  The problem appeared to be that the wider boom dispensed with the tank contents faster, requiring more frequent filling. And that of course was the big time user, accounting for 60% of the engine hours. 

The next step was to examine a larger tank, keeping the original 24 m boom. This change yielded big results, with productivity jumping to 11.1 ha/h, a 33% increase from the base condition. The larger tank reduced the frequency of filling, and that reduced its drag. Spraying efficiency jumped to 31%.

Another way to achieve a lower filling frequency is to lower the amount of water applied. This is a bit risky, as water volume is likely to most important variable that ensures good spray success, especially when dealing with dense, high yielding crop canopies. In cases where canopy penetration isn’t an issue, and systemic products can be used, less water may be an option. A modest decrease from 200 to 150 L/ha was tested.

Again, a large jump in productivity was observed, from the base of 8.0 ha/h to 9.7 ha/h, about 21%, resulting in 27% spraying efficiency.

What if fields were merged, or shelterbelts removed, resulting in longer spray passes? These would reduce the time lost to turning, which had been 8% of engine hours for the 300 m pass.  We decided to test a 600 m pass. But while it reduced the proportion of time spent turning to 4%, overall productivity barely nudged to 8.3 ha/h.  That’s a 4% improvement, not worth removing any trees over.

One of the biggest game-changers in sprayer productivity has been the 3” transfer pump and efficient product induction systems. Reducing fill time from 30 to 15 minutes did have a large effect here too, increasing productivity to 9.3 ha/h, a 16% increase from the base. There remain inefficiencies in the system, such as the time spent with partial jugs that require measuring. A faster pump doesn’t address these.

With the travel time associated with a home fill being such a large time consumer, introducing a field-based tendering system was expected to have a large impact. We combined this with a fast fill because a tender unit should have the larger pump. And the results were impressive, a jump to 13.7 ha/h. That’s a 72% increase from the base scenarios, boosting spray efficiency to 38%. 

The final scenario involves two large changes. A new, larger sprayer with a 5000 L tank and 36 m boom, combined with a fast fill tendering system. And the results were equally large, boosting productivity to 19.8 ha/h, more than doubling the performance of the base condition (a 148% improvement). Spraying efficiency did not increase further from the fast-filling tendering system alone, because the faster filling was accompanied by the faster emptying of the wider boom.

What is the value of this study? For one thing, we learned that a change that works in one geographic area may not work in another. For these smaller field scenarios, the benefit of a wider boom was undermined by the long downtime during fills. And obtaining a tender system when a single sprayer fill can cover a whole field wasn’t a slam dunk like it is elsewhere, where a field often requires several fills.

Does a producer actually need to spray everything faster? The answer will depend on each farm. A general observation we’ve made is that the windows of opportunity for spraying are getting narrower. Restrictions on wind speed or temperature leave fewer hours in a day to get the spraying done. The risk of falling behind is lurking. And that means that application may not get done when they’re most effective. Disease may have progressed. Weeds will have grown. Crop safety may be challenged. Being even a little more productive can help mitigate all those risks.

If nothing else, it’s critical for an applicator to know where the time goes. Use the calculator. Only then can you be strategic about correcting a problem.