Expert provides spray efficiency tips

Sprayer efficiency and efficacy can be increased by improving refilling and shortening ferry distance


Agronomy
A simple tanker and batching set-up for servicing spraying operations on multiple farms. PHOTO Bill Campbell

A simple tanker and batching set-up for servicing spraying operations on multiple farms. PHOTO Bill Campbell

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The efficiency of refilling operations can have a major impact on the cost-effectiveness of spraying and also on the lifespan of expensive equipment.

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The ability to maximise the area sprayed in a day is determined by how efficiently the sprayer can be filled, the time taken getting to and from the paddock and the operation of the sprayer itself.

New sprayers and tractors have the capacity to work faster, with more horsepower and better suspension and pumping capacity, which in turn increases the ability to lift travel speeds.

Available spraying hours are mostly limited due to meteorological conditions specified on the product labels. This includes surface temperature inversions, high wind speed, frosts, heat and rain. Extending the spraying window when conditions are marginal, such as during periods of high drift risk, must be discouraged.

Most growers want to maximise the hectares sprayed with the available time and labour, however, the ways to achieve this will vary from operation to operation.

Methods of increasing the area sprayed per day, such as increasing travel speed, also increase the potential for spray drift via updraft behind the boom. Higher speeds also increase wear on the machine, particularly the boom and drive system. As spraying speeds increase, spray coverage will reduce. Boom auto-height improves spray deposition and helps protect the boom but does not fully overcome updrafts behind the machine.

Making spraying as efficient as possible has the twin benefits of increasing the likelihood of better control through better timing of application, which in turn leads to lower costs.

Increase hectares per load

To increase the area per load, the options are to reduce application volume per hectare and/or increase tank size.

Reducing application volume requires a good understanding of the different products being used - how they work (mode of action), the target weeds, the effect of meteorological conditions and the spray quality being used. Lower water volumes with large droplets (less than 70 litres per hectare) may only suit the use of highly water-soluble pre-emergent herbicides in low levels of stubble, or translocated herbicides such as 2,4-D, as per the 2018 APVMA guidelines on moderate to larger target weeds.

Products that require good to excellent coverage or which are not well translocated, such as herbicides from groups A, C, D, F, G, H and L, as well as fungicides and some insecticides, require higher water volumes (80 to 100-plus L/ha). These require 10 to 20 per cent coverage, which can be checked using water-sensitive paper or fluorescent dye.

A larger spray tank is another way to improve the area sprayed per day as it reduces the number of fills per day. However, this can affect the stability of the spray unit. Paddock evenness and soil type, such as loose sand or heavily ploughed fields, will have a significant effect on spray rig behaviour.

Another factor needs to be considered if considering larger tanks is pump size and the effect on agitation. Too small a pump will not be able to run the boom and give enough agitation to keep all the products in solution, particularly in colder weather.

A batching trailer can be moved with the spray rig to permanent fill locations. PHOTO Warwick Holding

A batching trailer can be moved with the spray rig to permanent fill locations. PHOTO Warwick Holding

Take water and product to the paddock

More efficient methods to improve productivity will come from decreasing the distance to fill points.

For example, a four-kilometre fill station round trip at 20 kilometres per hour takes 12 minutes per load. With four to five loads per day, up to 60 minutes will be spent travelling and one less tankful sprayed that day. This doesn't include the time taken to fold and unfold the boom.

Many growers are now using portable mixing and transfer systems and water carts to reduce time the sprayer is out of the paddock, which also reduces the engine hours of the sprayer or tractor. Having the product for at least a full day's spraying on a batching trailer enables it to be moved to each refill site, either close to a watering point or moved with a water truck. If the tanker isn't big enough to hold water for a full day's spraying, a separate batching trailer enables it to be left behind while the water tanker is refilled.

Large operations will use semitrailer/road train set-ups, while small to medium operations may have a similar set-up fitted to a large trailer or truck.

Making spraying as efficient as possible has the twin benefits of increasing the likelihood of better control through better timing of application, which in turn leads to lower costs.

Some growers with smaller sprayers are opting for 'hot-loading', where a full spray load is premixed and loaded straight into the sprayer. Larger sprayers require pre-batching of chemicals, which are pumped separately to fresh, or pre-treated, water.

Depreciation on engine hours is estimated to be $100 to $130 per hour for self-propelled (SP) rigs. To run an SP to and from refilling is costing spray time and increasing the depreciation on the sprayer for no real productive benefit. This is why many growers are now looking at 'keyless fills' where the spray rig is shut down during refilling.

Keyless fills

With SP rigs being one of the most expensive machines on the farm, more and growers are reducing the depreciation by having fill and batching units directly fill the spray tank.

"Having the SP idling or using its pump to refill is like having four casual staff stand there and watch me refill," said one convert to keyless fill. "I can put that money to better use elsewhere on the farm."

More permanent fill points

Another option for reducing sprayer wear and tear and depreciation and increasing available spray time is having all-weather access water tanks around the farm with large-capacity external pumps. These tanks can also enable pre-conditioning large quantities of water with conditioners such as ammonium sulfate.

Eliminate folding and unfolding of the boom

Front fill is now standard on new self-propelled rigs. PHOTO AGRONOMO

Front fill is now standard on new self-propelled rigs. PHOTO AGRONOMO

Mixing and filling the sprayer close to the paddock also eliminates the need to fold and unfold the boom. On average it takes six minutes to fold and unfold a large boom and reset its level and correct height. Again, this can equate to another 30 minutes per day not spraying.

Having a fill point on the front of an SP allows the rig to drive up to the batching/fill station.

Spray efficiency comparison

When analysing the spray efficiency of your operations, it is important to be realistic about how long each operation takes. Minimum times for the different operations can easily be exceeded, resulting in fewer hectares sprayed per day.

The examples given in Table 1 are based on actual grower operations and look at the main components influencing 'sprayed hectares'. This table uses a 36m boom, 6100L tank and an application volume of 75L/ha. Minimising ferry distance, increasing fill speed and the combination of both shorter ferry distance and faster filling are compared with the standard grower practice at both 18km/h and 25km/h travel speeds.

Increasing boom width and tank size and reducing application volume have not been included in this analysis.

Increasing fill speed or shortening ferry distance gives equivalent increases in area sprayed per day, but combining both modifications more than doubles the increase in sprayed hectares.

Having a portable batching and fill system can eliminate the need for a permanent mixing site. However, when designing the system, containing and managing spills, access to personal protective equipment (PPE), first aid, clean water, safety data sheets (SDS) and record-keeping requirements must still be factored in.

Once fully operational, portable mixing and transfer systems can reduce the time not spraying and increase the effective life of the sprayer.

More information: Bill Campbell, bill@campbellag.com

GRDC GrowNotes, 'Spray Application Manual for Grain Growers', Module 5: Spray plans, and Module 9: Mixing, filling and transfer systems

GRDC Spraying Efficiency Fact Sheet, 'Fill-and-ferry savings optimise hectares sprayed on any given day'

GRDC Spray Mixing Requirements Fact Sheet, 'Mixing requirements for spraying operations'

GRDC GrowNotes, Mixing & handling - custom trailer

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