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A structured decision making approach to choosing and justifying the right sprayer

Take home messages

  • There are many variables to consider when choosing a sprayer and each will be weighted differently from business to business depending on the farming model (enterprise mix, farming system, typical rotation, spread of farming operations, etc.), the need or want to optimise efficiency, availability of labour and lifestyle decisions.
  • Before upgrading the machine there may be options to increase field and overall efficiency of existing machine.
  • First priority is for the machine to be ‘fit for purpose’.
  • The capital invested can be similar between a self-propel (SP) and a tow-behind outfit when aiming to match field capacity.
  • Alternative uses for the machine and the likelihood of spraying where higher clearance is required, are key cost-of- ownership drivers.
  • Tank size and boom width can sometimes be a trade-off against spraying speed.
  • Lifestyle considerations can affect the decision.


Choosing the right sprayer and justifying its ownership cost can be a challenging task. There’s a lot of variables and trade-offs to consider when making the decision and the importance of each varies from business to business. The sprayer is often the most used implement on the farm, and therefore, it’s important to get the decision right. Taking a structured decision making approach can help take the stress out of making this decision.

Structured decision making approach

Step 1. What capabilities do I need to ensure the machine will be ‘fit for purpose’?

Key variables to consider when determining this include:

  • Type of machine
    • Alternative uses – am I looking for a dedicated spraying outfit or do I need a ‘third’ tractor (for example, front end loader (FEL), spreader or chaser tractor), or self-propel (SP) that windrows also? An alternative use can effectively subsidise the cost of ownership.
    • Clearance height – what’s the likelihood of needing to spray where higher clearance is required (for example, taller crop types (e.g. canola, sorghum/corn) or late season applications (e.g. fungicides/insecticides/desiccation/crop-topping, late season liquid N)). If likely, are contractors available if you haven’t got the clearance?
  • Spraying objectives (timeliness)

Spraying objectives or targets around getting the spraying done on time can vary considerably from business to business. While often not written down, each business usually has a number of ‘spraying objectives’ they aim for to ensure timeliness of operations. Examples of some spraying objectives include:

  • Spraying grasses out before they tiller.
  • The ability to spray each crop variety in three days.
  • The ability to get clethodim out within a 4hr/day ‘window of opportunity’ during winter in the Western district.

In addition to clearance height identified above, the ability for your spraying outfit to meet your spraying objectives will be influenced by the field capacity of your sprayer and field and non-field efficiencies.

Field capacity and field efficiency

Theoretical field capacity (ha/hr) = [width of boom (m) x speed of travel (km/hr)]/10.

Effective field capacity = theoretical field capacity (ha/hr) x field efficiency (%).

Field efficiency (%) = percentage of time the machine operates at its full rated speed and width while in the field.

An example of the above calculation is provided in Table 1.

Table 1. Calculation of effective field capacity.


  • Water rate (will this limit speed due to inadequate pump capacity or nozzle size or number?).
  • Maximum spraying speed with appropriate spray efficacy.
    • How well is the machine ‘weighted/balanced’.
    • Wind-sheer limitations.
    • Technology - to allow correct droplet size at increased speed (e.g. AIM Command®, Three Tier System (3TS)®).
  • Paddock landform and topographic features.
    • Soil type and steepness which can affect trafficability.
    • Paddock shape, obstacles (trees, dams, channels, swamps, etc.) and terrain (rocks, corrugations) can affect speed and width (overlap).
  • Overall weight and ‘power to the ground’ considerations – will the sprayer sink, climb up sand hills, etc.
    • Breakdowns (lack of preventative maintenance).

Non-field efficiency

Factors outside the field that have an impact on the timeliness of the spraying operation are referred to as non-field efficiencies. These factors can sometimes be improved for low cost regardless of which spraying outfit you use.

Examples of these factors include:

  • Fill time
    • Pump and hose size (e.g. 1.5” connection to chemical shuttle =60L chemical/min; 4” water hose faster than 3” > 2”, etc.).
    • Induction technology.
    • Batching plant (often requires additional labour).
    • Mounted pump.
    • Quick fill systems (for example, overhead water loading, nose connector)
  • Travel time
    • Spread of farming operations and/or distance between paddocks.
    • Road speed (empty and loaded).
    • Block cropping (less clean-outs).
    • Distance to fill points (versus mobile tanker to take water to sprayer).
  • Clean out time
    • Flush technology.
    • Block-cropping.
  • Tank size – if tank size is matched to paddock size (subject to weight considerations) this can mean less time spent travelling and filling.
  • Breakdowns (lack of preventative maintenance).

Efficiency factors both field and non-field can be highly variable between farms. Growers should continually ask themselves what could I be doing differently to improve current efficiencies, and therefore, overall timeliness of the operation.

Step 2. Consider the type of sprayers available

Table 2 provides a comparison of different types of sprayers. In summary however a few features of each type of sprayer are listed. (Note: Less attention has been paid to truck mount sprayers given the limited number on Victorian farms):

  1. Tow-behind
    • Handles most applications.
    • Choice of larger tank sizes.
    • Clearance issues late in season.
    • Multiple alternative uses for towing tractor.
  2. Truck or tractor mount
    • Fastest road speed full or empty.
    • Choice of larger tank sizes.
    • Clearance issues late in season.
    • Visuals sometimes compromised.
    • Limited alternative use.
  3. Self-propel
    • Great clearance - specifically designed for spraying hence suitable for all spray applications.
    • Great traction.
    • Best comfort.
    • Superior visuals.
    • Good road speed.
    • Modern technology (for example, AIM Command®).
    • Higher fuel use (hydrostat).
    • Limitations on tank size.
    • Limited alternative use.

Table 2. Comparison of different types of sprayers.


Step 3. What can I justify?

Justifying an investment in a machine is a balance of financial and non-financial considerations.

The primary financial consideration is cost of ownership which will be influenced by:

  • Capital cost (i.e. the loss in value of the machine each year, plus the appreciation in value of its replacement). This ‘changeover’ cost can be 35-40% of the total cost, so keeping it to a minimum has a big influence on overall ownership cost. Factors that affect changeover cost include:
    • Engine hours on trade.
    • Age of trade
      • Obsolete model or technology.
      • Access to parts.
      • Poor condition.
    • New technology – the sky’s the limit so be critical on what you really need. For example, do I need auto-height, auto-greaser, etc.?
    • No-trade discount.
    • Factory incentives.
    • Exchange rate.
    • Poor reputation.
    • Poor dealer support.

Table 3. Some ‘actual’ variations in capital cost of SP sprayers sold within various regions of Victoria (Source: ORM).


Some growers have a defined policy around changeover time based on engine hours (for example, 2000 hours), age (for example, 5 years old) or model (for example, within one model of current model). Whereas others will keep an active eye on the market and buy whenever the price is right (for example, Wimmera grower in Table 3 will upgrade whenever changeover is < $100/

  • Field capacity and field and non-field efficiencies, as outlined in Step 1.
  • Alternative uses for machine - can ‘subsidise’ the sprayer costs.
  • The percentage of spraying needed to be done by contractors.
  • Other fixed costs (interest, rego/insurance) – can be up to 25% of total costs which is a big contributor.
  • Fuel usage – hydrostat SP can use double the amount of a tow-behind, but overall fuel cost is influenced by field capacity and field efficiency.
  • Labour cost – dependent on machine hours.
  • Scale – spread of costs (particularly the fixed costs) over area sprayed per annum ($/ha).

When assessing cost of ownership it is advisable to compare it to the cost of using a contractor. Once this comparison has been made an informed assessment can be made as to whether ownership is cost-effective. The final decision will however also be impacted by non-financial considerations and the timing of the planned upgrade.

Non-financial considerations include:

  • Job satisfaction – the sprayer is the most widely used implement on farm, operator comfort, health considerations (e.g. bad back) should be considered.
  • Interest and/or expertise in machinery – sometimes it’s easier to let the contractor worry about ownership issues and access to labour, and get the latest and greatest technology turn up each year.
  • Attracting and retaining employees – varies between regions.
  • No financial pressure.
  • Family time.
  • Stress – being able to get the contractors when you want them.
  • OHS

Non-financial considerations are harder to quantify than financial considerations. Each grower has to put their own weighting and dollars on these variables depending on their personal preferences.

In regards to timing, sometimes a decision to upgrade can be justified but there may be other immediate priority uses for that capital or existing financial commitments that already limit cash flow. Useful overall machinery investment benchmarks to consider include:

  • Alternative/priority uses for capital – i.e. what other ‘big-ticket’ items are coming due for an upgrade and will investing a certain amount of capital in improving your spraying capacity limit you from getting the balance and timeliness right in other areas?
  • Overall capital invested in machinery – ORM benchmarking show that the typical investment in machinery is $1 for every $1 of income generated, or a ratio of 1:1. Some businesses can maintain a 0.8:1 ratio without compromising timeliness, which means $200,000 of capital can be invested elsewhere.
  • Total (horse) power, machinery and labour cost (TPML) – what is the total annual cost of machinery capital, machinery operating costs (fuel, repairs, contractors), and labour (including your own). A figure under 40% of income is good, under 35% is great
  • Cash flow implications – machinery is often financed over five years and too much spent on machinery upgrade all at once can run down cash flow, particularly in a poor income year. Machinery repayments (principal and interest) fewer than 13% of income are generally OK if other key-cost areas in the business are balanced.


Choosing and justifying the right sprayer doesn’t have to be a difficult process. Having a sound understanding of what capability you need, and the options and costings associated with achieving that capability will enable you to make the right decision for your business.

Contact details

Brett Symes

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