Archive Article: 1997/12/13

13 December 1997

Considering a new sprayer? Peter Hill weighs up the choice.

IF YOUVE a modest acreage of cereals and, perhaps, a little oilseed rape to look after, deciding on the most appropriate sprayer is pretty straight-forward. After all, a tractor-mounted machine with a 15m to 18m boom should cope perfectly adequately and at reasonable cost.

Similarly, when an estate-size acreage is involved and capacity is the over-riding consideration, then the choice is likely to come out in favour of a self-propelled, perhaps with a 3,000 litres tank and 24m, or bigger, boom.

But what about the middle ground? When an 1,800 to 2,000 litres spray tank and 20m to 24m boom is enough, the choice becomes more complex. Should it be mounted, demount, trailed or self-propelled?

The choice is influenced by considerations that go beyond the spraying operation itself; most notably how the spraying vehicle fits in with the rest of the farms power fleet.

A tractor-mounted outfit offers the least expensive solution. A 1,200/800 litres rear tank-front tank combination makes it well-balanced with some element of self-propelled spraying characteristics.

Boom width may be compromised; 24m on a tractor-mounted sprayer is not an every-day specification, and it is not always an elegant solution in terms of cab access with booms folded. But nor is this application particularly demanding on a 70hp to 80hp machine that could have seen a few years service on other tasks before earning a slightly easier life.

It is also attractive that, as with other tractor-based sprayers, the investment goes into spraying kit rather than a power unit that, in the case of a specialist self-propelled, is likely to be a single-use vehicle.

That is the theory; except that a comprehensive wrap-around outfit does rather tie the tractor to spraying operations. Yes, the equipment can be dropped off to release it for other tasks. But in reality the time involved means the attraction of this cost-saving concept soon pales.

Weight and a lack of transmission speed control – relative to the hydrostatic drive of a self-propelled sprayer – also count against the tractor-based spraying outfit to some extent.

A demount sprayer, fitted to a systems tractor is one alternative. And as dedicated spraying machines, vehicles like the Mercedes-Benz Unimog, JCB Fastrac, Fendt Xylon and Clayton C-Trac have a lot going for them.

It is a neater solution, in some respects, than a front-and-back combination on a conventional tractor, with just one unit to dismount to release the machine for other work.

Add the Clayton and Fastracs four-wheel steering and there is the added attraction of improved manoeuvrability and single wheelings at headlands.

Conversely, weight – strongly rear-biased – and a relative lack of transmission versatility count against the system tractor based outfit. So does the lack of ground clearance -though less so with the Clayton C-Trac which can take quite large diameter rowcrop wheels.

All three machines offer spacious and comfortable driver accommodation and a greater degree of task versatility than a conventional tractor.

The Fastracs particular attraction is its high road speed – a key consideration for farms expanding through contract farming or acquisition of land away from the home block. And if there is a need for additional capacity, the concept can be pushed to include a front-mounted tank instead of having to change the entire outfit.

Trailed sprayers have made a comeback, particularly at the higher capacity end, with more modern controls and functions, and tracking drawbars that eliminate the wheelings penalty. Sophisticated axle suspension also makes them a viable alternative to a smaller self-propelled machine, while high-speed running gear matches the capability of a fast tractor.

A tractor-trailed sprayer combination can never match the manoeuvrability or relative compactness of the demount or self-propelled but it does have the advantage of spreading its weight over three axles.

Quick-coupling hydraulics, fewer electrical connections and semi-mounting on the tractor linkage arms mean the trailed sprayer can be separated from the power unit more readily than either front tank-rear tank or demount units, with nothing but a spray controller/monitor to hinder the tractors application on other duties.

Arguments against? With a chassis and running gear of its own, the trailed sprayer is a more costly solution than other tractor-based options and, unless a natty self-tracking drawbar is included, extra wheelings at headlands are a penalty. Sideling land can also prove problematic for trailer sprayers.

The self-propelled sprayer appeals to those who want the ultimate in dedicated equipment; some operators do try to improve utilisation of their investment by swapping spray gear for fertiliser spreaders, sometimes seed drills as well.

But, on the whole, spraying (which might include liquid fertiliser application) is the sole task for such machines.

With stiff competition at the 2,000 litres/20 to 24m level, how does the self-propelled sprayer justify itself? By being ready, at the drop of a hat, for any spraying task, for one thing. No juggling of workload, no hitching up of equipment, no compromises.

From the operators point of view, the self-propelled usually offers the best in-field driving characteristics in terms of steering manoeuvrability and speed control, good visibility from a mid or forward mounted cab, and an integrated sprayer control arrangement which places everything where it needs to be rather than where it best fits.

Co-ordinated steering also means single wheelings at headlands, while the coil spring, air and hydraulic axle suspension systems of modern designs give operator, chassis, sprayer and boom a smoother run.

Lower weight, greater wheel and tyre size flexibility and the fine and progressive speed control that comes with hydrostatic transmission or wheel motor drive, along with good crop clearance for late-season work, are other clear advantages for the self-propelled sprayer.

For many, that is enough to justify the substantially higher investment required for such a machine in comparison with any of the alternative solutions.

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