Sprayers

Self-propelled sprayers. With tank capacities ranging from 1,000 to 6,000 litres, self-propelled sprayers are popular on large arable farms and with agricultural con­tractors. Many of these sprayers have four-wheel steering which is switched to two-wheel steering for road work. Transmission may be hydrostatic or mechanical and the engine will be between 60 and 185 kW (80-250 hp), depending on the size of the machine.

Plate 13.1 A 24 metre self-propelled de-mountable sprayer with a 3,500 litre fibreglass tank.

A typical farmer-owned self-propelled sprayer will have a tank capacity in the range of 1,500-2,500 litres. It has the advantage of low ground pressure, which reduces soil compaction; also, a tractor is not tied up for the season and the sprayer is ready to use at any time. The driver sits in a front-mounted cab with excellent visi­bility of the crop. Some models have high clear­ance axles and wheels making them ideal for spraying tall crops.

Another type of self-propelled sprayer con­sists of a de-mountable tank, usually with a 3,000 to 5,000 litre tank and a 24 to 30 m spray bar carried on the load platform of a high speed, four-wheel tractor. The sprayer can be removed and replaced with a fertiliser spreader or a slurry tank and injector unit.

High speed self-propelled sprayers with low ground pressure tyres can be used to apply as little as 100 litres/ha at 24 km/h (15 mph). These sprayers work on a similar principle to aerial spraying and by varying the size of the droplets from the nozzles application rates of 40-100 litres/ha are possible with an output of up to 200 ha in a day.

A self-propelled crop sprayer used on some small farms consists of a sprayer unit mounted on a farm pick-up truck. Wide wheels and tyres are fitted to reduce soil compaction. The sprayer unit can be removed at the end of the spraying programme, leaving the truck free for other work.

Sprayer attachments with a battery powered electric pump, plastic tank and spraybar are also made for ATVs. They can be used for all-over spraying with standard nozzles or a hand lance.

Trailed sprayers. With tanks holding 1,500-4,000 litres, trailed sprayers are used on many large arable farms. Spray bar widths vary between 12 and 40 m; the chosen width may depend on tramline width. Their main advantages are the large capacity tank and simple attachment to the tractor.

Some trailed sprayers have a tracking system which keeps the sprayer wheels on the same track as the tractor. Electronic sensors linked to the tractor detect movement between it and the sprayer. The control unit actuates steering rams on the drawbar, which are connected to the tractor hydraulic system to keep the sprayer on the correct course, especially when working in tramlines or across sloping land. The system can be over-ridden when driving along curved tramlines or turning on the headland and is locked out when the sprayer is taken on the road.

A more advanced tracking system enables the driver to steer the sprayer hydraulically when making tight headland turns or engage crab steering mode to keep the sprayer wheels in tramlines when working across slopes.

Mounted sprayers. These are made in many sizes, ranging from small, simple machines with a tank capacity of about 600 litres to the more sophisticated models with a tank which holds 2,100 litres or more. Small sprayers with a 200 litre tank and a 6 m spraybar are made for tractors in the 12-15 kW (16-20 hp) range. Most mounted spray­ers have an adjustable spraybar which enables the driver to set it in a high position for spraying in standing crops, especially cereals.

Traditionally, sprayers have been grouped according to the amount of liquid applied per hectare (acre). Modern chemicals are generally applied at fairly low rates, so most sprayers can handle the full range of chemicals. Low volume application is up to 250 litres per hectare (20 gallons per acre), medium volume from 250-500 litres per hectare and high volume up to around 1,200 litres per hectare (100 gallons per acre).

Very low application rates, as little as 25 litres per hectare (2 gallons per acre), have become popular in recent years. This reduces the amount of water to be carried, gives more hectares per tankful and cuts the cost of chemicals. The very low rates can be achieved with rotary atomisers instead of the normal spray nozzles. The atomisers produce uniform, medium size droplets which make very effective use of the chemical.

There are statutory regulations concerning the application of chemicals at very low rates. Some can be applied at the full dose, with a reduced amount of water, others may only be used at very low volume if the product dose is also reduced to give the same concentration used for normal application rates. Always check the product label before using a spray chemical at very low volumes.

Plate 13.2 De-mountable sprayer unit with a 2,500 litre tank on the load platform of a multi-purpose tractor.

Plate 13.3 This trailed sprayer can have tank capacities of 2,500 to 4,000 litres and 9 to 15 metre spray booms.

Plate 13.4 This trailed sprayer with a 3,000 litre tank, 24 m spraybar and an electronic auto-steering drawbar has a high speed axle with leaf springs and air brakes which make it suitable for use with a high speed tractor.

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