Liquid fertiliser continues to increase in popularity as operators look to apply a costly input with more accuracy and get more out of their investment in high-tech sprayers.

Choosing the right application hardware is key to efficacy while also avoiding the risk of damage to growing crops.

Chafer Machinery has a long history with liquid fertiliser, from the companys early days as a supplier before the brand became Yara, to building and specifying sprayers with the corrosion resistance and application capability to apply it, says sales and marketing manager Joe Allen.

The company has also continued to develop application consumables.

He says: In the early days, flat fans were used to apply fertiliser to bare soil, but when working in the growing crop scorch becomes a risk.

Whereas with chemicals the aim is for products to land on the leaf, fertiliser needs to get into the soil, so we need to produce a large droplet which is carried by its weight at lower pressure to roll off the leaf onto the soil.

A cap or jet can lead to atomisation and scorch, so we have developed a Streambar for this purpose.

Application rate The Chafer design incorporates four outlets along a 50cm bar, directing the flow of liquid downwards.

Dribble bars have the advantage that the product can be applied at 20cm or two metres above the crop, with no variation in application rate, which was useful when boom ride tended to be poor, he says.

But with the improved boom control offered by modern sprayers, operators can set the boom low and work in a wider range of conditions without the stream of liquid being broken by the wind.

This is useful if operators wish to spray chemicals in the morning when winds are lighter and switch to fertiliser in the afternoon.

Dribble bars will also work at any angle to the ground, maintaining accuracy on undulating land, he adds.

The latest Streambar MR from Chafer can also offer a range of orifice sizes, increased via a slider, avoiding the need to change caps for different application rates.

A downside of dribble bars is that on a single spray line, it is necessary to swap them for nozzles every time the operator wishes to go back to applying chemicals.

But if the sprayer is fitted with a double body, such as the Hypro DuoReact, you can have a quad nozzle holder on one side and a single on the other, the latter holding the stream bar, says Mr Allen.

Where access to the field is alongside trees or hedges, bars being knocked out of line is another issue, but on the Streambar MR, they are connected by a flexible ‘O ring which allows them to spring back into position.

There are undoubtedly downsides, including the cost of setting up with dribble bars, but they do offer the opportunity to get the best out of an expensive product with the added opportunity for variable rate application and minimal risk of scorch, says Mr Allen.

Nozzle options For those sticking with caps, pulse width modulation (PWM) offers some opportunity for improving accuracy and making savings on fertiliser, Mr Allen says.

There were some concerns about atomisation, but there are also advantages.

Operators can benefit from instant rate changes and turn compensation, to cut the risk of lodging.

PWM can make fertiliser application more consistent but also work really well for variable rate, he says.

Duty cycle needs considering outlets are normally open 100% of the time, but PWM systems work at 25-75% for chemical applications.

The minimum for fertiliser would be 50% to avoid misses.

Theres a lot of interest in using sprayers equipped with PWM for fertiliser and we work closely with our customers to help them find the optimum settings.

Nozzles can offer the flexibility and practicality to get the most out of the increased accuracy offered by liquid applications, says Roger James, business development manager EMEA at Pentair Hypro.

Accuracy Using fertiliser nozzles, accuracy is better than ±5%.

We have achieved ±2% with our ESI nozzle compared with ±15% for granular application.

He explains the design challenges for a fertiliser nozzle encountered by the company when developing the ESI nozzle centred on placement ability versus the likelihood of blockages.

A single stream requires a large opening; at the wide range of nozzle sizes used, a smaller flow from more openings gives the best balance between blockage and coverage and our tests showed that six streams is the optimum.

The bands of fertiliser need to be equidistant and delivered at the same height, allowing the angle of distribution to be calculated at the 40-60cm boom height that can be maintained by the sprayer.

Mr James adds that while dribble bars are less affected by boom height, above 1m the stream can still suffer from interference by the wind, the motion of the sprayer and slipstreaming.

Set up is key, and while most operators aim to work at one to four bar pressure, Silsoe Spray Applications Unit testing at the development stage for ESI ran it at six bar to assess any added risk of scorch.

The primary drop does not land on the canopy as it has the velocity to push through; its secondary deposition that causes scorch and the trials showed that at one to six bar there were no ‘satellite drops, says Mr James.

As soon as the spray is intercepted by the crop it breaks up.

Its also worth remembering that conditions are influential to scorch.

Straightforward He adds that nozzles can be more straightforward to use.

Operators also benefit from the usability of a fertiliser nozzle as it can be easily fitted to a three-way holder and twisted to Multiple outlets on a fertiliser nozzle deliver streams of liquid and offer a compromise between coverage and the risk of blockages.

select, being as compact as a standard nozzle cap.

He suggests that twin lines offer the ideal set-up as fertiliser work tends to be carried out at a busy time of year, especially when combined with a multi-nozzle body, such as the Hypro DuoReact.

The fertiliser nozzle can be on one side and other nozzles on the four-way turret, so theres no need to rotate the nozzles when swapping between chemicals and fertiliser multiple times a day.

Iain Robertson, farm foreman for a large farming company, applies liquid fertiliser to 600 hectares of crops using a 24-metre, 3,000-litre Househam Spirit self-propelled sprayer and has used a number of application systems over the years.

I prefer nozzles to dribble bars and have been impressed with the Hypro ESI.

I have three sets for different application rates and I find that it is easy to calibrate and check the flow rate, whereas theres no real way to do that with a dribble bar.

With a range of nozzles, you can fine-tune applications.

Mr Robertson adds that he has not experienced any issues with atomisation, but stresses that sprayer set up is key.

If the pressure is too high you will get the stream breaking up the old Agroco umbrella system was notorious for this.

Good multi-nozzle bodies on newer sprayers mean you can easily swap between nozzles to give a variable rate as you are going along, keeping the pressure right.

Modern sprayers also have effective boom control systems to ensure the boom height is kept right, which is critical.

He adds that residual fertiliser can get left in dribble bars, trapped in the gap between the outlet and the chemsaver, dripping down onto the sprayer when the booms are folded.

Nozzles are cleaner and tidier, and less prone to damage, he says.

In a previous role, that farms Bateman sprayer was equipped with the manufacturers AccuRate dribble bars.

They were quite effective, but I still felt that nozzles were a better fit for our system, says Mr Robertson.

He has also tried variable rate nozzles, but found them either to be ineffective, due to the rubber bladder which affects consistency, or prohibitively expensive.

However, he adds that PWM nozzle control looks to offer considerable potential for variable rate application and is interested to try it out.