Making the most out of liquid N

With the birds singing and the days beginning to get longer, thoughts are rapidly turning towards top-dressing cereals and oil seed rape. For those committed to using liquid fertiliser for the task as oppose to solid, it means an even busier time for the sprayer and sprayer operator to get over the ground. As the nitrogen content depends on the product being used – maybe a home-mixed liquid urea or propriety brand, but possibly with added sulphur - this will influence the amounts used. Application rates will also depend on cropping, with root crops and specialist applications, such as vegetables, having specific requirements and so the pump capacity, as well as the spray line and nozzle output needed, will be set by the volumes required. Most sprayers are liquid fertiliser-proof when it comes to pumps and valves and so handling liquid is no problem so it is only a case of fitting the appropriate nozzles and making sure the sprayer has the output capacity required.
So with sprayers in general, the rule of thumb when purchasing a sprayer is to ensure that the pump capacity (based on 0.5m nozzle spacings) offers 5% of the tank volume for agitation + 5 litres/min per metre boom width for nozzle output. This means, for example, a 36m sprayer with a 4200 litre tank should have a pump capacity of 210 l/min for agitation plus 180 l/min for the boom making a total of around 400 l/min necessary. However, when applying liquid, generally agitation is not required and so that additional pump capacity can be pushed through the nozzles. Some sprayers, such as AMAZONE’s UX Super trailed or Pantera self-propelled, that utilise twin pumps - one for agitating and one for spraying - can switch over the agitation pump into spraying mode and thus maximise the output at the nozzle. Couple this with a second spray line and the nozzle output can be doubled to achieve even higher application rates or a subsequent increase in forward speed.
With the specific gravity of liquid fertiliser in excess of that of water, the operating pressure needs to be around 14% higher than the equivalent water rate to apply the correct dosage and nozzle sizes should take this into account.
However, particular care should be taken with regard to nozzle selection as droplet size is crucial when it comes to reducing the risk of scorch, particularly at this time of year when the plants are still vulnerable. Make sure that the droplet size is big enough to run off the plant to get maximum soil contact and minimal leaf damage. Frost can be a major factor when it comes to giving soils to ability to carry a heavy tractor/sprayer combination but these conditions are not conducive to applying liquid fertiliser so don’t take the risk and, in the same way, on dewy mornings don’t get started too early or wait until it is wet enough to wash off any product left on the leaf.
Keeping boom heights down to a minimum is a pet topic at AMAZONE when it comes to spraying and reducing drift risk but here, with liquid, it is imperative that the boom is kept high enough and the height is dependent on the nozzles used. With simple 3-hole ray jets then 120 cm high is not out of the way, whereas with umbrella jets or sluice jets then the height should be reduced to either 100 cm or 50-70 cm respectively. Dribble bars can also be used for these applications so set up the machine according to the nozzle’s requirements.
Back on the subject of scorch, pressure levels need to be kept an eye on, especially with modern sprayers with an electronic rate controller which will maintain output with forward speed and so droplet size is reduced at higher speeds. Plus, when following variable rate application maps where the required quantity will spike up and down depending on the demands of the map, again the droplet size will alter. Most nozzle solutions have a maximum pressure of around 3-4 bar which needs to be observed at all times so take care when pushing on.
As always, a well set up sprayer and a little background into the potential pitfalls will ensure the job is done right and so, for liquid fertilising, let AMAZONE look after every acre.