Spreading the Risk

Correctly maintained, set up and calibrated fertiliser spreaders are an integral part of a combined approach to careful fertiliser management and environmental protection. Rhys Evans and Stephen Podd look at why:

Have you ever gone out with the fert spinner and smugly got all your topdressing done only to be treated a few days later to a display of striping to rival the local golf course? Ok, so your pride might take a bit of hammering, but does inaccurate application really matter? Surely as long as the right amount of fertiliser is applied to the field, that's ok, isn't it?

Frankly, no! Even before the Ammonium Nitrate price rose to around £270/tonne and Triple Super Phosphate hit a mighty £400/tonne, every aspect of fertiliser use and its application was important. Independent trials have shown that if striping can be seen in a field of winter wheat, the resulting yield losses alone could be costing the farm over £20/ha.

These yield losses can be attributed to reduced quality levels from lower Hagberg Falling Numbers (HFN) and harvesting difficulties due to the problems associated with combining lodged crops.
But it's not only a problem for arable farmers, recent trials have shown that the Metabolisable Energy (ME) value of grass fell from 11.3MJ/kg Dry Matter (DM) when fertilised with an ‘acceptable' spread pattern to 10.7MJ/kg DM where the spreader was applying the product unevenly. This fall in ME could be translated into a yield loss of 44 litres of milk a cow over a typical 200-day cycle. Assuming a price of 25p/litre for milk, this equates to a loss of £11 a cow (source: Mark Tucker, Yara UK)
Although there are many factors which can contribute to striping (such as inaccurate tramline widths, compaction and poor fertiliser quality), arguably the most important element is the fertiliser spreader itself.
The evenness of spread is measured by assessing the machine's Coefficient of Variation (CoV). This can be defined as how much the existing spread pattern differs in percentage terms from what would be considered as the ideal/most even pattern. Consequently, a spreader giving a perfectly even spread pattern would have a CoV of 0%, although it should be mentioned that ‘in the field' this does not happen and a more realistic CoV of below 10% is considered to be acceptable. Striping becomes visible at a CoV of 20%, and it is not uncommon for some spreaders to be operating with a CoV of 30%! At a CoV of 30%, the financial effect on a winter wheat gross margin will be around £48/ha (source: Ian Richards ECOPT).
The CoV is measured using a set of trays laid out in a line to twice the machine's working width which catch the fertiliser as the machine passes over them. The contents of each tray are then transferred into a set of calibrated test tubes to give the final CoV. These tray tests usually cost around £170 (+vat) and are carried out by a number of specialist firms including Sprayer and Sprayer Testing Ltd who have engineers located across the country. The tests are valid for all types of machine - single or twin disc, ‘wagging spout' or pneumatic.
Within the 2007/8 Sussex Landcare Project, Sussex FWAG, in conjunction with John Davis of Spreader & Sprayer Testing Ltd, has tray-tested 26 fertiliser spreaders across Sussex. With the exception of 2 spreaders, 21 have needed some tweaking to produce an acceptable CoV, while 3 of the spreaders tested had serious faults which would almost certainly have led to CoVs of over 30%.
In addition to the tray test itself, the service provides an assessment of the spreader's general condition.
Starting at the tractor end, the PTO guards and safety chains are checked. Common faults include damaged or missing guards and anti-rotation chains. In the 2004-2005 period, on-farm accidents cost farmers in the South East an estimated 54.7 million due to factors such as lost output, increased administration, increased insurance premiums, legal fees and damage to equipment/buildings (source: Health and Safety Executive).
Staying on the health and safety theme, most modern spreaders will require some form of supplementary lighting if the main lights on the tractor are obscured by the spreader and the spreader will be driven on the public highway. If there are no lights on the spreader, or the existing lights are beyond repair, trailer lighting boards cost around £40 and provide a relatively inexpensive way of ensuring you stay within the law.
The actual PTO speed is then checked against the dash reading using a tachometer. Obviously higher or lower than intended PTO speeds will have a detrimental effect on the spread pattern of the machine.
Moving onto the general condition of the spreader itself, no-one needs reminding of the highly corrosive qualities of nitrogen fertilisers. In addition to assessing corrosion levels, a visual inspection of the machine will also identify missing/loose nuts and bolts, leaking hydraulic pipes and dust seals and damaged or missing grid screens which need to be replaced.
Initially the machine should be attached to the tractor so that it is level from side to side and front to rear. Occasionally, some ‘tilt' may be required to give the required spread pattern, and as always it is important to check the manual and setting charts for the exact recommendations. With regard to height, in most situations the spreading disc/s or spout should sit approximately 75cm above the crop; but once again, check the manual. Ideally this measurement should be checked with the spreader just over half full. (The height will change according to the weight in the hopper, so this gives a ‘happy medium').
The next area to receive attention is the actual spreading mechanism of the machine. All drive shafts, couplings, and bushes are checked to ensure they are in good condition. One fault highlighted in the tests carried out this spring was worn agitator drive sprockets. Looking at the working machine, the main drive chain appeared to be ‘going round' but closer inspection revealed that the chain was just sliding over the sprocket. This will obviously severely reduce the operational ability of the agitator, having major implications on the spreading rate and pattern of the machine. Attention should also be paid to the gearboxes on the machine, ensuring that there are no leaks and the box is filled with the correct amount of the right type of oil - see the machine's handbook.
Moving on, the vanes on each disc are checked. They should be free of significant wear, which usually becomes apparent when the spreading face of the vane becomes ‘rippled'. Operators should consult the manual for suggested vane angles.
The shutter mechanism is checked to ensure the apertures are opening evenly. Again, operators should check the manual for further details.
The final part of the check looks at the headland spreading mechanism - important if fertiliser is to be kept off cross compliance and stewardship margins, and out of water courses!
When you consider the latest feed wheat prices for November are around £155/tonne and fertiliser prices are rocketing in a seemingly endless upward trend, £170 not only buys you a test, but helps to guarantee the safety of your pocket and protect the environment.
Spreader & Sprayer Testing Ltd can be contacted on 0845 130 7175

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