Farm Ireland

Tuesday 23 January 2018

Do the Sums to maximise the benefit of Slurry

Timing and application method will help increase the number of nitrogen units in your farm's soils

Spreading in spring costs nothing extra, whereas improving the method increases the cost of spreading
Spreading in spring costs nothing extra, whereas improving the method increases the cost of spreading
Spreading in spring costs nothing extra, whereas improving the method increases the cost of spreading
However, by optimising timings and switching from traditional splashplate systems, you can up the nutrient benefits of slurry

Tom Ryan

The most important consideration when spreading slurry is timing, while the second is method of application. Focusing on getting slurry out in the spring instead of during summer months is worth the equivalent of an extra six units of nitrogen per 1,000ga spread.

The method of spreading also has the potential to increase the efficacy of your slurry by adding three units of nitrogen per 1,000ga spread. This improvement can be achieved by switching from a splashplate system to a trailing shoe option for example.

If someone changes their spreading dates from summer with the splashplate to spring with the trailing shoe, there is the potential to get the benefit of nine extra units of nitrogen per 1,000ga.

Spreading in spring costs nothing extra, but improving the method will lead to an increase the cost of spreading.

However, there are other benefits to the trailing shoe andband spreading systems over conventional splashplate systems to consider:

  • Flexibility -- The trailing shoe will give you more spreading options in the spring since it can be used on grazing fields because there is not as much smearing of the grass with the slurry. This allows the farmer to apply slurry on pastures with heavier covers without disrupting the grazing rotation significantly.

This allows farms that may be restricted on the total amount of chemical phosphorus that can be applied more opportunities to use slurry to boost grass growth on the grazing platform.

It also suits the contractor, since it spreads the workload of slurry spreading over a much longer period than the traditional windows of early spring and during the silage season.

Applying slurry to pastures with heavier covers has the added advantage of reducing nitrogen loss to the air.

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The savings you make on nitrogen may allow you to cover the contractor charges for trailing shoe systems, which tend to be €10/hr more than the traditional splashplate system.

Your neighbours will also appreciate a switch to a trailing shoe system, since it does reduce the smells associated with the job significantly.

The cost of a trailing shoe versus band spreader, to buy, is €18,000 versus €12,000. A bit expensive to buy since the grants have gone, but buying between two farmers is an option. Contractor rates are favourable and would be the most suitable option for most. n

  • Calibration application rate -- Accuracy is important.

Evenness of application is also important; correct setting up of the splashplate is essential and that ensures that it is undamaged. The trailing shoe and band spreader are, by design, more accurate than the splashplate.

Calibration of Vacuum Tankers/ trailing shoes

To make the best use of the nutrients in slurry, it is important to apply it evenly, at the right rate and at the right time. One method of determining the right rate is to measure the area covered with one load and relate this to the size of the vacuum tanker. The width of spread in metres multiplied by the length of the run(s) in metres for one load, divided by 10,000, will give you the area covered in hectares. If you prefer imperial measurements, the width of spread in yards multiplied by the length of the run(s) in yards for one load, divided by 4840, will give you the area covered in acres.

Chart method

Another method is outlined in the chart in the spreadsheet (see far right). If we know the spread width, forward speed and discharge rate for the vacuum tanker, we can read off the application rate in the table. If we want to spread at a certain application rate, we can choose the right combination of forward speed and spread width from the table.

Forward speed

Forward speed in km/hr can be determined from the tractor gear chart, digital readout or by measuring the time it takes to travel a certain measured distance and calculating the forward speed using the formula: Speed (km/hr) = 3.6 x measured distance (metres) divided by the time (in seconds) it takes to travel this distance.

You must keep to the units used in the formula, ie, metres for distance, kph for speed and seconds for time. A constant number used to link these units together is 3.6 and it doesn't change.

Discharge rate

The discharge rate can be measured by timing how long it takes to empty one load. Divide the capacity of the tanker by the time in minutes taken to empty it.

A 1,600ga tanker emptying in three minutes and 40 seconds gives us a discharge rate of almost 440ga/min (2m3/min). The discharge rate from most tankers is usually about 2m3/min (440ga/min). But to be sure, measure it and adjust your rate accordingly. A 10pc increase in discharge rate is a 10pc rise in application rate and vice versa. The discharge rate shown in the table is 440ga/min.

Useful unit conversions: 1ac = 4840yds2 = 4047m2; 1ha = 10,000m2 = 2.471ac; and 1m3 = 220ga. To convert km/hr to mph, multiply by five and divide by eight.

Indo Farming