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Spreading methods

The method of slurry or FYM application can impact on the amount of nutrients that are available to the crop. Minimising environmental losses by reducing the surface area of the slurry or by incorporating FYM into the soil where appropriate will increase crop yield from organic manures and reduce inorganic fertiliser requirements.

Application of slurry

Applying slurry carefully and at the right time will minimise environmental losses and ensure that the intended amount of nutrients are applied to the crop, allowing for more Nitrogen to be available for grass and crop uptake.

Traditionally slurry has been applied with a broadcast spreader, where the slurry is forced under pressure through a nozzle and onto the field. This method of application can result in up to 80% of the available N applied in the slurry being lost to the atmosphere in the form of ammonia. This results in a loss of a valuable nutrient, but also causes atmospheric pollution.

Following surface spreading, approximately 30% of the total ammonia loss takes place in the first hour and 80% within the first 12 hours. A basic concept to minimise such losses is to reduce the surface area of the spread slurry that is exposed to the air (thus minimising the area for ammonia to be lost from).

There are systems of slurry spreading that are available that will minimise the surface area of the spread slurry that is exposed to the air and as such lower ammonia losses. These include band spreading, trailing shoe applicators and shallow injection systems.

General benefits of low trajectory systems

Reduced odour and public nuisance
Reduced fertiliser inputs
The ability to apply to growing cereal crops
Reduced crop contamination and scorch
Uniform spread patterns
Increased overall farm fertility
Financial returns – work in Ireland has shown the value of N gained by applying slurry with a trailing shoe to be £36/ha more than if the same slurry was applied by a splash plate (Alternative Slurry Spreading Systems, AFBI, CAFRE).

Considerations

Additional purchase cost – capital costs are high for these machines. There is the option to use a contractor that has the equipment available, however this may mean a reduced window of opportunity for spreading.

Increased repair and maintenance costs – the machines have more moving parts and are more complex, and as such, there is a higher maintenance requirement.

Increased soil compaction – when using large tanks with heavy injection equipment mounted on the back, there is a risk of increased levels of soil compaction.

Blockages – any system that involves pumping slurry through relatively small bore pipes will be prone to blockages. With these techniques, it is necessary to remove any solids that might cause a blockage. This can be achieved by mechanical separation of slurry or by agitating the slurry. This is particularly important with slurry from cattle bedded on sand.

Application methods for slurry

What method would you choose?

A recent report looking at resource management on farms revealed that 75% of the farmers who took part in the survey always apply manure with a conventional muck or slurry spreader, with only 4% using a slurry injector or trailing shoe. It is important to weight up which method will be the most efficient all round.

Splash Plate

Most common method of applying slurry
Can result in up to 80% of the available N applied in the slurry being lost to the atmosphere in the form of ammonium.

Band spreaders

A boom is mounted behind the tractor or tanker where there is a number of evenly spaced flexible pipes. Slurry travels down these pipes to be deposited on the soil or crop surface.
These are simple systems with few moving parts and are useful for spreading large quantities of slurry easily.
Band spreaders don’t necessarily place the slurry on the soil surface which means that growing crops and grass could be contaminated or scorched by slurry. This is less of a problem with young growing crops where slurry is largely deposited on bare soil.
Because there is no contact with the soil there are no requirements for extra power or fuel to apply the slurry.
This method reduces the surface area of slurry exposed to the air lowering nutrient losses.
Gives a more uniform spread pattern.
There are reported ammonia reductions of 26% when slurry is trailed on corn stubbles and fallow ground with no growing crop, and 57% when the slurry band is enclosed by the crop (Project AM0126 Ammonia Mitigation Options, North Wyke and ADAS).

Trailing Shoe

Mainly used for applying slurry to grassland
A large number of “shoes” which are mounted on the toolbar behind the tractor / tanker parts the grass sward to allow slurry to be deposited on bare soil rather than on the plants themselves.
Ammonia emissions are reduced from the smaller emitting surface of the slurry and reduced further by the slurry bands being protected from air currents by the crop canopy (up to 57% reduction).
Another key advantage of the trailing shoe machine is that the method of application causes little damage to growing crops, even tall crops, which allows for greater flexibility in application date as well as the availability of a larger window to apply slurry without affecting silage or herbage quality.
Use of a trailing shoe in trials allowed slurry to be spread in each month, whereas the splash plate was limited due to the risk of spoiling the silage crop (Project AM0126, Ammonia Mitigation Options, North Wyke & ADAS). Trials in Ireland have shown that slurry can be applied 6 weeks before harvest with a trailing shoe with no adverse effects on silage quality (Alternative Slurry Spreading Systems, AFBI, CAFRE).
As the trailing shoe is pulled along the ground the shoes can wear with implications on running costs.

Shallow injection

A number of discs cut slots in the soil surface into which slurry is deposited.
This method leads to very little soil disturbance while depositing the slurry directly into the rooting zone, making it readily available to the roots of the growing crop.
The ammonia emissions are reduced by up to 73% when slurry is placed in the soil via shallow injection.
Shallow injection technology will also reduce grass contamination, as well as reduce odour levels which can be beneficial if you need to spread near housing.
The discs can help to aerate the soil, stimulating positive microbial activity.
Care must be taken as to the timing of injection – it is almost impossible on heavy clay soil in the summer when the soil is very dry and hard.

Deep injection

Is limited by soil texture, soil moisture, stone content and slope.
Should be avoided during the winter months and not used until the soil has sufficiently dried in the spring.
Slurry distribution in the soil is likely to be poor and the risk of drainage beyond crop use high wasting nutrients and increasing the risk of water pollution.

Comparison table

	Broadcast spreader	Band spreader	Trailing Shoe	Shallow injector
Typical range of dry matter	Up to 12%	Up to 9%	Up to 6%	Up to 6%
Requires separation or chopping	No	Up to 6% No Over 6% Yes	Yes	◊Yes
Relative work rate	••••	•••	•••	••
Uniformity across spread width	√	√ (simple) √√√ (advanced)	√√√	√√√
Ease of bout matching	√	√√√	√√√	√√√
Crop damage	◊◊	◊	◊	◊
Relative level of odours and ammonia emissions	♦ ♦ ♦ ♦	♦ ♦ ♦	♦ ♦	♦ ♦
Capital costs	£	££	£££	£££

Source: Managing Livestock Manures, Spreading systems for slurries and solid manures, 2007, ADAS, IGER, and Silsoe.

Application methods and availability of nutrients

The quantity of nutrients available for crop production will depend on the method of application as well as the source of the manure, its dry matter, soil type and season of application.

Click on the images below to get an indication of available nutrients (kg/m³) for different application methods. Images have been taken from Think Manures and values are from RB209, The Fertiliser Manual.

Don’t work in kg/m³? Click here to access the tables with the calculations in units/1000 gallons of slurry rather than kg/m³

Pictures

Sources: Managing Livestock Manures, Booklet 3, ADAS; AFBI Alternative Slurry Spreading Systems; Project AM0126: Further Evaluation of Ammonia Mitigation Options, North Wyke and ADAS; Images kindly reproduced with permission from Think Manures, EA & Tried and Tested.