Low Emissions Slurry Spreading (LESS)

How it works

Low Emission Slurry Spreading (LESS) relates to techniques of slurry spreading which reduce the loss of Nitrogen (N) gases into the atmosphere. There are several LESS techniques that can be adopted, each with their own benefits. These include:

• Dribble bar: Depositing slurry in rows on grass. Also known as the Band Spreader.
• Trailing shoe: Parting the grass and depositing slurry directly on the soil.
• Injection: Injecting slurry directly into the top soil.

The Dribble bar and Trailing shoe are the two most popular LESS methods and both are covered under the LESS scheme. Injection is also covered, but has not proved to be popular amongst Irish farmers or contractors.

Both Dribble Bar and Trailing Shoe come with their advantages and disadvantages.

Dribble Bar

Advantages

• Lower cost option available.
• Can be retro fitted to existing tanker.
• No increase in power requirement.
• Suitable for all ground conditions.
• Easy to use for less skilled operators.
• No ground contact.
• Reduced odour.
• Easy headland management.

Disadvantages

• Will leave smearing on the grass.
• Not suitable for use in heavy grass.

Trailing Shoe

Advantages

• Larger reduction in emissions.
• Suitable for use in heavy grass cover.
• Very little grass smearing.
• Slurry deposited at ground level.
• Can be grazed sooner.

Disadvantages

• More power required.
• Skilled operator required.
• Less suited to hilly ground.
• More complex headland turn operations.
• More wearing parts.
• No grant available on retro fit system.

Spring Application

Spring application is seen as the most beneficial time to utilise N by LESS techniques, where cool damp weather is usually observed. This is due to the fact that nitrogen is lost at an increased level when slurry is spread during dry, sunny and windy weather. Targeted application of LESS, therefore helps to reduce these loses directly after spreading. The typical value of 1,000 gal of cattle slurry applied using LESS methods in spring has an available N-P-K to a 50kg bag of 9-5-32. Slurry spreading should be avoided where heavy rain is forecasted within 48 hours.

LESS equipment should be used to apply slurry to fields with large nutrient demand, for example grass/maize silage fields, and under cool and damp conditions. Soil analysis on farms have shown that fields located far from the farmyard tend to be lower soil fertility and the largest nutrient demand especially K., and as such, should be the priority in relation to slurry spreading.

Impact at Farm Level

LESS machines retain more N on farm to grow grass, which will reduce fertiliser N requirements and expense. A LESS spreader will also retain an extra 3 units of N per 1,000 gallons of slurry vs. splash-plate. This is a 30–50% improvement in the slurry N values due to lower ammonia-N emissions. Low emissions slurry spreaders allow slurry to be spread under better soil conditions into higher covers thus increasing the window to target slurry nutrients to fields with low soil test P and/or K. 

It has been shown that cows prefer to graze LESS spread pastures due to lower grass contamination. The reduction in sward contamination from slurry via LESS also decreases grazing return times compared to the splash plate. LESS techniques also widen the window for spring slurry application, and as a result, better soil conditions are available at time of application.

Benefits to the Environment

The use of LESS helps to lower greenhouse emissions by 30-60% in comparison to splash plate. These emissions contribute towards air pollution and so by utilising LESS, it helps to contribute towards cleaner air by reducing ammonia losses. It can also help to improve soil fertility and ensure balanced soil fertility on the silage areas of the farm.

By reducing Nitrogen (N) losses from slurry application, more is retained in the soil, leading to higher nutrient use efficiency. For example, trailing shoe increases slurry N content by 3 units of N/1,000 gals. This allows farmers to reduce chemical N applications on the farm. There is a large loss of nitrogen when using a splash plate as the slurry is spread over a large area which leads to bigger N losses from the weather, wind and the effect of the sun. The process of loss is mainly through ammonia (NH₃) volatilization, the nitrogen in the form of ammonia is potentially a dangerous air pollutant to both human health and the environment as well as being a substantial economic loss from the farm. LESS places the slurry in a band reducing its surface area thus minimising the surface area to which slurry is applied and puts the slurry directly on the ground/soil. Due to the precise nature of LESS, it also reduces odour during and after application.

What do farmers need to do?

The Targeted Agriculture Modernisation Scheme (TAMS 3) currently provides grant aid for investments to farmers purchasing Low Emissions Slurry Spreading equipment. Young trained farmers or Registered Farm Partnerships may also avail of a higher rates and ceilings of funding. If farmers are interested in further information they should contact their Teagasc advisor or the local Teagasc office.

Moving to LESS

When making the move to LESS equipment, farmers will need to take some things into consideration. For example, a farmer will need to ensure they have a tractor with the correct horse power in order to carry out the spreading. This will depend on the size of the tank. A 2,000 gal tank will require 130Hp, while a 3,500 gal tank will need up to 150Hp. With LESS equipment such as the dribble bar and trailing shoe, slurry flows from the tank at a faster rate, meaning forward speed of the vehicle needs to be increased. In terms of weight, a dribble bar weighs 0.5t, while a trailing shoe comes in at 0.75-1t, meaning this will need to be accommodated. However, given a full 2,000 gal slurry tank weighs around 13t, so the weight of equipment for either of these LESS techniques is small relative to the weight of the tank.