Managing soil compaction during slurry application

Grass is Ireland’s most popular crop, and the backbone of the dairy and beef industries. Over the last few years a lot of attention has been focused on improving the quality of the sward.

Slurry is rich in nutrients and a great resource for farmers to improve soil fertility. Research has shown that slurry applied in spring is most effective in relation to nutrient recovery in grass.

Many farmers are aware of this and are moving towards spring application.

The average slurry tanker size has increased from 1,600 gallons and is now somewhere in the region of 2,500 gallons. The increase in size aids the efficiency of slurry spreading, yet it can also cause problems in some fields.

Knowing the soil characteristics

Heavy soils typically hold a larger volume of water, making them difficult but not impossible to manage. Rutting is a common problem in these soils, so choosing the correct method of application is vital.

Heavy soils are dense, with small pore spaces, making them slower to warm up and dry out for springtime application of slurry.

Loamy soils are more workable and should drain off winter rain earlier in January. These soils can also compact because they are less dense and have more pore spaces.

Getting the tyres right

Essentially, a tyre has two main functions – supporting the weight of the machine and delivering traction.

Larger tankers need to be fitted with flotation tyres to minimise compaction.

The greater the surface area of the tyre in contact with the ground the more weight spread over a larger contact area. Ideally these tyres should be inflated to around 1.5 bar of pressure.

A typical 2,500 gallon tanker will have an unladen weight of around 4,000kg. This size of a tanker will carry approximately 11,000 kg of slurry, giving a total weight of 15,000kg. Assuming that 3,000kg of the total weight is carried on the tractor drawbar, that leaves roughly 6,000kg on each tyre. In this situation a low-ground pressure tyre of at least 750/60R30.5 is needed to support the weight of the tanker. Compaction under a loaded tyre can travel down to a depth of 1m of the soil.

Controlled traffic

In many countries a system of controlled traffic is in place. This means that the tanker travels the same route year after year. This is controlled by GPS systems that have the ability to identify the driving position each year.

The benefit of a controlled traffic system is that the same area of the field is continually being used to support the weight of the slurry tanker and tractor.

Controlled traffic systems suit wide application widths and dribble bars for umbilical systems.

In theory, the rest of the field is protected from random driving characteristics. This system is best suited to a contractor who can spread the cost over a larger working area. A simple GPS system can also help with even application, by ensuring the correct overlap and hence reducing the number of passes made in the field. Use farm roadways as much as possible to travel to the fields and paddocks.

The umbilical option

Advantages of an umbilical system include high work rates, lighter traffic on fields with light impact on soil compaction and reduced overall traffic from yard to field.

Umbilical systems are ideal where ground conditions are poor. This is either because the terrain is hilly or the ground cannot support the weight of a tanker and tractor, or a combination of both. Typically, the tractor in the field is fitted with low-ground pressure tyres, and the spreading mechanism attached. Obviously, there is no tanker to add weight. Spreading slurry on tillage crops is best done through this type of system.

Heavy soils should also benefit from using an umbilical system. A concern with heavy soils is that if the soils are at field capacity for water, then some run-off can occur.

Yield reductions

Poor management of compaction will undoubtedly have an effect on yields. Flying a drone over some fields shows areas of poor growth in grass that may be caused directly or indirectly by compaction at some stage.

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Special focus: slurry 2017