Valuing slurry – the importance of testing

Organic manures such as slurry are a very valuable resource. Not only can they boost soil fertility, but when used effectively, they can allow for considerable savings on chemical fertiliser spend.

Joining Cathal Somers and Deirdre Glynn on a recent episode of the Environment Edge podcast, Teagasc Soil and Plant Nutrition Specialist, Dr. Veronica Nyhan detailed ways in which farmers – both grassland and tillage – can make more effective use of slurry.

Based on market prices for chemical nitrogen (N), phosphorus (P) and potassium (K) and a cattle slurry at 6.3% dry matter (DM), Dr. Nyhan explained that cattle slurry is worth the equivalent of €28 per 1,000 gallons. That’s based on it containing 9 units of N (achieved when spread via LESS), 5 units of P, and 32 units of K.

The above values, she explained, stem from research included in the Nitrates Directive and the Teagasc Green Book, which analysed slurry samples from 75 cattle farms – dairy, suckler or beef - across the country and are presented on the basis of average results.

This research, she noted, presented quite a degree of variability in terms of slurry dry matters. As previous Teagasc research has shown that dry matter content is correlated to the nutrients contained within, she advised farmers to test their slurry to make more effective of its nutrients.

Although the gold standard would be laboratory analysis, the cost of doing so is often a limiting factor to its uptake at farm level. Instead, Dr. Nyhan encouraged farmers to use a slurry hydrometer.

“We do encourage people to invest in a slurry hydrometer. It’s a very simple tool. It is a weighted graduated glass tube that when inserted into slurry, it will tell you the dry matter content of it.”

From the hydrometer reading, farmers can revert to the Teagasc Green Book to gain a better understanding of the nutrients contained within. Farmers importing slurry were also advised to test any slurry imported onto their farm in an effort to ensure crops are not over or under fertilised, and effective chemical fertiliser programmes can be developed around any organic manures applied.

For advice on how to take a slurry sample, click here.

Through the podcast, Dr. Nyhan also shared a number of steps to maximise fertiliser savings when using organic manures, these include:

• Start with a soil test and identify where there is a need to organic manures;
• Correct soil pH first and never apply slurry within three months of a lime application- apply the slurry before you lime;
• As soil fertility is expensive to build up, particularly P, target your index 1 and 2 soils with organic manures;
• Test your slurry – know what’s in it;
• Use the right technology, Low Emissions Slurry Spreading (LESS) will maximise the nitrogen used for crop growth;
• Balance your chemical fertiliser applications on the basis of the organic manure applied and its nutrient content.

Also discussed as part of the podcast, available to listen to below, was the key differences between available and total nutrients contained with organic manures and why incorporation is critical after applying slurry to tillage soils.

Listen in below:

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