The Value of Slurry Analysis
July 6, 2023
Cattle slurry is a variable product and recent slurry analyses carried out by farmers in local CAFRE Business Development Groups have shown a large variation in nutrient value. “The variation is due to the type of livestock it comes from, the diet fed to those animals and the way in which it is handled and stored. All these factors will influence the nutrient content of the slurry” says Elizabeth Calvin, Dairying Development Adviser, CAFRE. While there are standard ‘book values’ it is better to know precisely the nutrient content of your own farm slurries to allow for accurate nutrient management planning. This will allow you to tailor the type and rate of chemical fertiliser to best financial and environmental advantage.
A complete organic analysis will give you a full picture of the sample including some micronutrients. The analysis usually includes dry matter, pH, total nitrogen (N), ammonium N and nitrate N, P, K, Mg, Cu, Zn, S, and Ca. “An analysis can be carried out at any time of year, just prior to spreading” continues Elizabeth “but is particularly useful in early spring, ahead of the main slurry spreading period for first cuts. There is likely to more divergence from quoted nutrient content in slurry at this time when the largest volume is available. This will also allow early planning of what chemical inputs are required to be brought onto farm to grow forage”.
To get an analysis you will need to request a sample kit from your chosen laboratory and carefully follow the guidance on how to take the sample safely. It is essential to ensure that a representative sample is taken – the slurry should be well mixed prior to sampling. Do not mix samples from different buildings and stores but rather submit separate samples from each place.
“Having got your analysis report, it is important to understand and use it to ensure efficient use of this valuable product” comments Elizabeth. “Take regard of any soil analysis to target slurry to low P and K fields, consider the crop requirements, weather conditions and method of application, alongside the nutrient content of slurry to determine application rates”.
Table 1 shows the ‘book value’ of slurry as reported in the industry standard RB209, the basis of the Nutrient Action Program Guidance booklet.
“Recent analyses results within one group demonstrate the variation that can occur” states Elizabeth. “One member had cattle slurry sampled in May with 8% dry matter (DM) and 4.4 kg Total N/m3. Another had an analysis of 4.8% DM and only 2.4 kg N/m3”.
More diluted slurry as shown in the table above has a lower N content which should be considered when adjusting application rates. Dilution of slurry will, however, improve the N uptake (efficiency) as the slurry will infiltrate into the soil faster when compared to thick slurry. Using a more diluted slurry will also reduce grass contamination as it is more easily washed off the grass by rain. This is especially important when applying between grazing to ensure grass is palatable to cattle and sheep.
Slurry analysis allows for better nutrient management with economic and environmental benefits. Contact your local CAFRE development adviser for further information and advice on the subject.