Benefits of Organic Manure (Slurry) Analysis

April 10, 2025

As weather conditions improve, many farms are utilising their stores of organic manures. College of Agriculture, Food and Rural Enterprise (CAFRE) Technologist, Dr Alastair Cameron discusses the using organic manure on the farm.

The nutrient value of organic manures (cattle slurry and manure, pig slurry, poultry litter and increasingly anaerobic digestate) can be highly variable. The variation is due to the type of livestock, diet fed, storage conditions and handling. Whilst there are standard values (Table 1) it is beneficial to know the nutrient content of your own farm organic manures to allow for accurate nutrient management planning (NMP). This helps to minimise spend on chemical fertiliser and nutrient leakage to the environment.

Table 1.  Standard nutrient values of organic manures

Type of slurry	Dry Matter %	Nitrogen (kg N/m3)	Phosphate (kg P2O5/m3)	Potash (kg K2O/m3)	Sulphur (kg SO3/m3)
Cattle slurry	2	1.6	0.6	1.7	0.3
	6	2.6	1.2	2.5	0.7
	10	3.6	1.8	3.4	1.0
Pig slurry	2	3	0.8	1.8	0.4
	4	3.6	1.5	2.2	0.7
	6	4.4	2.2	2.6	1.0
Dirty Water	0.5	0.5	0.1	1.0	0.1

Organic manure analysis will provide figures for, percentage dry matter, pH, nitrogen (N), phosphorus (P) and potassium (K). Magnesium, copper, zinc, sulphur and calcium are also included. Sampling and analysis can be carried out at any time of year but is particularly useful in early spring ahead of the main slurry spreading period. This will allow planning of any chemical inputs required to optimise crop growth.

Organic manure has high readily available nitrogen, typically with greater than 30% of the total nitrogen content present readily available to the crop. The crop-available nitrogen supply from manures also depends on the application timing, application method and the delay between application and incorporation.

Sampling slurry and solid manure

It is essential that a representative sample is taken. The nutrient content of slurry can vary considerably within a store due to settlement and crusting – the slurry should be well mixed prior to sampling. Similarly, the composition of solid manure in a heap can vary depending on the amount of bedding and losses of nutrients during storage. If stored materials are to be analysed, it is important that the sample taken represents an average of what is found in the store or heap. Samples from different buildings and stores should be analysed separately. Always adhere to safe handling practices when dealing with organic manures.

Using your results

Weather conditions, method of application and time of year should also be considered as these affect the availability and uptake of nutrients from the organic manures. It is important to understand and use the results to refine your nutrient management plan. Following this, you should consider your soil analysis results and target slurry applications to crop requirement in low P and K fields. Analysis of manures and slurries provides information on their nutrient content, allowing you to make savings on chemical fertiliser and help to reduce the risk of environmental pollution.

What next?

Organic manure sampling kits and sampling instructions are available at DAERA Direct offices.

• Place the organic manure samples in the padded postal bag with the request form and take this to your local Post Office.
• Payment is direct to NRM Laboratories.
• NRM Laboratories will email an organic manure analysis report to you.

CAFRE Technologists are continually investigating innovative systems and technologies to help farmers improve sustainability and productivity. These innovations are demonstrated across the CAFRE Farms and form an integral part of CAFRE Knowledge Transfer Programmes.