It is good practice to sample your manures and slurries for nutrient content, to avoid the variability that can occur from using published values. However in order to obtain results that will aid nutrient management planning and allow you to take account of the nutrients in manures it is vital that a representative sample is taken.
How do I prepare organic manure samples for analysis?
Dry matter levels and nutrient content of stored slurry can vary considerably due to settlement and crusting. The composition of heaped solid manures can also vary depending on the amount of bedding and losses of nutrients during storage. It is therefore very important that you take several sub-samples from a range of positions within the store or heap, bulk them together, and then take a sample representing an “average”. When collecting any samples, remember to wear rubber gloves and protective clothing.
You can send samples to a lab for analysis, or analyse them yourself using a rapid on-farm method; a slurry-N meter (for example Quantofix or Agros metre) or slurry hydrometer.
If done on-farm, analysis should be carried out immediately; making sure that the sample is well mixed. If sending off to a lab, make sure containers or bags are clearly labeled and the samples are either dispatched immediately or kept in a refrigerator and dispatched within seven days.
Taking representative samples of slurries
To prepare a sample to analyse, you need to take at least five 2 litre sub-samples. Pour them in to a large container, stir thoroughly, and pour immediately into a smaller clean container. It is recommended that a sample sent to a lab should be dispatched in a clean 2-litre screw-topped plastic container, leaving at least 5cm of airspace to allow the sample to be shaken in the laboratory.
Above ground stores
Where possible, slurry should be fully agitated and sub-samples taken from the reception pit. If not, if there is safe access from an operator’s platform, the five sub-samples can be taken at a range of positions using a weighted 2 litre container attached to a rope.
Below ground pit
It may be possible to obtain sub-samples at different positions using a weighted container as above.
It is not recommended to take samples directly from a lagoon unless there is a secure operator’s platform which provides safe access. If there is no safe access, consider sampling in the field when spreading.
If the slurry has been well agitated, sub-samples can be obtained from the slurry tanker or irrigator. If the tanker is fitted with a suitable valve, five sub-samples can be taken from a stationary tanker at intervals during filling or while field spreading is in progress. To sample during field spreading, put appropriate weighted down containers across the field, mix all the samples together to obtain a representative sample and take the sample to be analysed.
When sampling enclosed slurry stores (pits or tanks) it is important to never climb down or lean into the store because of the risk of inhaling toxic gases.
Taking representative samples of solid manures
The important thing to remember when paying for analysis, is the results that you get back are only as good as the sample you send.
You need to take at least 10 sub samples of about 1kg each. Once you have collected sub-samples, place them on a clean, dry tray or sheet, break up any lumps and thoroughly mix. Then take a representative sample of around 2kg for analysis. It is recommended that samples be transported in 500 gauge polythene bags, with excess air expelled from the bag before sealing.
If the manure is dry and safe to walk on, you need to identify at least 10 locations that look to be representative of your heap (if you have a tidy, well maintained heap). If your heap is less tidy, and is not A-shaped, consider taking more samples, perhaps 15, and mixing them together to ensure that the results that you use in nutrient planning are representative. Clear away any weathered material with your spade or fork, dig a 0.5 metre deep hole and take a 1kg sample from each point. Alternatively take sub-samples from the face of the heap at various stages during spreading.
Weeping wall stores
Wait until the store is emptied before taking sub samples as it is not safe to walk on the surface of the stored material. Sub-samples can be taken from the face of the heap when emptying has commenced.
Sampling during spreading
It is possible to take samples while slurry or solid manure is being spread, simply by placing trays in the field, taking care to avoid stones and other objects that may be flung out by the spreading mechanism.
How to interpret laboratory analysis results
Labs that analyse slurry
Click on the laboratory name to access their website
Alliance Technical laboratories (Suffolk) – 01449 721192
Anglian Soil Analysis (Lincs) – 01205 460590
Envirosystems – NIRS technique (Lancashire) – 01772 860085
Eurofins – NIRS technique (Wolverhampton) – 0845 6046740
Lancrop Laboratories (York)- 01759 0305116
NRM (Berkshire) – 01334 886338
SAC (Scotland) – 0131 5353170
Expression of results
Analysis results can be expressed differently from one lab to another. You often need to convert them before they can be used or entered in decision support systems such as MANNER-NPK, or PLANET. Results from labs can be reported in the following ways:
- on a dry weight (DW or 100% DM) or fresh weight (FW) basis;
- in units of grams or milligrams per kilogram (g/kg, mg/kg), grams per 100 grams (g/100g), percent (%), grams or milligrams per litre (g/l, mg/l), kilograms per tonne (kg/t) or kilograms per cubic metre (kg/m3);
- as the nutrient element (N, P, K, Mg, S) or the nutrient oxide (P2O5 , K2O, MgO, SO3).
If you are in doubt about how the results are expressed always contact the laboratory to confirm.
Click here to access conversion tables if analysis results need to be converted.