Red clover. Photo: Missouri Dept Natural Resources, USA.
Sampling pastures for nutrient analysis
To get the most out of rotationally grazed pastures and to maximise livestock nutrition, testing your pasture for nutrient content is important. To compare results between paddocks and over time, you have to take and prepare pasture samples the same way every time. This article explains how to consistently collect pasture samples for nutrient analysis at the laboratory.
Sampling the paddock
Take pasture forage samples shortly before the livestock are turned on to the pasture. Walk over the paddock and collect 20 to 30 small grab samples: reach down and grab a random sprig of forage between the thumb and forefinger. Samples need to represent what the livestock will be eating, so select the species that the livestock actually eat (not thistles, for example), and remove the forage at the same height at which the livestock graze the pasture.
Aim to represent the actual species composition: try to take the same percentage of clover, grass etc. as grows in the pasture.
If obviously different forage associations (e.g. all grass, grass/clover, grass/shrub) grow in the pasture, select representative samples of each in proportion to the actual distribution: follow a plan or walk the paddock in a uniform grid. The same applies to paddocks made up of different soil types, because different species compositions will grow on the different soils.
Alternative sampling method
An alternative method for mixed pastures is to mark out 1 m2 and, using a pair of scissors, cut off everything above ground except unpalatable weeds and dead material. Do this in about 6 to 10 places. The advantage of this method is that by weighing you can estimate standing dry matter over the whole area. It also properly reflects the mix of legumes and grasses etc.
A subjective estimate of legume content may also prove valuable, since legumes tend to increase pasture intake by livestock and therefore increase animal performance. Write down a percentage that you think represents the proportion of legumes.
Note the date when the sample was taken. In rotationally grazed pastures, note the number of days since the pasture was last grazed, which indicates the forage’s maturity. List these notes on the back of the testing request sheet.
Sample preparation
Once the samples are collected, either begin drying them immediately or freeze them.
To dry samples, spread them out on newspaper in a warm dry place away from wind (so they don’t blow away). It is important to strike a balance between drying them fast enough so they don’t begin to age or rot, and slowly enough that you don’t lose the nitrogen. A week is a good time to dry them properly. If samples are to be mailed to the laboratory, they should be air-dried slowly to a crisp state to prevent them from spoiling during transit. For accurate estimation of energy and protein, samples should be air-dried.
If samples are not dried, they should be delivered to the laboratory frozen or on ice; otherwise, they may start to decompose, and the analysis may not accurately represent the true protein and energy contents of the forage in the paddock.
To freeze samples, place them in plastic bags (one per paddock), remove the excess air, close the bag tightly, and put the bags in the freezer. This will prevent decomposition and the loss of nitrogen and non-structural carbohydrates. Then pack them in an esky or polystyrene box with ice or dry ice, and send them by courier.
Test options
SESL offers the following test packages for pasture nutrient analysis:
Stock feed, forage, fodder & pasture analysis.
|
Code |
Package name |
Analysis included |
|
SFF |
Stock feed analysis |
% dry matter, % moisture, % crude protein, % fat, % digestibility (ruminants) and metabolisable energy (ruminants) |
|
RSF |
Routine stock feed dietary minerals |
Total N, P, K, S, Ca, Mg, Na, Fe, Cu, Mn, Zn, B, Mo |
|
FSF |
Full stock feed dietary minerals |
Above + Cl, Se, Co, I |
Keep records
When you get your results back, put them in a database so you can compare pasture quality between paddocks and from year to year. By developing a farm database of the quality of pasture that livestock are eating, you can increase your understanding and improve your management of pasture quality, and therefore determine whether you need to supply supplements and when best to supply them for cost-effective results.
Further reading
NSW Agriculture. 1997. Establishing pastures (DairyLink series).
NSW DPI. Pasture management publications.