Herbage sampling is used to identify the macro and micronutrient status in plants. The results from herbage testing can be used to mitigate deficiencies, help fine-tune a fertiliser programme and maximise a crop’s yield potential.

As well as providing information about the plant’s nutrient status, herbage tests can be used for animal nutrition purposes, highlighting imbalances that can affect grazing animal performance. Boron (B) is essential for plants, but not animals, while cobalt (Co), iodine (I) and selenium (Se) are essential for animals but not plants. Cobalt is also required by the nitrogen (N) fixing bacteria in clover nodules known as rhizobia.

Environmental influences, such as weather conditions, can impact on the element levels in herbage results, as can soil type, pH, soil moisture, soil texture and organic matter. Therefore, using a combination of herbage and soil testing is the best way to create an overall picture of the nutrient status.

There are several sampling methods recommended for different crops. For example, forage crops such as brassicas have a slightly different sampling method to a complete pasture profile.

Most brassicas require 20 to 30 leaves of the youngest, most mature leaf taken at mid-growth. In a complete pasture profile test, results are given separately from the clover. This requires two bags of sample to be sent to the laboratory for testing: one bag of pasture and one of clover. The clover is tested separately due to the N fixing bacteria rhizobia as it requires around ten times more molybdenum (Mo) than plants do, so deficiencies of Mo will be seen in legumes first.

It can be difficult to identify by eye a nutrient deficiency on a growing plant. Nitrogen and sulphur (S) deficiencies, for instance, show similar symptoms, such as yellow-green chlorosis and reduced growth. However, S typically occurs on young leaves first and N on the oldest. Therefore, a herbage test is recommended to correctly identify what deficiency is expressing itself, allowing for the correct fertiliser programme, whether foliar or granular, to be implemented to meet the plant’s needs.

When planning a herbage test, it is important to ensure the samples arrive at the laboratory on the same day or overnight. If left for a few days, the results can be affected.

Herbage testing is a useful management tool to help maximise crop performance. Contact your local PGG Wrightson Technical Field Representative for assistance sampling your crop or pasture.