Herbage testing: It's all in the detail

Herbage testing: It's all in the detail

27 July 2017

Herbage testing for key trace elements supports animal health and production.

Trace elements (or micro-nutrients) are taken up from the soil by pasture and forage crops are then eaten by grazing stock. Some of these trace elements are needed by both plants and animals; and some are needed by one but not the other. Taking a proactive approach to trace elements will support quality pasture and healthy animals.

Plant uptake of trace elements can be affected by soil type, soil pH and the levels of other micro-nutrients. With so many factors at play, you cannot accurately use soil tests to predict trace element levels in pasture. Herbage testing, on the other hand, is the right tool for the job.

When it comes to animal health, testing trace element levels in blood and tissue samples will complement herbage testing.

What do you need to measure?

There are two types of herbage tests commonly used in pastoral farming:

  • Clover-only: Clover is the ‘canary in the mine’ for your pasture and will show signs of nutrient deficiency sooner than grasses. As well as measuring macro-nutrient levels, a clover-only test can examine levels of boron and molybdenum – key trace elements for healthy clover growth and improving pasture quality.
  • Mixed pasture: This will show what your animals are actually eating. In addition to monitoring trace element content, mixed pasture samples can be analysed to measure feed value or nitrate-nitrogen levels.

The trace elements most commonly applied to pasture to sufficiently supply animals are selenium and cobalt, followed by copper. But remember to also consider the trace element content of any supplementary feed.

When should you measure?

Trace element concentrations can vary due to factors such as seasonal soil moisture and growth rates. Testing is generally timed to allow application prior to periods of peak animal demand. For example, late spring is the time to test for cobalt in anticipation of weaning. Copper is best assessed in early autumn and selenium is usually measured in spring prior to mating.

How do you take samples?

Mixed pasture testing requires bulk samples weighing around 500 grams (g) for each representative paddock within the farm block. This helps ensure blocks reflect different soil types, topography and farm management, etc. Each bulk sample should contain 15 to 20 sub-samples from random parts of the paddock/block. Take care to avoid stock camps, fence lines, troughs, dung and urine patches. Use clean shears and cut to the height to which the pasture would be grazed. Avoid gathering any soil or root material as this will affect results.

Cut clover-only samples from plants during the spring flush when temperature or moisture isn’t limiting growth.

Bag and label samples with the paddock/block name, farm name and date and send to the lab as soon as possible, preferably the same day the sample has been collected, or refrigerate to minimise deterioration.

How do you address a deficiency?

Serious deficiency requires direct-to-animal supplementation in conjunction with a long-term strategy to correct trace element levels in pasture. Where it is hard to immediately counteract factors affecting a particular trace element’s availability (such as high pH), it may be more effective and economic to opt solely for direct-to-animal solutions. Consult your vet or farm advisor about the best options.

Correcting deficiencies in pasture using fertiliser is a matter of applying the right amount at the right time to elevate herbage levels within the appropriate range so pasture can supply the trace element when it is needed.

Selenium targets

With selenium, ensuring sufficiency is as important as avoiding deficiency. A level between 0.1 and 0.3 milligrams of selenium per kilogram of dry matter (mg Se/kg DM) has advantages for the performance of lactating cows and young stock. Ballance offers a selenium product that contains 20 percent in immediately available form and the remaining 80 percent in slow-release form. The slow-release component makes it uniquely suitable for annual application as part of your regular maintenance fertiliser programme.

For more information contact your local Fonterra Farm Source TSR.

Article supplied by Ballance Agri-Nutrients