Scoring pastures for renewal

Scoring pastures for renewal

27 February 2021

Herbage testing is the only way to accurately assess levels of micronutrients important for production.

“If productivity is less than expected, a macro- or micronutrient deficiency, or both, could be the issue,” says Ballance Agri-Nutrients Nutrient Dynamic Specialist Jim Risk.

A shortage of any essential nutrient affects plant growth, and in turn, grazing stock. Regular soil testing identifies macronutrient deficiencies, but what about micronutrients?

“Testing micronutrient levels is important. Even though they’re only required in small amounts, a deficiency can have a major impact. For example, a deficiency of the micronutrient molybdenum (Mo) can limit pasture production even if macronutrients – such as phosphorus (P), potassium (K) and sulphur (S) – are adequately supplied,” Jim says.

Measure levels in plants

Herbage testing can measure both micro- and macronutrient levels in a plant, and is the only way to accurately assess if micronutrient levels are adequate for production. This is because plant uptake of micronutrients can be affected by soil type, soil pH, soil moisture and other factors.

“For example, plants in high pH alkaline soils, which can happen if lime is overapplied, are prone to induced boron (B), zinc (Zn), iron, copper (Fe) and manganese (Mn)

deficiencies.”

Commonly-used herbage tests for pastoral farming are clover-only or mixed pasture, and the choice depends on what is tested. Jim says a clover-only test is most appropriate if you’re testing for a suspected nutrient deficiency.

Clover shows signs of nutrient deficiency – especially P, S, K, magnesium (Mg), Mo and copper (Cu) – sooner than grasses. A clover-only test reveals macronutrient levels, as well as key micronutrients such as B and Mo – both are crucial for vigorous clover growth and for improving pasture quality.

“If you want to determine the nutritive value of the plant to animals, a mixed pasture test shows what stock are actually eating, and can be analysed to measure feed value or nitrate-nitrogen levels, as well as monitoring key macronutrients such as K and Mg, and micronutrients such as cobalt (Co) and selenium (Se).”

When and how to test

“Herbage testing is best timed around periods of peak animal demand, giving you time to address micronutrient deficiencies. For example, it’s best to test Co before weaning, in mid to late spring, and Se in autumn and once again in spring before mating. Timing may not necessarily align with soil testing.”

Clover-only testing should be done during the spring flush when temperature or moisture is not limiting growth.

The following practices are important for getting meaningful results from herbage testing:

  • Use clean shears to cut bulk samples at grazing height.
  • Collect a bulk sample of around 500 grams (g) for each representative paddock within the farm block, ensuring blocks reflect different soil types, topography, farm management and so on.
  • Each bulk sample should contain 15 to 20 sub-samples from random parts of the paddock/block, avoiding stock camps, fence lines, troughs, and dung and urine patches.
  • Bag and label the samples and send them to the lab as soon as possible, ideally the same day, or refrigerate to reduce deterioration.

Using test results

Levels in the herbage can vary throughout the year based on pasture uptake and growth, so it is important consider this when analysing test results.

If herbage test results indicate a micronutrient deficiency in pasture, it can generally be corrected by applying the right amount of fertiliser at the right time to elevate levels to within the appropriate range. A serious deficiency requires direct-to-animal supplementation together with a long-term strategy to correct micronutrient levels in pasture.

Herbage testing can also confirm soil test results, especially for nutrients such as K and S, which are mobile in the soil so can have variable results over time.

The micronutrient Se – essential for animal health, growth and productivity – is often lacking in New Zealand pasture, and is relatively easy to address via fertiliser. Ballance NutriMax Selenium contains both fast and slow-release Se in the one granule, making it suitable for annual application as part of a regular maintenance fertiliser programme. More information on the NutriMax range is available at ballance.co.nz/micronutrients.

Article supplied by Ballance Agri-Nutrients.