All nutrients great and small

Herbage testing can identify if micronutrient deficiencies are causing a decline in pasture productivity.

A shortage of any essential nutrient can impact plant growth and animal health. So if there’s a decline in production, checking levels of both macro- and micronutrients (trace elements) can help to identify the cause.

While soil testing identifies shortages of macronutrients such as phosphorus and sulphur, which are required in relatively large quantities by plants, it is not a reliable indicator of essential micronutrient status (with the exception of boron for brassica crops). 

Micronutrients, including copper (Cu), zinc (Zn), selenium (Se), cobalt (Co), manganese (Mn), boron (B) and molybdenum (Mo), are required in only trace amounts by plants and animals. Their availability is influenced by complex interactions between micronutrients, as well as factors such as soil pH and parent material. For example, plants growing in high pH alkaline soils (which can occur following excessive lime application) are susceptible to induced plant B, Zn, Cu, iron and Mn deficiency. 

Herbage testing provides the most reliable means of identifying micronutrient deficiencies in pasture and serves as an extremely valuable tool to complement standard soil tests. These tests are essential for diagnosing plant nutrient stress and evaluating whether the pasture’s nutritive value is sufficient to support animal health. Two types of herbage tests are commonly used in pastoral farming: 

• Clover-only: Nutrient deficiencies typically appear in clover before grasses, because clovers are less effective foragers for nutrients and more sensitive to nutrient stress than grasses. In addition to assessing macronutrient levels, clover-only testing measures Mo and B, which are essential for vigorous clover growth and, consequently, improved overall pasture quality. 
• Mixed pasture: This provides an indication of the nutritive value of the pasture available to grazing stock, as it samples a broader range of species within the sward. It helps assess whether the pasture is supplying sufficient nutrients to support animal health, particularly micronutrients such as Se and Co. 

Micronutrient levels in herbage can vary throughout the year due to pasture growth and nutrient uptake. Herbage testing is most effective when carried out during the active phase of plant growth – when moisture and temperature are not limiting. The ideal times are: 

• Spring for Co in anticipation of weaning. 
• Spring for Se prior to mating. 
• Early April for Cu, before peak demand in autumn and winter, when pasture is less able to meet animal need. 

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

• Use clean shears to cut pasture at grazing height i.e. top two-thirds of the plant. 
• Collect a bulk sample containing 15-20 sub-samples for each representative paddock within the farm block, ensuring the blocks reflect the various soil types, topography and farm management practices. The bulked sample should weigh approximately 500g. Avoid sampling areas that are not typical, such as water troughs, dung or urine patches, gateways, fence lines and irrigation runs. 
• Bag and label samples, and send to the laboratory as soon as possible, ideally on the same day, or refrigerate to minimise deterioration until they can be sent. 

When herbage testing identifies a micronutrient deficiency, a well planned fertiliser programme can lift pasture micronutrient levels to support optimum plant growth and grazing stock health. Products in the NutriMax range such as NutriMax Selenium 1%, NutriMax Copper 25% and NutriMax Cobalt 10% make it easy to incorporate micronutrients into fertiliser applications. 

Severe deficiencies typically require direct-to-animal supplementation to safeguard stock health, alongside corrective pasture applications to restore plant micronutrient status. Where soil pH or other underlying factors limiting micronutrient availability cannot be corrected in the short term, direct-to-animal supplementation options should be discussed with a veterinarian or farm advisor.

Talk to your local your Ballance Nutrient Specialist or Farm Source TSR about herbage testing and managing micronutrients on your farm.
 

Article supplied by Ballance