A micronutrient with mojo

Identifying and addressing a molybdenum deficiency can significantly improve production.

Plants and animals may only need a small amount of the micronutrient molybdenum (Mo) but a deficiency can majorly impact plant growth and in turn, grazing stock. “A Mo deficiency can limit pasture production even if macronutrients such as phosphorus and sulphur are adequately supplied,” Ballance Agri-Nutrients Nutrient Dynamics Specialist Jim Risk says. “Rhizobia bacteria that fix atmospheric nitrogen (N) in legumes need more Mo than non-leguminous plants do, so legumes suffer first if Mo is deficient, with symptoms similar to an N deficiency.” Signs of deficiency in legumes include small, pale green to yellow leaves, reduced growth, and slim stems, with colourless nodules and poor nodulation. Brassicas can have pale green, narrow, upward curving leaves, although this is rare. Molybdenum deficiencies were first identified in New Zealand in the early 1950s but deficiency in stock has not been seen here. Molybdenum was overapplied in the 1950s and 60s, mainly due to the frequency of application, resulting in excess Mo affecting copper absorption in stock. “Molybdenum supplies can deplete over time and some soils are naturally low in it due to their parent material.” North Island sedimentary soils, South Island sedimentary soils (particularly those derived from greywacke rock) and deep peat soils have naturally low Mo levels. In addition, soils with a pH lower than 5.8 are more likely to be deficient.

| Applying Mo to deficient pasture is a cost-effective way of significantly improving production.

“To determine if Mo levels are adequate, use clover-only herbage analysis, not soil tests,” Jim says. “The sampling strategy and type of analysis depends on whether you’re addressing pasture or lucerne production or animal health. “Applying Mo to deficient pasture at the right rate and frequency is an incredibly cost-effective way of significantly improving production. It improves N fixation efficiency and N cycling, driving clover and pasture growth.” In a 1997 trial, sodium molybdate applied to responsive sites resulted in statistically significant increases in pasture and clover production at all sites within 2 years1 . In soils vulnerable to Mo deficiencies, maintenance applications of NutriMax molybdenum (1%), at 2 kg/ha (20 g Mo/ha), can prevent deficiencies from occurring. “Mo is deficient if it’s below 0.1 ppm in clover-only herbage analysis, with N below 4.5 percent. Again, apply NutriMax molybdenum (1%) at 2 kg/ha (20 g Mo/ha) to overcome deficiencies. It’s ideal to test the same paddocks the following summer, provided moisture’s sufficient, to check if the application has raised levels adequately.” A rule of thumb is application every 4 to 5 years to maintain adequate Mo levels, although application frequency is ideally guided by herbage testing. If new pasture is being established, or existing pasture oversown, clover seed can be coated with Mo before being sown. “Copper deficiency issues in stock are easily avoided by good management via herbage testing, and by applying Mo at the right rate when needed,” Jim says.

For more information, contact your Ballance Nutrient Specialist, your Farmlands Technical Field Officer or the friendly team at your local Farmlands store.

Article supplied by Ballance Agri-Nutrients.

1 Morton JD, Morrison JD, 1997. Molybdenum requirements of pasture. In: Proceedings of the Fertiliser Research Conference

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