Magnesium fertiliser for animal health

Magnesium fertiliser for animal health

28 May 2020

A farmer-initiated research project has provided valuable insights for future research into the use of Mg fertiliser for animal health.

In New Zealand, dairy cows traditionally receive Mg supplements by dusting pasture or hay and silage, drenching, water trough treatment and lick blocks before and during calving to prevent hypomagnesaemia (Mg deficiency).

Ballance Agri-Nutrients Science Extension Officer Aimee Dawson says using fertiliser to improve soil Mg content, and in turn pasture content, "can provide dairy cows with the Mg they require".

However, she adds, "lower soil temperatures in winter and early spring, when animals most need Mg, can mean levels of herbage Mg content fall below levels required for animal health".

Canterbury farmer Andrew Barlass was keen to see if a rapid uptake Mg fertiliser might overcome the issue of low herbage Mg content in early spring, and provide more consistent amounts of Mg to cows compared to dusting magnesium oxide (MgO) on feed.

He had read about kieserite, a Mg fertiliser commonly used in horticulture and containing 16 percent soluble, fast-release Mg. Andrew approached his Ballance Nutrient Specialist with his idea and kindly offered Dalkeith Farm in Methven as a location for small plot trials to test it.

Testing the idea

Kieserite was applied to plots of autumn saved pasture on 8 July and 8 August 2019, at varying rates of zero, 25, 50 and 100 kilograms of Mg per hectare (kgMg/ha). Monthly herbage tests were taken over spring (August to November) to determine uptake of Mg, and before and after soil tests were taken to determine changes in soil Mg.

Notable results from the trial were:

  • Kieserite applied in July did not significantly increase the Mg pasture content compared to the control (zero kgMg/ha) in the monthly herbage tests from August to November.
  • Kieserite applied in August at both 50 kgMg/ha and 100 kgMg/ha significantly increased herbage Mg content. Only the 100 kgMg/ha treatment increased the herbage into the animal health range (>0.2 percent), however, this wasn't until November.
  • As the soil temperature increased over spring, the herbage Mg content also increased, with the highest values seen in November.

In summary, the trial found that the kieserite applied in late winter (July and August) did not sufficiently increase the pasture Mg content into the animal health range for early spring grazing. This is due to the cooler soil temperatures experienced at Dalkeith Farm, reducing Mg uptake into the pasture.

Future directions

Given the trial involved just one location and year, Aimee says "further research over multiple years and at different locations will determine if kieserite applied in late winter could increase Mg content sufficiently for animal health purposes".

Previous trials completed in the warmer North Island climates were able to increase Mg pasture content into the animal health range, demonstrating location (and soil temperature) plays a key role in early spring pasture Mg content.

"It's possible that in cooler climates, kieserite or other Mg fertilisers applied in autumn may improve the uptake of Mg into the herbage, providing higher Mg in those autumn saved pastures for spring grazing."

Current advice

The recommended Mg level for stock health is Quick Test 25-30, but as this trial has shown, lower soil temperatures in locations with cooler winter conditions can still limit early spring pasture Mg levels.

Direct animal supplementation is still the best option for achieving animal health outcomes during early calving and lactation, and more research is required to determine the benefit of kieserite application in either autumn or late winter for animal health outcomes.

For more information, contact your Ballance Nutrient Specialist or your local Farm Source TSR.

Article supplied by Ballance Agri-Nutrients.