Tuesday, 8 February 2022

Is Molybdenum deficiency holding your clover back?


With the current price pressure on fertiliser N and the N-190 restrictions now in play, it’s time to ensure your clover growth is not limited by molybdenum deficiency.

Molybdenum (Mo) is a trace element that plays an integral part in ensuring clovers and other legumes can both fix and cycle nitrogen (N) optimally.

It is widely known that molybdenum availability can be closely linked with soil pH. Mo deficiencies can occur in acidic soils (pH lower than 5.5) where the Mo (an anion) is bound more tightly to the soil colloids.

Liming can sometimes overcome Mo deficiency as the availability of Mo to plants increases as soil pH increases. However, if the soil does not naturally contain much Mo, Mo applied as fertiliser will be required.

Some soil types, particularly in the South Island, may have an absolute Mo deficiency and require Mo irrespective of soil pH. For this reason, herbage testing is required to check the Mo status of your soils. Samples should not be collected when soil is very wet or very dry.

Malcolm and Raewyn Menzies farm near Cust in Waimakariri. Working with their agri manager, they collected some mixed pasture and clover-only herbage tests in spring 2020 which indicated that Mo levels in the clover were low and warranted including Mo in the next round of maintenance sulphur super in autumn 2021.

Sourcing their maintenance fertiliser from Christchurch works, Malcolm and Raewyn were able to make use of the Precision Blending Plant (PBP) and apply a Surflex Moly coated sulphur super product. This product is created through the PBP by mixing a molybenum trace element-infused polymer coating with superphosphate or sulphur super products.

Malcolm was really pleased to learn of this product, as it is far superior compared with the alternative of adding a 50 – 60g/ha of sodium molybdate powder into a mix with fertiliser.

Using a Surflex Moly sulphur super ensured he achieved an even spread of Mo across his application area. It also eliminated the risk of the powder ending up concentrated in one area, which could be a possibility with the alternative method and could contribute to copper deficiencies in stock.

Malcolm has been pleased with the results this past spring.

“There is definitely an improvement to the clover across the farm after applying the molybdenum coated sulphur super. It’s really obvious. We haven’t had clover like this for years.

“We used to do more cropping about 10 years ago and we used to find clover like that after cropping but not since then. The clover is definitely doing really well.

“There was one paddock we missed out applying the molybdenum to in the autumn because it was in rape, but we will catch that one up this coming autumn.”

Malcolm had heard the stories regarding the over-use of molybdenum historically, but his recent blood and liver work on his heifers returned good copper results which was reassuring. He stresses that “you need to stick to the recommendations and not apply too much, or too often, just like with selenium”.

Where herbage tests indicate that molybdenum application is required, maintenance rates on pasture are 50 – 60g/ha of sodium molybdate equivalent applied every four to five years.

If comparing the cost of a maintenance rate of Surflex Moly sulphur super and the same amount of phosphorus and sulphur via sulphur super without Mo, the additional cost for the Surflex Moly sulphur super is approximately $4/ha.

It’s important to remember that application of Mo where required is just one tool in the toolbox. It is just as important to ensure that that all of the other macro nutrients (P, K, S, Mg, Ca,) are all within the optimal range in order to provide the conditions for your clover to thrive.