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  • Writer's picturePat Poletti

Fertiliser - Who is the Major Stakeholder?

It must be spring. Cows are calving, ewes are lambing and Doug Edmeades has had his annual rant at the “pseudo-science” of Albrecht ratio theory. Yes, there are problems with the ratio theory and (wash my mouth out) there are also problems with Liebig’s Law of the Minimum – the theory that underpins Edmeades’ argument (which states a plant will grow at a rate limited by the most deficient nutrient). Sadly, Liebig’s Law does not take into consideration a major stakeholder – the animal. The Law neither considers the effect of too much nutrient nor does it consider nutrients and levels that the animal may need irrespective of what the plant needs.

Easy answer from Team Edmeades is to just apply any deficient mineral as supplement direct to the animal on one hand and ignore any effects of toxicity on the other. But, minerals have a habit of interacting with each other in any number of complex ways. A high level of one mineral reduces the absorption of another, e.g. potassium is highly antagonistic to magnesium. The higher the pasture potassium content the more magnesium the cows will need so the more supplement you’ll need to get into the cow. The greater the supplement demand the greater the risk of failure to provide enough, particularly if you rely on inefficient methods such as dusting. Get it wrong and health and production is compromised. And don’t forget about the cost of the supplements.

Similarly, for other minerals. High phosphorus is a milk fever risk and magnesium antagonism increases at higher levels. High sulphur affects pasture palatability and appetite, is highly copper and selenium antagonistic, and is responsible for most of the anti-nutritional problems with brassica crops. All this suggests a better answer would be to control these high levels in grass in the first place and perhaps save some dollars on nutrient.

Conversely, calcium and magnesium content of pasture is generally low. Can we lift the levels of these minerals in pastures to minimise the supplementation problems? As Bob the Builder said before Barack Obama, Yes We Can! But to do it we have to lift soil levels higher than the minimum to grow grass. What should we lift them too? How much is too much? How do we calculate how much we need?

Clearly, besides a Law of the Minimum we also need a Law of the Maximum. There is one body of work that provides some guidance. Yes, William Albrecht. Albrecht was Emeritus Professor of Soil Science at the University of Missouri. He identified relationships between poor soil health and diseases of crops and animals, and human food quality, and published extensively from 1938 to 1970 – the guy deserves some respect. Yes, cation ratio theory has been found wanting with respect to plant production but it becomes very useful across the spectrum of soil-plant-animal. Particularly when there is no other “science” we can draw on.

The annual pseudo-science diatribe by Edmeades is symptomatic of a polarised debate that is severely limiting animal health and production in New Zealand. Better to keep an open mind I would think.

#AnimalMineralSupplementation #Fertiliserrecommendations #Mineralbalance #mineralsufficiency #Pasturegrowth

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