Sulphur Fertiliser – Unsung Hero or Unintended Foe?
I recently came across marketing material from a fertiliser company touting the importance of sulphur fertiliser. In their rundown of why sulphur is the “Unsung Hero”, they went so far as to claim that sulphur is rarely found in excess and is more often deficient. While this is definitely true for certain soil types, as a blanket statement this claim is misleading. In fact, our tendency to throw sulphur fertiliser at our pastures without fully understanding the consequences could be causing more trouble than good. How so?
Let’s consider pasture sulphur levels. Levels considered sufficient for optimal pasture growth and health are in the range 0.27 - 0.32% DM. Of 250 client pasture samples (ryegrass/clover) taken from across the country <30% of samples had herbage sulphur levels identified as low with respect to active pasture growth.
The dietary sulphur range considered optimum for animal health is between 0.21 – 0.30% DM. Interestingly ~85% of pasture samples were above the optimal range for animal health, and ~70% above the range for optimal plant growth. Basically, a large proportion of pasture samples have excess sulphur with respect to animal requirements.
Other than in the context of high sulphur swede and kale crops, the notion that livestock may be consuming too much sulphur receives very little attention. But like other nutrients, sulphur can be consumed in excess at levels that can be harmful.
I recognise it’s possible our sample population is biased, as farmers come to us because they are experiencing animal health issues and limitations to production that they haven’t otherwise been able to solve. In the majority of cases excess dietary sulphur, while not the sole cause, is implicated in these health and production issues.
In fact, it has previously been identified that diets containing 0.3-0.5% showed reduced animal performance.
“There is a very real possibility that you are limiting your cows’ productivity by the effects of high sulphur” Dan Gould, Colorado State University Veterinary Teaching Hospital
At >0.4% DM sulphur can become toxic, and cases of polio encephalitis in sheep, lambs and cattle have been reported with dietary levels as low as 0.4% DM. With 20% of our client herbage samples with pasture sulphur at or above this level that represents a significant risk to animal health and performance.
I’d argue it’s time we took a more considered approach to the use of sulphur fertiliser. More sulphur isn’t always better and very rarely is it the panacea required to increase production. Before you apply sulphur fertiliser, consider the impact soil moisture, soil temperature and microbiological activity are having on your soil Sulphate Sulphur test results. Including Organic Sulphur and Total Sulphur in your soil test will give you a much better idea of the overall sulphur status of your soils. Pair it with a herbage test and you can be even more confident with your decision to apply sulphur fertiliser or not.
By applying unnecessary sulphur fertiliser to our pastures, we are at best wasting money on nutrient we don’t need, and at worst we’re limiting the productivity of our livestock. So, ask yourself what impact sulphur is having on productivity and animal health outcomes on your farm? Is it your unsung hero, or could it be your unintended foe?