Trace elements are essential for maintaining life in plants, animals and humans. So a shortage of any one of them can cause a deficiency, compromising health, growth, and even survival in some cases.
So when it comes to maximising production of pasture and crops in NZ, the presence of trace elements in the soil is of extreme importance.
Trace elements are essential for healthy soil, plants, and animals.
What are trace elements?
Trace elements are micronutrients. In plants, we measure them in micrograms per gram (µg g⁻¹) of dry matter as they are only required in tiny amounts. This is in contrast to macronutrients like nitrogen, phosphorus, and potassium, and the secondary nutrients sulphur, calcium, and magnesium, all of which are required in much larger quantities.
As farmers in NZ, the trace elements we are most familiar with include those needed by plants such as boron, copper, iron, manganese, molybdenum, and zinc.
Other trace elements we’re used to dealing with are iodine and selenium, required by livestock in addition to all those just mentioned above apart from boron.
Cobalt can be added to both of these lists because we know that it’s needed by clover for nitrogen fixation, and ruminants for the production of vitamin B12.
The importance of trace elements
The importance of trace elements for plant growth was discovered in the late 1800s, although it wasn’t until the second half of last century that scientific methods were sufficiently developed to link diseases observed in plants with deficiencies of various trace elements.
It also took some time for scientists to work out which trace elements were essential and what role they play in plant growth. It turns out that although present in such miniscule amounts, trace elements are involved in a very diverse number of plant functions.
For example, many participate in basic plant processes like photosynthesis and respiration, and in producing enzymes for plant metabolism. Others are key for supporting plants undergoing stress from drought or extreme temperatures, and attacks from bacteria, fungi, or viruses.
So it’s clear that trace elements need to be present in the soil for optimum yield and quality of our pasture and crops, which in turn, support the health of our livestock.
Issues with trace elements
A major issue with trace elements in NZ is that our soils are inherently deficient in many of them.
For example, soils formed from pumice like those in the North Island Central Plateau, Hawkes Bay, and Poverty Bay, are naturally low in cobalt. Brown soils in Southland and the hill country of the Wairarapa can also be short of cobalt. Podzols in Northland, the West Coast, and Golden Bay, tend to have lower levels of trace elements in general.
But soil type is not the only cause of deficiency. Soil conditions can also be an issue.
A general rule of thumb is that as soil pH increases (becomes more alkaline), trace elements become less available to plants. The one exception is molybdenum, which becomes more available with increases in pH.
In free-draining soils, iron and manganese occur in forms that make them less soluble, while in waterlogged soils, the opposite situation applies. And where soil moisture is low, boron and cobalt are less available to plants.
An additional complexity is that the presence of one trace element in the soil can affect the behaviour of another. For example, as iron and manganese become more soluble and available for plant uptake, they make other micronutrients like copper, cobalt, and zinc more available too.
Maintaining soil levels
Unfortunately, due to greater intensity of pastoral farming, deficiencies are becoming more evident in all soil types. To address this, the best strategy is to regularly soil and herbage test for trace elements to build up a picture of their status on your property.
There is no doubt that optimal elemental nutrition will be of increasing importance in the future and that maintaining trace element levels in the soil will be paramount to achieving that goal.
This article was published in the Coast & Country News.
