Any kind of nutrient deficiency can reduce crop yields. Trace elements are only needed in small amounts but untreated, deficiencies can cause important crop losses. Also, crops won’t make the most of nitrogen (N) fertiliser if they can’t access the trace elements.
Nutrient use efficiency is a measure of how much yield benefit came from applying fertiliser. Nitrogen use efficiency measures the benefit seen from N fertiliser. Agronomists can calculate N use efficiency after harvest if you grow a crop strip without the N fertiliser.
Nitrogen supply so often limits crop yields that it is the most abundant fertiliser nutrient applied. If N is not the only limiting nutrient or constraint, growers can see poor nitrogen use efficiency. Even if the N rate used was spot on for the crop’s potential in that season.
Balanced nutrition includes trace elements
Balanced nutrition means making sure crops can get enough of everything. Crops need the full suite of nutrients to grow optimally. That can be from either soil reserves or fertiliser. All the N in the world won’t be much help if a trace element deficiency holds the crop back. Having adequate trace element levels will improve N use efficiency.
Which are the limiting nutrients?
It’s not always obvious what will be the next most limiting nutrient – after you improve the supply of nitrogen. Indicators of complete nutrient status of a paddock and crop nutrient needs can come from:
- soil tests
- leaf and/or grain tests
- nutrient performance indicators (such as N use efficiency)
- paddock history
- seasonal yield predictions
- crop symptoms.
Good agronomists and farmers gather information from as many sources as possible to make fertiliser decisions.
Use more nitrogen, need more trace elements
When nitrogen inputs support better growth the uptake of other nutrients goes up too. High yielding crops export more nutrients from the paddock. Include trace elements in nutrient budgets to help keep track. Many cropping soils will sustain decades of micronutrient exports in grain. It still pays to keep a handle on the situation.
Watch out for copper
If copper (Cu) levels are low or marginal, consider adding Cu when you apply extra N. High nitrogen can cause Cu deficiency or make an existing Cu deficiency worse. High N in plant tissues limits the movement of Cu from old leaves to new growth. This impacts growth and yield most where Cu supply is low in the surface soil.