A lot. Especially when they get going.
To appreciate the demands of big canola crops, we are repeatedly plant testing some plots in a trial with very high yield potential - near Brookton.
The photos below show the crop on 24 June and again on 8 July.
It has been fertilised with 220 kg N/ha but the plots sampled have not had any potassium fertiliser.
Big crops grow fast.
In the space of two weeks this crop was growing at an average growth rate of 180 kg of dry matter per hectare per day!
And based on plant analysis, we are able to calculate that over these two weeks, this crop was taking up 8 kg of nitrogen and 3 - 4 kg of potassium per hectare per day.
For the growing season up to 8 July, it had taken up 220 kg of nitrogen and 110 kg of potassium per hectare.
These are big numbers, and highlight the potential demand of big crops going into stem elongation.
Even with half the crop, we are still looking at big numbers which should make us think more about crop requirements.
Soils can have large reserves of these nutrients, but increasingly they don’t. That’s a big part of why soil and plant tissue testing is so important.