Articles, Blog

Rob Norton: Nitrogen use efficiency

February 18, 2020


There’s a lot of interest in Nitrogen
Use Efficiency but in fact that depends here you develop that metric to assess
it and what I mean by that is how do you know what efficiency means we’ve just completed some surveys on
farms in Victoria and southern New South Wales and we saw that Nitrogen
Use Efficiency that is the amount of grain Nitrogen that’s removed versus the
amount of Nitrogen that was applied or supplied whether by legume or
fertiliser, the number varied from 30 percent that is 30 percent of the
Nitrogen applied was removed in the grain to 500 percent, so five
times more nitrogen removed in the grain then was present– then was supplied from
fertiliser or from legumes. Neither of those efficiencies are sustainable.
In terms of a nutrient sustain– nutrient efficiency sustainability now somewhere
around 100 percent is what we should be looking at where removal is equal to
supply and obviously in terms of soil health that means with preserving soil
organic material which is where most of the nutrients become supplied from
particularly Nitrogen so aiming to measure your productivity versus your
fertiliser use is a pretty good strategy for growers and then developing a target
for your Nutrient Use Efficiency or phosphorus use efficiency or whatever
the new trend is you’re most concerned with their way they’re good metrics in
the same way that water use efficiency is quite a useful metric.
The biggest Nitrogen Use Efficiency is if you don’t use any which means you get
you don’t put on any fertiliser you get a little bit of yield which is coming
from the soil resource and really we want to preserve and improve the soil
resource which is where fertilisers come in to help improve soil fertility and
build soil health through the strategic use of fertilisers. Within that broad
spectrum of Nitrogen Use Efficiency you know from the point three no 30% to the 500% there are strategies you can use to help
get the most out of the Nitrogen that you would apply either from pulse crops
that use that supply through mineralised organic fixed Nitrogen then
remineralised or by fertiliser management and it all comes back to
these three of the four R’s that is making sure that the Rate that you
supply is appropriate to the yield target that you have and for a wheat
crop let’s say that’s 40 kilograms of Nitrogen per ton of yield potential, for
canola crop it’s about 80 kilograms of Nitrogen per yield per tonne of yield
potential so there’s a there’s a benchmark if you like for initial
Nitrogen supply but then the way you supply that through the timing and the
placement are also important so the most efficient placement is in the soil at
seeding but that’s the riskiest placement because that’s the time at
which as we’ve said you know least about the crop yield but then the the timing
also extends to in crop application and so if with canola and weed in crop
application is within limits as effective as early application at
seeding application so again this sort of rule of thumb is a third, a third, and
maybe another third, so a third at seeding, a third at GS
growth stage 30 start of stem elongation and maybe another third in terms of
meeting your yield potential

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1 Comment

  • Reply Bass Town Ncs February 18, 2020 at 1:44 pm

    epicly awesome

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