Hi it’s Graham Schwenke here from New
South Wales Department of Primary Industries and today I’m just giving a
little talk about some recent work that we’ve been doing on total Nitrogen losses in cropping systems of northern New South Wales and similar works been
going on in Southern Queensland as well and we’ve been focused the last three
years on dryland sorghum crops. So what we’ve been looking at is using
isotype labelled fertilizer so the isotope is 15N nitrogen and the reason we’ve
been using that is a means of tracing the fate of that fertilizer that we put
on usually at sewing with the crop and we want to see where that fertilizer
ends up by the end of the season; how much goes into the grain, how much
goes into the leaves of the crop and and also how much is remaining the soil
and then by difference knowing how much we put in at the start, we can calculate
the amount of total nitrogen loss. So we’ve done this in six experiments at
Tamworth and near Quirindi and on the Liverpool Plains at Breeza and there’s
been another I think 11 experiments done in southern Queensland as well near Toowoomba and Kingaroy predominantly and all using the same techniques of using this
isotope labelled fertilizer put in at the start now we’ve put in different rates
of fertilizer, we’ve put it in with in conjunction with nitrification
inhibitors and we also looked at the timing of the fertilizer going in and I
guess something to take home from across all of these experiments is that we’ve
had quite surprisingly high total nitrogen losses over the season so
perhaps on average around about twenty-five to thirty percent of the
nitrogen that we put on at the start of the season hasn’t been either in the
plant or in the soil at the end of the season. So we believe that most of that
has been lost through the process of denitrification that
occurs in soil where there’s a low-oxygen environment there is labile carbon
and there’s excess nitrogen available for the microbes to denitrify and turn
that nitrate nitrogen into first nitrous oxide which is a global warming
greenhouse gas and then through to dinitrogen or N2 which eighty percent of the atmosphere is made up of so so there’s both
environmental and agronomic consequences of these losses and as I said we’ve been
looking at some different ways of trying to minimize particularly the losses of
the nitrous oxide but also ways of preventing that overall loss of the of
the dinitrogen thanks.