On-Farm Understanding for Farmers
7
Nitrification Inhibitors
Nitrification inhibitors are commercial products that can be applied to pastures to reduce the risk of
nitrate leaching and nitrous oxide emissions.
C l i m ate C h a n ge a n d G H G e m i s s i o n s
Nitrification
Inhibitors
Nitrification inhibitors have been effective at reducing nitrogen losses but
their effect on increasing pasture production across a range of pastoral
farming environments is less well known.
Nitrification inhibitors (NI) and the soil nitrogen processes
To understand how nitrification inhibitors work, we need to understand the behaviour of nitrogen in the
soil, and pathways through which nitrogen is lost or gained within the pastoral system.
Forms of nitrogen in the soil
Nitrogen in the soil exists in a number of forms but plants can only utilise two distinct forms: ammonium
N and nitrate N.
Ammonium N is positively charged and more likely to be held by the negatively charged soil particles,
making it less susceptible to leaching than nitrate N which is negatively charged. Nitrate is also used by soil
bacteria and transformed into nitrous oxide gas.
Processes responsible for
transforming nitrogen in the
soil
There are a number of processes that
transform N from one form to another. Here
we discuss the processes that are affected by
nitrification inhibitors: nitrification and
denitrification. When urea is added to the soil
(fertiliser or urine), it changes quickly to
ammonium. This ammonium is then subject to
a process called nitrification whereby soil
bacteria convert the ammonium N to nitrate N.
Any ammonium N that is not taken up by plants
is likely to be converted to nitrate N. In turn,
nitrate N is then subject to losses through
leaching and denitrification. Denitrification is a
process whereby soil bacteria convert nitrate N
into nitrous oxide gas.
Denitrification occurs when nitrate is available
and oxygen levels are depleted (e.g. waterlogged soils).
www.thisland.illinois.edu/50ways/50ways_5.html
The role of nitrification inhibitors
When a NI product is introduced to the soil it affects
the bacteria (nitrosomonas) responsible for
converting ammonium N to nitrate N, slowing down
the conversion rate and keeping nitrogen in the less
mobile ammonium form for longer.
How are nitrification inhibitors used?
Nitrification inhibitors are applied either with nitrogen fertiliser or sprayed directly onto pasture. Since NI
influence only the reaction of ammonium N to nitrate N, they can only be used effectively with fertilizer
products that contain or convert to the ammonium N form e.g. urea, ammonium sulphate and ammonium
nitrate, as well as on urine patches.
Optimal application time and rate
NI currently available on the market contain the active ingredient dicyandiamide (DCD) which rapidly degrades
in warm soils where soil temperature generally exceeds 12 C. Under these conditions (i.e. October – April in
the lower North Island) NI slow down nitrification for a shorter time period. Research is underway to determine
optimal rates and timings in different regions.
Benefits of using nitrification inhibitors
1. Reduces the risk that N will be lost through leaching.
2. Reduces the risk of N loss as the greenhouse gas nitrous
oxide,
3. Has the potential to enhance pasture production by
retaining more available N in the soil.
Key Points
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•
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NI are products that restrict the conversion of
ammonium N to nitrate N.
NI are most effective at slowing down nitrification
when soil temperature is below 12oC.
Under ideal conditions, NI can reduce nitrous
oxide N emissions and nitrate N leaching, and
potentially increase pasture production.
Current limitations
Nitrification inhibitors have been effective
at reducing nitrate N leaching and nitrous
oxide N emissions under small scale plot
measurements. There is limited published
information on how effective this
technology is under normal pastoral
farming conditions.
The benefits to water quality and
greenhouse gas reduction of using this
technology are compelling. However the
effects of NI on pasture production are less
well known and may depend on
geographical region.
Further reading
http://www.maf.govt.nz/climatechange/slm/inhibitors/KelliherCloughClarkFinalReport.pdf
http://www.thisland.illinois.edu//50ways/50ways_5.html
www.pggrc.co.nz/Portals/0/annual%20reports/PGgRc_5yearfull%20chapter%206.pdf
Disclaimer:
While every effort has been made to ensure the information in this
publication is accurate, MAF, SFF and AgResearch do not accept any
responsibility or liability for any error of fact, interpretation or
omission.
Farming, Food and Health. First
Te Ahuwhenua, Te Kai me te Whai Ora. Tuatahi