••••
T RADE N E W S
El Niño or La Niña
Manage nitrogen (N) in the soil to ensure maximum maize yield,
maximum profit and minimum risk
DR ERIK ADRIAANSE
MANAGER: PRODUCT DEVELOPMENT
AND TECHNICAL SUPPORT
T
he quantity of measurable
inorganic N that should be
in the soil throughout the growing
period for maximum yield does
not differ between El Niño (dry)
or La Niña (wet) or average rainfall seasons but the actual yield,
profitability and risk will differ to
a large extent between these conditions.
The quantity of N that is taken
up and utilised by the crop will
also differ largely between dry and
wet seasons. For this reason it can
be expected that more N will be
applied during a wet season to
maintain the quantity of N in the
soil. It can also be expected that
more N will be left over in the
soil after a dry season which can
effectively be utilised during the
next season. The management of
a threshold value for N in the soil
42
for every season will effectively
result in fertilisation according
to obtained yield and N removal
from the soil over seasons.
N-losses and N-toxicity
effects will, however, be very
strongly affected by an under or
over supply of rain. Apart from
soil N-measurements, choice of
N-source and N-management
practises can effectively be used to
reduce these negative effects.
El Niño conditions also coincide with high temperatures
resulting in volatilisation losses
from ammonia forming products
such as urea. Ammonia losses can
result from surface applications
as well as soil incorporated applications when the topsoil dries
out. Ammonia released in close
proximity of plant roots will be
toxic under dry conditions. Urease
inhibitors such as NBPT will
effectively reduce or delay volatilisation and toxicity from urea but
will not eliminate these effects.
Almost no N will volatilise from
LAN even at high temperatures.
LAN will only be moderately toxic
at high concentrations. The band
placement of high concentrations
OCT/NOV 2016 • SENWES Scenario
ammonia forming N-sources at
planting but even before planting
should therefore be avoided.
La Nina conditions also coincide
with heavy downpours over short
periods resulting in N-leaching in
well drained soils or water logging
in poorly drained soils. Urea-N
and nitrate-N are equally leachable
but due to the fact that nitrate
uptake is much quicker it will
effectively leach much less than
urea. Ammonium-N does not leach
significantly and is also taken up
much quicker than urea-N. LAN
will therefore also leach much less
than urea. Due to the possible risk
of leaching, pre-plant applications
should rather be avoided and
multiple post-plant topdressings
considered.
N is not taken up effectively in
soils that are waterlogged for prolonged periods. Oxygen is required
for N-uptake but also for the
nitrification process. Consequently
high levels of ammonium-N and
nitrite-N, which are toxic, will
accumulate. Nitrate-N dissolved
in soil water near the soil surface
will be converted to atmospheric N
through the denitrification process
and lost. Vertical or lateral drainage
of soils should improve this condition.
For enquiries and sales of LAN
28 please contact your nearest
AFGRI Town&Country, Farm City
and Senwes Village branch, trademarks of Hinterland.
For more information contact
Sasol Fertilisers at 0860024361
or [email protected]
NB: Consult a qualified agronomist
for locality specific applications.