"Nitrogen supply -
A determinant in
water use efficiency
of winter wheat grown
under free air
CO2 enrichment."
Manderscheid, R., Dier, M.,
Erbs, M., Sickora, J. and
Weigel, H.-J.
2018
Agricultural
Water Management
Water Management
210: 70-77.
In a field study
over two
growing seasons,
Manderscheid et al. (2018)
examined the
combined effects
of elevated CO2
and nitrogen supply
on winter wheat
(Triticum aestivum, cv Batis)
at the Thünen-Institute
in Braunschweig, Germany,
in 2014 and 2015.
CONCLUSION:
Elevated CO2 will
increase wheat yields
in the future,
while requiring
less total water
than at present,
to do so.
Elevated CO2 levels
improved
wheat biomass,
consistently
among the three
different levels
of nitrogen supply
and across years;
averaged across
both growing seasons.
A +207 ppm
CO2 enrichment
increased biomass
production by 17%, 18%
and 15% in the deficient,
adequate and excessive
nitrogen supply treatments,
respectively.
Nitrogen supply had
a positive effect
on the aboveground
biomass of wheat.
Plant water use efficiency (WUE)
was also strongly influenced
by soil nitrogen levels and
atmospheric CO2 enrichment.
Focusing on CO2,
data averaged
for both seasons
indicated a
CO2-induced WUE increase
of approximately 21% in the
nitrogen-deficient treatment
and 30% under both adequate
and excessive soil nitrogen.
The positive effects
of elevated CO2
on biomass and WUE
resulted in
an overall reduction
of evapotranspiration
(sort of like people sweating)
by 2, 9 and 10 percent
in the deficient, adequate
and excessive soil nitrogen
supply treatments,
respectively.
Manderscheid et al.
conclude that
"the decrease
of evapotranspiration
suggests that
seasonal water use
of well-fertilized wheat
will improve
under elevated CO2."
DETAILS
Two atmospheric
CO2 concentrations
(ambient, at 393 ppm,
or elevated, at 600 ppm)
and three levels of soil nitrogen
(deficient, adequate or excessive,
accomplished by adding 40, 180
or 320 kg N ha-1, respectively,
in 2014 and 35, 200
and 320 kg N ha-1 in 2015).
Elevated CO2 levels were maintained
using free-air CO2 enrichment (FACE)
technology; but the CO2 enrichment
was only applied during daylight hours
from the three leaf stage until the end
of grain filling (i.e., harvest)
in each growing season.
Irrigation was also applied, as needed,
by the authors to maintain the soil water
capacity within 50-90% of field capacity
to prevent drought and nitrate leaching.