Summary. In many subtropical environments, cereal crops
develop and mature largely on residual water in the soil. This research
involves evaluation of the impact of plant available nitrogen (N) and water in
soil at sowing on grain protein in wheat and barley in such a subtropical
environment.
Estimates of grain protein concentration of wheat (cv. Hartog) were made using
plant available water and available N (soil nitrate-N and fertiliser N, where
applied) at sowing using data obtained from an experiment conducted at Warra,
Queensland, from 1987 to 1995. Treatments included: grass + legume leys
of 4-year duration followed by continuous wheat with 0 or 50 kg N/ha.year
applied as urea at sowing; 2-year rotation of lucerne and wheat; 2-year
rotation of annual medics and wheat; 2-year rotation of chickpea and wheat,
no-tillage wheat; and conventional tillage wheat. Fertiliser N as urea was
applied to both no-tillage wheat and conventional tillage wheat at 0, 25 and
75 kg N/ha.year. The conventional tillage wheat also received N at 12.5
and 50 kg N/ha.year. Estimates of wheat grain yield required both rainfall
during the fallow period or plant available water in the soil profile at
sowing and rainfall from sowing to anthesis and, therefore, it could not be
predicted precisely at sowing. Increasing plant available water (mm) in soil
at sowing linearly reduced grain protein. In comparison, available N at sowing
increased grain protein curvilinearly from 10.0% at 50 kg N/ha to
14.5% at 200 kg N/ha (0–120 cm depth). Variation in grain
protein concentration was best accounted for by the available water :
available N ratio at 0–90, 0–120 or 0–150 cm depths. The
protein concentrations of wheat (cv. Hartog) grown in 1996 at Warra and
Nindigully, and wheat (cv. Cunningham) grown from 1991 to 1995 at Billa Billa,
and barley (cv. Tallon) grown in 1996 at Nindigully and Formartin, Queensland,
were successfully predicted using the relationship between the available water
: available N ratio and wheat grain protein concentration developed using data
from Warra during 1987–95. Thus, available water should be matched by N
supply at sowing to ensure the production of Prime Hard grade wheat and
malting grade barley in the subtropical environment. As a ‘rule of
thumb’, for 0–120 cm depth of soil sampling, each millilitre of
available water matched with each kilogram of N per hectare of available N, at
sowing, would produce about 13% protein wheat in this semi-arid region.
It requires only 0.5 kg of N/ha for each millilitre of available water in
0–120 cm depth of soil to produce malting grade barley of about
10.5% protein concentration. Available water in soil at sowing can be
approximated with rainfall during the fallow period, with rainfall (mm) :
available N (kg/ha for 0–120 cm depth) ratios of 3.7 and 7.4 for
respective 13 and 10.5% grain protein concentrations for both wheat and
barley.
Wheat Grain Yield and Grain Protein Concentration Response to Nitrogen Rate During the 2018–2019 Growing Season in Kansas