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cardinal temperatures for major crop plants at which crops can grow and high yield can
be achieved and used as a benchmark in this study.
f(T)
is calculated using the fol-
lowing equations:
(
T
−
T
)(
T
−
T
)
B
f
(
T
)
=
1
2
, (3)
B
(
T
−
T
)(
T
−
T
)
0
1
2
0
=− −
.
(4)
where
T
is the average temperature for one period, which is an asymmetric parabolic
function in the range of 0-1 determined by
T
1
,
T
2
and
T
0
which are the lower, upper and
optimum temperatures for crop growth and development, respectively. In this study,
the crop growth period is divided into five stages: seedling, vegetative, nutrition and
reproduction, nutrition and grain-filling, and maturity stages.
f(T)
is calculated sepa-
rately for each stage.
The potential climate productivity is calculated by further revising the water indi-
cator based on the potential thermal productivity, which is calculated from the fol-
lowing formula:
BTT TT
(
) (
)
2
0
0
1
.
(5)
YYf W
=⋅
( 1
− +⋅
I
)
YI
wT
r
2
r
where
I
r
is the irrigation coefficient;
Y
2
is the potential thermal productivity;
Y
W
is the
potential climate productivity. The study of the potential thermal productivity can be
summed up as research on the function of water. There are no authoritative models for
the water calculation at this time, so the model recommended by the United Nations
Food and Agriculture Organization is used here:
fW
()1
=−
K
× −
1
Pe ET
/
)
.
(6)
y
m
Where
K
y
is the reactive yield coefficient;
ET
m
is the maximum evapotranspiration
(mm);
Pe
is the effective precipitation, which can be calculated from the model de-
signed by the US Department of Agriculture Soil Conservation Service:
/ 125 (125
(If R<250mm), (7)
Pe
=
R
⋅
−
0.2
⋅
R
)
(If R>250mm). (8)
Pe
=+⋅
125
0.1
R
where
R
is the total precipitation; and
ET
m
is the maximum evapotranspiration during
the crop growing period, which can be calculated from:
ET
=⋅
K
ET
.
(9)
m
1
0
where
K
1
is the crop coefficient, which is related to the season, the crop breed and the
crop colony structure;
ET
0
is the reference evapotranspiration, which is calculated
using the improved Penman-Monteith model:
900
0
408
Δ
(
R
−
G
)
+
γ
u
(
e
−
e
)
n
2
s
a
T
+
273
ET
=
. (10)
0
Δ
+
γ
(
+
0
34
u
)
2
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