Agriculture Reference
In-Depth Information
At the end of every time step, Δ
i
, the variable, Г
i
is calculated as
D
[
]
(54)
Γ
=
i
ϑ
k
+
A
+
Δ
t
−
ϑ
i
i
i
c
Δ
t
where
k
ϑ
is the volumetric soil moisture content at the beginning of time step,
A
i
, representing
the terms on the right-hand side of Eqs. (51)-(53), and
ϑ
is a wet reference parameter like
field capacity or volumetric soil moisture content at saturation, depending on soil texture. If
the condition Г
i
>0 is satisfied, then the Г
i
becomes runoff, which is added to the
corresponding subsurface runoff,
R
i
. Consequently, at the end of the time step, the calculated
value of the volumetric soil moisture content
c
ϑ
takes the value
ϑ
.
k
+
i
c
3.
S
IMULATION OF
S
OYBEAN
C
ROP
W
ATER
B
ALANCE
3.1. Description of Data Sets Used in Simulation
For simulations by the LAPS scheme we selected the following locations where the
soybean is cultivated: Marchfeld plain, Austria (48° 12' N, 16° 34' E, mean altitude 153 m)
during May-September 1995; Caumont, France (SAMER No. 3, 43
0
41
'
N, 0
0
06
'
W, mean
altitude 113 m) during May-September 1986; and Paragominas, Brasil (2°58' S, 47°28' W,
mean altitude 100m) during February-June 2007. The main features of the data sets, and
corresponding land, morphological, physiological parameters, forcing data and initial
conditions are described in Mihailovic and Eitzinger (2007), Cajic (2003), Mihailovic et al.
(2006) for Marchfeld plain [46,47,39]. For Paragominas soil parameters are described in El-
Husny et al. (2003) [48], while soybean characteristics during growing season provided by
Jose Paulo (personal communication).
We have considered in more details HAPEX-MOBILHY experiment at Caumont because
it includes a full year of atmospheric forcing and weekly soil moisture measurements up to
1.6 m depth, with 0.1 m interval [49]. Therefore we were able to perform the sensitivity test
for the LAPS hydrological module estimating its capabilities for other runs. The HAPEX data
set in its present form was prepared by Shao et al. (1995) [50]. The data were obtained from
the HAPEX-MOBILHY. Detailed information on the SAMER network and the site can be
found in Goutorbe and Tarrieu (1991) [51]. Most of the forcing data were taken from
Caumont, particularly during the intensive observation period (May-July, 1986). If data at
Caumont were missing, measurements from neighboring meteorological stations were used.
The atmospheric forcing data (downward short wave radiation, downward infrared radiation,
precipitation, air temperature at 2 m, wind speed at 2 m, atmospheric pressure at 2 m and
specific humidity at 2 m) were available on 30 min intervals for one continuous. The chosen
location was a soybean crop field, where soybean plants start to grow in May and are
harvested at the end of September. Although the HAPEX data set was collected in a
heterogeneous area, the immediate surroundings of Caumont can be considered as uniform on
the scale of several hundred meters. For the HAPEX area at large, surface fluxes reveal the
signature of the two main ecotypes: coniferous forest and crops (SAMER-3 represents one of
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