Agriculture Reference
In-Depth Information
Table 10.2. The minimum and optional weather datasets required as inputs for
crop simulation models.
Minimum
Optional
Daily solar radiation
Daily dewpoint temperature
Daily maximum temperature
Daily wind run
Daily minimum temperature
Daily net radiation
Daily precipitation
Precipitation intensity
Source: Ritchie and Alagarswamy (2002).
maximum and minimum temperature are considered the minimum needed for rela-
tively accurate crop simulation. The main weather element of greatest concern in
most agricultural regions is the temporal distribution of rainfall. Solar radiation is
the main weather variable for describing the energy available for crop growth and
evapotranspiration (ET). Temperature is necessary to simulate crop phenology and
to modify growth and ET.
Ideally, weather data should be obtained at a site near the area where the
model is to be applied, especially for daily rainfall. Temperature and radiation
are more spatially uniform, so the weather station need not be on-site. Most
weather stations record rainfall and temperature but not always solar radia-
tion. Accurate solar radiation data can be obtained from NASA ( http://power.
larc.nasa.gov/cgi-bin/cgiwrap/solar/agro.cgi) , although the spatial resolution is
given in 1° grid cells. This NASA site also provides all the daily weather data
required by DSSAT and SALUS, but with the same spatial resolution issues as
with solar radiation.
The minimum soil information required to run crop simulation models such as
SALUS is listed in Table 10.3. On-site measurement of soil properties is recom-
mended where possible to validate the model for a specific site. Not all soil input
data may be available, in which case soil characteristics such as texture, bulk den-
sity, and organic matter content can serve as surrogate measures. However, the lower
limit of available soil water and the field capacity or drained upper limit (DUL)
water content are often more accurate when measured in the field than when using
laboratory measurements of field soil samples. These measurements must be made
when field conditions are at or near their lower and upper limits. In well-drained
soil, the DUL can best be measured after the profile has been thoroughly wetted and
allowed to drain without irrigation until drainage practically stops. The lower limit
is best measured during a dry period in the growing season when water content
ceases to decline in the root-zone because of a shortage of soil water.
The minimum crop management information required to run crop simulation
models such as SALUS is listed in Table 10.4. When irrigation is used, the dates,
amounts and mode of application are required. Information on the type, dates,
and mode of fertilizer application is necessary to simulate nutrient dynamics,
although often model assessments of crop yield assume that nutrient availability
is not limiting.
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