Agriculture Reference
In-Depth Information
dynamics. The model is integrated in a geographic information systems
(GIS)/database environment in order to obtain inputs on weather, soil
physics and agricultural management on a regional scale. A more detailed
description of the construction and evaluation results of the CANDY
model has been published (Franko 1996; Franko et al ., 1997).
A landscape unit is considered as a composition of homogeneous
patches that are independent from each other with regard to the processes
in the soil. The construction of the homogeneous patches is a result of
an overlay of a soil map with a map of the farm fields and a map of
precipitation patterns. It is very useful to use identical shapes for farm fields
and precipitation patterns in order to reduce the number of patches to a
reasonable level. The soil map and the farm field map as well as the map of
climate structure have a database background with detailed information.
The soil mapping units are characterized by a list of soil profiles,
weighted by their part in the whole area of the item. A soil profile
description contains a list of horizons with their depths. The soil physical
parameters of density, texture, field capacity and wilting point are assigned
to each horizon.
Climatic data include air temperature, global radiation and precipita-
tion provided by a station situated nearby. A precipitation index has been
calculated for every farm field from long-term averages of regional precipi-
tation distribution expressing the relationship of precipitation intensity
between a given point in the area and the position of the climate station.
During the simulation runs, this index is used in order to adapt the local
precipitation data.
Farm field management is described by a date, an action, a specifica-
tion and an intensity. Actions are cropping, tillage, application of fertilizer,
manure or pesticides, and irrigation. Cropping data have to include the
yield and/or the nitrogen uptake of the crop at harvest.
Investigation Area and Simulation Scenario
The study was performed on an area of 3850 ha of arable land on Haplic
Chernozem with loess as parent material. The water-holding capacity of the
upper 100 cm is ~310 mm, with 190 mm available to plants. Clay content
varies between 18 and 20%. Long-term averages of air temperature and
annual precipitation are 8.7
C and 520-560 mm, respectively.
Land use data for every farm field were collected for a time period from
1981 to 1996. With the re-unification of Germany, there were changes in
the agriculture of Eastern Germany concerning setaside of land, reduction
of animal breeding, crop rotations and yields because of improved
agrochemicals and technology. An important question is how this change
in land use will affect the SOM dynamics. The land use change in the
°
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