ALLOCATION OF SOIL RECLAIMING MATERIAL BASED ON DIGITAL PROCESSING OF AERIAL
PHOTOGRAPH
T. Tóth!, L. Pásztor!, M. Kertész, B. Zágoni! and Zs. Bakacsi' |
!'research fellows of the Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences,
? senior research fellow of the Institute of Ecology and Botany of the Hungarian Academy of Sciences
Commission VII
KEY WORDS: aerial photograph, digital processing,
sampling plan, estimation error, salt-affected soil, soil
reclamation, gypsum requirement, Hungary
ABSTRACT
Precision farming has two requirements, such as i) correct
dosage of agricultural materials realized at ii) the exact
location in the plot where these are needed. Our objective was
to introduce the direct use of remotely sensed images into the
practice of soil reclamation as a source of information on 1) the
probable dosage of required amendment and ii) precise
location of reclaiming materials.
The remotely sensed image was used in two phases, for the
selection of optimal soil sampling plan to reclaim the plot and
for the compilation of actual plan of reclamation.
The basic material of the study was a panchromatic aerial
photograph on a sodic plot with patches of higher sodium-
affection.
As a first step the relationship between gypsum requierement
and the intensity of the aerial photograph was established. It
turned out to be linear and therefore the aerial photograph was
used directly for the analysis of alternative sampling plans.
As a test of the utility of sampling plans, a set of potential
sampling points were used for the interpolation of the original
aerial photograph and the precision of the interpolation was
measured by the sum of squares of the differences between the
original and the interpolated photographs.
The optimal sampling plan was selected accordingly and the
field sampling, which was carried out for its test, confirmed the
previous selection.
INTRODUCTION
All over the world large tracts of sodic soils receive gypsum as
reclaiming material. We do not describe its mechanism here,
just make reference to that the calcium ions released upon the
dissolution of gypsum replace the harmful sodium ions and
create favourable conditions for the soil solute transport and
plant growth (McBride, 1994) .
The present status of within-plot reclamation of salt-affected
soils in Hungary does not follow the technological
advancements (MSZ 9693/1-77). When there is a special map
series of the status of salt accumulation, it is perfectly suitable
for the production. If it is not available, the corresponding
national standard prescribes the reclamation based on average
samples. In view of the mosaic pattern of such lands the use of
average samples easily can result in largé sub- or
overestimation of the necessary dosage of reclaiming materials.
This mosaic pattern of the salt-affected soils is manifested in
several properties of the soil, most importantly its natural
vegetation (Csillag et al., 1993, Kertész and Toth, 1994, Toth
and Kertész, 1996, Tóth and Pásztor, 1996, van Meirvenne et
al., 1996). On croplands, when there is no vegetation cover,
the areas with different salt accumulation status can often be
distinguished on remotely sensed images (aerial photograph,
satellite images) (Metternicht and Zinck, 1996, Tôth et al,
1991a and b) based on the surface features of the soil.
Our objective was to improve the reclamation of salt-affected
soils with the direct use of aerial photographs.
MATERIALS AND METHODS
Preliminary sampling and its evaluation
In order to describe the character of the relationship between
the intensity of aerial photograph and the gypsum requirement,
on a sampling route representing the intensity distribution of
the aerial photograph (Fig 1), we collected soil samples at 13
points, and measured field bulk electric conductivity in situ at
another 50 points. The location and elevation of the sampling
points was recorded with a field station, therefore we could
find out the intensity from the aerial photograph.
intensity
sampling track represents the within plot distribution
5505288838389 3E
Fig 1. Airborne image of the sample plot with the preliminary
sample sites
The preliminary sampling showed that there is linear
relationship between the gypsum requirement (GR) determined
in the laboratory and the intensity value of the pixels, and these
results suggested that the aerial photograph could be used
directly for the realization of the sampling plan.
178 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
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