Abstract form

Methodology of the analysis of the maps of soil salinity to judge the
dynamics of salinization-desalinization processes
Dmitry I. RUKHOVICH*, Polina V. KOROLEVA, Yekaterina V. VIL'CHEVSKAY
Natalia V. KALININA, , Svetlana V. RUKHOVICH, Elena B. DOLININA
V.V. Dokuchaev Soil Science Institute, Russian Academy of Agricultural Sciences,
Pyzhevskiy per. 7/2, Moscow, 119017 Russia
*Corresponding author’s e-mail: ruh@agro.geonet.ru
Salinization is one of the most dynamic soil properties. Secondary salinization
intensifies salt transfer in the soil profiles. In the newly irrigated area of the Golodnaya
Steppe (Uzbekistan), the salt status of soils may change from nonsaline to strongly
saline and vice versa within a year. Despite such a considerable dynamism of
salinization–desalinization processes, traditional methods to assess the dynamics of soil
salinity are based on the comparison of two maps of soil salinity developed at different
times with an arbitrarily chosen time interval between them.
Maps of soil salinity reflect the chemical type and the degree of salinization. Nonsaline,
slightly saline, moderately saline, strongly saline, and very strongly saline soils are
specified. Nonsaline and slightly saline soils can be grouped in one category. Thus, for
the soils with the same chemistry of salinization, four legend units characterize the
degree of salinization. If two maps for different years are compared, seven
combinations are possible: (1–3) soils, whose salinity has decreased by three, two and
one grades, respectively (desalinization of different intensities); (4) soils, whose salinity
has not changed; and (4–7) soils, whose salinity has increased by one, two and three
grades, respectively (salinization of different intensities). It is supposed that the
direction of salinization–desalinization processes in the particular area remains
unchanged during the studied time interval.
We have developed 7 maps of soil salinity for the Usman Yusupov farm (no. 10) in the
Golodnaya Steppe of Uzbekistan for different years from 1983 to 2008 on the basis of
aerial and satellite images. Their analysis proved that the extrapolation or interpolation
of tendencies for a period exceeding one year is incorrect. Thus, a comparison of the
maps for 1983 and 1985 indicates the intense salinization, whereas the maps for 1985
and 1986 indicate the intense desalinization for the same area. If only two maps are
compared, the error of the estimate of salinization–desalinization tendencies may be as
high as 70–80%. To judge the dynamics of these processes, the following series of the
maps is suggested. (1) Maps showing the areas with stable salinization. From year to
year, their portion is about 25% for each salinity grade; for the entire period, it is only
2.5% of the territory. (2) The map showing the trend of salinization (slope of the curve
approximating distribution of saline soils by years); for the studied farm (80 km 2 ), this
map contains more than 50 000 polygons attesting to the high spatial variability of
salinization-desalinization processes. (3) The map of salinization-desalinization
dynamics characterizes the average amplitude (the dynamics coefficient) of salinizationdesalinization
processes. In our case, it was calculated on the basis of five maps for
1983–1989: k = ‏,‏‎5‎‏/(׀e-a׀+׀d-e׀+׀c-d׀+׀b-c׀+׀b‏-׀a‏)‏ where a, b, c, d and e are the degrees
of soil salinization at a given point (or on a given plot) in 1983, 1985, 1986, 1988 and
1989, respectively. The map demonstrated that the degree of salinization changes by
more than one grade on more than a half of the studied territory. Overall, a set of eight
maps is suggested to judge the dynamics of salinization–desalinization processes.
Key words: soil salinity mapping, salinization–desalinization dynamics, image analysis
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