Abstract
Drying of Urmia Lake in the north-west of Iran threatens all the agricultural lands around the Lake. Therefore, soil salinity appears to be the major threat to the agricultural lands in the area. The aim of the present study was to investigate the spatial variation of top soil salinity by taking into account of underground water quality data as secondary information. The research was performed on a grid of 500 m in an area of 5000 ha. Soil samples were gathered during the autumn of 2009 and were repeated in the spring of 2010. Electrical conductivity of soil samples was measured in a 1:2.5 soil to water suspension. Then covariance functions were build for each data set and soil salinity prediction were done on a grid of 100 m using kriging estimator with taking into account the mean variation. Afterwards sodium activity ratio derived from underground water quality database was used as covariate to develop cross-semivarograms in prediction of top soil salinity using cokriging method. Results demonstrated that soil salinity varied from values lower than 0.5 to more than 35 dSm-1 as a function of distance to the Lake. Cross-validating the results from salinity predictions using only kriging estimator to that of cokriging with sodium activity ratio data revealed that kriging offered better estimations with ME of 0.04 for autumn 2009 and -0.12 for spring 2010. Cokriging estimator had more smoother and diffused boundaries than that of kriging and resulted in more bias estimations (ME= -0.11 and -0.21 for first and second data sets). Although kriging method had better performance in top soil salinity prediction, but cokring method resulted in smoother boundaries and reduced the negative effects of mean variation in the area. DOI: http://dx.doi.org/10.3329/ijarit.v4i1.21093 Int. J. Agril. Res. Innov. & Tech. 4 (1): 57-63, June, 2014
Highlights
Urmia Lake is one of the biggest hyper saline lakes in the world and the biggest one in the Middle East, which is located in the north-west of Iran (Zarghami, 2011; Hassanzadeh et al, 2011)
The increase of soil salinity mean value during spring 2010 was due to the seasonal variation of soil salinity, which is caused by rainfalls and water table fluctuations
Soil salinity had a wide range of variation in the study area, from very low values in agricultural lands distant from Urmia Lake to very high values in lands adjacent to the lake (Fig. 2)
Summary
Urmia Lake is one of the biggest hyper saline lakes in the world and the biggest one in the Middle East, which is located in the north-west of Iran (Zarghami, 2011; Hassanzadeh et al, 2011). Salinity of soils around Urmia Lake can be divided to two categories, lands, which are inherently and primarily salty, and areas affected by secondary salinization. Secondary salinization can occur due to the use of low quality saline irrigation water. Kriging methods have widespread use in geostatistical methods and in soil salinity prediction models, which have been discussed in detail in several papers (Li and Heap, 2008). There have been numerous attempts in mapping spatial variability of soil salinity using kriging methods (Peck and Hatton, 2003; Triantafilis et al, 2004; Malins and Metternicht, 2006; De Clercq et al, 2009; Giordano et al, 2010; Acosta et al, 2011; Li et al, 2011)
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