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Comparing the efficiency of ordinary kriging and cokriging to estimate the Atterberg limits spatially using some soil physical properties

¹ Soil Fertilizer and Water Resources Research Institute, 06172 Yenimahalle-Ankara, Turkey,² Department of Soil Science, Faculty of Agriculture, University of Ankara, 06110 Diskapi-Ankara, Turkey,³ Department of Soil Science, Faculty of Agriculture, University of Ondokuz Mayis, 55139 Kurupelit-Samsun, Turkey

^* E-mail: ogbaskan{at}yahoo.com

(Received 16 July 2008; revised 11 November 2008)

The spatial distribution of the Atterberg limits can be used to distinguish the consistency and behaviour of a soil and its engineering properties, which strongly depends on the water content of the soil and types of silts and clays in the soil. By spatial modeling, and comparing the results of ordinary kriging with the cokriging approach, this study aims to find correlations between the Atterberg limits and the selected physical soil parameters in order to examine how effective they are in generating an understanding of the dynamics of a physical soil system.

In 156 soil samples, the Atterberg limits and soil moisture conditions were determined, and auxiliary functions were selected by application of cokriging using correlation analysis and regression equations obtained by the residual maximum likelihood (REML). These techniques were evaluated by the results of the mean absolute error (MAE) and the mean squared error (MSE). Cokriging analysis was found to be more effective at estimating the liquid limit (W_LL) and the plastic limit (W_PL) than kriging analysis and with smaller error values. On the other hand, the kriging approach, which had smaller MAE and MSE values, was more effective at estimating the plasticity index (W_PI) values than the cokriging method. Unlike the REML regression equations, the field capacity (FC) value was the more suitable parameter for the cokriging estimates. When the necessary labour and time were considered for determining the Atterberg limits, both kriging and cokriging were found to be applicable for estimation of these limits.

KEYWORDS: kriging, cokriging, Atterberg limits, consistency limits, soil water content