Spatial variation of fluorine in an Indo-Gangetic alluvial plain of India

Spatial variability of water-soluble fluorine (F) in Haryana soils was studied geostatistically. Semivariogram based on 470 samples at a node of 10 x 10 km grid showed F to be correlated over space for a separating distance of 225 km between two observations. Fluorine was estimated by point and block kriging methods at unsampled sites (5 x 5 km grid). The means obtained by these three methods were almost the same, though the estimation variances calculated by point and block kriging were 1.19 and 8.76 times less than those obtained by the classical theory. However, block kriging variance was 7.34 times less than the point kriging variance, a good gain in efficiency. An isarithmic map of F drawn from the paint kriged estimates was very spotty and discontinuous, whereas in the map prepared by block kriged estimates the spottiness disappeared to a greater extent, resulting in a better continuity. The estimated number of samples were 125 (classical), 104 (point kriging) at 99 per cent confidence level. However, the number of samples required at this precision were only 14 by block kriging, a good gain in precision.