Affiliations: Department of Systems Ecology, Research Center for
Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China.
E-mail: [email protected]
Note: [] Corresponding author
Abstract: The spatial variation of soil nutrients in topsoil (0-20 m) was
analyzed using semivariogram in the Zunhua County of Hebei Province, China. The
effect on semivariogram with randomly delet ed data and kriged estimates using
various reduced sample sizes wasalso analyzed. The semivariograms of available
N, total N, available P, organic matter were best described by a spherial
model, except for available K, which best fitted a complex structure of
exponential model and linear with sill model. The ratio of nugget to total
sample variance ranged from 34.4% to 68.4%, indicating the spatial correlation
of tested soil nutrients on a large scale was moderately dependent. Among five
soil nutrients, available nitrogen and available phosphorus had the shortest
spatial correlation range (5 km and 5.5 km), available K had the longest range
(25.5 km), whereas total nitrogen and organic tter had intermediate spatial
correlation range (14.5 km and 8.5 km). The semivariograms of available N,
total N, available P, and organic matter were insensitive to a 50%-60%
reduction in originalsampling density, while for available K, it is up to 70%.
The estimated spatial distributions of total N by kriging, under various
reduced sample sizes, all correlated significantly (p= 0.001) with those
obtained from original data. The results showed that the semivariogram was a
relatively robust tool when used in a large region and sufficient spatial
variation information could be retained regardless of a higher deletion
proportion of the original data. The original sample data could be reduced by
kriging and the estimates showed no loss of spatial information, however, the
results may be unreliable unless a clearly identified semivariogram model could
be obtained. The results may provide useful information for determining the
appropriate sampling densities for these scales of soil survey.
