Reduction of Sample Size in the Analysis of Spatial Variability of Nonstationary Soil Chemical Attributes

Abstract

In the study of spatial variability of soil attributes, it is essential to define a sampling plan with adequate sample size. This study aimed to evaluate, through simulated data, the influence of parameters of the geostatistical model and sampling configuration on the optimization process, and resize and reduce the sample size of a sampling configuration of a commercial area composed of 102 points. For this, an optimization process called genetic algorithm (GA) was used to optimize the efficiency of the geostatistical model estimation based on the Fisher information matrix. The simulated data evidenced that the variation of the nugget effect or practical range did not significantly alter the sample size. GA was efficient in reducing the sample size, determining for soil chemical attributes a sample size between 30 and 40 points (29.41 to 39.22% of the initial sampling grid). The presence of spatial dependence was observed for all soil chemical attributes in the two sampling configurations (initial and optimized). The optimized sampling configuration evidenced an increase in trend intensity in the north direction and a more efficient estimation of parameters of the linear spatial regression model.

Reduction of Survey Sites in Dialectology: A New Methodology Based on Clustering

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Reduction of Sample Size in the Soil Physical-Chemical Attributes Using the Multivariate Effective Sample Size

“…The costs of collecting and analyzing samples of soil attributes have led to the development of many studies within the scope of sample resizing, aiming to reduce sampling costs, considering a minimal loss of information in spatial prediction. Among these, we can mention from the optimization algorithms (Guedes et al, 2016;Wadoux et al, 2017;Maltauro et al, 2019) to the use of the Effective Sample Size (ESS) . The calculation of the effective sample size considers the effect of spatial autocorrelation between the sampled points collected.…”