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

Letícia Ellen Dal Canton,Miguel Angel Uribe-Opazo,Luciana Pagliosa Carvalho Guedes

doi:10.5296/jas.v9i1.17473

Letícia Ellen Dal Canton, Miguel Angel Uribe-Opazo + Show 1 more

Open Access

https://doi.org/10.5296/jas.v9i1.17473

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Abstract

Financial investment with collection and laboratory analysis of soil samples is an important factor to be considered when mapping agricultural areas with soybean planting. One of the alternatives is to use the spatial autocorrelation between the sample points to reduce the number of elements sampled, thus restricting the collection of redundant information. This work aimed to reduce the sample size of this agricultural area, composed of 102 sample points, and use it to analyze the spatial dependence of soil macro- and micro- nutrients, as well as the soil penetration resistance. The agricultural area used in this study has 167.35 ha, cultivated with soybean, which the soil is Red Dystroferric Latosol, and the sampling design has used in this agricultural area is the lattice plus close pairs. The reduction of the sample size was made by the multivariate effective sample size (ESSmulti) methodology. The studies with the simulation data and the soil attributes showed an inverse relationship between the practical range and the estimated value of the univariate effective sample size. With the calculation of ESSmulti, the sample configuration was reduced to 53 points. The Overall Accuracy and Tau concordance index showed differences between the thematic maps elaborated with the original and reduced sampling designs. However, the analysis of the variance inflation factor and the standard error of the spatial dependence parameters showed efficient results with the resized sample size.

Highlights

Throughout economic cycles, the Brazilian agribusiness has shown to be fundamental to the country's development, in addition to ensuring a prominent position capable of influencing the international market
The estimated values of the univariate effective sample size (ESSuni) evidenced that the simulated variables divided into three groups (Figure 3 – A): variables V5, V7, V8, V13, and V14 made up the first group, the second group consisted of variables V1, V2, V3, V4, and V6, and variables V9, V10, V11, and V12 constituted the third group
Most of the variables had intermediate to high values of the spatial dependence radius, which possibly contributed to the similarity of scenarios S1 and S4 in relation to the estimated value of ESSmulti

Summary

Introduction

Throughout economic cycles, the Brazilian agribusiness has shown to be fundamental to the country's development, in addition to ensuring a prominent position capable of influencing the international market. Agricultural expansion around the planted area is encouraged by the favorable climate and topography and by competitive hectare prices in some states in the North and Northeast of the country (Bolfe et al, 2016). Paraná ranks among the states with the highest soybean productivity in the country and contributed approximately 17% of the national planted area of this crop, as well as 18% of the national production of this grain between the 2009/10 and 2019/20 crop years (CONAB, 2020). These prove the importance of the commodity in the national and state context

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