Abstract
Knowledge of spatial variability is an important factor to be considered in planning a program of soil sampling and crop management under precision agriculture (PA). In this context, the aim of this work was to evaluate the efficiency of the dimensions of sampling grids used in the state of Rio Grande do Sul (RS), Brazil to characterise the spatial variability of the attributes pHwater, base saturation (V%), calcium (Ca) and magnesium (Mg) levels. The study was carried out on 30 agricultural sites located in the northern region of RS, having soils classified as Oxisols and managed using the tools of PA. The dimensions of the grids under study were: 100 x 100 m (10 areas), 142 x 142 m (10 areas) and 173 x 173 m (10 areas). Soil was collected at a depth of 0.00 to 0.10 m. The data for pHwater, V%, Ca and Mg were subjected to exploratory statistical analysis and to geostatistical analysis by means of semivariograms. The areas showed high Ca (>4.0 cmolc dm-3) and Mg (>1.0 cmolc dm-3) levels and localised problems of soil acidity (pHwater <5.5 or V<65%), justifying the carrying out of liming at specific sites. For the geostatistical procedures, the sample grids used at the sites of the Oxisols managed under PA in RS are not efficient in capturing the scales of spatial variability of the attributes pHwater, V%, Ca and Mg, which could compromise the accuracy of corrective prescriptions for specific sites.
Highlights
Oxisols are widely distributed across almost all regions of Brazil, and make up the predominant taxonomic class, occupying 31.61% of the surface of the country (2.69 million km2) (ANJOS et al, 2012)
Understanding spatial variability in the soil is a factor that should be considered when planning a program of soil sampling and of crop management (KERRY; OLIVER; FROGBROOK, 2010; MALLARINO; WITTRY, 2004; MONTANARI et al, 2008; MONTANARI et al, 2012; NANNI et al, 2011; SOUZA et al, 2004; STEPIEN; GOZDOWSKI; SAMBORSKI, 2013)
The areas being analysed were sampled for the first time by georeferencing, so they did not suffer the effects of previous variable-rate applications of lime and fertilizer
Summary
Oxisols are widely distributed across almost all regions of Brazil, and make up the predominant taxonomic class, occupying 31.61% of the surface of the country (2.69 million km2) (ANJOS et al, 2012). In the state of Rio Grande do Sul (RS), Oxisols occur mainly in the north, a region located in the geomorphic province of the Plateau, formed by a succession of volcanic flows, followed by cooling on the surface of the earth’s crust and the formation of predominantly basaltic rocks (STRECK et al, 2008). These are weathered, deep, well-drained and acidic soils and display high homogeneity in the profile (ANJOS et al, 2012; MONTANARI et al, 2008; STRECK et al, 2008). Understanding spatial variability in the soil is a factor that should be considered when planning a program of soil sampling and of crop management (KERRY; OLIVER; FROGBROOK, 2010; MALLARINO; WITTRY, 2004; MONTANARI et al, 2008; MONTANARI et al, 2012; NANNI et al, 2011; SOUZA et al, 2004; STEPIEN; GOZDOWSKI; SAMBORSKI, 2013)
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