Abstract
There is no consensus in the literature regarding how many subsamples are needed to perform accurate on-farm soil penetration resistance (SPR) mapping. Therefore, the objective of this study was to define the number of subsamples per sampling point needed to quantify the SPR. The experiment was performed in a 4.7 ha area and employed a 50 × 50 m grid system (18 sampling points). The SPR was evaluated using a digital penetrometer in two different years with 1, 2, 3, 4, 5, 6, 9, 12, and 15 subsamples per sampling point. The SPR maps produced with increasing numbers of subsamples were compared to the reference maps (15 subsamples) using the relative deviation coefficient and Pearson´s linear correlation. A reduction in the number of subsamples promoted an increase in the variability of the SPR data. Generally, the results from this study suggest the use of at least four subsamples per sampling point to achieve SPR maps with a coefficient of relative deviation less than 10% (30% maximum error per point around the mean) and significant correlation with the reference maps (15 subsamples).
Highlights
Soil penetration resistance (SPR) is a measurement utilized to quantify the mechanical impedance of the soil for plant root growth (Bengough, Mckenzie, Hallet, & Valentine, 2011)
The higher microvariability observed in the surface soil layer is due to various factors, including the soil and crop management practices, effects of plant roots, wetdry cycles, and the potential surface sealing that is commonly observed in no-tillage systems, especially when little straw is present (Cherubin et al, 2011; Silva, Bianchi & Cunha, 2016)
High variation of microvariability of the SPR data was observed between sampling points (Figure 2)
Summary
Soil penetration resistance (SPR) is a measurement utilized to quantify the mechanical impedance of the soil for plant root growth (Bengough, Mckenzie, Hallet, & Valentine, 2011). SPR is considered one of the main parameters for the diagnosis of the levels of soil compaction and determination of the most restrictive soil layers for root growth (Girardello et al, 2014). This tool has been widely used by researchers and service providers because it is rapid and used in the field compared to other more conventional methods, such as soil bulk density (Molin, Dias, & Carbonera, 2012). Since the introduction of precision agriculture in Brazil in the early 2000s, systematic sampling protocols to assess the SPR have been widely applied in commercial
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