Abstract
The intensive agricultural machinery traffic to which soils under coffee crops are exposed may cause significant changes in soil structure. The goals of this study were to: a) characterize the spatial variability of precompression stress (σp) and volumetric water content (θ) of a Red-Yellow Latosol (Oxisol) and determine their spatially dependent structures using ordinary kriging semivariograms; b) using this date to construct a load-bearing capacity (LBC) map for the site, identifying the depth with higher ; and c) use the map as a decision support tool regarding agricultural machinery logistic management in coffee plantations. The research was conducted on an experimental farm of the Agricultural Research Company of Minas Gerais (Epamig), Patrocinio, MG, on a clayey Oxisol. Samples were collected from 2.0 × 1.5 m sampling pits at intersections of a rectangular 40 × 150 m grid, totaling 28 sampling points. The soil samples were collected with metal rings (0.0254 m in height and 0.0630 m in diameter) using an Uhland sampler. Sampling at each pit was at 3 layers: 0.00–0.03 m, 0.10–0.13 m, and 0.25–0.28 m, and seven samples arranged in a matrix form were collected at each layer, totaling 588 samples. The σp and θ showed a spatially dependent structure. The depth of 0.00–0.03 m showed higher LBC, indicating that this depth was more compacted compared to other depths. Based on the σp maps, the tractor and the combine should not traffic into the areas at water content of 0.45 m3 m-3, because the soil has a LBC of 200 kPa. If this condition is not respected, additional compaction will occur. Tractor traffic is permissible when the water content reaches values less than 0.36 m3 m-3, whereas for combine traffic, the water content values must be less than 0.30 m3 m-3.
Highlights
The application of modern farming and harvesting techniques in coffee culture has increased vulnerability to land degradation and this poses a serious challenge to long-term productivity of the farms
At all the studied layers, the water content showed a low coefficient of variation, whereas the coefficient of variation of the precompression stress was in the average, class according to the criteria of Warrick and Nielsen (1980)
The precompression stress and volumetric soil moisture showed an asymmetric distribution to the right
Summary
The application of modern farming and harvesting techniques in coffee culture has increased vulnerability to land degradation and this poses a serious challenge to long-term productivity of the farms. The use of heavier agricultural machinery in most of the production stages without adequate control of applied pressure, vis-a-vis soil moisture, is known to promote the degradation of soil structure and could reduce crop yield (ARAÚJO JÚNIOR et al, 2011). One widely agreed on parameter, which characterizes the mechanical strength of the soil, is the precompression stress (AJAYI et al, 2009). Precompression stress, defines internal soil strength of soils and effectively depicts the maximum pressure the soil had been subjected to in the past (HORN and FLEIGE, 2003). The precompression stress (σp) is derived from the compression curve, which is a plot of the changes in soil bulk density or void ratio against the logarithm of the applied pressure to the soil. Σp has been used by several authors as an indicator of sustainability of soil structure
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