Long Term Conventional Tillage Effect on Spatial Variability of Some Soil Physical Properties

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Abstract
Soil compaction affects crop yield in many ways. Knowing its spatial variability provides possibilities for site-specific soil treatments that can increase the profitability and sustainability of crop production. The purposes of this study were (1) to investigate the spatial variability of particle size distribution, gravimetric water content, bulk density, and penetration resistance using classical and geostatistical methods in a field in which conventional soil tillage methods and a particular crop rotation were applied, and (2) to evaluate the spatial relations among soil properties in the field studied. Topsoil (0 to 20 cm) and subsoil (20 to 40 cm) were separately sampled at each of 94 predetermined sampling points based on an irregular grid design in a 45 ha areaypic Ustifluvents). Bulk density showed the lowest variability (CV = 9.09% for topsoil and 6.00% for subsoil), and the penetration resistance showed the highest variability among the soil properties investigated (CV = 64.08% and 42.69%, for topsoil and subsoil, respectively). Gravimetric water content and bulk density showed high correlation particularly with clay and sand content, whereas no significant correlation occurred between penetration resistance and any of the textural components. Spatial correlation ranges varied from 72 to 510 m. Clay content had strong spatial dependence in topsoil, whereas, only moderate spatial dependence occurred in subsoil. Spatial dependence classes of other soil properties evaluated did not change with depth. Strong spatial dependence occurred for penetration resistance and sand content, and a moderate spatial dependence occurred for bulk density, gravimetric water content, and silt content. Comparisons of kriged maps of bulk density, penetration resistance, and textural components revealed that greater penetration resistance and bulk density were associated with greater sand content. However, most of the soils of study area had a clayey texture. Therefore, farmers need to be careful in application of soil tillage and other management practices that could cause compaction.