Crop residue management effects on soil mechanical impedance

Soil penetration resistance was evaluated in different crop residue managem ent practices. The experimental design was a randomized complete block with five replications (block). The soil strength data, measured to a depth of 52.5 cm using a recording penetrometer, were corrected to a common water co ntent and then submitted to a multivariate approach consisting of a combina tion of principal component analysis (PCA) and multivariate variance analys is, considering crop season and sampling date within season as repeated fac tors. The first two principal components (PC) explained 95% of the variance . The first one, related to the similar to 25-52 cm deep layer, accounted f or 84% of total variance, while the second PC, which seems to measure the p enetration resistance at 3-25 cm depth, explained more than 11% of total va riance. The results of variance analysis proved that crop residue managemen t had significant effects on soil penetration resistance only for the first PC. Crop season, date of measurement within each season, the two-way inter actions: season with date, season with management, date with management and the three-way interactions: season with date and block, and season with da te and management were highly significant in both PCs. This study has also shown the location effect of penetrometer measurements is fundamental when soil characteristics are altered by crop residue management. (C) 2001 Silso e Research Institute.