Crop Residue Management Effects on Soil Mechanical Impedance

Soil penetration resistance was evaluated in different crop residue management 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 content and then submitted to a multivariate approach consisting of a combination of principal component analysis (PCA) and multivariate variance analysis, considering crop season and sampling date within season as repeated factors. The first two principal components (PC) explained 95% of the variance. The first one, related to the ~25-52 cm deep layer, accounted for 84% of total variance, while the second PC, which seems to measure the penetration resistance at 3-25 cm depth, explained more than 11% of total variance. The results of variance analysis proved that crop residue management had significant effects on soil penetration resistance only for the first PC. Crop season, date of measurement within each season, the two-way interactions: season with date, season with management, date with management and the three-way interactions: season with date and block, and season with date 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.