SOIL POROSITY AND COMPACTION AS INFLUENCED BY TILLAGE METHODS

摘要

The research referred here has been carried out in three forest nurseries of Forestry Department in Arad, Romania during 2014-2015, on different soil types. The following tillage methods have been tested in order to point out their influence on soil compaction: classical tillage system (plough + 2X disks) and minimum tillage system (paraplow + rotharrow). The influence of several conditions on soil compaction has been described in our previous studies. In the actual study, a more in-depth analysis of the studied process is presented and discussed, especially through mathematical tools. Multivariate analysis was performed in order to obtain information about.the tillage systems statistical differences when considering all variable at the same time. The considered variables are: the total porosity (i.e. TotPoros) and soil compression degree with values at three depth levels: 0-10 cm (i.e. d0), 10-20 cm (i.e. d1), 20-30 cm (i.e. d2). At first point, there was performed the principal component analysis (PCA) with the correlation matrix as input and between groups algorithm. The PCA biplot does not come with consistent information about how considered tillage systems modify the soil properties in quantitative and qualitative ways. However, PCA results shows that soil bulk density and compaction degree are strong correlated and the first variable can be excluded from further analysis. Thus, the multivariate analysis of variance (i.e. MANOVA) followed by canonical variants analysis (i.e. CVA) were performed. The CVA is a generalised version of linear discriminant analysis (LDA) when there are more than two groups involved as in our case, with 15 samples of combined nursery location and tillage systems. In order to have a consequent samples grouping in CVA, the MANOVA pairwise between groups multi-comparison statistical significance p-results were done considering the sequential Bonferroni correction (data not shown due table huge size). This research attempted to emphasise the fact that the process of compaction plays a negative role on the physical-mechanical properties both in the classical and minimum tillage system. In the case of the minimum tillage system, the state of compaction of the soil is expected to reduce considerably in at least one year, without doing activities of fragmentations. An important role in the soil compaction is also played by the agricultural equipment, through their weight and traffic. Using multivariate analysis we were able to highlight precious information about soil tillage executed in three nurseries for the three sampling depths considering the values of bulk density, total porosity and the degree of compaction. Finally the CVA and HCA analyses emphasised the samples clusters generated by variables total porosity and soil compaction degree, and the pattern of soil modifications after the analysed tillage systems.