Soil porosity, permeability and static and dynamic strength parameters under native forest/grassland compared to no-tillage cropping

Improper soil management, increasing farm machinery mass and traffic frequency threaten the ecological functionality of soils under intensive agricultural use. Especially in Brazil, no-tillage (NT) cropping was adopted as a type of soil management that possibly preserves soil functions. Hence, the objective of the present study is to evaluate the effect and intensity of long-term NT compared to soil under natural forest (NF) or grassland (NG) based on parameters of composition (density, porosity, water retention) and functionality by means of mechanical strength (precompression stress σp, cyclic compressibility cn), air permeability Ka, and saturated hydraulic conductivity ks. The studied Hapludox, Hapludalf and Quartzipsamment from southern Brazil under subtropical climate mostly reacted based upon their grain size distribution, namely clay, loamy sand and loamy fine sand. The largest impact appeared in the Hapludox, where compaction occurred (higher σp, lower cn and smaller porosity, especially macroporosity). ks and Ka were highest at the surface of the Hapludox under NF, but were reduced strongly under NT. In both the Hapludox and the Hapludalf deeper soil layers were also affected by NT, but in the clayey Hapludox the applied pressure resulted in the largest compacted layer. The Hapludalf of loamy sand texture showed, supposedly due to shallow soil operations, a weak, but permeable surface layer under NT above a dense layer, while the other layers were only slightly affected by cropping. In the Quartzipsamment, there was no increase in σp and little in cn, whereas density in deeper layers slightly decreased. While ks was increased strongly under NT compared to NG, the opposite was found for Ka which could not be explained by the investigated parameters. The results demonstrate that soil under NT might be significantly affected by soil compaction with regard to soil functions if not adequately managed by adjusted machinery. This is of even greater importance in fine-textured soils like the investigated Hapludox, compared to coarse-textured soils of poor aggregation like the investigated Quartzipsamment.