Abstract

MUNOZ VILLALOBOS, Jesús Arcadio et al. Physical properties of a mollic Andosol under conservation tillage. Rev. Mex. Cienc. Agríc [online]. 2011, vol.2, n.spe1, pp.151-162. ISSN 2007-0934.

The physical properties of mollic andosols are conditioned by a fine texture, although the clay content does not usually overpass 20 to 25%, poor in sands and the more the higher the evolution. The knowledge of its structural stability allows the andosols to maintaining a quite porous structure (Porosity between 71 and 78%) with a very low bulk density, between 0.5 and 0.8 kg m-³, and a very high permeability. When the primary particles get dried (clays) in the aggregates, they contract themselves quite strongly and for this reason the water holding capacity can be reduced up to 60% from the initial. The objective was to evaluate the effects of conservation tillage on gravimetric moisture, the mechanical resistance and bulk density as indicators of the physical quality of andosol, under conservation tillage management and conventional tillage in two sampling dates. The study area was located in the basin of Lake Patzcuaro, Michoacán. Samples of gravimetric moisture, mechanical resistance and bulk density were taken at a depth of 0 to 10 and 10 to 20 cm. A completely randomized statistical analysis, means tests by the method of Tukey and Pearson correlation analysis were done. In the conservation tillage management treatment, the maximum gravimetric moisture got documented (60.8%) during the first sample, the percentage decreased up to 56.41%, four years later, when the second sampling was performed. It is noteworthy that differences in the andosol's gravimetric moisture, are highly significant between conventional tillage with conservation tillage in the first sampling (R= 0.804), whereas in the second one, this difference was not statistically significant. According to the statistical analysis, it was shown that the mechanical resistance increased from one sampling (2001) to another (2004) and their values span a wide range from 184.4 to 274.9 kPa for the conventional tillage treatment, which is further increased under zero tillage, reaching values between 152.8 and 285.4 kPa. The bulk density showed significant differences (p≤ 0.05) between the compared treatments. In general, during sampling, pb increased from 0.53 to 0.57 kg m-³ in the conventional tillage, ranging from 0.51 to 0.55 kg m-³ in the field with conservation tillage. A high correlation between the mechanical resistance, gravimetric moisture and bulk density was found, concluding that these properties are indicators of the andosol's integrated nature indicative of the dynamics of their physical properties, as a measurable degree of compaction as a result of its management, which allows instantaneous diagnosis recognition of the soil's physical quality deterioration.

Keywords : bulk density; gravimetric moisture; mechanical resistance.