科研之友
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摘要
Soil structure dependent properties are subject to temporal changes as a consequence of tillage and environmental factors. These changes are well documented in soils with bulk densities >1 Mg m(-3); however, no major studies have been carried out in soils with extremely low densities, such as those normally presented by Andosols. Thus, in order to study the temporal dynamics of a volcanic ash soil's physical properties, this study aimed to assess the impact of tillage on soil structure-dependent properties and their development throughout the year. The soil water and temperature dynamics, as well as rainfalls and the penetration resistance, were registered in the field. In order to characterize the effect of mechanical and hydraulic stresses, 10 soil samplings (5-10 cm depths) were conducted before/after tillage, during crop development (Tritricum aestivum) and after grazing. The water retention and shrinkage curves, air and saturated hydraulic conductivity, precompression stress, aggregate strength and cohesion between particles were measured. Our results show that the soil structure behaves dynamically at different scales due to mechanical and hydraulic stresses which impact the soil mechanical stability, porosity and related soil-pore functions. In spite of the low bulk density of the Andosol, the mechanical disturbance did not affect the soil structure and related pore functions significantly throughout the year, demonstrating the ability of the soil to recuperate its functions. As observed for the precompression stress (Pc < 90 kPa), bulk density (<1.7 Mg m-3), air capacity (>8%) and hydraulic conductivity (>20 cm d(-1)), the physical properties of the Andosol did not reach critical values in terms of subsoil compaction. The well-known high resilience capacity of volcanic ash soils allowed the integral functionality of these soils' pores to recover, presenting the same or even greater values as compared to their initial condition; i.e. both hydraulic (k(s)) and air (k(l)) conductivity clearly decreased after the roller compacted the soil due to a decrease in the amount and continuity of macropores; however, as soon as wetting and drying cycles occurred and the biological activity started (root development during the growing season), k(s) and k(l) tended to increase as a consequence of a more continuous pore system, thus soil pores were able to reach the initial values previous to soil tillage. Finally, the shrinkage curves show the soil pores' instability after tillage. At the same time, they illustrate the dynamic behavior of the soil structure, highlighting the fact that soils do not behave as a rigid body and temporal variability of hydraulic properties (macropores, hydraulic conductivity) must be expected. Therefore, better hydrological models which consider this dynamic behavior are needed.
- 出版日期2012-9
