Abstract
Soil structure that favours infiltration is essential for successful functioning of vegetated buffer zones. We measured bulk density, air permeability and precompression stress in a clay soil (Vertic Cambisol) and a sandy loam (Haplic Regosol) in Finland, to identify management-related changes in the physical and mechanical properties in the surface soil of buffer zones. In addition, the impact of texture on these properties was studied at depths down to 180?200 cm. Soil cores (240 cm3) were sampled from a cultivated field, from buffer zones harvested by grazing (only in a clay soil) or by cutting and removing the vegetation, and from buffer zones covered with natural grass vegetation. The samples were equilibrated at a matric potential of -6 kPa and compressed at a normal stress range of 20-400 kPa (7 h), followed by stress removal (1 h). Generally, the clay soil was more compressible than the sandy loam. Due to trampling by cattle, the young grazed buffer zone (0-3 cm) had the largest bulk density and the smallest total porosity. For the grazed sites, reduced air permeability (2.7-5.1 × 10-5 m s-1) was found, compared with that of the buffer zone under natural vegetation (15-22 × 10-5 m s-1), indicating decreased pore continuity. Although the old grazed site was easily compressed, compared with the younger site, it showed a greater resilience capacity due to the protective cover of organic residues accumulated on the soil surface.
Highlights
Vegetated buffer zones (BZs) have been successful in removing suspended solids and particle-bound nutrients from agricultural surface runoff in the Nordic climate (Syversen and Borch 2005, Uusi-Kämppä2005)
The efficiency of the vegetated BZs is mainly based on the decrease in the amount and velocity of surface flow and the enhancement of infiltration (Dorioz et al 2006), and proper soil structure is important for the successful functioning of BZs in terms of erosion and nutrient transportation by surface runoff water
Data from the confined compression test showed that the precompression stress values were rather low throughout the soils, probably due to the sampling which was done after winter when the soil structure is weak
Summary
Vegetated buffer zones (BZs) have been successful in removing suspended solids and particle-bound nutrients from agricultural surface runoff in the Nordic climate (Syversen and Borch 2005, Uusi-Kämppä2005). The efficiency of the vegetated BZs is mainly based on the decrease in the amount and velocity of surface flow and the enhancement of infiltration (Dorioz et al 2006), and proper soil structure is important for the successful functioning of BZs in terms of erosion and nutrient transportation by surface runoff water. Owing to the reduction in volume of large pores and pore continuity, soil deformation reduces air permeability and hydraulic conductivity and has an adverse impact on the functioning of pores for water and gas transport. It is not the textural pore space, i.e. matrix porosity, but the structural pore space that is susceptible to compaction (Richard et al 2001). The critical function of BZs in minimizing nutrient inputs to surface water will diminish
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