Land use effects on aggregation and erodibility of luvisols on undulating slopes
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The aim of this study was to investigate the effects of land use changes on the aggregate size distribution, soil structural stability, and soil erodibility in Luvisols on Central Serbia's rainfed farms at a depth of 0.00-0.30 m. Six sites, selected for the study, contained adjacent land uses of natural grassland and arable land that have undergone conversion from grassland for more than 10 years. The inherent problems of Luvisols include weak structured surface horizons susceptible to structure deterioration, where tilled when wet or when heavy machinery is used. Aggregate size distribution and soil structural stability in the topsoil was tested by soil dry and wet sieving. Soil erodibility was assessed with the USLE-K factor. The natural grassland served as a control against which to assess changes in soil properties resulting from the removal of natural vegetation or cultivation of soil. The results showed that conversion of natural grassland to dry land farming led to a significant... degradation of the soil structure. Aggregate separation by dry-sieving indicated that the natural grassland had significantly fewer unfavorable cloddy aggregates (>10 mm) and more agronomically most valuable aggregates (0.25-10 mm) than the arable soils. The mean weight diameter of dry aggregates (MWDdry) was greater in the grassland (7.0 mm) compared to the arable soils (9.7 mm). The arable soil had significantly lower (1.03) structure coefficient (Ks) than grassland soils (2.77). Higher percentages of water stable aggregates (WSA) >0.25 mm were found under natural grassland (50 %) than in arable fields (41 %). In addition, grassland soil had significantly higher mean weight diameter (0.92 mm) of wet stable aggregates (MWDwet) than arable soils (0.81 mm). Tillage of the unaltered grassland significantly increased the soil erodibility measured by the USLE-K factor. The USLE-K factor was approximately by 17% greater in the arable soil than in the grassland, indicating the vulnerability of the arable soil to water erosion. In summary, the results showed that the tillage of the grassland degraded the soil structure, leaving soils more susceptible to the erosion in the temperate climate zone. This suggests that land disturbances should be avoided in the grasslands in the study region of the Central Serbia.