COMPARING ADJACENT CULTIVATED- AND "VIRGIN" SOILS IN WIND EROSION AFFECTED ENVIRONMENTS CAN LEAD TO ERRORS IN MEASURING SOIL DEGRADATION

ITURRI, LAURA A.; AVECILLA, FERNANDO; HEVIA, GRACIELA; BUSCHIAZZO, DANIEL E.

GEODERMA

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 264

0016-7061

Soil degradation has been frequently evaluated by comparing cultivated soils with paired reference pedons, which were considered as not disturbed. This cannot be the case in semiarid environments, where aeolian processes can also affect reference soils. The purpose of this study was to evaluate some physical and chemical properties of cultivated and reference soils of a semiarid environment in a 9 year period in order to evaluate possible changes in both management situations. Evaluated were 7 degraded soils of variable textures, which are cultivated since more than 50 years, and 7 paired neighbor pedons placed in the less disturbed Caldenal savanna-like ecosystem of the central semiarid region of Argentina. Results indicated that soil properties of both, neighbor cultivated and reference soils changed in this period. The driving factor of these changes was wind erosion, which produced decreases in the proportion of the fine sized particles (silt and clay) in cultivated soils due to deflation processes, and increased them in reference soils due to the sedimentation of material transported from neighbor cultivated and eroded soils. Medium textured soils (sandy-loam) suffered the largest textural changes in agreement with more aggressive management practices that promoted wind erosion. The coarsest- (sandy) and the finest textured soils (loamy sand) did not show remarkable textural changes because they were, respectively, managed with more conservative practices and were more resistant against erosion than medium textured. The accumulation of fine materials and the probable higher deposition of plant residues under moister conditions of the studied period increased by 50% the contents of total carbon (OC), total carbohydrates (CHt) and nitrogen (N) in most reference soils, apparently produced to a large extent by humification. After the 9 year period, cultivated soils presented between XX and XX% less OC, CHt and N than reference soils, but these differences were produced mainly by increases in reference soils rather than by decreases in cultivated. The C/N and C/CHt ratios decreased mainly in medium textured cultivated soils. Such decreases were the origin of the differences with reference soils, which showed mostly no changes of these ratios. The wind erodible fraction (EF, the < 0.84 mm sized aggregates) showed increases mainly in medium textured cultivated soils and decreases in all reference soils, in association with losses of the fine textural fractions and OC in cultivated soils and their increase in reference. pH values were higher only in some cultivated- than their reference pairs after 9 years, but such differences were produced mainly by pH decreases in reference soils (in association with higher OC contents) rather than by increases in the cultivated. We concluded that the simple comparison of cultivated and reference soils can lead to important errors in measuring soil degradation in semiarid environments, if changes occurring also in reference soils are not considered. The driving factors of such changes are aeolian processes that include not only deflation in cultivated soils but also deposition of fine material in reference soils.