Land use and soil development in southern Chile: Effects on physical properties

Abstract

Different physical properties of volcanic ash soils were investigated along a transect of 120 km from the western slope of the Central Cordilleras (40°20'S, 72°06'W) to the eastern slope of the Costal Cordillera (39°39'S, 73°11'W) in southern Chile with respect to the degree of soil development (Arenosol versus Andosol stage; Arenosol: young volcanic ash soil, free of clay, tephric properties, Andosol: older volcanic soil, clayey). The Andosols show a higher total pore volume and a higher field capacity, especially due to an increase in fine pores, than the Arenosols. Furthermore, the precompression stress (Pc) as a parameter for the mechanical soil strength is higher for Andosols despite of a lower bulk density. A land use (cropland, meadow, forest) dependent variation of the investigated parameters was less distinct for Andosols. A reduction of macropores and saturated hydraulic conductivity (ks) due to agriculture could be determined in the field, but in general the values are still on a high level with ks-values >100 cm d -1 . However, at higher stresses using an oedometer test the ks-values of the Andosols are highly negatively affected with values <10 cm d -1 . Aggregation is of major importance for soil stability of Andosols, whereas a homogenization of soil structure will lead to a distinct decrease of Pc of approx. 50%.

Land use conversion in humid tropics influences soil carbon stocks and forms

“…Physical properties such as the bulk density, compression strength and pore volume can be affected by different land use systems (Fleige et al, 2016). Continuous animal movement and trampling actions can result in the soil compaction in livestock grazing areas (Gebremariam and Kebede, 2010).…”

Validation of Cryogenic Vacuum Extraction of Pore Water from Volcanic Soils for Isotopic Analysis

“…Table 1 presents the physical characteristics of loamy-sand and loam soils, which are representative of the site. Arenosols are young ash soils, with low clay content (70-80% sand and 20-25% silt), while Andosols are clayey, older ash soils (over 40% clay) [28]. Andosols show a higher total pore volume and a higher field capacity than Arenosols, mainly due to a higher volume of fine pores [28].…”

“…Arenosols are young ash soils, with low clay content (70-80% sand and 20-25% silt), while Andosols are clayey, older ash soils (over 40% clay) [28]. Andosols show a higher total pore volume and a higher field capacity than Arenosols, mainly due to a higher volume of fine pores [28]. Thus, loamy-sand soil was classified as Arenosols and Loam soil was classified as Andosols.…”

“…Depending on the pedological development, volcanic soils can present high clay content Andosols or high sand content Arenosols that are both part of the same pedological (hillslope) units with high organic matter content (7-12%) and high water retention capacity due to the development of interand intra-aggregate voids [24][25][26][27][28]. Moreover, soils attain very low water content during the austral spring and summer (October to March).…”

The nitrogen fixing specie Sophora cassioides (Fabaceae), is nutritionally favored and their rhizosphere bacteria modified when is co-cultivated with the cluster root forming Embothrium coccineum (Proteaceae)

“…For centuries, volcanic activity has occurred throughout southern South American thus influencing the soil development and diversity of vegetation. In Chile, volcanic activity is responsible for many allophanic soils, which implies high capacities to fix P into the soil (Fleige et al, 2016;Goebel et al, 2017). Moreover, pyroclastic materials can induce crucial physical changes in soils that can negatively impact vegetation, preventing the successful establishment of new plants Fleige et al, 2016).…”