The aquands found in southern Chile are derived from volcanic ash and contain high levels of organic matter. Due to the presence of an impermeable stratum, they have shallow soil profiles, which induce waterlogging for several months each year. These fragile soils, locally known as ‘Ñadi’, cover an area of 475 000 hectares and have undergone intensive land use changes, which have affected the soil physical properties. These are still not well understood but are relevant for the design of efficient drainage systems. The aim of this research was to analyse the impact of the land use change in Ñadi soils on the spatial and temporal variability of their soil physical properties. For the land use change from secondary native forest (sNF) to naturalized grassland (NG), the effective soil depth was measured at defined points. Time‐ and space‐dependent changes of water‐table depth and penetration resistance were recorded. Volumetric water content and soil temperature were measured with sensors installed at three depths and the water retention curve and air permeability at these depths were also determined. The changes in land use over time have induced a reduction in soil depth. Soils under NG showed a smaller soil water storage capacity, air capacity and permeability compared with soils under sNF, as well as waterlogging during winter and greater mechanical strength and soil profile temperatures during summer. Therefore, the land use change affected the spatial and temporal variability of soil physical functions across the field.
60 %). El mantillo (Oe/Oa) presentó condiciones adecuadas para el desarrollo radicular. Existe comúnmente un horizonte blanco (frecuentemente 10 YR 5/1-2) inmediatamente debajo del mantillo, con textura franco limosa y estructura masiva, con arraigamiento muy bajo. Se plantea como hipótesis que este horizonte se originó por depósitos de cenizas volcánicas y procesos de podzolización. Se concluye que la fertilidad de estos suelos es baja debido a limitantes físicas (dificultades de arraigamiento) y químicas (acidez, toxicidad de aluminio, baja oferta de bases)]]>
Aquands are soils derived from holocenic volcanic ashes located in southern Chile. Due to the presence of very high levels of organic matter (30 %), these soils present a high total porosity (80 %) but at the same time, a limited water storage capacity due to their shallow soil depths. The aim of this work was to analyze the influence of land use change of a Duric Histic Placaquand (Ñadi) soil on soil physical properties and their consequences on water and temperature dynamics. The volumetric water content (θ Field ) and soil temperature (T) were registered at different depths in a Ñadi soil under a secondary native forest (sNF) and naturalized grassland (NG). Undisturbed soil samples were collected to analyze the water retention curve, saturated (Ks) and unsaturated (Ku) hydraulic conductivity and water repellency. The dynamics of rainfall and water table depth (WT) were registered using a rain gauge and groundwater wells. The land use change of a Ñadi soil from sNF to NG induced soil structural changes in the first 15 cm of soil reducing the amount of macropores under NG and affecting the hydraulic conductivity function as well as θ Field and T dynamics, i.e. while the WT in winter reached the soil surface in the NG, under sNF the air-filled pores were still present. Similarly, the T gradients increased as Ɵ Field decreased, being more intensive under NG. A nonhomogeneous soil wetting and water infiltration was assessed, which can be related to an increased spatial water repellency, soil hydraulic properties and rainfalls.
In the Andes of Chile, two valuable Nothofagus tree species coexist (Nothofagus dombeyi (Mirb.) Oerst. and Nothofagus nervosa (Phil.) Krasser). They could provide an opportunity for mixed plantations because of their ecological differences. In a mixed plantation with a checkerboard design on a good site where the two species naturally coexist, we evaluated their performance according to aspect and type of competition. Nothofagus dombeyi had a greater survivorship (90% vs. 65%) and growth (twice in diameter and 20% greater in height). Forking was significantly lower in N. nervosa (23% vs. 70%). Aspect did not significantly affect the performance of N. dombeyi. The north aspect had a significant negative effect on survivorship of N. nervosa, but aspect did not significantly affect growth or forking of this species. The aspect -type of competition interaction was only significant for N. nervosa in diameter and marginally significant in height. The checkerboard design allowed for a clear separation of interspecific and intraspecific competition in this mixed plantation. Interspecific competition favored growth of N. nervosa on the north aspect (facilitation) and was detrimental to N. nervosa on the south aspect (competition). These results have a direct application when planting mixtures of species of complementary ecological characteristics that can increase the value of the plantation.Résumé : Deux espèces arborescentes précieuses du genre Nothofagus (Nothofagus dombeyi (Mirb.) Oerst. et Nothofagus nervosa (Phil.) Krasser) qui coexistent dans les Andes chiliennes pourraient fournir une occasion de plantations mixtes étant donné leurs différences écologiques. Dans une plantation mixte avec un dispositif en damier sur une station de bonne qualité où les deux espèces coexistent naturellement, nous avons évalué leur performance en fonction de l'exposition et du type de compétition. Nothofagus dombeyi avait le plus haut taux de survie (90 % vs 65 %) et de croissance (le double en diamètre et 20 % de plus en hauteur). Il y avait significativement moins de troncs fourchus chez N. nervosa (23 % vs 70 %). L'exposition n'avait pas d'effet significatif sur la performance de N. dombeyi. L'exposition au nord avait un effet négatif significatif sur la survie de N. nervosa mais n'avait pas d'effet significatif sur la croissance ou la production de fourches chez cette espèce. L'interaction entre l'exposition et le type de compétition était significative seulement chez N. nervosa dans le cas de la croissance en diamètre et marginalement significative dans le cas de la croissance en hauteur. Le dispositif en damier a permis de distinguer clairement la compétition interspécifique et intraspécifique dans cette plantation mixte. La compétition interspécifique favorisait la croissance de N. nervosa lorsque la plantation était exposée au nord (facilitation) et défavorisait N. nervosa lorsqu'elle était exposée au sud (compétition). Ces résultats ont une application directe pour la plantation de mé-langes d'espèces dont les caractéristique...
Soil scarification has been used as a silvicultural method to eliminate competition in tree regeneration, but it modifies soil characteristics. In order to evaluate soil changes due to silvicultural management, we characterized a volcanic soil subjected to a mechanized scarification in a Nothofagus spp. forest in the Andean region of southern Chile (39° 54' S, 71° 56' W; 970 m asl). Scarification removed between 20 and 40 cm of topsoil in forest gaps. Two scarified areas were selected in different periods and in an undisturbed forest area. Physical properties (bulk density, penetration resistance, porosity, texture) and chemical (pH, soil organic matter, total-N, P-Olsen, K, Mg and Ca extractable, Al saturation) were analyzed in both the scarified soil and undisturbed forest. The morphology of the soil was a result of the formation of a stratified soil. Bulk density was higher in the superficial layer of the scarified soil (0.9 to 1.2 g cm -3 ) when compared to the undisturbed forest (0.3 g cm -3). With regards to the undisturbed forest, soil scarification exposed a superficial soil of coarser texture, lower total porosity (50-60% vs. 80%) and it decreased the soil nutrient supply. There were no large variations in soil properties when comparing the oldest scarified soil with the most recent one. There were important changes in morphology, physical and chemical properties of the scarified soil.
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