The enabling of forests to achieve productive systems is one of the most significant causes of land use change in Southern Chile, and it can be evaluated through changes in soil structure. The structural stability of a volcanic soil and its relationship with the colloidal fraction under forest and grassland was evaluated in this study. Disturbed and undisturbed samples were collected for soil chemical characterization and evaluation of hydraulic and mechanical properties, aditionally qualitative properties of the organic matter were determined, for both uses, at three depths (5, 20 and 50 cm). For the purposes of statistical analysis land use was consider as a factor. The land use change from grassland to forest caused: i) an increase of 38% in bulk density at 5 cm, an increase of 44% and 75% of the organic matter content at 20 and 50 cm; ii) an increase of 33% allophane at 5 cm and a reduction in the effective porosity of 14% between 5 and 20 cm; iii) an increase of 180% in air permeability at 50 cm, a 54% decrease in the variation of the average diameter of aggregates and a 32% decrease of the repellency index at 5 cm. Soil physical functioning improved after a land use change. This might be determined by the qualitative properties of soil organic matter and its interaction with the matrix, oxides and hydroxides of Al and Fe.

Se analizó las características de intensidad y precocidad de las respuestas a "El Niño 1997-98" manifestada por el fitoplancton superficial, macroalgas de la orilla rocosa y macrobentos de fondo blando en la Bahía de Ancón (11º46' LS y 77211' LW), entre diciembre de 1996 y agosto de 1998. Este evento se caracterizó por un incremento significativo de la temperatura desde abril (17,4ºC) y del oxígeno (2,46 mi x l") a partir de mayo de 1997, en los fondos del área de estudio. En el fitoplancton superficial se registró la presencia de especies indicadoras de aguas oceánicas cálidas desde enero y un inusual aumento en la densidad de dinoflagelados y microflagelados a inicios de abril de 1997. La densidad de la población de la macroalga Chondracanthus chamissoi alcanzó 2 684 indo x 32 m' de línea de orilla en octubre de 1997, y la proporción de gametofitos se incrementó durante 1998. La densidad y el número de especies del macrobentos de fondo blando alcanzaron los valores máximos de 90 indo x 0,04 m•2 y 20 especies en junio y noviembre de 1997, respectivamente; estas variaciones correlacionaron bien con los cambios en la intensidad de "El Niño". La biomasa llegó a su máximo valor de 0,55 g pssc x 0,04 m•2 recién en enero de 1998. Finalmente, se demuestra que el impacto biológico de "El Niño 1997-98" fue menor al del evento de 1982-83, no obstante la similitud en la intensidad de ambos eventos; y que las aguas someras presentaron indicadores tempranos y confiables de "El Niño", tanto en el fitoplancton como en el bentos. Además, la presencia de un período post-Niño demuestra que el impacto de "El Niño" sobre las poblaciones y comunidades puede ser complejo.

White clover may generate morpho-physiological adaptations to face soil phosphorus (P) deficiency. Phosphorus use efficiency (PUE) of 9 naturalized white clover accessions (WCAcc) and 2 commercial cultivars Huia and Will (controls) was evaluated under glasshouse conditions. The treatments consisted of increasing levels of P in soil mounted on PVC pots (0.025 m 2 x 1 m deep), with 3 replicates and randomly arranged inside a glasshouse. Total dry matter production (DM) and internal P concentration of the above ground materials (PIC) was determined. P uptake and components of PUE were calculated (PAE and PUtE). Additionally, the glasshouse results were compared descriptively with those obtained under field conditions (Acuña and Inostroza, 2013). Six accessions had higher DM production and were more efficient in terms of their general PUE compared to the cv. Huia control, but they did not exceed the cv. Will control. All of the accessions were more efficient in their PUE in the low-middle range of P availability showing no differences compared to the cv. Will control. This behavior was observed under glasshouse and field experimental conditions, both PAE and PUtE of the WCAcc differ in magnitude of the response, which may be associated with interspecific competition and grazing under field conditions. These results indicate that under limited availability of P in the soil the WCAcc collected have a better adaptative response. In addition, the glasshouse results were consistent with the field experiment used in the evaluations.