Adsorption of glyphosate in chilean soils and its relationship with unoccupied phosphate binding sites

The objective of this work was to investigate glyphosate adsorption by soils and its relationship with unoccupied binding sites for phosphate adsorption. Soil samples of three Chilean soils series - Valdivia (Andisol), Clarillo (Inceptisol) and Chicureo (Vertisol) - were incubated with different herbicide concentrations. Glyphosate remaining in solution was determined by adjusting a HPLC method with a UV detector. Experimental maximum adsorption capacity were 15,000, 14,300 and 4,700 mg g¹ for Valdivia, Clarillo, and Chicureo soils, respectively. Linear, Freundlich, and Langmuir models were used to describe glyphosate adsorption. Isotherms describing glyphosate adsorption differed among soils. Maximum adjusted adsorption capacity with the Langmuir model was 231,884, 17,874 and 5,670 mg g-1 for Valdivia, Clarillo, and Chicureo soils, respectively. Glyphosate adsorption on the Valdivia soil showed a linear behavior at the range of concentrations used and none of the adjusted models became asymptotic. The high glyphosate adsorption capacity of the Valdivia soil was probably a result of its high exchangeable Al, extractable Fe, and alophan and imogolite clay type. Adsorption was very much related to phosphate dynamics in the Valdivia soil, which showed the larger unoccupied phosphate binding sites. However relationship between unoccupied phosphate binding sites and glyphosate adsorption in the other two soils (Clarillo and Chicureo) was not clear.

Efecto de la fertilización fosforada sobre el contenido de cadmio en cuatro suelos de Chile

Los fertilizantes fosforados pueden contener cadmio (Cd) y al utilizarlos pueden entrar en las cadenas tróficas. El objetivo de este estudio fue evaluar el efecto de la fertilización fosforada sobre la concentración de Cd disponible en cuatro tipos de suelos de Chile, que pertenecían a los ordenes Inceptisol, Alfisol, Ultisol y Andisol. Los dos tratamientos usados fueron el testigo sin fertilización y la aplicación de una dosis de corrección con un fertilizante comercial, superfosfato triple (SFT), que tenía una concentración de 53,2 mg de Cd por kg de fertilizante. La dosis de fertilizante aplicada fue la necesaria para alcanzar un nivel de 30 mg kg-1 de POlsen. Los suelos se incubaron en estufa durante 90 días, a 25ºC y humedad de capacidad de campo. El diseño experimental fue completamente al azar, con tres repeticiones para cada suelo y donde la unidad experimental fue un contenedor con 250 g de suelo seco. Se midió Cd disponible a los 1, 2, 7, 14, 21, 36, 49, 63, 77 y 90 días después de la incubación. La aplicación de P en dosis agronómica, utilizando fertilizante con alto contenido de Cd, tuvo un efecto estadísticamente significativo sobre la concentración de Cd disponible en los suelos estudiados, sin embargo, no hubo efecto del tiempo de incubación en la disponibilidad de Cadmio.

Soil penetration resistance analysis by multivariate and geostatistical methods

The penetration resistance (PR) is a soil attribute that allows identifies areas with restrictions due to compaction, which results in mechanical impedance for root growth and reduced crop yield. The aim of this study was to characterize the PR of an agricultural soil by geostatistical and multivariate analysis. Sampling was done randomly in 90 points up to 0.60 m depth. It was determined spatial distribution models of PR, and defined areas with mechanical impedance for roots growth. The PR showed a random distribution to 0.55 and 0.60 m depth. PR in other depths analyzed showed spatial dependence, with adjustments to exponential and spherical models. The cluster analysis that considered sampling points allowed establishing areas with compaction problem identified in the maps by kriging interpolation. The analysis with main components identified three soil layers, where the middle layer showed the highest values of PR.

Changes in water availability in the soil due to tractor traffic

Frequent traffic of tractors in agricultural soils, promotes soil compaction and affects the flow and water availability. The aim of this research was to study the effect of compaction induced by tractor traffic on water availability in the soil under different traffic intensities on the same path (0, 1, 3, 6 and 10 passages), to two tractors with 3.3 and 2.6 ton of weights, over three different surface conditions. The study was conducted in an Andisol, representative soil of the study area. It was determined the behavior of the water retention curve, obtaining the gravitational water, available water and hygroscopic water, to 10 and 30 cm of depth. The hygroscopic water is the most prevalent with values ​​of up to 80% of the total water present in the soil. The water retention curves showed increases in the values ​​of field capacity and wilting point and behaviors "flattened" indicating a high sensitivity to the applied treatments, representative of compacted soils, which give the surfaces studied characteristics do not suitable for normal crop development.