Abstract
Hillslope curvatures are associated with specific environments that correlate to chemical and mineralogical attributes of soil, so determining specific management zones. Phosphorus is one of the main limiting factors to the development and longevity of sugarcane. The type and the mineralogical constitution of the clay fraction play an important role in the phosphorus (P) adsorption of soil. High proportion of gibbsite (Gb) in soil may be the major responsible for P adsorption. The relationships among spatial variability as a function of hillslope curvature, the proportion of kaolinite (Kt) and Gb, and phosphorus adsorption were evaluated in an Alfisol cultivated with sugarcane. Two plots of 1 ha of a concave and a convex hillslope area were selected and 121 samples were collected in each area. The maximum P adsorption was determined in six samples taken randomly in each area. Data were submitted to descriptive statistical and geostatistical analysis. The lowest average values of available phosphorus were found in the convex area. In this area, the proportion of gibbsite, expressed by the values of the ratio [Gb/(Gb + Ct)] and the values of maximum adsorption capacity of phosphorus were higher than in the concave area.
Highlights
The hillslope curvatures and steepness make up a complex pattern of water and solute transportation in a soil landscape (Marques Júnior & Lepsch, 2000; Franzen et al, 2006)
The objectives of the present study were to evaluate: (i) the relationships between phosphorus adsorption and the occurrence of kaolinite and gibbsite in the soil clay fraction from samples of an Alfisol cultivated with sugarcane; and (ii) the spatial variability of several soil attributes as a function of differences in hillslope curvatures
Rolim Netto et al (2004) found that the most significant correlations for the maximum P sorption capacity were associated with the presence of gibbsite and the clay content
Summary
The hillslope curvatures and steepness make up a complex pattern of water and solute transportation in a soil landscape (Marques Júnior & Lepsch, 2000; Franzen et al, 2006). Similarities between the spatial distribution of the soil clay minerals and their chemical properties may explain the cause/effect relationship between these properties and the relief curvature (Franzen et al, 2006). This relationship is important because it can guide farm management decisions, such as the number of soil samples necessary to characterize an area (Souza et al, 2006) and the required amount of fertilizer
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