Stability of soil aggregates in Latosols and Cambisols via standard method and sonification

Abstract

The results of determining the stability of aggregates in water are sometimes contrasting, and do not permit a definition of the energy level or force involved in this analysis. The objective of this study was to compare two methods to determine the geometric mean diameter (GMD) and the percentage of aggregates > 2 mm in Latosol and Cambisol submitted to management under coffee. To conduct this study we collected soil blocks with preserved structure at the following depths, having gypsum as the soil surface reference: Hilled layer (soil above the gypsum layer) and depths of 0.0-0.20 m and 0.20-0.40 m below the gypsum line, with three repetitions, in two soil classes: Latosol and Cambisol. The aggregate stability was determined via wet sieving (standard method) and sonification. For the sonification, 5 g of aggregate were subjected to increasing levels of ultrasonic energy, 2.2, 6.4, 12.8 and 25.5 J mL-1 . After sonification at each energy level, samples were passed through the same set of sieves used in the standard method. Geometric mean diameter of the aggregates and the percentage of aggregates > 2 mm was calculated. The data were submitted to variance analysis and the averages were compared by the Scott-Knott test (p < 0.05). In Cambisol, the GMD and percentage of aggregates > 2.0 mm were higher when these aggregation indices were determined by the standard method, and sonification demonstrated a difference in depth regarding aggregate stability, the 0.20 to 0.40 m depth being more susceptible to breakdown. sonification methods S15 and S30, which respectively correspond to ultrasonic energy levels 6.4 and 12.8 J mL-1 , were more sensitive in detecting differences in depth in the GMD aggregation index of the soil used.