Aggregate stability under different soil management systems in a red latosol in the state of Parana, Brazil

Several management systems can be used to improve the soil physical conditions. The study of aggregates is one way to quantify whether or not the management is improving the soil natural characteristics and agricultural capacity. The effects of two tillage systems and three crop rotations on the aggregation indices were studied. Samples were collected at the IAPAR Experimental Station, Londrina, state of Parana, Brazil, from an experiment that has been carried out for 21 years in a dystrophic red latosol (Typic Haplorthox). Treatments consisted of two planting systems (conventional-tillage (CT) and no-tillage (NT)), under three crop rotations (soybean/wheat/soybean (S/W/S), maize/wheat/maize (M/W/M) and soybean/wheat/maize (S/W/M)) and two layer depths, 0-20 and 20-40 cm, arranged in a split plot design with three replications. The aggregation indices used were the mean weight diameter (NWD), geometric mean diameter (GMD) and the aggregate stability index (AS%). Carbon content was determined in the aggregate size fractions using the Walkley-Black method. The no-tillage system had the best aggregation indices for the 0-20 cm layer due to the increase in the organic carbon content. The greatest quantities of organic carbon were found in the 2 mm aggregate size class. The crop rotations studied did not affect the aggregate stability indices. (C) 2002 Elsevier Science B.V. All rights reserved.