A Erodibilidade do solo em sistema de plantio direto aumenta com o tempo de manejo

Abstract

In recent years, it to discussions the efficiency of the no tillage system in soil and water conservation has been expanded, especially in areas with long periods of continuous use. In this way, the objective of this work was to test if the soil erodibility increases in no-till of long-term. This work was developed in four agricultural areas under no-tillage system with different management times (6; 17; 24 and 38 years) and forest area located in the Centro-Sul region of Paraná, Guarapuava microregion. The soil erodibility was performed with laboratory rainfall simulations using undisturbed soil samples, and each sample was submitted to two rain simulations, one in soil moisture field capacity and the other in saturated soil. During the simulation, the water and the sediments transported by the splash effect and the surface and subsurface flow were collected. The stability of aggregates of the total soil mass and macroaggregates was performed by wet method. For this, samples were collected at five points (randomly chosen) at the top of the soil (0.0-0.1 m) in each area. The stability of aggregates was determined through the weighted average diameter, geometric mean diameter and aggregate stability index. The areas presented low coefficient of surface runoff. The runoff showed no significant difference between the areas of forest, no-tillage 6 years, no-tillage 17 years and no-tillage 24 years, in simulation with field moisture. With the saturated soil there was no significant difference between the areas, but with tendency to increase the runoff with the management time. Conversely to the surface runoff, the subsurface flow (infiltration) presented reduction with the management time. The soil loss presented elevation according to the management time in both repetitions. The no-tillage 38 years area was the only one to show difference in relation to the other managed areas and the forest. Of the soil loss, over 80% was represented by the splash in all plots and repetitions, the loss by surface runoff was less than 5%. The aggregation indicators of the total soil mass did not present a significant difference between the different evaluated areas. When evaluating the aggregate stability index by class of macroaggregate, it is observed that the class of 4-8 mm and 2-4 mm are the ones that suffer the greatest effect and better represent the degradation of the no-tillage after a long period of management. The macroaggregates presented reduction of organic carbon related to the time of management. It was observed a correlation of stability index of macroaggregates with the soil losses in at least one of the simulations (field moisture and / or saturated moisture), especially in class with a size greater than 2 mm. Even the no-tillage system being considered a conservationist system, and presenting advantages over other management systems, it presents degradation of the physical properties after a long period of management (> 24 years), evidenced by the reduction of the stability of macroaggregates and the content of organic carbon, as well as increased rates of soil loss.