Soil management for improvement of soil physical characteristics related to erosion in Uruguay

In Uruguay various soil physical characteristics are studied in three field experiments and by means of several laboratory analyses in order to relate those characteristics to the ability of the soils to resist the impact of rainfall erosion. The top layer is characterized by measuring several indicators of structure quality and the results are related to the behaviour with respect to rainfall, either natural or simulated. The subsoil is studied mainly on its hydraulic properties, since they are a constraint for water movement. Modelling of rainfall redistribution in layered profiles is used to obtain fast predictions of water behaviour when soil characteristics are varied. Based on the above analyses and simulations, we define limits that allow to assess the ability of the soil to resist erosion. The characteristics found to be most relevant are i) the presence of an argillic B horizon, ii) the susceptibility for crust formation expressed by a sealing index, iii) the stability of structure expressed by the wet sieving diameter and iv) the arrangement of aggregates expressed by the total porosity. Once the quality of the soil is known, the appropriate management has to be selected according to the limiting factors. A soil of medium quality can be improved by reduced tillage systems together with cover crops to be incorporated as green manures. When the quality is low, tillage intensity cannot be reduced yet. Chiselling has to be considered together with crop incorporation. From our research, the improvement of physical conditions of the B horizon has been shown as highly relevant, and it needs to be studied further by means of deep chiselling or subsoiling together with crops especially adapted to deep rooting through the limiting layer.