Wetenschap - 21 november 1996

Less tillage can yield more

The degree to which soils resist erosion caused by rainfall can be expressed on a scale. Soil quality can be classified as low, medium and high, depending on certain site specific, physical properties of different soil layers. These factors determine the infiltration capacity of soils. If the quality is low a combination of reduced tillage (chiselling) and green manure is recommended. If a soil is classified as medium an appropriate crop rotation should be applied to ensure sufficient soil coverage for as long as possible.

PhD student Ana Terzaghi, together with other researchers, came up with these concrete recommendations for the soils in Paysandu, West Uruguay. She studied the relation between soil management and changes in the physical properties of the soil, and used the information to determine the degree to which these changes increase susceptibility to rainfall erosion.

Terzaghi, who graduated Wednesday 13 November, states that farmers in Uruguay are aware of the need to adopt measures against soil erosion. She feels however, that most of these are not effective because they do not correct basic errors in farmers' soil management practices, especially excessive tillage activities. Terzaghi designed a decision tree for each research site. At each step all relevant physical properties are quantified, which results in a soil quality classification.

Professor Perdok of the Department of Soil Tillage, one of Terzaghi's supervisors, explains that the value of her research goes beyond the level of a case study. In the field of soil tillage, Terzaghi is the first to design a promising model capable not only of assessing the soil's susceptibility to erosion but also of recommending appropriate methods of soil tillage and other agronomic measures.