Evaluation of no-tillage as an alternative management for the improvement of the physical condition of agricultural soils through the analysis of water retention curves.

Physical degradation of agricultural soils manifests itself in different ways: decrease in infiltration rate and water storage, poor aeration and, compaction. All these symptoms have a common cause: the deterioration of the soil's natural structure due to the usual agricultural management practices.

Soil water retention curves are a valuable tool for diagnosing the physical state of the soil. Soil properties are the ones that regulate the shape of this curve, with special relevance to texture and structure. For example, changes in macroporosity –associated to soil aggregates and therefore to its structure– would be reflected in changes in the shape of this function in the low suction range.

This work evaluates no-tillage as an alternative to conventional tillage in a typical soil of Navarre (Spain), based on the analysis of soil water retention curves (SWRC).

Two plots were selected, identical in soil type and use, but contrasting in their management: (i) no-tillage (18 continuous years) after conventional tillage and (ii) conventional tillage. In both treatments, undisturbed soil samples were taken (0-5 cm). From these, SWRCs were obtained in the laboratory using the Hyprop device. Dexter’s S index was determined for each SWRC.

The S index did not show significant differences between the two treatments. However, the SWRCs present significant differences between treatments regarding pore size distribution. The tilled soil showed higher macroporosity (gravitational water). Therefore, the soil (surface horizon) under no-tillage could store ca. 10 % more water for the crop.