Soil pore geometry changes in surface horizons under different irrigation regimes

The influence of irrigation practices on the surface soil structure is well known by farmers and agricultural scientists. Breakdown of surface aggregates into finer particles and redistribution of these letter within the top few millimetres produce a crust-like surface structure which affects many soil physical properties such as water infiltration, water retention features, mechanical impedance. The aim of this work is to study soil pore geometry changes in surface horizons under furrow and sprinkler irrigation regimes, using a quantitative approach. Undisturbed samples of a bared and cropped clay-loam soil, before and after the irrigation treatments, were collected. Porosity against depth up to 75 mm and pore size distribution of the upper 1 cm thick layer have been measured by means of image analysis techniques on digital images of sections of the specimens at a resolution of 40 ?m. Major impact on the soil structure of the furrow irrigation versus the sprinkler system has resulted both in terms of compactness and thickness of the crusts. Sprinkler system produced reduction in porosity mainly in the largest pore size classes (>800 ?m) while the furrow system upon the whole range of sizes. Crop has showed a mitigating effect on compactness but an increase of the thickness of the compacted soil. The quantitative analysis of the size distribution of the pore system described in this paper has showed to be easily performable even for very thin layers of soil where other measurements (i.e. hydrology) may be difficult to be employed.