Effect of various cultivation methods on the structure and hydraulic properties of a soil in a semi-arid climate

In the absence of irrigation, the cultivation of cereals in semi-arid zones provides a poor yield. To study the consequences of fallow tillage on the soil structure and hydraulic properties, we conducted an experiment from 1991/1992 to 1997/1998 using various techniques (chisel or disc plough, early or late tillage) on a calcisol of the high plateaus of eastern Algeria. In the middle of the tilled horizon (between 8 and 25 cm depth), we measured the near-saturated hydraulic conductivity at four soil water tensions (or potentials) using multidisc infiltrometers, and quantified the morphology of the macropore space using image analysis. Results indicated that tillage increased soil conductivity mainly at low water potential (0.06 and 0.3 kPa). This increase was more significant with the chisel (1.84 x 10-5 m s-1 at 0.06 kPa) than with the disc plough (1.25 x 10-s m s-1), but was attenuated during the crop cycle. Significant differences appeared between tillage treatments for surface macroporosity (5.1% for chisel, 1.1% for disc), pore-space morphology (thin cracks separating compact aggregates under disc, loose fine soil assemblage separating smaller aggregates under chisel) and porosity distribution pattern (equivalent diameter of the macropores varied from 1 mm under disc to more than 2-3 mm under chisel). Analyses of porosity distributions indicate a possible relationship between the structure of the surface horizon and soil hydraulic properties. Durum wheat grain yield varied from 1.08 to 2.85 t ha-1 during the 7-year trial. Grain yield under shallow tillage was significantly higher than under disc plough treatment during wet years. Tillage-date varied across seasons and early tillage effect was more apparent when the fallow season was less rainy. (Résumé d'auteur