INTRODUCTION GÉNÉRALE

Conservation agriculture is an approach to management of agro-ecosystems for improved and sustainable productivity, thereby conserving natural resources and the environment. It uses minimal soil disturbance (no tillage) and permanent soil cover (mulch) as sustainable cultivation practices for the future. In Algeria, conservation agriculture was introduced only about 10 years ago. In this study, plough tillage (PT), reduced tillage (RT) and no-till (NT) were evaluated regarding their effects on physical, chemical and microbiological soil parameters in an on-farm research approach in two agricultural regions of Algeria (Annaba and Sétif) with differing site and agricultural soil management conditions. Soil samples were taken from fields on commercial farms, at Annaba on soils containing mainly recent clayey alluvium in a Mediterranean climate and at Sétif on soils with limestone rock parent material and a semi-arid continental Mediterranean climate. The interactions between soil structural properties and microbial biomass and activities were examined using disturbed and undisturbed soil samples collected on two occasions from the top 20 cm of soil in all three tillage systems. The results showed a generally intensive loosening effect of PT compared with RT and NT, which led to lower bulk density and higher porosity. The parameters macroporosity and air permeability demonstrated that the air-filled pore space in the topsoil differed in its transport efficiency between the tillage systems, with rather random organisation in PT and RT and a more continuous arrangement in NT. Structural stability of the topsoil layer and its resistance to compaction was inversely correlated with tillage loosening intensity. The content of tot-C and tot-N showed significant correlations between in the two regions and all tillage systems. Comparable differences between tillage systems and regions for tot-C and the C/N ratio in the entire set of samples suggest that more input of new, litter-derived organic matter with large C/N ratios promotes larger tot-C concentrations in the study two site. These results of C/N ratio indicate that we have a good mineralization of the SOM in RT, NT and PT successively for the two regions, but in Annaba, it was good and fast on the surface and takes a slow regime at depth, but the Sétif mineralization was slow and only returns a small amount of mineral nitrogen to the soil. Two microbiological parameters, biomass and basal respiration, were positively affected by RT and showed a distinct effect of sampling date, with the highest values observed shortly after tillage. Site-specific effects were also observed. Based on the results, it was not possible to identify an ideal tillage system associated with only positive effects on soil quality parameters, but it seems to be the TCS have been identified as an optimal tillage system for the regions studied. These preliminary results from on-farm research are of a tentative nature and must be confirmed in further studies in order to deliver reliable recommendations for farmers in Algeria.