In arid and semi-arid soils, organic residues undergo rapid degradation and their consequences are positive on both soils and living biota. Probably, humic substances, which are organics that resist biodegradation, can bring further positive consequences on soil characteristics and biota living therein on the short run. To investigate this hypothesis, a pot experiment was conducted using two sandy (calcareous vs non calcareous) soils amended with organic substances (compost and biogas manure) and their extracts (humic acid (HA) and fulvic acid (FA)). Applications of compost and biogas manure were based on  a constant N-input,  equivalent to 36 kg N ha^-1, while in case of organic extract treatments, soils received supplementary doses of ammonium sulphate (20.5%N) to raise N-content in soils to the recommended dose. Control treatments, that received a full dose of N as ammonium sulphate, were also considered for data comparison. The experimental design was a complete randomized one. All pots were planted with faba bean seeds and incubated under the greenhouse conditions for 80 days. Results indicated that organic applications stimulated total counts of soil bacteria and fungi by the end of the experimental period. These organic treatments increased significantly values of soil EC and CEC. On the other hand, their impacts on soil bulk density and pH were not detectable. Further significant improvements in soil chemical characteristics and total bacterial and fungal counts were attained owing to application of the organic extracts (HA or FA) as compared to their sources; yet, organic manures retained higher residual organic carbon (ROC) than their extracts did. In conclusion, application of organic amendments and especially their extracts recorded positive impacts on soil characteristics on the short run; yet, improvements in soil bulk density are mostly related to long term microbial activities.