Changes in Soil Organic Matter, Enzymatic Activities and Hea Vy Metal Av Ailability Induced by Application of Organic Residues

A 3-year field experiment on a sandy soi] supporting a strawberry crop was carried out to study the effects of the application of three organic residues (AC, olive mill wastewater sludge compos!; MWC, municipal solid waste compost; and PW, paper mill waste) on organic matler content, enzymatic activities, and available heavy metals. Significant increases in organic carbon content (total organic carbon (TOC), total extractable carbon (TEC) and humic acid carbon (HAC)) were observed in soils, depending on fue nature of organic arnendments. The application of fue organic residues also caused significant increases in dehydrogenase, phosphatase, B-glucosidase, urease and BAA-protease activities. This favourable effect on soil biological activity was more noticeable in MWC and PW treatrnents. Significant positive correlation (p < 0.01) between enzymatic activities and total organic carbon was found for all treatrnents. Available heavy metal contents increased slightly in fue soils treated wifu MWC and PW but did not affect negatively soil enzymatic activities. A discriminant analysis generated two functions (Fl and F2) based on linear contributions offue variables (TOC, TEC, RAC, DHase, Phosp, P-glu, Ure, and BAA). Fl is correlated wifu DH-ase, TOC and BAA and separates treatrnents C and AC from PW and MWC. Fl underlines fue effect of !he higher doses of organic matler applied wifu MWC and PW. F2 is correlated wifu hurnic substances (TEC and RAC), and p-glu separates treatrnents C and PW from AC and MWC. This function shows fue difference of the effect of composted (AC and MWC) and fresh residues (PW) on soil properties. Results showed fuat the application of organic residues to a sandy soil improves its agronomic quality by increasing soil organic matler and enhancing soil enzyme activities.