Soil and plant responses in three contrasting soils after amendment with orange waste compost as by a mesocosm experiment

The decline of organic matter content of many soils in Europe is becoming a major process of soil degradation; especially in Mediterranean croplands where climatic conditions and anthropogenic pressures accelerate the processes of mineralization. Addition of organic amendments is an efficient practice to recover the soil’s productivity. In Southern Italy, 720.000 t of by-products from citrus processing plants are produced yearly, thus composting may represent a valuable strategy for recycling this waste biomass for potential use in agriculture and alleviating the serious environmental problems concerning its safe disposal. This work aimed to investigate soil and plant responses after amendment with orange waste compost in three contrasting soils (a Typic Haploxeralf, a Typic Xerofluvent, a Vertic Eutrudept) as by a mesocosm experiment. Mesocosm soils were added with compost at two rates (0 and 60 t ha-1), and managed across the growing season with forage legumes (vetch and tick-bean) or forage grasses (orchard-grass and tall fescue). Soil chemical variables (pH, TOC, TN, CEC, EC) were monitored at sowing and harvest. Shifts in the molecular structure of soil bacterial community were assessed by denaturing gradient gel electrophoresis (DGGE) analysis. TOC and TN were responsive to compost addition depending on soil type. DGGE fingerprinting revealed that soil bacterial community structure was fairly resilient to the short-term soil treatments (compost amendment, cropping systems). Compost addition was found to influence selectively the above-ground biomass production. Results indicate that orange waste compost may represent a valuable organic resource for managing soil fertility in Mediterranean degraded agricultural lands.