Increasing Sustainability of Vegetable Production by Using Urban Waste Compost: Results of a Two Year Rotation

Vegetable production is typically characterized by an intense cropping system due to the high input level applied needed to adequately sustain crop production and because of the rapid crop succession. As a consequence, this sector of agriculture has probably the highest environmental risks also because it is often carried out in areas considered “highly sensitive” for their pedological and hydrological features. From the other side more and more organic residues are becoming available as a consequence of the increased composting activity of urban wastes and sludge. The aim of this experiments was to evaluate the possibility to partially or completely substitute mineral nitrogen fertilizers with compost in a vegetable 2 year rotation. Crop succession in the first year was, processing tomato and spinach (used as a cover crop) and in the second year was beans and French bean as a main crop and spinach and beets as a second crop. Treatments compared were five, including a non fertilized control (T0) and a mineral N fertilizer control (TMIN). On the base of the amount of N distributed in TMIN two additional treatments where applied, T50 with 50 % of N distributed as mineral N and 50% using compost, and T100 with 100% of N was organic. The last treatment was T200 where a double amount of N respect TMIN was distributed as compost. The first year of experiment although no strong differences were found, mainly because of the high initial fertility of the soil, however a little delay of senescence of plant receiving high doses of compost was observed. Crops grown in the second year were more affected by treatments. For both the leguminous species T50 was the treatment that allowed the highest yield and, only for bean, the highest harvest index. Beet and spinach responded differently to the treatments, probably because of the morphology  of the root systems. Beet reached the maximum yields with T100 e T200 while spinach responded better to the mixed fertilization (T50). Both crops showed a reduction in the leaf nitrate content when compost was used. Concentration of macronutrients in soil water during and after spinach crop showed that N potentially leached was bigger with TMIN than in plots where compost was used. As a general conclusion, the experiments demonstrated that compost can be used to replace, although not completely, mineral nitrogen fertilizers in vegetable crop rotation reducing potential environmental risk and maintaining unaffected the production.