Compost amendments vs mineral fertilization under greenhouse: effects on soil biological quality and on productivity and nutrient contents of different cultivars of lettuce and endive.

A three-year fertilization trial was carried out in Campania region (southern Italy) in a tunnel greenhouse of 800 m2, half amended annually with 15 t ha-1 (d.m.) of a certified quality compost derived from the organic fraction of municipal solid wastes (COMP) and half treated with conventional mineral fertilizers (MIN). Different cultivars (six in 2010 and four in 2011) of lettuce and seven cultivars of endive in 2012 were transplanted. At the end of the crop cycles, soil microbial biomass and respiration and three soil enzymatic activities, i.e. acid and alkaline phosphatases and FDA hydrolysis, were measured. Fresh weight of lettuce and endive heads and nutrient (Ca, K, Mg, Na) concentrations in the edible leaves were also determined. After the first compost amendment, only FDA hydrolysis activity was significantly higher in COMP than in MIN. The weight of lettuce heads was only slightly lower (from 3.6 to 8.8 %, depending on the cultivar) in COMP than in MIN. The two successive compost applications progressively improved soil quality showing the ability of compost to sustain the crop productivity, although to a different extent for different cultivars. Regarding leaf nutrient concentrations, the analysed plants generally showed no significant differences among cultivars and between treatments. Soil compost amendments do not determine main differences in crop yield and quality in respect to soil mineral fertilization, but improve soil biological quality.