Crop diversification in spatial and temporal patterns can optimize the synchronization of nutrients plant demand and availability in soils, as plant diversity and soil microbial communities are the main drivers of biogeochemical C and nutrient cycling. The introduction of multi-cropping in organic vegetable production can represent a key strategy to ensure efficient complementation mediated by soil microbiota, including beneficial mycorrhizal fungi. This study shows the effect of the introduction of multi-cropping in five European organic vegetable systems (South-West: Italy; North-West: Denmark and Belgium; North-East: Finland and Latvia) on: (i) soil physicochemical parameters; (ii) soil microbial biomass stoichiometry; (iii) crop root mycorrhization; (iv) bacterial and fungal diversity and composition in crop rhizosphere; (v) relative abundance of selected fungal pathogens species. In each site, three cropping systems were considered: (1) crop 1—monocropping; (2) crop 2—monocropping; (3) crop 1—crop 2—intercropping or strip cropping. Results showed that, just before harvest, multi-cropping can increase soil microbial biomass amount and shape microbial community toward a predominance of some bacteria or fungi phyla, in the function of soil nutrient availability. We mainly observed a selection effect of crop type on rhizosphere microbiota. Particularly, Bacteroidetes and Mortierellomycota relative abundances in rhizosphere soil resulted in suitable ecological indicators of the positive effect of plant diversity in field, the first ones attesting an improved C and P cycles in soil and the second ones a reduced soil pathogens' pressure. Plant diversity also increased the root mycorrhizal colonization between the intercropped crops that, when properly selected, can also reduce the relative abundance of potential soil-borne pathogens, with a positive effect on crop productivity in long term.

A pot and a field experiment were conducted to evaluate the effects of different nitrogen and chloride fertilizer levels on the nitrate content of beetroot. The yield and dry matter content were also determined. Sulphate fertilization was used as a control to chloride fertilization. There was a considerable decrease in the nitrate content of beetroots during the growing season. High nitrogen fertilization caused nitrate accumulation in both experiments. Chloride had a significant decreasing effect on the nitrate accumulation towards the middle of the growing period in the pot experiment. In the field experiment, chloride also decreased nitrate accumulation towards the middle of the growing period, soon after additional application of ammonium nitrate limestone (13.8 % NH4-N; 13.7 % NO3-N). Chloride tends to decrease nitrate accumulation only at an early stage of root development when nitrate is not the only source of nitrogen in the soil. The yield was higher on high nitrogen supply, in the pot experiment also on chloride application. Nitrogen decreased the dry matter content, but chloride had this effect only in the field experiment.

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