The challenging management of C stock and N fluxes in soils of different organic vegetable cropping systems under Mediterranean greenhouse

Abstract Organic greenhouse production in Europe is a very intensive system of production, and its environmental sustainability is questioned. Geographical and climatic conditions strongly influence organic systems of production implemented in different European regions, and a direct comparison between the ones implemented in the Mediterranean and in Central and Northern European greenhouses is extremely difficult, if not impossible. This article deals with organic greenhouse production in Mediterranean countries, comparing and assessing different organic systems with a special focus on soil fertility management, C stock and N dynamics. A system research approach was adopted, and each compared system was designed to perform optimally and to express its potentiality as the result of multiple components and their interactions. The compared systems were the following: Business As Usual (BAU), intensive system based on an input substitution approach; Agroecological (AGROEC), organic based on an agroecological approach to soil fertility management; Biodynamic (BIODYN), biodynamic approach; Control (CNT), not fertilized control. Compared systems were assessed during a 3‐year trial for the impact of their different soil fertility management systems on marketable yields, plant available nitrogen, nitrogen efficiency indexes, soil C and N balance and spontaneous flora. Marketable yields resulted not significantly different, even though external nitrogen inputs (fertilizers and amendments) ranged between 0 in CNT and 827 kg N ha −1 in BAU, while the highest value of N apparent loss (1193 kg N ha −1 ) was shown by BAU. Soil solarization, an agricultural practice adopted only in BAU, was responsible for the highest peak of soil mineral nitrogen at transplanting (over 300 kg N ha −1 ) and for the highest apparent loss of nitrogen. Soil C balance showed a general decrease of C stock in soil for all compared systems, which lost not only part of the initial soil C content but also the carbon input of green manure, organic fertilizers and amendments.