Different organic farming systems under greenhouse do not improve soil C storage but affect microbial functions across soil aggregates

Vegetable crops production is usually based on organic fertilizers purchased off‐farm while the care of soil fertility based on the maintenance of adequate level of soil organic matter receives few attentions. Organic production in plastic tunnel‐greenhouses represents the most intensified organic production system. Therefore, we compared four alternative organic production systems mainly characterized by the combination of fertilizer application practices based on compost, cover crops and commercial organic fertilizers. The systems were: input substitution organic method (BAU), biodynamic method (BIODYN), organic‐agroecological (AGROEC) and a not fertilized but organically managed control (CNT). The objective of this study was to explore in a 3‐year long trial, the effects of different organic systems on soil organic carbon (SOC) balance and the possible effects on soil chemical–physical characteristics, enzymatic activities involved in the C, N and P cycling, total bacterial biomass (16S rRNA), and the microbial functional genes cbbL and amoA in bulk soil and in three aggregate size fractions (macroaggregates >250 μm, free microaggregates 250–53 μm and free silt plus clay (free‐SC)