S06 - Session O8 - Prediction of organic nitrogen mineralization from fertilizers in soilless production.

Authors: Patrice Cannavo *, Sylvie Recous, Matthieu Valé, Sophie Bresch, Mohammed Benbrahim, René Guénon

Consumers are concerned about the quality of food they consume and the environmental impact of its production. Producers are thus moving towards agro-ecological practices such as organic fertilisation. In pots and containers, the plant grows in a finite volume of growing media (GM) with limited buffering capacity (water, temperature, pH and nutrients in particular). The use of organic fertilisers requires adapting practices because organic fertilisers should be mineralised by the microbiota of the GM before being assimilated by the plant. Thus, matching the rate of nutrient release by micro-organisms to the plant demands is essential to achieve. If nitrogen mineralization have been thoroughly studied in soils, knowledge gaps exist in GM. Since GM presents low biodegradability, one can wonder whether indigenous microbial communities are suitable for organic nitrogen mineralisation, depending on temperature and moisture conditions. More generally, the transposition of mineralisation knowledge from soils to GM is questioned. The objective of this study is to characterize and model the dynamics of organic nitrogen mineralization of different GM-fertilizer couples at 5 different temperature and 4 matric suctions. A 49 days incubation without plants was carried out to monitor the mineral nitrogen dynamic resulting from the biodegradation of 2 organic fertilizers, in 4 different GMs. Based on these incubation data, two prediction models of mineralization were established, a multi-variable regression and a first order kinetic model. A temperature action law applicable to all GM could be established. This was not possible for humidity where each GM reacted differently. Nevertheless it was possible to model the mineralized nitrogen. The two models were validated on other data sets from in situ experiments at the producers' sites.