Prediction of organic nitrogen mineralization from fertilizers in soilless production

Consumers are concerned about the quality of the food they consume and the environmental impact of its production. Producers are thus moving toward agro-ecological practices such as organic fertilisation. In conventional soilless production (cultivation 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 introduction of organic fertilisers requires adapting practices because organic fertilisers must be first mineralised by the microbiota of the GM before being assimilated by the plant. Thus, matching the rate of nutrient release by microorganisms to the plant demands is essential to achieve. If N 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 N 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 4 different temperature and 3 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, a first order kinetic model was established, and showed satisfactory calibration results. The model was validated on other data sets from in situ experiments at the producers’ sites. The model must now be calibrated and validated on more GM-fertilizer couples to gain in genericity.