Compost tea as a tool for sustainable nitrogen management and microbial stimulation in lettuce cultivation

In a context where agriculture is called to combine productivity, resource efficiency and resilience to climate change, reducing the use of synthetic fertilizers is imperative. This study evaluated Nitrogen Use Efficiency (NUE) in a lettuce (Lactuca sativa L.) crop treated with four increasing doses (0, 170, 340, and 680 mL m−2) of compost tea (CT) under no fertilization (NoFert), sub-optimal (Half), and optimal (Full) conditions. Considering the complex interactions between soil and plants, enzymatic and microbiological analyses of the soil were conducted, the mineral content in the soil and leaf tissues were determined and the biometric parameters associated with fresh biomass production were measured. The results show that only plants grown under suboptimal fertilization conditions got a boost from CT. Specifically, the highest dose led to an increase in yield (+15.7 %) and N uptake (+14.7 %) compared to the control without CT (Half x 0). This effect was related to a higher amount of the amoAOB gene, which is involved in ammonia oxidation. On the other hand, the apr and ureC genes showed an increase at the 340 but a decrease at 680 mL m−2of CT. This suggests dose-dependent microbial responses. Under optimal fertilization conditions, the application of the highest dose of CT reduced the abundance of all genes analyzed and N uptake compared to the control (Full x 0). From an agronomic point of view, the application of CT at a dose of 680 mL m−2is promising for reducing the use of synthetic fertilizers, reducing the production gap between optimal and suboptimal fertilization, while increasing the NUE of lettuce.