*Article* **Nutrient Availability for** *Lactuca sativa* **Cultivated in an Amended Peatland: An Ionic Exchange Study**

**Jacynthe Dessureault-Rompré \*, Alexis Gloutney and Jean Caron**

Soil and Agri-Food Engineering Department, Laval University, 2480 Hochelaga Blvd., Quebec City, QC G1V 0A6, Canada; alexis.gloutney.1@ulaval.ca (A.G.); jean.caron@fsaa.ulaval.ca (J.C.) **\*** Correspondence: jacynthe.dessureault-rompre@fsaa.ulaval.ca

**Abstract:** Few conservation strategies have been applied to cultivated peatland. This field study over one growth cycle of *Lactuca sativa* examined the effect of plant-based, high-C/N-ratio amendments in a real farming situation on peatland. Plant Root Simulator (PRS®) probes were used directly in the field to assess the impacts of incorporating *Miscanthus x giganteus* straw and *Salix miyabeana* chips on nutrient availability for lettuce. The results showed that lettuce yield decreased by 35% in the miscanthus straw treatment and by 14% in the willow chip treatment. In addition, the nitrogen flux rate was severely reduced during crop growth (75% reduction) and the plant N uptake index was much lower in the amended treatments than in the control. The phosphorus supply rate was also significantly lower (24% reduction) in the willow treatment. The influence of sampling zone was significant as well, with most macro-nutrients being depleted in the root zone and most micronutrients being mobilized. Additional work is needed to optimize the proposed conservation strategy and investigate the effects of consecutive years of soil amendment on different vegetable crops and in different types of cultivated peatlands to confirm and generalize the findings of this study. Future field studies should also explore the long-term carbon dynamics under plant-based, high-C/N-ratio amendments to determine if they can offset annual C losses.

**Keywords:** nitrogen; miscanthus; willow; field experiment; lettuce; plant-based amendment; rhizosphere
