Cumulative index of water stress intensity as control parameter of irrigation in Sphagnum Farming

Peatlands around the world have been drained to facilitate urbanization, agriculture, forestry and peat extraction. About peat extraction, it is harvested to be used in combustion or as a substrate for the greenhouse and nursery industry. Nevertheless, peatland drainage results in emissions of carbon dioxide and nitrous oxide of more than 2 Gt CO2-eq yr-1. Sphagnum biomass is an alternative to use these zones after peat extraction, producing an interesting substrate, already used in the biofilters construction, seedling substrate, among others. To promote the growth of this non-vascular plant, it is necessary to maintain the water table stable and close the soil surface. The objective of this presentation is to show the implemented irrigation system coupled with water table measurements to limit water table fluctuation in the sphagnum farm site. This project used the available data from the sphagnum culture project in partnership with Laval University. The available data (groundwater level and biomass harvested per year) relate to 2,3 and 4 years of culture. Index of water stress (SEW) was calculated as sum of the distance from the reference depth (RD) to the water table on each day that the water table was deeper than RD. SEW includes not only the duration of wet conditions, but the optimal depth of the water table for growing. RD was determinate using the coefficient R2 as indicator evaluator to describe the relationship between the SEW and biomass accumulation. In this case RD=20 cm (R2=-0,69) was obtained.