Effets de différentes régies d'irrigation sur la croissance, la nutrition minérale et le lessivage des éléments nutritifs des semis d'épinette noire (1+0) produits en récipients à parois ajourées en pépinière forestière

To reduce the quantity of irrigation water used and the amount of mineral nutrients lost because of leaching, we used time domain reflectometry to monitor and maintain four irrigation regimes (15, 30, 45 and 60%, v/v) during the first growing season for 1+0 black spruce (Picea mariana (Mill.) BSP) seedlings. The seedlings were produced in air-slit containers (IPL 25-350A), filled with a peat substrate and were grown under a polyethylene tunnel at a forest nursery. Similar fertility levels were maintained in all four irrigation regimes even though the water content of the sub- strate could be very low (15 and 30%). Irrigation regime did not affect growth, root architecture or tissue nutrient con- tents at the end of the growing season. Monitoring water use over the course of the growing season clearly showed that the amount of irrigation water could be reduced by 62 to 76% without compromising seedling quality relative to the 60% irrigation regime. Leachate losses varied exponentially as a function of irrigation regime. The mean amount of water leached, relative to the quantity of water applied during the sampling period, was 10, 7.1, 28.4, and 62.2% for the 15, 30, 45, and 60% irrigation regimes, respectively. The losses of mineral nitrogen at the beginning of August were 49.7, 35.9, 55.2, and 88.2%, respectively, for the 15, 30, 45, and 60% irrigation regimes. To optimize irrigation and decrease leaching, a dynamic model for irrigation management is proposed that accounts for the phenological de- velopment of black spruce seedlings grown under tunnel conditions in forest nurseries.