White spruce establishment: initial fertilization,weed control,and irrigation evaluated after three decades

Outplantings of white spruce (Picea glauca Moench] Voss) in a factorial experiment in 1962 (P62) and 1963 (P63), near Ottawa, Ontario, addressed the problem of prolonged unsatisfactory growth of outplanted white spruce, a condition commonly termed check. Applied in the first 2 growing seasons, the treatments (3 levels of nitrogenous fertilization ×± weed control ×± irrigation) subjected the trees to differential fertility and soil moisture on each of three soils (clay, loam, and sand). There were 5 (P62) and 6 (P63) replications of 9-tree plots. The P62 Loam planting was destroyed by fire in 1966. Initial survival in the P63 Clay was too low to warrant long-term monitoring. Monitoring of the P62 Clay planting was discontinued after 20 years when it was clear that site factors unrelated to the experimental treatments were controlling stand development. After 30 growing seasons in the P62 Sand and 29 growing seasons in the P63 Sand and P63 Loam plantings, neither initial nitrogenous fertilization nor initial irrigation was influencing performance, but on all three sites the positive effect of initial weed control remained significant (P<0.001).