Projected long-term productivity in Saskatchewan hybrid poplar plantations: weed competition and fertilizer effects
2007
Welham, C. | Van Rees, K. | Seely, B. | Kimmins, H.
An ecosystem management model was used to project total aboveground and belowground production in hybrid poplar plantations for two sites in Saskatchewan that were previously in agricultural production and that differed in their soil organic matter and nitrogen content (categorized as poor and rich sites). Stemwood production (the primary measure of treatment response) was always negatively affected by the competition that resulted when weeds were abundant; the effect was more severe on the poor than on the rich site. Stemwood biomass was greater when weed competition was low, but peak production declined over successive rotations on both sites, regardless of whether fertilizer was used. Fertilization always enhanced stemwood production but less so on the rich than on the poor site. A single fertilizer application in the second or seventh year after plantation establishment resulted in consistently higher stemwood production than midrotation fertilization (year 12). Fertilization was more beneficial to stemwood production when weed competition was high than when it was low. Low weed competition in conjunction with early fertilization produced the highest stemwood production. The simulations indicate that the relative benefit of a given management regime cannot be considered independently of the site nutrient status and the particular rotation.
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