Late-season fertilization of Picea mariana seedlings under greenhouse culture: Biomass and nutrient dynamics

Abstract

Conventional nursery culture of containerized black spruce (Picea mariana Mill. B.S.P.) seedlings usually involves a late-season interval, commonly called the "hardening period", when fertilization and water are withheld to promote frost-hardiness. Considerable growth may occur during this time which may lead to internal nutrient dilution, a condition often detrimental to subsequent field performance. Continued late season fertilization (at 6 or 12 mg N seedling-1) of seedlings during the hardening period was tested as a technique to prevent late season nutrient dilution and possibly to increase nutrient reserves. Root growth was increased much more than shoot growth during this period. Late-season fertilization raised N, P and K uptake as much as 164, 70 and 32% respectively, compared to conventionally fertilized seedlings with no late-season fertilization. Depending on dose rate and pre-hardening nutrient loading, this technique demonstrates the potential to build internal nutrient reserves in seedlings. Nutrient dilution was temporarily averted by late-season fertilization suggesting that intensive and prolonged nutrient supplementation during the hardening period may further delay or eliminate nutrient dilution in seedlings.