Evaluation of a mini-container, accelerated transplant system : the black spruce summer crop

Abstract

The production of black spruce ( Picea mariana (Mill.) B.S.P.) bare root stock in Ontario nurseries presents two main problems. First, seedlings at the end of the first growing season are small, and thus susceptible to frost heaving. Second, it takes a long time, 3 years, to produce shippable seedlings. Trying to solve these problems the Ministry of Natural Resources Thunder Bay Nursery is testing an accelerated transplant system. Seedlings are sown in a greenhouse in a mini-container and after 10 weeks are transplanted outdoors for two growing seasons. There is a winter and a summer crop from the greenhouse each year. The objective of this paper was to evaluate the effect of 3 factors on summer crop seedlings. The 3 factors were SOWING DATE (levels: July 5, 15, 25, and August 4), the duration of an initial 18-h LONG DAY treatment (levels: 7, 10, or 13 weeks), and the duration of a subsequent 8-h SHORT DAY treatment (levels 0, 6, or 12 days). Finally, all seedlings were held under natural photoperiod until the total length of the SHORT DAY and natural photoperiod treatments was 11 weeks. Bud initiation was monitored during this 11 week period. Bud diameter, number of primordia, basal caliper, and root dry weight were measured immediately prior to placing the seedlings in cold storage for the winter. LONG DAY was the most important factor. Seedlings that received the ten-week LONG DAY treatment gave the best response. Even though 13-week LONG DAY seedlings were significantly taller, 10-week specimens showed a similar bud diameter and basal caliper, as well as a significantly heavier root dry weight, and more primordia. Eventually, the containers were too small for 13-week LONG DAY seedlings that showed a potbound situation. Although there were some significant differences, the various levels of the factors SOWING DATE and SHORT DAY did not produce any considerable effect on the growing regime. At the end of the first growing season in nursery beds, seedlings from the best treatment combinations of the summer crop reached almost a shippable size. This confirms the feasibility of the studied system to produce bare root stock in two years or less.