Nursery root treatment, root geometry, and young tree stability of Pinus radiata

"Toppling" or juvenile instability, and subsequent stem sinuosity and "butt sweep" cause serious economic and management problems in young Pinus radiata plantations in New Zealand. Root morphology has been shown to be one of the factors associated with toppling. A randomised complete block experiment with ten replications was established on fertile Waiotira clay soils in Northland (Grid Reference Q07 193.855) each year for three years to test a range of nursery root treatments and measure biomass increments and stability in two plant stock types. The plant stock types were seedlings (standard nursery root treatment, super trim, box pruned and root trainer grown), and cuttings with a physiological age of five years (standard nursery root treatment and box pruned) The seedlings and aged cuttings were considered to have equivalent Growth and Form Rating (GF) in each year, although the GF rating of the plant stock increased each year. This study has established that nursery root treatments modify pre-planting root geometry and weight. At 12 months treatment differences were only significant in vertical root number and quadrant 1 lateral root number. A significant treatment*toppling interaction was found in vertical root number, and a significant toppling effect found in vertical root number and root/shoot ratio. Root number was more important than other factors in toppling frequency, and toppling direction was associated with wind direction. At 24 months there were significant effects in treatment*toppling relating to quadrant 4 lateral root number, and calculated vertical root weight. Significant toppling effect was found in root/shoot ratio, and many factors relating to root basal area index and root weight. Significant treatment effects were found in root/shoot ratio, all above ground weights, and many root factors relating to root basal area index, lateral root weights and stump weight. Stability was associated with a high root/shoot ratio, high root basal area index and high root weights. This paper details the results from the first year's planting, as well as noting superior stability of cuttings compared to seedlings on this fertile farm site in all three years.