Ten-year growth and nutrition effects of a straw treatment and of repeated fertilization on jack pine

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Abstract
Straw was added over snow to smother ground vegetation (straw experiment) in sample plots in a 45-year-old jack pine (Pinusbanksiana Lamb.) stand in Quebec. Sample plots in the same stand were fertilized six times with N, P, and K in a 10-year period to maintain four foliar N regimes (optimum nutrition experiment). Smothering of ground vegetation with straw improved N nutrition and produced a sustained increase in tree growth. Sustained growth increases were obtained by repeated applications of 56 kg N/ha associated with 1.4% N foliar concentrations in current foliage. Gross volume increments of about 3 m3 • ha−1 • year−1 were sustained with these low applications. Repeated heavy N applications killed trees and reduced growth. Repeated additions of P and K with N did not produce appreciable differences in response from additions of N alone. Increment cores showed the annual development in growth as increasing over most of the 10-year period for low repeated N additions, and as increased and stable over the same period for the straw addition.

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