Nitrogen Relations in a Douglas-fir Plantation

A 42-year-old Western Washington Douglas-fir Pseudotsuga menziessii(Mirb.) Franco] plantation which was N-deficient was studiedin relation to the application of N applied as urea to the forestfloor, and carbohydrate applied to the forest floor to widenthe C/N ratio and thus intensify the existing N deficiency.After 1 year, needle size was measured and needles were alsoanalyzed for pigment content N, P, K, Ca, Mg, and Mn. As a resultof N fertilization needle size and weight had increased. Needleretention (years) was increased in the N treatments and reducedin the carbohydrates treatments. This effect was reflected inthe quantities of leaf litter-fall. Nitrogen concentrationswere increased in treatments where N was applied as were pigmentcontents but other nutrients decreased in concentration probablyas a result of growth dilution. While there was no significantdecrease in needle N concentration where carbohydrate was applied,the N uptake was reduced because of needlesize and retentiontimechanges. The results are discussed in relation to nutrientdiagnostic work.