Factors influencing the availability of nitrogen in thinned and unthinned Douglas-fir stands in the central Oregon Cascades

Soil N mineralized during 7-day anaerobic incubation at 40 degrees C ('available' N) was compared at two soil depths and correlated to soil and site factors in Douglas-fir stands with different combinations of thinning and multinutrient fertilization. Available N expressed either on an area basis (kg ha(-1)) or on a concentration basis (mg kg-l) at the two depths did not vary significantly by stocking density, treatment, or density-treatment interaction. There was a significant difference between the soil depths, averaging 39 mg kg(-1) at 0-20 cm depth, and 20 mg kg(-1) at 20-40 cm depth. Available N was positively correlated with total soil N, exchangeable Ca, and adjusted aspect (the former two factors accounting for 46% of the total variation), and negatively with rock content and slope steepness. Stand density had no effect. (C) 1997 Elsevier Science B.V.