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, treatm ent, or density-treatment interaction. There was a significant differe nce 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 correla ted with total soil N, exchangeable Ca, and adjusted aspect (the forme r two factors accounting for 46% of the total variation), and negative ly with rock content and slope steepness. Stand density had no effect. (C) 1997 Elsevier Science B.V.