Predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir

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Abstract
The mineralization potential of forest soils is a useful tool in predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir. As the mineralization potential of the soil increased, diameter growth for 200 lbs/A of added N decreased. Significant growth response could not be detected when mineralizable nitrogen level was above 46 ppm. Percent stocking is also an important variable in predicting diameter growth response in these stands. For a given nitrogen level, response decreased with increasing stocking. When stocking and mineralizable nitrogen are used together, they account for a significant portion (86%) of the variation in growth response.