Management of Ponderosa Pine Nutrition Through Fertilization 1

The results of a series of replicated fertilization trials established throughout the Inland Northwest were reviewed for information specific to ponderosa pine (Pinus ponderosa P. and C. Lawson) nutrition. Ponderosa pine nitrogen (N) status was often better than the N-status of other Inland Northwest species, and therefore growth response to N fertilization was often lower than that of other species. Fertilization of ponderosa pine with N alone sometimes appeared to cause increased tree susceptibility to mortality by insect, disease and perhaps abiotic stresses. Growth and mortality response to N fertilization appeared to be related to foliage potassium (K)/N ratio in some cases. The application of K and micronutrients in combination with N may have protected the trees from N-related mortality while stimulating a growth response. Sulfur fertilization was not found to evoke a growth response in ponderosa pine, and may have increased mortality rates slightly. On certain rock types and vegetation series, ponderosa pine showed high growth response to macronutrient plus micronutrient fertilization as well as herbicide treatment. Ponderosa pine generally did not show a strong growth response to N fertilization, except on ‘good ’ rock types on moist sites. Multinutrient (macro- plus micronutrient) fertilization combined with an herbicide treatment often provided a better response than N alone on moderate to dry sites and/or ‘bad ’ rock types. Other species in mixed-conifer stands, particularly grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), often showed a better growth response to fertilization than ponderosa pine. The nutritional ecology of ponderosa pine is unique among Inland forest tree species and should be considered when evaluating nutrient management options