Exponential Nutrient Loading as a Means to Optimize Bareroot Nursery Fertility of Oak Species

Abstract

Conventional fertilization in nursery culture of hardwoods may involve supply of equal fertilizer doses at regularly spaced intervals during the growing season, which may create a surplus of available nutrients in the beginning and a deficiency in nutrient availability by the end of the growing season. A method of fertilization termed “exponential nutrient loading” has been successfully used in propagation of several conifer species, but this technique has not been tested in hardwood culture. By supplying fertilizer nutrients in an exponential manner, nutrient supply more closely matches plant nutrient demand, which may improve fertilizer uptake and use efficiency. The amount of fertilizer needed to maximize nutrient reserves and growth before inducing toxicity is termed the “optimum” nutrient loading level. Because optimum levels have not been established for hardwoods, we examined the response of northern red oak (Quercus rubra) and white oak (Q. alba) to a range of nutrient loading treatments at a bareroot nursery in Indiana. Ammonium nitrate was applied at rates ranging from 0X to 4X the current conventional rate. Seedling morphological and nutritional parameters exhibited responses consistent with the conceptual model for nutrient loading depicting points of deficiency, sufficiency, luxury consumption, and toxicity. Maximum seedling biomass production occurred at 1.0X the current seasonal rate, establishing the sufficiency level. Maximum nitrogen (N) content in seedling tissues peaked at 2.0X the current seasonal rate reflecting the optimum loading rate. Toxicity occurred at 3.0X the current seasonal rate and above, which increased tissue N concentration, but reduced dry mass and N content. This type of analysis may assist nurseries in refining fertilization practices and producing high quality seedlings for outplanting.

Parent Publication

• National Proceedings: Forest and Conservation Nursery Associations-2005

Citation

Birge, Zonda K. D.; Jacobs, Douglass F.; Salifu, Francis K. 2006. Exponential Nutrient Loading as a Means to Optimize Bareroot Nursery Fertility of Oak Species. In: Riley, L.E.; Dumroese, R.K.; Landis, T.D., tech. coords. 2006. National Proceedings: Forest and Conservation Nursery Associations - 2005. Proc. RMRS-P-43. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 147-151