Amino Acid Fertilization of Fraser Fir (Abies fraseri), Red Pine (Pinus resinosa), and Hybrid Poplar: Effect on Foliar Chemistry and Nutrient Dynamics

Plants have the ability to assimilate and use amino acids as a nitrogen source.  This process has been identified in plants growing in boreal, alpine tundra, arctic, and temperate ecosystems in addition to controlled environments where plants are grown in containers.  This principle has seldom been tested in a field production setting, although it has been shown that agricultural plants can utilize amino acids.  This two-year study (2009–2010) evaluates the effects of amino acid fertilization on the foliar chemistry of two conifer seedlings—Fraser fir (Abies fraseri) and Red pine (Pinus resinosa)—and one hardwood (hybrid poplar) and the nutrient dynamics in a these short rotation tree production system.  The amino acid fertilizer used, arGrow complete®, contains arginine and other plant essential macro- and micronutrients, and was applied at varying rates (0, 50, 100, 200, and 300 lbs N/acre).  Granular ammonium sulfate (21% N) was applied to positive control treatments at a rate of 100 lbs N/acre.  Foliar nutrient concentrations (N, P, K, Ca, Mg, and Mn) were monitored at the beginning and end of the growing season in both years of the study. Soil exchangeable cation concentration (K, Ca, and Mg) was determined at the beginning and end of the growing season in 2010 by ammonium acetate extraction.   Lysimeters were installed prior to beginning the study, and cation nutrient losses (N, K, Ca, and Mg) through the rootzone were quantified weekly during both growing seasons. In both growing seasons, Ca and Mg content in leachate of A. fraseri treatments was significantly greater in ammonium sulfate treatments.  This trend was observed for P. resinosa treatments only for Ca in 2010.  Treatment had no effect on cation leaching in hybrid poplar plots, probably due to charge balances in the soil as a result of nitrate leaching.  Soil exchangeable cation concentrations were statistically similar in May and in August among treatments for all species, with the exception of reduced Mg in ammonium sulfate hybrid poplar treatments, which was likely due nutrient limitations. Overall amino acid fertilization had a more significant effect on foliar nutrient concentrations in the first year of the study, and the less prominent effect in the second year was suggested to be due to competition with non-target organisms for nutrients when trees were establishing in field soils.