Effect of Irrigation and Nitrogen Fertilization On Growth and Foliar Chemistry of Abies Fraseri (Pursh) Poir. Grown In Containers

A two year greenhouse study was established to investigate the effect of irrigation and nitrogen fertilization on the growth and foliar chemistry of Abies fraseri (Pursh) Poir. The experimental setup was a factorial design with 4 irrigation levels (0.625, 1.25, 2.50 and 3.75 cm/week) and 3 fertilization levels (28, 56, and 112 kg/ha). Fertilizers were applied as top dress and weekly irrigation water divided into daily ration applied to each container 5 days a week. Parameters measured included morphological characteristics such as relative height growth (RHG), stem diameter growth (SDG), and leader bud density (LBD), and foliar nutrient content. Biomass partitioning response to the various treatments was also evaluated. In addition, a statistical numerical optimization was used to determine the optimal level necessary for each factor to achieve a simulated target response for morphological response and foliar nutrient content. After two years, the RGH response was significantly affected by irrigation in 2007 and 2008 (P=0.000) and by fertilization (P=0.02 and P=0.03), but the interaction between the two variables was not statistically significant (P=0.579 and P=0.465).  SDG positively responded to irrigation for both years (P=0.003 and P=0.000). The SDG response to fertilization was statistically significant in 2007 (P=0.016), but not significant in 2008 (P=0.071). The interaction between fertilization and irrigation was not significant for both 2007 and 2008. LBD data was statistically significant in 2007, but not significant in 2008. Biomass accumulation in roots was not significantly affected by fertilization and irrigation, however, stem and needle biomass positively responded to irrigation and fertilization. Needle nitrogen content was positively affected by nitrogen fertilization and negatively affected by irrigation. The statistical numerical optimization showed that for the target height growth of 10 cm/year, the combination of 3.75 cm/week irrigation and 28 kg/ha fertilization will be effective with a desirability factor of 91.0%. These results suggest that in difficult economic times, Fraser fir growers can achieve acceptable production goals with reduced fertilization applications and optimal irrigation.