Effects of Nitrogen Fertilizer on the Growth and Development of Ceanothus velutinus1

Snowbrush ceanothus ( Ceanothus velutinus Dougl. Ex Hook.) is an evergreen shrub with dark green leaves and creamy white flowers. It is a nitrogen-fixing species that enhances soil fertility through nodulation. This study evaluates the effects of various nitrogen concentrations on the growth and development of C. velutinus . Seedlings transplanted into calcined clay and inoculated with 30 mL of soil containing the nitrogen-fixing actinobacteria Frankia were treated with 0.0 to 8.4 g·L −1 of controlled released fertilizer (CRF, 15N-3.9P-10K) or a nitrogen-limited nutrient solution with or without 2mM ammonium nitrate (NH 4 NO 3 ). Plant growth and photosynthesis increased linearly or quadratically with increasing CRF application rates. Visual score, plant growth index, number of shoots, leaf area, SPAD, leaf and root dry weights, and net photosynthetic rate of inoculated plants treated with 2.1 g·L −1 of CRF were similar to those of uninoculated or plants grown in autoclaved native soil and treated with the manufacturer-recommended application rate of 3.2 g·L −1 of CRF. Nodules were observed only in plants receiving 0.0, 0.3, 0.5, 1.1, or 2.1 g·L −1 of CRF, and the number of nodules were too small to analyze statistically. The study indicates that CRF significantly boosts C. velutinus growth and development. However, the nodulation of the plant and nitrogen-fixing capacity of the nodules remain unknown. Further investigation is needed to determine the effect of nitrogen on the nodulation of C. velutinus . Species used in this study: Ceanothus velutinus Dougl. Ex Hook., Frankia sp .