E.F. Gilman, T.H. Yeager and D. Kent
Fertilizer rate and type impacts magnolia and oak growth in sandy landscape soil
Journal of Arboriculture 26(3): 177-182
Southern magnolia (Magnolia grandiflora) planted as 3-liter (1 gal) liners into sandy soil did not respond to nitrogen applications above 20 g N/m2 (4.2 lbs N/1000 ft2)/year the first two years after planting. The 40 g N/m2 (8.3 lb N/1000 ft2)/year rate resulted in greater height than the 20 g (4.2 lb) rate in the third year and greater height and trunk diameter the fourth year after planting. N rates greater than 40 g N/m2 did not result in more growth. Seedling magnolia and 10-13 cm (4-5 in) caliper field-grown live oak (Quercus virginiana) trees receiving nitrogen soon after transplanting responded the first year of application by growing faster than those that received no nitrogen. Nitrogen source had little impact on growth or tissue nitrogen concentration (1.4%) of 10-13 cm (4-5 in) caliper live oak in the first three years after field transplanting, and there was no N source effect on root extension from the trunk. All fertilizers containing nitrogen promoted growth. Nitrogen applications increased trunk growth on 23 cm (9 in) caliper live oak beginning about 16 months after transplanting with a tree spade. Potassium and/or phosphorus, when applied in conjunction with nitrogen, had no effect on growth.