Sweetgum half-sib seed source response to nitrogen and phosphorus fertilization in Mississippi
1990
Nelson, L.E. | Switzer, G.L.
This field experiment was undertaken to determine the response to N and P of sweetgum (Liquidambar styraciflua L.) under plantation culture, and the variation in response among seedlings derived from four half-sib seed sources from alluvial and upland sites. Two-year-old seedlings were planted in a Mathiston silt loam (fine-silty, siliceous, acid, thermic Aeric Fluvaquent) in 1972. In 1973, 0-0-0, 100-0-0, 100-100-0, and 200-100-0 kg/ha of N-P-K were broadcast. In 1975, the N treatments were repeated. Height, diameter at breast height (DBH), and foliar N were monitored through nine field growing seasons. There was no response to P. At 9 yr, the mean total height of the unfertilized half-sibs was 7.1 m, mean DBH was 7.8 cm, basal area was 5.0 m2/ha, stem volume outside bark was 15 m3/ha, and woody biomass was 8.1 Mg/ha. Increases from fertilization were 9, 14, 28, 39, and 40%, respectively. There was a half-sib X fertility interaction with maximum response of three half-sibs to 200 kg N/ha and one to 400 kg N/ha. The response of the two half-sibs from alluvial seed sources was about double that of the two from upland seed sources. Foliar N concentrations of all treatments decreased during the 9 yr; however, foliar concentrations in fertilized trees were only slightly higher than in the unfertilized throughout. Although increases in annual increments due to fertilization were measurable for only 1 or 2 yr following fertilization, the resulting differences in volume and biomass were maintained in subsequent years.
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