Timothy J. Albaugh (1, 2), H. Lee Allen (1) and Thomas R. Fox (3)
1. Department of Forestry and Environmental Resources, Box 8008, North Carolina State University, Raleigh, NC 27695-8008, USA / 2. Corresponding author () / 3. Department of Forestry, 228 Cheatham Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA / Received June 25, 2007; accepted August 28, 2007; published online May 1, 2008
Summary
We quantified nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) content, use (nutrient amount for
one growth year), retranslocation (nutrients recycled before foliage senescence), uptake (use minus retranslocation), volume
production per unit of uptake and fertilizer-uptake efficiency (percent applied taken up) in a 2 × 2 (nutrient and water)
factorial experiment replicated four times in an 8-year-old loblolly pine (Pinus taeda L.) stand growing on a nutrient-poor sandy soil in Scotland County, North Carolina, USA. Over 14 years, we applied 1140,
168, 393, 168 and 146 kg ha–1 of elemental N, P, K, Ca and Mg fertilizer, respectively, and an average of 710 mm year–1 of irrigation. All plots received complete vegetation control. Fertilization about doubled tissue N, P, K and Mg contents
at age 21, whereas irrigation resulted in smaller increases in nutrient contents. Maximum annual uptake was 101, 9.3, 44,
37 and 13 kg ha–1 year–1 and volume production per unit of nutrient uptake was 0.35, 3.5, 0.66, 1.1 and 3.1 m3 kg–1, for N, P, K, Ca and Mg, respectively. Irrigated plots had greater volume production per unit of N, P, K and Mg uptake than
control plots, likely because irrigation allowed photosynthesis to continue during dry periods. Fertilized plus irrigated
plots had less volume production per unit of these elements than the fertilized plots either because nutrient uptake exceeded
the requirement for optimum growth or because available water (rainfall plus irrigation) was insufficient for the leaf area
achieved with fertilization. At age 19, fertilizer-uptake efficiencies for N, P, K, Ca and Mg were 53, 24, 62, 57 and 39%,
respectively, and increased with irrigation to 68, 36, 78, 116 and 55%, respectively. The scale of fertilizer uptake was
likely a result of low native site nutrient availability, study longevity, measurement of all tissue components on site, a
comprehensive assessment of coarse roots, and the 3-m rooting depth. Ecosystem nitrogen retention (applied nitrogen found
in living plant material, litter fall and soil to 150-cm depth) was estimated at 79% at age 17, a value that would likely
be greater when including soil nitrogen to rooting depth and calculating retention at age 21 when the study ended. The ecosystem
retention value provides evidence that intensive site resource management can be accomplished with low likelihood of applied
materials moving offsite.
Keywords:
fertilizer efficiency, leaf area index, volume production.
