Abstract
This study was conducted to determine the efficacy of using enhanced efficiency fertilizer (EEFs) products compared to urea to improve fertilizer nitrogen use efficiency (FNUE) in forest plantations. All fertilizer treatments were labeled with 15N (0.5 atom percent) and applied to 100 m2 circular plots at 12 loblolly pine stands (Pinus taeda L.) across the southeastern United States. Total fertilizer N recovery for fertilizer treatments was determined by sampling all primary ecosystem components and using a mass balance calculation. Significantly more fertilizer N was recovered for all EEFs compared to urea, but there were generally no differences among EEFs. The total fertilizer N ecosystem recovery ranged from 81.9% to 84.2% for EEFs compared to 65.2% for urea. The largest amount of fertilizer N recovered for all treatments was in the loblolly pine trees (EEFs: 38.5%–49.9%, urea: 34.8%) and soil (EEFs: 30.6%–38.8%, urea: 28.4%). This research indicates that a greater ecosystem fertilizer N recovery for EEFs compared to urea in southeastern pine plantations can potentially lead to increased FNUE in these systems.
Highlights
Pine (Pinus taeda L.) is the most widely planted and commercially valuable tree species in the United States [1,2], with large areas in the southeastern United States managed intensively in plantations
The fine branch N concentrations increased from the control (5.1 ± 0.3 g·kg−1 ) to CUF (7.3 ± 0.6 g·kg−1 ) and NBPT (6.7 ± 0.3 g·kg−1 ), while the coarse branch N concentration increased between the control (2.8 ± 0.2 g·kg−1 ) to urea (3.9 ± 0.4 g·kg−1 )
The N concentration of the bark increased between the control (2.1 ± 0.2 g·kg−1 ) and NBPT (2.9 ± 0.1 g·kg−1 ), while the N concentration for the growth ring for the year after fertilization (CGR) increased from 1.8 ± 0.1 g·kg−1 for the control to between 2.3 ± 0.1 g·kg−1 and 2.7 ± 0.1 g·kg−1 for all fertilizer treatments
Summary
Pine (Pinus taeda L.) is the most widely planted and commercially valuable tree species in the United States [1,2], with large areas in the southeastern United States managed intensively in plantations. Loblolly pine stemwood can exceed 10 m3 ·ha−1 ·year−1 in intensively managed plantations [3], growth of many stands is less due to low levels of plant available nitrogen (N) and phosphorous (P) in the soil [4,5]. Temporal patterns in N availability often lead to N deficiencies developing during later parts of the rotation [3,11,12]. Following disturbance, such as harvesting, plant N availability in the soil is high due to N mineralization of organic matter [13,14]. The average growth response in mid-rotation southeastern pine plantations averages
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