Abstract
Intensively managed forest plantations often require fertilization to maintain site fertility and to improve growth and yield over successive rotations. We applied urea-based “enhanced-efficiency fertilizers” (EEF) containing 0.5 atom% 15N at a rate of 224 kg N ha−1 to soils under mid-rotation black walnut (Juglans nigra L.) plantations to track the fate of applied 15N within aboveground ecosystem components during the 12-month period after application. Treatments included Agrotain Ultra (urea coated with a urease inhibitor), Arborite EC (urea coated with water-soluble boron and phosphate), Agrium ESN (polymer-coated urea), uncoated urea, and an unfertilized control. Agrotain Ultra and Arborite EC increased N concentrations of competing vegetation within one month after fertilization, while neither Agrium ESN nor uncoated urea had any effect on competing vegetation N concentrations during the experiment. Agrotain Ultra and Arborite EC increased δ15N values in leaves of crop trees above those of controls at one and two months after fertilization, respectively. By contrast, Agrium ESN and uncoated urea had no effect on δ15N values in leaves of crop trees until three months after fertilization. Fertilizer N recovery (FNR) varied among ecosystem components, with competing vegetation acting as a sink for applied nutrients. There were no significant differences in FNR for all the urea-based EEF products compared to uncoated urea. Agrium ESN was the only EEF that exhibited controlled-release activity in this study, with other fertilizers behaving similarly to uncoated urea.
Highlights
Black walnut (Juglans nigra L.) is the highest value tree species in the continentalUnited States [1], and it typically occurs as a minor component of mixed deciduous forests in central and eastern parts of the U.S [2]
Black walnut leaf dry mass was affected by fertilizer treatment (p = 0.0384) and time (p < 0.0001; Tables 1–3)
Crop tree leaf area was not affected by fertilizer treatment (p = 0.0710; Tables 1 and 2), it was influenced by time (p < 0.0001; Tables 1 and 3)
Summary
Black walnut (Juglans nigra L.) is the highest value tree species in the continentalUnited States [1], and it typically occurs as a minor component of mixed deciduous forests in central and eastern parts of the U.S [2]. Black walnut (Juglans nigra L.) is the highest value tree species in the continental. The demand for high quality hardwoods, such as black walnut, that are used in fine furniture, cabinetry, gunstocks, paneling, and specialty crafts has been increasing dramatically. Due to its high value, black walnut has been routinely harvested from natural forests, causing depletions in the supply of quality trees. Only about 5585 ha of black walnut plantations exist in the U.S (representing about 1% of total black walnut cubic foot volume in the U.S.) [5], plantation area is rapidly increasing. In Indiana, which is centrally located within black walnut’s native range, 2400–3200 ha of trees are planted every year and black walnut represents about 18% of planted trees [6]
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