Nitrogen mineralization in short-rotation tree plantations along a soil nitrogen gradient

Abstract

We measured soil nitrogen (N) mineralization along an N fertilization gradient (control; irrigation only (I + 0 N); irrigation with 56 (I + 56 N), 112 (I + 112 N), and 224 (I + 224 N) kg N·ha–1·year–1, respectively) in 7-year-old cottonwood (Populus deltoides Marsh.), cherrybark oak (Quercus falcata Michx. var. pagodifolia Ell.), American sycamore (Platanus occidentalis L.), and loblolly pine (Pinus taeda L.) plantations established on a well-drained Redbay sandy loam (a fine loamy, siliceous, thermic Rhodic Paleudult), in Florida, USA. Nitrogen mineralization was measured monthly for 1 year, beginning in April 2001, with the buried bag incubation technique. Irrigation alone or fertigation (irrigation + N) affected annual net N mineralization rates under hardwood species, but no effect was found under loblolly pine. Overall, the rates were higher under cherrybark oak (108 kg N·ha–1·year–1) and cottonwood (101 kg N·ha–1·year–1) than under sycamore (82 kg N·ha–1·year–1) and loblolly pine (75 kg N·ha–1·year–1). Significant correlations were observed between N mineralization and stem volume in all species but loblolly pine. These results suggest that N mineralization response to irrigation or fertigation (irrigation + N) is heavily dependent on species-specific feedback mechanisms. Our results also support the hypothesis that the N mineralization versus productivity relationship is a fundamental feature of forests, resulting from the impact of N availability on productivity and the long-term feedback effects of vegetation on N availability.

Functional groups show distinct differences in nitrogen cycling during early stand development: implications for forest management

“…Calculating the proportion of fertilizer N acquired, or FUE, requires quantification of N AV based on both the amount of N applied via fertilization and N MIN . Although the actual amount of N MIN was unknown, the use of paired fertilized and non-fertilized plot N UP provided approximations of N MIN rates that are comparable to those found by others in the region (Lee and Jose 2006;Gurlevik et al 2004). Mineralization following fertilization can be higher (Connell et al 1995) or lower (Johnson et al 1980), and can depend on the forest type (Lee and Jose 2006), so the magnitude of mineralized N available in fertilized plots was only approximated and some inconsistencies exist.…”

“…Although the actual amount of N MIN was unknown, the use of paired fertilized and non-fertilized plot N UP provided approximations of N MIN rates that are comparable to those found by others in the region (Lee and Jose 2006;Gurlevik et al 2004). Mineralization following fertilization can be higher (Connell et al 1995) or lower (Johnson et al 1980), and can depend on the forest type (Lee and Jose 2006), so the magnitude of mineralized N available in fertilized plots was only approximated and some inconsistencies exist. Both N UP and NPP were positively influenced by irrigation, but the lack of an irrigation effect on FUE suggests that, although more N may have been available with irrigation, the amount that could be acquired was not influenced.…”

Mid-Rotation Silviculture Timing Influences Nitrogen Mineralization of Loblolly Pine Plantations in the Mid-South USA

“…The 81 kg·ha −1 annual Nmin mean of the CONTROL treatment in this study was similar to the 75 kg·ha −1 annual Nmin reported for a 7-year-old loblolly pine plantation in Florida, USA on sandy loam soil [33]. The 81 to 146 kg·ha −1 annual Nmin range of this study was somewhat higher than the 22 to 96 kg·ha −1 annual Nmin range for a 14-year-old loblolly pine plantation in North Carolina, USA on a highly weathered, eroded clay loam receiving fertilizer and herbicide [2].…”

“…The increases in soil NO3-N and the NO3:exchangeable N ratio at the Lucky site and the increases in soil NO3-N at the Dodson in response to FERTVS treatment conducted post-thinning suggest that this treatment exceeded stand N demand. These results show that avoiding fertilization preor post-thinning at an N-sufficient site and applying herbicide in the year of thinning and fertilization at the range of site conditions in this study could minimize NO3-N concentration increases, which can help in reducing N leaching loss potential and improving fertilizer use efficiency [33].…”

Nitrogen dynamics and soil nitrate retention in a Coffea arabica—Eucalyptus deglupta agroforestry system in Southern Costa Rica

“…The measured annual N mineralization (280 kg N ha À1 yr À1 ) was much higher than N fertilization in 2002 but part of this mineralized N may have been derived from previous microbial immobilisation of chemical N fertilizer. Positive fertilizer-mineralization interactions were reported by Kolberg et al (1999) for cropping systems and by Lee and Jose (2006) for tree plantations. The method used, although adequate to compare adjacent plots, may over-estimate absolute values because roots are cut (Jussy et al 2004).…”