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21.
Carbon,nitrogen and phosphorus leaching after site preparation at a boreal forest clear-cut area 总被引:1,自引:0,他引:1
Clear-cutting followed by mechanical site preparation is the major disturbance influencing nutrient and water fluxes in Fennoscandian boreal forests. The effects of soil harrowing on the fluxes of dissolved organic carbon (DOC), dissolved nitrogen compounds (organic N, NH4+ and NO3−) and water soluble phosphorus (PO43−) through a podzolic soil were studied in a clear-cut in eastern Finland for 5 years. The old, mixed coniferous stand was clear-cut and stem only harvested in 1996 followed by soil harrowing in 1998 and planting in June 1999. Zero-tension lysimeters were used to collect soil water from below different soil horizons in the three types of microsites that resulted from site preparation treatment: low ridges (25% of clear-cut area), shallow furrows (30%) and the undisturbed soil (45%). After soil harrowing, the leaching of DOC, N and P from below the B-horizon increased compared to pre-treatment levels. However, the increases were short-lasting; 1–2 years for inorganic N and P, and 5 years for DOC and organic N. The highest concentrations were associated with the ridges and lowest with the furrows, reflecting the differences in amount of organic matter present in each microsite type and, for N, to enhanced mineralization and nitrification. Leaching from below the B-horizon over the 5 years following soil harrowing for the whole clear-cut area was 36.5 kg ha−1 for DOC, 0.88 kg ha−1 for NH4-N, 0.46 kg ha−1 for NO3-N, 1.24 kg ha−1 for organic N and 0.09 kg ha−1 for PO4-P. Site preparation increased temporarily the risk for nutrient leaching into watercourses and groundwater from the clear-cut area but soil fertility was not affected since the leached amounts remained small. The main reasons for the observed low leaching values were the rapid recovery of ground vegetation and low N deposition loads. 相似文献
22.
Ur?a Vilhar Michael Starr Klaus Katzensteiner Primo? Simon?i? Lu?ka Kajfe?-Bogataj Jurij Diaci 《European Journal of Forest Research》2010,129(4):729-740
Two models for calculating the forest water balance were applied to different development stages of managed and non-managed
forests in the Dinaric Karst for two hydrologically contrasting growing seasons. A simple model WATBAL, which calculates water
balance on a monthly basis, and the BROOK90 model, which calculates water balance on daily basis, were used. Differences between
calculated drainage fluxes between the models were less pronounced in the drier growing season and were lower in the forest
stands compared to forest gaps. Average calculated drainage fluxes of the two growing seasons were highest in the gaps and
lowest in the stand in the virgin forest remnant, followed by the mature stand in the managed forest. According to model fitting,
testing the calibration robustness and sensitivity analysis the BROOK90 model was considered best at simulating the water
balance of the various research sites. The difference in model behaviour is considered to be mainly the result of the difference
in model time step and the inclusion of macropore flow in BROOK90. The greater complexity of the BROOK90 model meant it could
be parameterized to describe more fully the complexity of the horizontal and vertical structure of forest stand and soil properties.
A disadvantage of the BROOK90 model is the greater need of input data. WATBAL, however, was useful for obtaining rougher estimates
of the water balance components and can be applied to areas where there is less data available. Choice of model is therefore
determined by data availability. 相似文献
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Slavin JA Acuña MH Anderson BJ Baker DN Benna M Gloeckler G Gold RE Ho GC Killen RM Korth H Krimigis SM McNutt RL Nittler LR Raines JM Schriver D Solomon SC Starr RD Trávnícek P Zurbuchen TH 《Science (New York, N.Y.)》2008,321(5885):85-89
Observations by MESSENGER show that Mercury's magnetosphere is immersed in a comet-like cloud of planetary ions. The most abundant, Na+, is broadly distributed but exhibits flux maxima in the magnetosheath, where the local plasma flow speed is high, and near the spacecraft's closest approach, where atmospheric density should peak. The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity. Two outbound current sheet boundaries were observed, across which the magnetic field decreased in a manner suggestive of a double magnetopause. The separation of these current layers, comparable to the gyro-radius of a Na+ pickup ion entering the magnetosphere after being accelerated in the magnetosheath, may indicate a planetary ion boundary layer. 相似文献
25.
Kefyalew Girma Starr Holtz Brenda Tubaña John Solie William Raun 《Journal of plant nutrition》2013,36(2):165-182
Midseason fertilizer nitrogen (N) rates based on predicted yields can be projected if the quantity of N accumulated in winter wheat (Triticum aestivum L.) and corn (Zea mays L.) is known especially early in the growing season. This study was conducted in 2006 and 2007 to establish the amount of N accumulated in corn and winter wheat over the entire growing season. Plots representing three N fertilization rates 0, 45, and 90 kg ha?1 at Stillwater and 0, 67, and 112 kg ha?1 at Lahoma were selected from two long-term wheat experiments located at research stations in Stillwater and Lahoma, Oklahoma. For corn, three N fertilization rates 0, 112 and 224 kg ha?1 at Lake Carl Blackwell and 0, 56 and 112 kg ha?1 at Perkins were selected from N studies, located at research stations near Lake Carl Blackwell and Perkins, Oklahoma. Sequential aboveground biomass samples were collected from 1 m2 area of wheat and 1.5 m long row (0.76 cm spacing) for corn throughout their respective growing seasons. In general, this work showed that more than 45% of the maximum total N accumulated could be found in corn plants by growth stage V8 (8th leaf collar fully unfolded). For winter wheat, more than 61% of the maximum total N accumulated at later stages of growth could be accounted for by Feekes growth stage 5 (F5, leaf strongly erected). Our findings are consistent with those of others showing that yield potential can be predicted at mid-season since such a large percentage of the total N accumulated was accounted for early on in the growing cycle of either wheat or corn. 相似文献
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Mesele Negash Mike Starr Markku Kanninen Leakemaraiam Berhe 《Agroforestry Systems》2013,87(4):953-966
Coffee, Coffea arabica L., which is native to Ethiopia, is the world’s most widely traded tropical agricultural commodity. While much is known about the productivity and management of coffee for coffee beans little attention has been given to the plants overall biomass production and carbon sequestration. The objective of this study was to develop and evaluate allometric equations for estimating the aboveground biomass of C. arabica plants growing in indigenous agroforestry system in the Rift Valley escarpment of south-eastern Ethiopia. Coffee plays an important role in providing income and in sustaining these productive systems. Biomass harvesting of 31 plants with 54 stems was carried out in a 40 km2 area varying in elevation from 1,500 to 1,900 m. The stem accounted for most (56 %) of plant biomass, followed by branches (39 %) and twigs plus foliage (5 %). Plant mean biomass was 22.9 ± 15.8 kg. Power equations using stem diameter measured at either 40 cm (d 40) or at breast height (d, 1.3 m) with and without stem height (h) were evaluated. The square power equation, $ Y \; = \; b_{ 1} d_{ 40}^{ 2} $ , was found to be the best (highest ranked using goodness-of-fit statistics) for predicting total and component biomass. The reliability of the prediction decreased in the order: stem > branches > twigs plus foliage. A cross-validation procedure showed that equation parameterization was stable and coefficients reliable. Our parameterized square power equation for total aboveground biomass was also found to be better than the equations parameterized by Hairiah et al. (Carbon stocks of tropical land use systems as part of the global C balance: effects of forest conversion and options for clean development activities, International Centre for Research in Agroforestry, Bogor, 2001) and Segura et al. (Agroforest Syst 68:143–150, 2006) for C. arabica grown in agroforestry systems, confirming the importance of parameterization of allometric equations with site specific data when possible. 相似文献