首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The objective of this study was to explore if more crop-specific plant growth modules can improve simulations of crop yields, and N in tile flow under different management practices compared with a generic plant growth module. We calibrated and evaluated the Root Zone Water Quality Model (RZWQM) with the Decision Support for Agrotechnology Transfer (DSSAT v3.5) plant growth modules (RZWQM-DSSAT) for simulating tillage (NT — no till, RT — ridge till, CP — chisel plow, and MP — moldboard plow), crop rotation {CC — continuous corn, and CS — corn (Zea mays L.)-soybean [Glycine max (L.) Merr.]}, and nitrogen (N) (SA — single application at preplant, and LSNT — late spring soil N test based application) and manure (SM — fall injected swine manure) management effects on crop production and water quality. Data from 1978 to 2003 from a water quality experiment near Nashua (Nashua experiments), Iowa, USA, were used. The model was calibrated using data from one treatment plot and validated for the rest of the plots. Simulated management effects on annual N loading in tile flow were agreeable with measured effects in 85%, 99%, 88%, and 78% of the cases for tillage, crop rotation (CS vs. CC), N application timing (SA vs. LSNT), and swine manure applications (SM vs. SA), respectively. On average, the LSNT plots were simulated to have 359 kg ha− 1 higher corn yield compared to SA, when the observed increase was 812 kg ha− 1. Grain yield simulations were not sensitive to differences between RT and NT, between SM and SA treatments, and between CS and CC. We conclude that considering the uncertainties of basic input data, processes in the field, and lack of site specific weather data, the results obtained with this RZWQM-DSSAT hybrid model were not much better than the results obtained earlier with the generic crop growth module.  相似文献   

2.
Nitrogen mineralization and nitrification in the soil of sub-alpine ruderal community of Mount Uludağ, Bursa, Turkey was measured for 1 year, under field conditions with Verbascum olympicum and Rumex olympicus being the dominant pioneer species under dry and wet sites, respectively. Seasonal fluctuations were observed in N mineralization and nitrification. The net N mineralization and nitrification were high in early summer and winter, due to high moisture. The annual net N mineralization rate (for the 0–15 cm soil layer) was higher under R. olympicus (188 kg N ha−1 yr−1) than under V. olympicum (96 kg N ha−1 yr−1). A significant positive correlation between net N mineralization and soil organic C (r2 = 0.166), total N (r2 = 0.141) and water content (r2 = 0.211) was found. Our results indicate that N mineralization rate is high in soils of ruderal communities on disturbed sites and varies with dominant species and, a difference in net N mineralization rate can be attributed to organic C, total N and moisture content of soils.  相似文献   

3.
  相似文献   

4.
Diverting the infiltrating water away from the zone of N application can reduce nitrate–nitrogen (NO3–N) leaching losses to groundwater from agricultural fields. This study was conducted from 2001 through 2005 to determine the effects of N-application methods using a localized compaction and doming (LCD) applicator and spoke injector on NO3–N leaching losses to subsurface drainage water and corn (Zea mays L.)–soybean (Glycine max L.) yields. The field experiments were conducted at the Iowa State University’s northeastern research center near Nashua, Iowa, on corn–soybean rotation plots under chisel plow system having subsurface drainage ‘tile’ system installed in 1979. The soils at the site are glacial till derived soils. The N-application rates of 168 kg-N ha?1 were applied to corn only for both the treatments each replicated three times in a randomized complete block design. For combined 5 years, the LCD N-applicator in comparison with spoke injector showed lower flow weighted NO3–N concentrations in tile water (16.8 vs. 20.1 mg L?1) from corn plots, greater tile flow (66 vs. 49 mm), almost equivalent NO3–N leaching loss with tile water (11.5 vs. 11.3 kg-N ha?1) and similar corn grain yields (11.17 vs. 11.37 Mg ha?1), respectively, although treatments effects were found to be non-significant (p?=?0.05) statistically. The analysis, however, revealed that amount and temporal distribution of the growing season precipitation also affected the tile flow, NO3–N leaching loss to subsurface drain water, and corn–soybean yields. Moreover, the spatial variability effects from plot to plot in some cases, resulted in differences of tile flow and NO3–N leaching losses in the range of three to four times despite being treated with the same management practices. These results indicate that the LCD N-applicator in comparison with spoke injector resulted in lower flow weighted NO3–N concentrations in subsurface drain water of corn plots; however, strategies need to be developed to reduce the offsite transport of nitrate leaching losses during early spring period from March through June.  相似文献   

5.
Distinguishing between root and non-root derived CO2 efflux is important when determining rates of soil organic matter turnover, however, in practice they remain difficult to separate. Our aim was to evaluate two methods for determining the component of below-ground respiration not dependent on plant roots (i.e., basal soil respiration; Rb). The first approach estimated Rb indirectly from the y-intercept of linear regressions between below-ground respiration (BGR) and root biomass. The second approach involved direct measurements of soil respiration from bare plots. To compare the contrasting approaches, BGR and crop biomass measurements were collected throughout the year in a range of agricultural systems. We found that both methods were very closely correlated with each other. Values of Rb determined by the intercept approach, however, were slightly higher than those determined by measurement of bare plots. Both approaches showed a seasonal trend with estimates of Rb lowest in winter months at 0.02 t C ha−1 month−1 for the y-intercept approach and 0.11 t C ha−1 month−1 for the bare plots approach, even after the data had been corrected for the influence of soil temperature. Highest rates of Rb occurred from the height to the end of the crop growing season (0.8-1.5 t C ha−1 month−1). The annual CO2 efflux due to Rb was estimated to be 8.1 t C ha−1 y−1 from the y-intercept approach and 6.8 t C ha−1 y−1 from bare plots. Annual BGR was 12.1 t C ha−1 y−1. We conclude that both methods provide similar estimates of Rb, however, logistically the bare plots approach is much easier to undertake than the y-intercept approach.  相似文献   

6.
Evaluation of carbon dynamics is of great concern worldwide in terms of climate change and soil fertility. However, the annual CO2 flux and the effect of land management on the carbon budget are poorly understood in Sub-Saharan Africa, owing to the relative dearth of data for in situ CO2 fluxes. Here, we evaluated seasonal variations in CO2 efflux rate with hourly climate data in two dry tropical croplands in Tanzania at two sites with contrasting soil textures, viz. clayey or sandy, over four consecutive crop-cultivation periods of 40 months. We then: (1) estimated the annual CO2 flux, and (2) evaluated the effect of land management (control plot, plant residue treatment plot, fertilizer treatment plot, and plant residue and fertilizer treatment plot) on the CO2 flux and soil carbon stock at both sites. Estimated annual CO2 fluxes were 1.0–2.2 and 0.9–1.9 Mg C ha?1 yr?1 for the clayey and sandy sites, respectively. At the end of the experiment, crop cultivation had decreased the surface soil carbon stocks by 2.4 and 3.0 Mg C ha?1 (soil depth 0–15 cm) at the clayey and sandy sites, respectively. On the other hand, plant residue application (7.5 Mg C ha?1 yr?1) significantly increased the surface soil carbon stocks, i.e., 3.5–3.8 and 1.7–2.1 Mg C ha?1 (soil depth 0–15 cm) at the clayey and sandy sites, respectively, while it also increased the annual CO2 fluxes substantially, i.e., 2.5–4.0 and 2.4–3.4 Mg C ha?1 yr?1 for the clayey and sandy soils, respectively. Our results indicate that these dry tropical croplands at least may act as a carbon sink, though the efficiency of carbon accumulation was substantially lower in sandy soil (6.8–8.4%) compared to clayey soil (14.0–15.2%), possibly owing to higher carbon loss by leaching and macro-faunal activity.  相似文献   

7.
After the 1998 North 25 Fire in the Wenatchee National Forest, eight study sites were established on steep, severely burned hillslopes to examine the effectiveness of postfire seeding and fertilizing treatments in increasing cover to reduce hillslope erosion, and to measure the nutrient content of the eroded sediment. At each site, four 4 by 9 m plots were located with four randomly applied treatments: seed (winter wheat, Triticum estivum) at 34 kg ha− 1, fertilizer (75% ammonium nitrate and 25% ammonium sulfate) at 31 kg ha− 1, seed and fertilizer, and untreated control. Sediment fences were installed at the base of each plot to measure erosion rates and sample the eroded sediments. In addition, precipitation amounts and intensities, surface cover, canopy cover, and nutrient concentrations in the eroded sediments were measured for four years after the fire. Total precipitation was below average during the four-year study period, and most erosion occurred during short duration, moderate intensity summer rainfall events. The overall first year mean erosion rate was 16 Mg ha− 1 yr− 1, and this decreased significantly in the second year to 0.66 Mg ha− 1 yr− 1. There were no significant differences in erosion rates between treatments. In the first year, the seeded winter wheat provided 4.5% canopy cover, about a fourth of the total canopy cover, on the seeded plots; however, the total canopy cover on the seeded plots did not differ from the unseeded plots. The below average precipitation in the spring after seeding may have affected the winter wheat survival rate. In the fourth year of the study, the mean canopy cover in the fertilization treatment plots was 74%, and this was greater than the 55% mean canopy cover in the unfertilized plots (p = 0.04); however, there was no accompanying reduction in erosion rate for either the seeding or fertilization treatments. Revegetation by naturally occurring species was apparently not impacted by seeding during the four years of this study. The pH of the sediment as well as the concentrations of NO3–N, NH4–N, and K was not affected by seeding or fertilizing. The nutrient loads in the eroded sediment were minimal, with most of the nutrient loss occurring in the first postfire year. These results confirm that seeding success is highly dependent on rainfall intensity, amounts, and timing, and that soil nutrients lost in eroded sediments are unlikely to impair the site productivity.  相似文献   

8.
The interplay between the carbon and other nutrient cycles is the key to understand the responses of soil ecosystems to climatic change. Using the free-air CO2 enrichment (FACE) techniques, we carried out a multifactorial experiment in a Chinese rice-wheat rotation system, to investigate the response of soil nematodes to elevated CO2 under different application rates of N fertilizer (225.0 kg N ha−1 (HN) and 112.5 kg N ha−1(LN), respectively) and residue incorporation (0 kg C ha−1 (ZR), 1000 kg C ha−1 (MR) and 2000 kg C ha−1 (HR), respectively). This study was conducted during the wheat growing season of 2007 after expose to the elevated CO2 for three years. The results in our study indicated that seasonality is an important factor in determining changes in the nematode abundance and diversity. The residue addition effects were more obvious than the elevated CO2, which significantly influenced the abundance of total nematodes and plant-parasites, and some ecological indices. The interactions between residue addition and CO2 significantly influenced nematode dominance and structure indices. High level of N fertilization was found to decrease the nematode diversity, generic richness and maturity indices at wheat jointing stage. There are significant interactions between N fertilization and elevated CO2 for abundance of total nematodes and different trophic groups.  相似文献   

9.
Thoroughly tested simulation models are needed to help quantify the long-term effects of agriculture. We evaluated the Root Zone Water Quality Model (RZWQM) response to different N management strategies and then used the tested model with observed weather data from 1961-2003 to quantify long-term effects on corn (Zea mays L.) yield and flow weighted nitrate-N concentration in subsurface “tile” drainage water (Nconc). Fourteen years (1990-2003) of field data from 30, 0.4 ha plots in northeast Iowa were available for model testing. Annual crop yield, nitrate-N loss to subsurface “tile” drainage water (Nloss), Nconc, and subsurface “tile” drainage amount (drain) for various management scenarios were averaged over plots and years to create five chemical fertilizer and five swine manure treatments. Predicted corn yield and Nconc for the 10 treatments were significantly correlated with observed data (R2 > 0.83). The Root Mean Square Errors (RMSE) were 15% and 18% of its observed average Nconc for chemical fertilizer and manure treatments, respectively. Corresponding RMSEs for corn yields were 8% and 10% of its observed average corn yields for chemical fertilizer and manure treatments. The long-term simulations indicate that average corn yield plateaus and Nloss accelerates as quadratic functions of increasing spring UAN-N rates from 100 to 200 kg N/ha. Winter wheat (Triticum aestivum L.) sowed after corn and soybean [Glycine max (L.) Merr.] harvest was predicted to reduce long-term Nloss by 5 to 6 kg N/ha, which appears consistent with published field studies and may be a treatment to ameliorate agricultural management with potential for elevated Nloss such as swine manure application to soybean. The results suggest that after calibration and thorough testing, RZWQM can be used to quantify the relative effects of corn production and Nconc under several alternative management practices.  相似文献   

10.
Methane (CH4) uptake by soil can possibly be suppressed more in regions with heavy summer precipitation, such as those under the East Asian monsoon climate, as compared to that in regions with a dry summer. In order to determine how precipitation patterns affect seasonal and spatial variations in CH4 fluxes in temperate forest soils, such fluxes and selected environmental variables were measured on different parts of a hill slope in a cypress forest in central Japan. On the upper and middle parts of the slope, CH4 uptake was observed throughout the year, and the uptake rates increased slightly with soil temperature and decreased with soil water content. The CH4 flux predicted using data for the middle and upper parts of the slope ranged from −1.12 to −0.83 kg-CH4 ha−1 y−1 (i.e. CH4 uptake by soil) and from −2.30 to −2.04 kg-CH4 ha−1 y−1, respectively. In contrast, in the relatively wet lower part of the slope near an in-stream wetland, large CH4 emissions (>2 mg-CH4 m−1 d−1) were observed during the rainy summer. In this wetter plot, the soil functioned as a net annual CH4 source in a rainy year. Hence the variation in CH4 flux with a change in soil water conditions and soil temperature on the lower part of the slope contrasted to that on the upper and middle parts of the slope. The predicted CH4 flux for this lower plot ranged from −0.45 kg-CH4 ha−1 y−1 in a dry year to 1.80 kg-CH4 ha−1 y−1 in a rainy year. Our results suggest that consideration of the soil water conditions across a watershed is important for estimating the CH4 budgets for entire forest watershed, particularly in regions subject to a wet summer.  相似文献   

11.
A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha−1 vs. control). Nitrate (NO3−) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO3− loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct (P = 0.021), with greater soil-NO3− and biochar-NO3− contents in the high biochar treatment. Biochar addition increased wheat root length ratio (P = 0.053) and lowered root N uptake (P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO3− within the rhizosphere of biochar-amended soils which has implications for NO3− loss and improved nitrogen use efficiency.  相似文献   

12.
Accurate pre-harvest assessment of a staple food crop is an integral part of policy formulation in relation to food security issues. Here, two different approaches were attempted to estimate wheat yield using time series multi-year satellite (MODIS Aqua) optical-thermal data from a single earth observation (EO) mission. Surface energy budgeting was used to estimate evapotranspiration in terms of latent heat fluxes from net available energy and evaporative fraction to predict wheat yield over four agro-climate zones in semi-arid climate of Gujarat, India. Satellite based estimates of latent heat fluxes were found to show substantially less error with respect to the area-averaged heat flux measurements from LAS (large aperture scintillometer) as compared to measurements from BREB (Bowen Ratio Energy Balance) alone. The deviations in satellite based zonal CWU were found to have a strong correlation (r = 0.71) with the deviations from zonal wheat yield. Among both the approaches, the radiation use efficiency (RUE) based approach produced better accuracy in the predicted yield with lower root mean square error (RMSE) of 390 kg ha−1 (14.8% of reported mean) and higher correlation coefficient (r = 0.92) than the water use efficiency (WUE) based approach (RMSE 573 kg ha−1, 21.8% of reported mean; r = 0.80). Uncertainties in the satellite based core inputs resulted into a net 10-12% error in predicted yield in case of RUE approach. Our demonstrative case studies recommend that the coupled use of satellite observations from multiple EO missions and radiative transfer simulation would be effective to make efficiency based approaches operationally viable for regional wheat yield forecasting in near real time.  相似文献   

13.
Shifts in oxic and anoxic conditions in soil are most frequently caused by water table fluctuations, heavy rain, snowmelt or flooding, with potentially significant impacts on microbial processes and the ability of soils to convert mineral nitrogen to nitrogen gases efficiently. The impact of oxic/anoxic cycles on nitrogen transformation rates was therefore explored in the upper layer (0-30 cm) of partially degraded peat soil. We hypothesized that high denitrification potential would be conserved due to the high organic matter content of this soil. Mineral nitrogen was applied to approximately 1-cm deep layers of homogenized soil in microcosms, with no external source of readily degradable carbon. Microcosms were subjected to three cycles, each consisting of an oxic phase of 8-11 days and an anoxic phase of 21-28 days. Approximately 2% of the ammonium load was lost through ammonia volatilization during oxic phases and the remainder was nitrified. The accumulated nitrate decreased soil pH from 8.0 to 6.8 before its transformation through denitrification. Nitrification and denitrification rates during the three oxic/anoxic cycles (approximately three months) were 2.9-3.2 kg N ha−1 d−1 and 1.0-2.3 kg N ha−1 d−1, respectively. Extrapolation of these values to 30-cm deep soil layers gave rates that were sufficient for complete transformation of at least 1700 kg N ha−1 of ammonium to nitrogen gases, which is ten-fold greater than the annual nitrogen application of 170 kg N ha−1 permitted by the European directive. Denitrification rates decreased linearly during the three cycles (from 36 ± 2 to 16 ± 1 μg N g−1 d−1 dry soil), projecting cessation of denitrification activity and CO2 production during the fifth cycle. Storage of peat soil at 4 °C most probably allowed slow degradation of organic matter that was completely oxidized to CO2 after the soil was exposed to higher temperature (28 °C). Storage of soil for one year did not affect nitrification rate, but reduced denitrification rate, unless soil was amended with a readily degradable carbon source. The data suggest that, despite the high carbon content of this soil, it cannot sustain transformations of high N loads to nitrogen gases for prolonged periods without amendment with readily available carbon.  相似文献   

14.
Identifying the nitrogen (N) fate is complicated and a great challenge in karst watersheds because of the co-existence of natural pools and anthropogenic sources. The objective of the study was to use stable isotopic composition of dual-isotope (δ15NNitrate and δ18ONitrate) and LOADEST model approaches to trace N sources, pathways in karst watershed. The study was conducted in the Houzhai watershed, which is a typical agricultural karst watershed from July 2016 to August 2018, to reveal the N fate and the coupled carbon(C)–N processes occurring in the riverine-watershed with agricultural activities. We found that the wet deposition of total nitrogen (TN) flux was 33.50 kg hm−2·a−1 and dissolved nitrogen (DN) flux was 21.66 kg hm−2·a−1. The DN runoff loss was 2.10 × 105 kg·a−1 and the loss of DN during the wet season accounted for 95.4% over a year. In the wet season, NO3−-N daily efflux was 977.62 ± 516.66 kg ha−1·day−1and 248.77 ± 57.83 kg ha−1·day−1 in the dry season. The NH4+-N efflux was 29.17 ± 10.50 kg ha−1·day−1 and 4.42 ± 3.07 kg ha−1·day−1 in the wet and dry seasons, respectively. The main form output load of N was NO3−-N which was more than 30 times as much as NH4+-N output loss. The NO3−-N caused by rainfall contributed 11.82%–53.61% to the export load. Nitrate from soil contributed over 94% of the N to Houzhai river caused by N leaching. In addition, manure and farmland soil were the main sources of groundwater in the Houzhai watersheds, the contribution rates were 25.9% and 22.5%. The chemical N fertilizers affected carbonate weathering strongly, and the HCO3− flux caused by nitrification due to N fertilizers application in soil accounted for 23.5% of the entire watershed. This study suggested that carbonate weathering may be influenced by nitrogen nitrification in the karst watershed.  相似文献   

15.
 This study was conducted to determine effects of long-term winter cover cropping with hairy vetch, cereal rye and annual ryegrass on soil N availability and corn productivity. From 1987 to 1995, with the exception of the first year of the study, the cover crops were seeded each year in late September or early October after the corn harvest and incorporated into the soil in late April or early May. Corn was seeded 10 days to 2 weeks after the cover crop residues had been incorporated, and N fertilizer was applied as a side-dressing at rates of 0, 67, 134, or 201 kg N ha–1 each year. While the average annual total N input from the above-ground biomass of the cover crops was highest for hairy vetch (72.4 kg N ha–1), the average annual total C input was highest for cereal rye (1043 kg C ha–1) compared with the other cover crops. Hairy vetch was the only cover crop that significantly increased pre-side-dressed NO3 –-N (Ni) corn biomass and N uptake at 0 N. At an N fertilizer rate of 134 kg N ha–1 or higher, the cover crops had a minimal effect on corn biomass. This indicated that even after 9 years of winter cover cropping, the effect of the cover crops on corn growth resulted primarily from their influence on soil N availability. The amount of available N estimated from the cover crops (Nac) was significantly correlated with relative corn biomass production (r 2=0.707, P<0.001). The total amount of available N, comprising Nac and N added from fertilizer (Nf), was strongly correlated (r 2=0.820, P<0.001)) with relative corn biomass production. The correlation was also high for the available N comprising Ni and Nf (r 2=0.775, P<0.001). Although cereal rye and annual ryegrass did not improve corn biomass production in the short term, they benefited soil organic N accumulation and gradually improved corn biomass production compared with the control over the long term. Received: 10 August 1999  相似文献   

16.
Previous studies have suggested grazing may alter nitrogen (N) cycling of grasslands by accelerating or decelerating soil net N mineralization. The important mechanisms controlling these fluxes remain controversial, and more importantly, the consequences on carbon storage and site productivity remain uncertain. Here we present results on the seasonal patterns of soil inorganic N pools and net N mineralization and their linkages to ecosystem functioning from a grazing experiment in the Inner Mongolia grassland, which has been maintained for five years with 7 levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep ha−1). Net N mineralization and nitrification rates were determined using an in situ soil core incubation method. Our findings demonstrated that, in the non-growing season, the net N mineralization rate was reduced by 181% in the lightly and moderately grazed plots (1.5-4.5 sheep ha−1) and by 147% in the heavily grazed plots (6.0-9.0 sheep ha−1), and the net N immobilization was observed in all grazed treatments. In the early growing season, however, it was increased by 107% in the lightly and moderately grazed plots and by 128% in the heavily grazed plots. In the peak growing season, grazing diminished the net mineralization rate by 71% in the lightly and moderately grazed plots and 108% in the heavily grazed plots. The seasonally dependent effects of grazing on soil inorganic N pools and net N mineralization were strongly mediated by grazing-induced changes in soil temperature and moisture, with soil moisture being predominant in the peak growing season. Grazing alterations of soil inorganic N and net N mineralization were closely linked to the changes in aboveground primary productivity, biomass N allocation, N use efficiency, and soil total nitrogen. Based upon the five year study, we conclude that grazing at moderate to high intensities is unsustainable in terms of productivity and soil N cycling and storage in these systems.  相似文献   

17.
In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the 137Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m− 2). All the sampling sites were eroded and 137Cs inventories varied widely (between 245 and 3670 Bq m− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha− 1 yr− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha− 1 yr− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha− 1 yr− 1 and reaching a maximum of 48.8 t ha− 1 yr− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha− 1 yr− 1) to 25° (40. 8 t ha− 1 yr− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha− 1 yr− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha− 1 yr− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.  相似文献   

18.
To test the hypothesis that N isotope composition can be used as evidence of excessive compost application, we measured variation in patterns of N concentrations and corresponding δ15N values of plants and soil after compost application. To do so, a pot experiment with Chinese cabbage (Brassica campestris L. cv. Maeryok) was conducted for 42 days. Compost was applied at rates of 0 (SC0), 500 (SC1), 1000 (SC2), and 1500 mg N kg−1 soil (SC3). Plant-N uptake linearly increased with compost application (r2 = 0.956, P < 0.05) with an uptake efficiency of 76 g N kg−1 of compost-N at 42 days after application, while dry-mass accumulation did not show such linear increases. Net N mineralized from compost-N increased linearly (r2 = 0.998, P < 0.01) with a slope of 122 g N kg−1 of compost-N. Plant-δ15N increased curvilinearly with increasing compost application, but this increase was insignificant between SC2 and SC3 treatments. The δ15N of soil inorganic-N (particularly NO3−-N) increased with compost application. We found that plant-δ15N reflected the N isotope signal of soil NO3−-N at each measurement during plant growth, and that δ15N of inner leaves and soil NO3−-N was similar when initial NO3− in the compost was abundant. Therefore, we concluded that δ15N of whole plant (more obviously in newer plant parts) and soil NO3−-N could reveal whether compost application was excessive, suggesting a possible use of δ15N in plants and soil as evidence of excess compost application.  相似文献   

19.
Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15-0.26 μmol m−2 s−1 and 2.65-4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux.  相似文献   

20.
Starting in the 1980's, the Rainbow Smelt (Osmerus mordax) population of the Boyer River (Canada) gradually declined due to water eutrophication and excessive siltation in the spawning area. Sediments and agricultural nutrients reach hydrosystems through runoff and soil erosion. The objectives of the study were to quantify the soil and sediment loss from agricultural fields and to identify the areas at risk, using 137Cs measurements. Using a Geographical Information Systems (GIS), the watershed was subdivided into 6 isosectors presenting specific soil/slope combinations. Representative fields from each isosector were sampled for 137Cs. Using GIS, the data for individual fields were extrapolated to isosectors and the whole cultivated area of the watershed. Based on this approach, it was estimated that around 30% of the arable lands of the watershed show erosion rates higher than 6 t ha− 1 yr− 1, which is considered as a tolerable level for Canadian soils, and that 45% of the residual area presents an erosion rate close to that limit. The average sediment production at the edge of fields was estimated at 2.8 t ha− 1 yr− 1, for an annual production of more than 60 000 t of material. Loamy soils with a slope higher than 2% were estimated to generate the highest sediment rate (6.9 t ha− 1 yr− 1) and nearly 40% of the overall sediment production.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号