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101.
Mitigation of methane and nitrous oxide emissions from drained irrigated rice fields 总被引:23,自引:0,他引:23
One of the important cultural practices that affect methane and nitrous oxide emissions from tropical rice plantations is the water drainage system. While drainage can reduce methane emissions, it can also increase nitrous oxide emissions, as well as reduce yields. In this experiment, four different water drainage systems were compared in a rice field in central Thailand including: (1) continuous flooding, (2) mid-season drainage, (3) multiple drainage and (4) a local method (drainage was done according to local cultural practice) in order to find a system of drainage that would optimize yields while simultaneously limiting methane and nitrous oxide emissions. Methane and nitrous oxide emission were observed and compared with rice yield and physical changes of rice plants. It was found that drainage during the flowering period could reduce methane emission. Interestingly, nitrous oxide emission was related to number of drain days rather than the frequency of draining. Fewer drain days can help reduce nitrous oxide emission. The mid-season drainage and the multiple drainage, with 6.9% and 11.4% reduction in rice yield, respectively, had an average methane emission per crop 27% and 35% lower when compared to the local method. Draining with fewer drain days during the flowering period was recommended as a compromise between emissions and yield. The field drainage can be used as an option to reduce methane and nitrous oxide emissions from rice fields with acceptable yield reduction. Mid-season drainage during the rice flowering period, with a shortened drainage period (3 days), is suggested as a compromise between the need to reduce global warming and current socio-economic realities. 相似文献
102.
Behavior and prediction of photochemical degradation of chlorinated polycyclic aromatic hydrocarbons in cyclohexane 总被引:3,自引:0,他引:3
The photochemical degradation of 11 chlorinated polycyclic aromatic hydrocarbons (ClPAHs) and the corresponding 5 parent PAHs was examined to simulate the compound’s fate on aerosol surfaces. All the ClPAHs and PAHs decayed according to the first-order reaction rate kinetics. The photolysis rates of ClPAHs varied greatly according to the skeleton of PAHs; the rates of chlorophenanthrenes (ClPhes) and 1-chloropyrene were higher than those of corresponding parent PAHs, whereas chlorofluoranthenes, 7-chlorobenz[a]anthracene and 6-chlorobenzo[a]pyrene were more stable under irradiation compared to respective parent PAH. Considering the photoproducts of ClPhes detected, the oxidation could occur immediately at positions of the highest frontier electron density. Finally, the quantitative structure-property relationship models were developed for direct photolysis half-lives and average quantum yields of the ClPAHs and parent PAHs, in which the significant factors affecting photolysis were ELUMO+1, total energy and surface area, and ELUMO, ELUMO − EHOMO and total energy, respectively. 相似文献
103.
较系统地研究了香蕉组培苗的营养与施肥,试验方案包括了NPK13种用量水平、10种不同NPK配比和中微量元素混施.试验结果表明,在一定的NPK施肥基础上.再增施NPK均能获得不同程度的增产,其中增施N的增产幅为4.7%-15.0%,增施P、K的分别为3.4%-15.1%和6.6%-12.6%.增N有利于植株增高、茎围增粗、长叶增快和提早吐蕾;增P对植株增高和提早吐蕾也有一定的作用;增K主要有利于茎围增粗,但在高N高P下增K也同样具有增N的多种效果.增K的另一效应是延缓吐蕾期而使吐蕾期较集中一致,这有利于田间管理和收获;施用中微量元素的增产效果显著,同时也改善和提高了果实品质.应提倡应用和推广. 相似文献
104.
Peggy?Gunkel Estelle?Roth Bernard?FabreEmail author 《Environmental Chemistry Letters》2003,1(1):92-97
Agricultural practices can lead to copper accumulation in soils and at high concentration it can become toxic for plants.
One common toxic effect of copper on plants is a decrease of crop yield. Here, we studied 1) the crop yield of maize grown
on plots of a soil intentionally enriched with copper sulphate and 2) the possible relationship between the copper concentration
in chemical soil fractions and the maize crop yield. Anthropogenic copper is mainly bound to manganese oxides, to iron oxides
and to the organic matter. Maize (Zea maize L.) was grown on outdoor experimental plots. The crop yield was evaluated for three development stages: the 6–10 leaf stage,
the female flowering stage and the maturity stage, 2, 4 and 6 years after the soil copper enrichment. Strong crop yield reductions,
proving a toxic effect of copper on maize growth were noted 2 years after the copper input at the maturity stage and 4 years
after the copper input at the 6–10 leaf stage. Variations in maize crop yield are described with linear multiple regression
equations including the variable copper content in soil, and other variables when needed such as soil pH, soil organic carbon
level and the climatic variables, the precipitation rate and the ambient temperature. The crop yield study at the 6–10 leaf
stage and at the female flowering stage does not provide significant regression equations, while the crop yield study at the
maturity stage does. Request variables for the models are the total copper content or the copper bound to the organic matter
and the meteorological data.
Electronic Publication 相似文献
105.
研究了大田栽培条件下紫外辐射增强对冬小麦孕穗、抽穗、开花、灌浆、结实以及产量的影响。结果表明,UV B辐射增强使小麦植株矮化,叶面积减小,穗重、茎重、叶重减小,灌浆速度变慢,灌浆不充实,此外,UV B辐射增强还使花粉败育率增大。 相似文献
106.
We present a strategy for using an empirical forest growth model to reduce uncertainty in predictions made with a physiological process-based forest ecosystem model. The uncertainty reduction is carried out via Bayesian melding, in which information from prior knowledge and a deterministic computer model is conditioned on a likelihood function. We used predictions from an empirical forest growth model G-HAT in place of field observations of aboveground net primary productivity (ANPP) in a deciduous temperate forest ecosystem. Using Bayesian melding, priors for the inputs of the process-based forest ecosystem PnET-II were propagated through the model, and likelihoods for the PnET-II output ANPP were calculated using the G-HAT predictions. Posterior distributions for ANPP and many PnET-II inputs obtained using the G-HAT predictions largely matched posteriors obtained using field data. Since empirical growth models are often more readily available than extensive field data sets, the method represents a potential gain in efficiency for reducing the uncertainty of process-based model predictions when reliable empirical models are available but high-quality data are not. 相似文献
107.
Bradford P. Wilcox Clayton L. Hanson J. Ross Wight Wilbert H. Blackburn 《Journal of the American Water Resources Association》1989,25(3):653-666
ABSTRACT: An excellent hydrologic record on sagebrush range-land has been developed at the Reynolds Creek Experimental Watershed in southwestern Idaho. The objectives of this paper were two-fold: (1) to analyze and describe the hydrologic record (8–18 years) from four sagebrush watersheds (1–83 ha); and (2) to evaluate the hydrology component of SPUR, a comprehensive rangeland model. The watersheds represent a gradient in elevation (1180–1658 m) and precipitation (240–350 mm/yr). Runoff was a small fraction (> 2 percent) of the total water budget for all of the watersheds. It occurred very infrequently at the three lower elevation watersheds: Summit, Flats, and Nancy Gulch. At Lower Sheep, the highest elevation watershed, runoff occurred most years for a period of 1 to 17 weeks in the winter. Frozen soil combined with rainfall or snowmelt was associated with most of the runoff from Flats and Nancy Gulch. At Summit summertime thunderstorms produced all of the runoff. The average annual sediment yield from all of the watersheds was low (17–950 kg/ha). It was highest from Summit, which had well developed alluvial channels and very steep slopes. SPUR was able to simulate runoff with reasonable accuracy only at Summit, where frozen soils were not a factor. There was poor correlation between predicted and actual annual 8ediment loss. The model tended to overpredict evapotranspiration early in the growing season and underpredict it in the late summer. 相似文献
108.
Dragan A. Savic Donald H. Burn Zolt Zrinji 《Journal of the American Water Resources Association》1989,25(5):977-983
ABSTRACT: An analysis of four streamflow generation schemes for the use in the estimation of the required conservation storage for a single reservoir is presented. The comparison of the generating schemes should aid in the selection of an appropriate model type for the reservoir sizing problem. The streamflow generation models are compared using two criteria. The first comparison is between the statistics of the generated streamflow sequences and the corresponding statistics from the historical record. The second evaluation compares the median reservoir size determined by each model with the required storage based on the historical flow sequence. The results of a comparative analysis for monthly streamflow data for the Rzav River in Yugoslavia are presented and discussed. The results indicate that both evaluation criteria are required to discriminate between the various options. 相似文献
109.
110.
Stanley L. Ponce James R. Meiman 《Journal of the American Water Resources Association》1983,19(3):415-419
The demand for more water is increasing throughout the country. Research on upland watersheds clearly demonstrates that water yield can be increased using forest and range management practices. Based on the experience of the past several decades and a review of six papers in a recent AWRA series on water yield augmentation through vegetation management, the following issues and concerns are discussed: predicting increased yields from large basins; economic evaluation of additional flows; court acceptance and need for system models; the legal question of ownership and transferability of increased yields; and management emphasis on private and federal lands. The immediate potential for water yield augmentation is on carefully selected watersheds that have the bio-physical potential to produce high value water under environmentally acceptable multiple use management. We predict water yield management on a broader scale will result from increased pressures to solve the legal and economic issues involved. 相似文献