耕作制度发展矛盾及对策——以黄土高原为例

建国 5 0年来 ,我国的耕作制度发生了翻天覆地的变化 ,耕作制度的改革有新的起点与突破 ,仅以占全世界 7%的耕地养活了占全世界 2 2 %的人口 ,取得了举世瞩目的成就。本文根据中国近几年耕作制度合理利用自然资源和社会资源 ,运用各种高新技术 ,实现农业持续、稳定和高效的增产 ,使农业生产各关联部门得以协调发展的实际 ,阐明了耕作制度的发展趋势 ,探讨了耕作制度在新形势下面临的挑战 ,研究了耕作技术发展的对策 ,可供同类地区研究者参考。

土壤养分对小偃22叶片光合特性影响的初步研究

在大田不同供肥条件下 ,于小麦灌浆后期对小麦旗叶光合特性参数进行了连续测定。结果表明 ,小麦叶片气体交换参数均有明显的日变化趋势 ,肥力条件对其日变化进程具有明显的调控作用。不施肥处理小麦叶片 Pn有明显午休现象 ,而低肥处理第一高峰不明显 ,没有明显午休现象 ;高肥处理的 Pn呈单峰曲线 ,峰值来得也较晚。养分条件可改善小麦叶片水分利用效率

延安试区人工刺槐林地的土壤干层分析

8 0年代以来 ,以林草地地力衰退为特征的人工林草地土壤退化日趋严重 ,其中以土壤水分严重亏缺为特征的土壤干化现象愈益引起了人们的重视。土壤干化的直接后果是形成土壤干层 ,导致土壤退化 ,植物生长速率减缓 ,群落衰败以至大片死亡 ,严重地威胁到我国北方地区特别是黄土高原地区生态环境的建设。因此 ,研究和解决土壤干层问题已成为黄土高原植被建设的迫切任务。根据延安试区的土壤水分和植被生长状况调查资料 ,初步分析了不同条件下刺槐人工林地的水分状况。结果表明 :试区刺槐人工林地普遍形成了土壤干层 ,且已相当严重 ;坡向对土壤干层有明显影响 ,阳坡形成的干层较阴坡严重 ;坡度愈大 ,土壤干化愈剧烈 ;林龄对干层严重程度影响不明显。同时 ,研究指出了解决土壤干层问题的意义。

长期定位施肥对黑垆土剖面养分分布特征的影响

对黄土高原旱地 1 5年连续施肥后土壤剖面养分分布的研究发现 ,施化肥对土壤剖面有机质、全N、全P含量的影响深达 1 0 0cm以下 ,所有施肥处理有机质、全N、全P、NO3- N、有效P含量在耕层 (0～ 2 0cm)都有不同程度增加 ;40～ 60、60～ 80cm土层有机质、全N、全P都低于长年不施肥处理 ,造成土壤下层养分的亏缺。长期大量施用氮肥造成N素养分下淋累积 ;长期大量施用磷肥土壤耕层有效P显著提高 ,而 2 0cm以下土层变化不大。

应用Vc发酵弃渣防治保护地病害

The prevention and control of tomato plant diseases were conducted in protective ground using Vc fermentation waste residue treated by enzymolysis and ultrasonic wave. The results showed that the seedlings planted for 3 weeks on the protective ground soil continuously cropped tomato plant for 9 years and fertilized 75, 150 and 300 kg·hm -2 grew well. Their biomass were increased by 123%, 164% and 182%, and the disease incidence rates were decreased by 59%, 78% and 85%, respectively. Under application of 300 kg·hm -2 Vc fermentation waste residue, the products of tomato grown for 10 weeks on the soil continuously cropped tomato plant for 9, 6 and 2 years were increased by 60%, 43% and 14%, respectively, and the disease incidence rates were all decreased by 50%.

Grassland degradation in the

Supported by MSS images in the mid and late 1970s, TM images in the early 1990s and TM/ETM images in 2004, grassland degradation in the "Three-River Headwaters" region (TRH region) was interpreted through analysis on IRS images in two time series, then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s. The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale, and rapidly strengthen phenomenon did not exist in the 1990s as a whole. Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s. Since the 1970s, this degradation process has taken place continuously, obviously characterizing different rules in different regions. In humid and semi-humid meadow region, grassland firstly fragmentized, then vegetation coverage decreased continuously, and finally "black-soil-patch" degraded grassland was formed. But in semi-arid and and steppe region, the vegetation coverage decreased continuously, and finally desertification was formed. Because grassland degradation had obviously regional differences in the TRH region, it could be regionalized into 7 zones, and each zone had different characteristics in type, grade, scale and time process of grassland degradation.

Web-based spatiotemporal visualization of marine environment data

With long-term marine surveys and research, and especially with the development of new marine environment monitoring technologies, prodigious amounts of complex marine environmental data are generated, and continuously increase rapidly. Features of these data include massive volume, widespread distribution, multiple-sources, heterogeneous, multi-dimensional and dynamic in structure and time. The present study recommends an integrative visualization solution for these data, to enhance the visual display of data and data archives, and to develop a joint use of these data distributed among different organizations or communities. This study also analyses the web services technologies and defines the concept of the marine information gird, then focuses on the spatiotemporal visualization method and proposes a process-oriented spatiotemporal visualization method. We discuss how marine environmental data can be organized based on the spatiotemporal visualization method, and how organized data are represented for use with web services and stored in a reusable fashion. In addition, we provide an original visualization architecture that is integrative and based on the explored technologies. In the end, we propose a prototype system of marine environmental data of the South China Sea for visualizations of Argo floats, sea surface temperature fields, sea current fields, salinity, in-situ investigation data, and ocean stations. An integration visualization architecture is illustrated on the prototype system, which highlights the process-oriented temporal visualization method and demonstrates the benefit of the architecture and the methods described in this study.

Reducing H2S production by O-2 feedback control during large-scale sewage sludge composting

Hydrogen sulfide (H2S) production patterns and the influence of oxygen (O-2) concentration were studied based on a well operated composting plant. A real-time, online multi-gas detection system was applied to monitor the concentrations of H2S and O-2 in the pile during composting. The results indicate that H2S was mainly produced during the early stage of composting, especially during the first 40 h. Lack of available O-2 was the main reason for H2S production. Maintaining the O-2 concentration higher than 14% in the pile could reduce H2S production. This study suggests that shortening the interval between aeration or aerating continuously to maintain a high O-2 concentration in the pile was an effective strategy for restraining H2S production in sewage sludge composting. (C) 2010 Elsevier Ltd. All rights reserved.

Model analysis of dissolved inorganic phosphorus exports from the Yangtze river to the estuary

In this paper, we estimate the inputs of phosphorus (P) to the Yangtze River Basin and exports of dissolved inorganic phosphorus (DIP) from the river to the estuary for the period 1970-2003, by using the global NEWS-DIP model. Modeled DIP yields range from 2.5 kg P km(-2) yr(-1) in 1970 to 4.6 kg P km(-2) yr(-1) in 1985, and then dramatically increase to 14.1 kg P km(-2) yr(-1) in 2003. No significant difference between the modeled and measured values at the level of P = 0.05 is observed. The study also demonstrates variable source contributions of P to the modeled DIP during the period 1970-2003. Point sewage P input accounted for approximately 100% in the period 1970-1985 and substantially decreased to 24.8% in 2003. Chemical fertilizer contributed 25.4% of DIP yields in 1986 and increased continuously to 50.3% in 2003, while a stable trend in manure P contribution averaging 22.9% of DIP yields was shown in the same period. The study concludes that P inputs to the Yangtze River Basin and the river DIP export to the estuary have substantially increased during the study period consequence to human pressure.

Diagnostic experiments for transport mechanisms of suspended sediment discharged from the Yellow River in the Bohai Sea

Five diagnostic experiments with a 3D baroclinic hydrodynamic and sediment transport model ECOMSED in couple with the third generation wave model SWAN and the Grant-Madsen bottom boundary layer model driven by the monthly sediment load of the Yellow River, were conducted to separately diagnose effects of different hydrodynamic factors on transport of suspended sediment discharged from the Yellow River in the Bohai Sea. Both transport and spatio-temporal distribution of suspended sediment concentration in the Bohai Sea were numerially simulated. It could be concluded that suspended sediment discharged from the Yellow River cannot be delivered in long distance under the condition of tidal current. Almost all of sediments from the Yellow River are deposited outside the delta under the condition of wind-driven current, and only very small of them are transported faraway. On the basis of wind forcing, sediments from the Yellow River are mainly transported north-northwestward, and others which are first delivered to the Laizhou Bay are continuously moved northward. An obvious 3D structure characteristic of sediment transport is produced in the wind-driven and tide-induced residual circulation condition. Transport patterns at all layers are generally consistent with circulation structure, but there is apparent deviation between the depth-averaged sediment flux and the circulation structure. The phase of temporal variation of sediment concentration is consistent with that of the bottom shear stress, both of which are proved to have a ten-day cycle in wave and current condition.

Growth mechanism. of synthetic imogolite nanotubes

By controlling the surface effects during droplet evaporation of imogolite solutions, imogolite nanotubes were dispersed individually and directly observed by transmission electron microscopy (TEM), and the structure evolution of imogolite nanotubes in the synthetic process was investigated. It was found that the number of imogolite nanotubes continuously increased with time in the whole reaction. The average length grew slowly over time after a remarkable increase in the initial 24 h, and the length distribution experienced a similar variation with the polydispersity index always below 2. No appreciable changes in tube diameters were detected under TEM observation.

Grafting of maleic anhydride onto linear polyethylene: A Monte Carlo study

Monte Carlo simulation was used to study the graft of maleic anhydride (MAH) onto linear polyethylene (PE-g-MAH) initiated by dicumyl peroxide (DCP). Simulation results revealed that major MAH monomers attached onto PE chains as branched graft at higher MAH content. However, at extremely low MAH content, the fraction of bridged graft was very close to that of branched graft. This conclusion was somewhat different from the conventional viewpoint, namely, the fraction of bridged graft was always much lower than that of branched graft under any condition. Moreover, the results indicated that the grafting degree increased almost linearly to MAH and DCP concentrations. On the other hand, it was found that the amount of grafted MAH dropped sharply with increasing the length of grafted MAH, indicating that MAH monomers were mainly attached onto the PE chain as single MAH groups or very short oligomers. With respect to the crosslink of PE, the results showed that the fraction of PE-(MAH)(n)-PE crosslink structure increased continuously, and hence the fraction of PE-PE crosslink decreased with increasing MAH concentration.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

A nonmonotonic dependence of standard rate constant on reorganization energy for heterogeneous electron transfer processes on electrode surface

In the present work a nonmonotonic dependence of standard rate constant (k(0)) on reorganization energy (lambda) was discovered qualitatively from electron transfer (Marcus-Hush-Levich) theory for heterogeneous electron transfer processes on electrode surface. It was found that the nonmonotonic dependence of k(0) on lambda is another result, besides the disappearance of the famous Marcus inverted region, coming from the continuum of electronic states in electrode: with the increase of lambda, the states for both Process I and Process II ET processes all vary from nonadiabatic to adiabatic state continuously, and the lambda dependence of k(0) for Process I is monotonic thoroughly, while for Process II on electrode surface the lambda dependence of k(0) could show a nonmonotonicity.

Tunable photonic crystals by mixed liquids

Tunable photonic crystals were prepared by infiltrating mixed liquids into the voids of silica opals. The stop bands of the tunable photonic crystals were continuously tuned by changing the relative refraction index contrast n(mix)/ns(pheres) of the spheres and the mixed liquids by varying the volume fraction of the component of the mixed liquids. The peak wavelengths of the stop band have a red shift as the refractive index of the mixed liquids increases. The transmittance at the stop band decreases with the increase of the refractive index contrast n(mix)/n(spheres). The larger the diameter of silica opals is, the wider the tunable range of the stop band is. The position and transmittance of the peak wavelength obtained by the photonic band calculations agreed very well with the experimental data.