1,720,986 research outputs found
Derivation and application of hydraulic equation for variable-rate contour-controlled sprinklers
No full textThe variable-rate contour-controlled sprinkler (VRCS) for precision irrigation can throw water on a given shaped area and the flow rate is also varied with the throw distance of the sprinkler for the purpose of high uniformity irrigation. Much of past research work were concentrated on the mechanical availability of variable-rate application and the design of VRCS main construction without considering the theoretical operation principles of VRCS. This study aimed to develop the mathematic models describing the relationship between hydraulic parameters of VRCS and these models will be the theoretical guidance for the design of VRCS. The hydraulic operational equation that describes the internal connection of flow rate, rotating speed and throw distance of VRCS was derived using mathematical theory of limitation and double integral. The derived operational equation indicates that the flow rate of VRCS is proportional to the product of rotating speed and square throw distance. The square wetted area sprinklers were used to illustrate the application of the operational equation of VRCS. The theoretical throw distance equation for the square wetted area sprinkler was built. With the operational equation and theoretical throw distance equation, the theoretical flow rate and rotating speed equations of the square wetted area sprinkler were derived. These results of this study provide fundamental principles for the design of VRCS
The effects of no-tillage practice on soil physical properties
No full textNo-tillage (NT) is now widely recognized as a variable concept for practicing sustainable agriculture. The objectives of this study were to summarize the effects of no-tillage on soil physical properties and outline the environment capability of no-tillage practice. The effect of no-tillage on soil bulk density was a debated question, and in order to make it comparable, the study conditions (soil texture, climate conditions, planting system, straw covering conditions on soil surface, soil water content and the no-tillage practiced period) were first addressed. Total porosity, a measure of the porous space left in the soil for air and water movement, was inversely related to bulk density. When the conventional tillage practices were used, the volume of soil macropores (>0.05 cm) was higher than that under no-tillage practice. With time, it decreased greatly, but the conventional tillage treatment still kept the lead. As a result of soil agitation, the soil aggregate rate under conventional tillage cropland was generally lower than that under the no-tillage practiced cropland. The studies of no-tillage on soil temperature and on crop yield also have conflicting results because of the absence of systemically long term monitoring, and there was little information on the effects of no-tillage on crop quality. Therefore, future perspectives of no-tillage research were put forward
Limited water scarcity mitigation by expanded interbasin physical and virtual water diversions with uneven economic value added in China
No full textInterbasin water diversion projects and virtual water transfers embedded in exchanged goods and services are two effective solutions to water deficits. However, the associated real responses in water quantity and quality scarcities and the economic efficiencies remain unclear. Here, we tracked the blue water scarcities, water pollution levels, and economic value added through interbasin physical and virtual water diversions across nine river basins by sector in China from 2007 to 2015. The total national blue and grey water footprints were 365 Gm3yr-1 and 592 Gm3 yr-1, in which the Yangtze River basin accounts the most for 32 % and 37 %, respectively, by 2015. The physical water diversions increased by 52 % to 16.9 Gm3yr-1. The blue virtual water transfers increased by 24 % to 176 Gm3yr-1, whereas the grey virtual water transfers decreased by 10 % to 266 Gm3yr-1. Agriculture related interbasin virtual water flows showed opposite directions to those driven by the industry sector. Although with uneven value added while growing, limited effects mitigated water quantity and quality stresses, especially in the drier Yellow, Northwest, and Hai River basins where the capital is located. Half of the basins had low and declining synergy scores, suggesting an urgent need to achieve synergies between resources, the environment, and the economy across basins
Soil moisture variability along transects over a well-developed gully in the Loess Plateau, China
No full textKnowledge of soil moisture distributions in gullies, which are highly variable spatially and temporally, is important for both restoring vegetation and controlling erosion in them, but little attention has been paid to this spatio-temporal variability to date. Therefore, we examined soil moisture profiles and their variability along three transects traversing sidewalls of a well-developed gully with steep slopes in a hilly area of the Chinese Loess Plateau. We took intensive measurements at 20-cm intervals from 0 to 160 cm depth, using a portable time domain reflectometer, from September 3 to October 20 2009 and from April 5 to July 20 2010. The results indicate that the mean, standard deviation and coefficient of variation of moisture content vary with time, their responses to precipitation vary at different depths, and moisture content is most variable when mean values are moderate (15-20%). Revised fitting functions developed and introduced by Famiglietti et al. (2008) captured with confidence the relationship between spatial variability (SD and CV) and spatial mean of moisture content (RMSE ranging from 0.0015 to 0.0293). Soil moisture clearly varied along the transects, the vertical distribution of soil moisture differed in different seasons, and correlation analysis showed that soil texture influenced the variability of surface soil moisture more strongly than terrain attributes (except during distinct rainfall events, when this pattern reversed). The results presented here should improve understanding of spatio-temporal variations in soil moisture profiles in well-developed gullies in the Loess Plateau, and potentially elsewhere. (C) 2011 Elsevier B.V. All rights reserved
Estimating spatial mean soil water contents of sloping jujube orchards using temporal stability
No full textEstimating spatial mean soil water contents from point-scale measurements is important to improve soil water management in sloping land of semiarid areas. Temporal stability analysis, as a statistical technique to estimate soil water content, is an effective tool in terms of facilitating the upscaling estimation of mean values. The objective of this study was to examine temporal stability of soil water profiles (0-20, 20-40, 40-60 and 0-60 cm) in sloping jujube (Zizyphus jujuba) orchards and to estimate field mean root-zone soil water based on temporal stability analysis in the Yuanzegou catchment of the Chinese Loess Plateau, using soil water observations under both dry and wet soil conditions. The results showed that different time-stable locations were identified for different depths and the temporal stability of soil water content in 20-40 cm was significantly (P < 0.05) weaker than that in other depths. Moreover, these time-stable locations had relatively high clay contents, relatively mild slopes and relatively planar surfaces compared to the corresponding field means. Statistical analysis revealed that the temporal stability of root zone soil water (0-60 cm) was higher in either dry or wet season than that including both, and soil water exhibited very low temporal stability during the transition period from dry to wet. Based on the temporal stability analysis, field mean soil water contents were estimated reasonably (R(2) from 0.9560 to 0.9873) from the point measurements of these time-stable locations. Since the terrains in this study are typical in the hilly regions of the Loess Plateau, the results presented here should improve soil water management in sloping orchards in the Loess Plateau. (C) 2011 Elsevier B.V. All rights reserved
Effects of Elevated Ammonia Concentration and Nitrogen Status on the Growth and Yield of Winter Wheat
No full textElevated atmospheric NH(3) may affect productivity of crops in part by altering N assimilation, and the effect may be responsible for the N status of the plant. To investigate this possibility, measurements of plant height, leaf area per plant, net photosynthesis rate (P(n)), plant biomass production, shoot/root (SIR) ratio, grain yield and its components were used to examine the effects of elevated NH(3) concentration in combination with N status on growth and yield in pot-grown winter wheat (Triticum aestivum L.) using open-top chambers. After 2 month of NH(3) injection, elevated NH(3) significantly increased plant height, leaf area per plant, shoot biomass production (total biomass), and S/R ratio in the N-deprived plants in both years, but the corresponding values in the N-sufficient plants were reduced. The P(n) values were increased with NH(3) enhancement both in the presence and absence of N in the potting soil in each experimental year, but the increment of P(n) in N-deprived plants was two times higher than that of the N-sufficient plants in both years. At harvest, grain yields of N-deprived winter wheat exposed to elevated levels of NH(3) were increased by 21% and 23% than that of N-deprived winter wheat exposed to 0 levels of NH(3), while grain yields of N-sufficient winter wheat exposed to elevated levels of NH(3) were decreased by 27% and 23% than that of N-sufficient winter wheat exposed to 0 levels of NH(3) in 2007 and 2008, respectively
Effects of alfalfa coverage on runoff, erosion and hydraulic characteristics of overland flow on loess slope plots
No full textAn evaluation of the interactions between vegetation, overland and soil erosion can provide valuable insight for the conservation of soil and water. An experiment was conducted to study water infiltration, runoff generation process, rate of sediment erosion, and hydrodynamic characteristics of overland flow from a sloping hillside with different draw-off discharges from alfalfa and control plots with 20A degrees slope. The effect of alfalfa on runoff and sediment transport reduction was quantitatively analyzed. Alfalfa was discussed for its ability to reduce the overland flow scouring force or change the runoff movement. Compared to the bare-soil plots, alfalfa plots generated a 1.77 times increase in infiltration rate. Furthermore, the down-slope water infiltration rate for the bare soil plots was higher than in the up-slope, while the opposite was found in the alfalfa plots. In addition, alfalfa had a significant effect on runoff and sediment yield. In comparison to the control, the runoff coefficient and sediment transportation rate decreased by 28.3% and 78.4% in the grass slope, respectively. The runoff generated from the alfalfa and bare-soil plots had similar trends with an initial increase and subsequent leveling to a steady-state rate. The transport of sediment reduced with time as a consequence of the depletion of loose surface materials. The maximum sediment concentration was recorded within the first few minutes of each event. The alfalfa plots had subcritical flow while the baresoil plots had supercritical flow, which indicate that the capability of the alfalfa slope for resisting soil erosion and sediment movement was greater than for bare soil plots. Moreover, the flow resistance coefficient and roughness coefficient for the alfalfa plots were both higher than for the bare-soil plots, which indicate that overland flow in alfalfa plots had retarded and was blocked, and the flow energy along the runoff path had gradually dissipated. Finally, the ability to erode and transport sediment had decreased
One of frontiers in agricultural and environmental biotechnology for the arid regions: Micro-pressure drip irrigation technology theory and practices
No full textWith the goal of reducing cost and energy consumption of drip irrigation systems, the relationship between pressure and cost of drip irrigation systems, as well as the feasibility of reducing the operating pressure, were analyzed. The irrigation quality and reliability of micro-pressure drip irrigation systems were also studied. A theory of micro-pressure drip irrigation technology is proposed, and the components of this type of irrigation system are presented. The results indicate that micro-pressure drip irrigation technology is feasible and that it can significantly decrease initial drip irrigation system cost and recurring operating expenses. Micro-pressure drip irrigation can also overcome some of the clogging problems of conventional drip irrigation systems. It is suggested that micro-pressure drip irrigation will be a topic of importance in the future of agriculture and environmental biotechnology
Application of virtual water trade theory in inter-regional grain allocation and transportation in China
No full textChina was partitioned into eight regions, and the virtual water flow due to regional grain allocation and transportation among these regions was calculated in 2008 based on virtual water and virtual water trade theories. Then, we analyzed the relations between virtual water trade structure and water resources utilization. Results show that the grain output regions in China were Northeast, Huang-Huai-Hai and the Middle-Lower Yangtze regions, where the grain outputs were 5.3x10(7)t, 2.8x10(7)t, and 5.6x10(6)t respectively and the corresponding virtual water exports were 5.55x10(10)m(3), 2.78x10(10)m(3), and 0.53x10(10)m(3), respectively. There were large amounts of virtual water import in the Southern, Southeast and Northern China, and the sum of the three region was up to 7.0x10(10)m(3). The whole country saved about 3.05x10(10)m(3) water resource as a result of the well correspondence between structure of grain allocation and transportation and the comparative advantage of regional water utilization efficiency; but the virtual water export and import conditions in each region mismatched the Endowment of Resources Principle when considering water resource condition. The distribution of national grain production and water resource was not suited with each other. The Chinese government should proposed corresponding measures
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