区域水资源承载力研究综述᠃

概述了区域水资源承载力的研究现状、概念、特征、研究方法、评价指标、度量。强调了系统研究区域水资源承载力的重要现实意义。指出了当前研究中存在的不足，以及有待进一步研究的问题。     

Investing in water for food, ecosystems, and livelihoods: An overview of the comprehensive assessment of water management in agriculture

The authors of the recently completed Comprehensive Assessment of Water Management in Agriculture (CA) concluded that there are sufficient water resources to produce food for a growing population but that trends in consumption, production and environmental patterns, if continued, will lead to water crises in many parts of the world. Only if we act to improve water use will we meet the acute fresh water challenge. Recent spikes in food prices, partially caused by the increasing demand for agricultural products in non-food uses, underline the urgent need to invest in agricultural production, of which water management is a crucial part. The world experienced similar pressure on per capita food supplies and food prices in the 1960s and 1970s, but the challenges now are different than those we experienced 50 years ago. The world's population is substantially larger, there are many more people living in poverty, and the costs of many agricultural inputs are much higher. The current situation and the long-term outlook require a fresh look at approaches that combine different elements such as the importance of access to water for the poor, providing multiple ecosystem services, rainwater management, adapting irrigation to new needs, enhancing water productivity, and promoting the use of low-quality water in agriculture. This special issue highlights the analysis behind a number of policy options identified by the CA, a five-year multi-disciplinary research program involving 700 scientists. This introductory article sets the background and context of this special issue, introduces the key recommendations from the CA and summarizes the papers in this issue.     

An economic perspective on the potential gains from improvements in irrigation water management

In recent years, several researchers have introduced new terms describing irrigation efficiency to enhance the information available when evaluating water policy alternatives. Some of the definitions expand the physical boundary considered when evaluating water use, while others account for the changes in water quality that occur as drainage water is reused in an irrigated area. While the concepts of basin, global, and effective efficiency have enhanced our understanding of water use in agriculture, public officials may derive incorrect policy implications when reviewing empirical estimates of those measures, particularly if information describing the economic impacts of water use and allocation decisions is not available. For example, some authors suggest that when estimates of basin-wide efficiency approach 100%, there is little opportunity to save water by improving water management and achieving higher levels of classical, farm-level efficiencies in upstream portions of an irrigated region. However, there may be significant opportunities to increase the net values generated with limited water resources by improving the distribution of water among farmers and reducing the negative, off-farm effects of irrigation and drainage activities. Economic analysis is helpful in identifying those opportunities and in designing policies that encourage farmers and water agency personnel to improve water management practices in ways that enhance social net benefits.     

An approach to estimating the potential production benefits from improved irrigation water management for rice

Production benefits of improved allocation of irrigation water are often difficult to measure. In situations of irrigated wet rice cultivation, bothex post estimates of such benefits andex ante estimates of the maximum potential benefits of further improvements in allocation of a given water supply are possible using a conceptual framework which (1) functionally relates weekly water supplies to weekly measures of average water shortage on individual paddy fields; (2) aggregates the weekly water shortage measures into a seasonal water shortage index; and (3) relates, via a production function, the seasonal water shortage index to yields. An empirical application of this framework estimates the potential increase in production from further improvements in water allocation in one Philippine irrigation system to be negligible.     

土壤抗剪强度测定理论教学与实践

根据工学院人才培养目标和人才培养规格．以理论与实践相结合为原则,制定教学大纲与实践教学大纲,建立农学基础课程的教学计划体系以及相应的章节内容,并按大纲的要求进行教学与实践,教学进程紧紧围绕理论与实践两条主线进行．为学生适应农业现代化服务提供理论支持。     

Simulation of water harvesting potential in rainfed ricelands using water balance model

Using daily water balance simulation in rainfed ricelands, the study estimates the probable supplemental irrigation (SI) requirement to meet the water deficits during the reproductive stage of rice and surface runoff (SR) generated that can be harvested in OFR for meeting the aforesaid SI. Value of SI of rice during reproductive stage at 25% probability of exceedence (PE) was found to be 144 mm, neglecting distribution and application losses. Water harvesting potential of the study area indicates that at 50% PE, 85% of SI of rice can be met from the SR generated from the ricelands and stored in OFR. Rest amount of SI can be met from the direct conservation of rainfall in a lined OFR of 2 m depth with 1:1 side slope occupying 9% ricelands. Economic analysis of OFR irrigation system reveals that OFR of 9% ricelands gives net profit (NP) of Indian Rupees (Rs.) 13445 (US $295.49) for 1 ha sown with dry seeded rainfed upland rice with benefit–cost ratio (BCR) of 1.25. Values of NP and BCR indicate that investment in OFR irrigation system is profitable in the study region.     

Soil water content and water balance in rainfed fields in Northeast Thailand

Northeast Thailand has a semi-humid tropical climate which is characterized by dry and rainy seasons. In order to stabilize crop production, it may be necessary to develop new water resources, such as soil moisture and groundwater, instead of rainfed resources. This is because rainfed agriculture has already been unsuccessfully tried in many areas of this region. In this study, we investigate the soil water content in rainfed fields in Khon Kaen in Northeast Thailand, where rice and sugarcane were planted, over a 1-year period that contained both dry and rainy seasons, and estimate the actual evapotranspiration (ET_a) using micrometeorological data. In addition, we assess the water balance from the results of the soil water content investigation and the actual evapotranspiration. Although the soil water content at depths above 0.6 m in both the lower and the sloping fields gradually decreased during the dry season, the soil water content at a depth of 1.0 m was under almost constant wet conditions. Two-dimensional profiles of the soil water content demonstrated that at the end of the dry season, the soil layers below a depth of 0.4 m showed a soil water content of more than 0.10-0.15 m³ m⁻³, thus suggesting that water was supplied to the sugarcane from those layers. The range in ET_a rates was almost the same as that in the previous study. The average ET_a rates were 3.7 mm d⁻¹ for the lower field and 4.2 mm d⁻¹ for the sloping field. In the dry season, an upward water flow of 373 mm (equivalent to a flux of 1.9 mm d⁻¹) was estimated from outside the profile. The source of this upward water flow was the sandy clay (SC) layer below a depth of 1 m. It was this soil water supply from the SC layer that allowed the sugarcane to grow without irrigation.     

城市公交车制动能量回收方式综述

文章在分析城市公交车运行工况的基础上,说明了城市公交车能量回收系统的必要性。分析了三种制动能量回收方式的结构原理,对三种制动能量回收系统在城市公交车上的应用进行了分析比较。     

Soil water dynamics model for trickle irrigated tomatoes

A soil water dynamics model for establishing the wetting pattern of point source trickle emitters under a tomato crop has been developed and verified. Infiltration from the point source trickle emitters in the presence of water extraction has been investigated by assuming a hemispherical shape of the wetted soil volume and analytic expressions have been derived for determining the position of wetting front. Water extraction by the plants has been estimated by using a macroscopic model of uptake utilizing root length. Daily values of water uptake have been used to update the volumetric moisture content in the root zone layers. The values of soil moisture content predicted by the model compared well with the field-observed values. The predicted values were used to predict the radius of the hemispherical wetted soil volume which forms a basis for deciding emitter spacing for various crops and operating conditions.     

Estimating the potential gains from water markets: a case study from Tunisia

Water markets can improve water use efficiency through the transfer of water to users who can obtain the highest marginal return from using it. Existing water markets are implemented among farmers or between farmers and urban water companies or hydropower companies. Several studies have shown that farmers may benefit from trading water mainly in countries where water scarcity is increasing and new water supply projects are either very costly or not possible because of environmental concerns. This paper estimates the potential benefits and losses of implementing water market among farmers and between farmers and urban water company in Tunisia. We used linear programming to examine four separate farm models and an aggregate model. The method is applied to an irrigation area of 4500 ha in Northern Tunisia. Results indicate that water trading among farmers would be quite limited and would have a minor impact on farmers’ income. In contrast, the market among farmers and the urban water company offers higher volumes of water trades to urban users and helps increase farmers’ profitability by up to 7.9%. The sale of water to the urban company is accompanied by a decrease in occasional labor by as much as 34.8% and a decrease of up to 17.6% in farmers’ expenditures for inputs and machinery. Additionally, results obtained in this paper show that inter-year storage of irrigation water may be more advantageous than selling water to the urban utility. Whether farmers would opt to sell water or inter-temporarily store it would depend on the establishment of water rights and the empowerment of farmers.     

Responses of five almond cultivars to irrigation: Photosynthesis and leaf water potential

In the Trás-os-Montes region, almond orchards are usually planted in the dry soils on the upper valley of the Douro river and are typically cultivated under non-irrigated conditions, leading to low yields. This study aimed to compare the physiological responses of five almond varieties (Francoli, Ferragnès, Glorieta, Lauranne and Masbovera) growing under non-irrigated and irrigated conditions. In irrigated conditions, all cultivars had higher photosynthetic rates, with maximum rates in a range of 10–12 μmol CO₂ m⁻² s⁻¹. Study of daily photosynthesis (June–August) indicates that, irrigated plants showed maximal values at 11 h (32 °C), while in water stressed ones highest values were found at 9 h (28 °C). The irrigation induced an increase in photosynthesis of around 173% in Lauranne, 187% in Francoli, 204% in Glorieta, 266% in Masbovera and 331% in Ferragnès. In relation to values of water potential that allow half-rate of photosynthesis (ψ_w50), they were calculated as −2.95, −2.50, −3.10, −3.20 and −3.30 MPa for Ferragnès, Glorieta, Masbovera, Francoli and Lauranne, respectively.     

Micro-catchment water harvesting potential of an arid environment

Micro-catchment water harvesting (MCWH) requires development of small structures across mild land slopes, which capture overland flow and store it in soil profile for subsequent plant uses. Water availability to plants depends on the micro-catchment runoff yield and water storage capacity of both the plant basin and the soil profile in the plant root zone. This study assessed the MCWH potential of a Mediterranean arid environment by using runoff micro-catchment and soil water balance approaches. Average annual rainfall and evapotranspiration of the studied environment were estimated as 111 and 1671 mm, respectively. This environment hardly supports vegetation without supplementary water. During the study period, the annual rain was 158 mm in year 2004/2005, 45 mm in year 2005/2006 and 127 mm in year 2006/2007. About 5000 MCWH basins were developed for shrub raising on a land slope between 2 and 5% by using three different techniques. Runoff at the outlets of 26 micro-catchments with catchment areas between 13 and 50 m² was measured. Also the runoff was indirectly assessed for another 40 micro-catchments by using soil water balance in the micro-catchments and the plant basins. Results show that runoff yield varied between 5 and 187 m³ ha⁻¹ for various rainfall events. It was between 5 and 85% of the incidental rainfall with an average value of 30%. The rainfall threshold for runoff generation was estimated about 4 mm. Overall; the soil water balance approach predicted 38-57% less water than micro-catchment runoff approach. This difference was due to the reason that the micro-catchment runoff approach accounted for entire event runoff in the tanks; thus showed a maximum water harvesting potential of the micro-catchments. Soil water balance approach estimated water storage in soil profile and did not incorporate water losses through spillage from plant basins and deep percolation. Therefore, this method depicted water storage capacity of the plant basins and the root zone soil profile. The different between maximum water harvesting potential and soil-water storage capacity is surplus runoff that can be better utilized through appropriate MCWH planning.     

Soil surface shrinkage to estimate profile soil water

Summary The surface elevation of a shrinking soil provided good estimates of the change in profile water content under alfalfa. Surface shrinkage was found to change linearly with water content as measured by neutron and gamma attenuation devices. Extracted soil cores were tested in the laboratory to obtain the linear shrinkage ratio, b. In the field, shrinkage was calculated as the average elevation change of small ceramic plates. Compaction of the soil by harvesting machinery had no adverse effect on the linearity of the shrinkage/water loss relationship, but lack of compaction resulted in nonlinear shrinkage as the soil was unconsolidated and may have exhibited sub-surface horizontal cracking. These cracks were attributed to roots which anchored the soil during shrinkage. In a second study, local values of swelling (b) from initial measurements before and after irrigation were superior estimators of measured water loss compared to a single universal b value from independent tests.     

土壤水分入渗参数的非线性预报模型

以山西地区黄土高原区土壤为研究对象,通过实施大量大田耕作土壤水分入渗试验,获取了Kostiakov二参数入渗模型参数的实测大样本,建立了各个土壤水分入渗参数与土壤理化参数间的非线性关系模型;通过MATLAB软件,实现了Kostiakov入渗模型系数的求解。结果表明,常规土壤理化参数土壤含水率、体积质量、粉粒、砂粒和有机质质量分数作为非线性预报模型的输入参数是合理的,所建立的非线性关系模型高度相关,预测参数的实测值与预测值的相对误差可控制在8%以下。因此,用土壤常规理化参数对土壤水分入渗参数进行非线性预报是可行的。     

Water productivity in rainfed systems: overview of challenges and analysis of opportunities in water scarcity prone savannahs

Addressing the Millennium Development Goals on food and poverty over the coming decade puts enormous pressure on the world’s finite freshwater resources. Without water productivity (WP) gains, the additional freshwater in agriculture will amount to 5,600 km³ year⁻¹ in 2050. This is three times the current global irrigation use. This paper focuses on the underlying processes and future opportunities of WP gains in water scarcity prone and poverty stricken savannah regions of the world. The paper studies the consumptive (green) WP dynamics rainfed farming systems, and shows that the often assumed linear relationship between evapotranspiration (ET) and yield (Y) does not translate into constant WP over a wide range of yields. Similarly, crop transpiration (T) and Y show non-linearity under on-farm and low yield conditions. This non-linearity is validated against several on-farm research experiments in semi-arid rainfed farming systems. With integrated soil and water management, focusing on dry spell mitigation and soil fertility can potentially more than double on-farm yields, while simultaneously improve green (ET) WP and productive green (T) WP. Through the adoption of appropriate soil and water management in semi-arid smallholder farming systems, crop yields improve and result in improved livelihoods and WP gains.     

Effect of soil water osmotic potential on growth and water relationships in barley during soil water depletion

Summary Barley plants (Hordeum distichum, L., cv. Zita) grown in a sandy soil in pots were adjusted during a pretreatment period of 5 days to three levels of soil water osmotic potential by percolating 61 of a nutrient solution with additional 0, 22.3 and 44.6 mM KCl. A drying cycle was then started and the plants were harvested when the soil water matric potential had decreased to –1.4 MPa, respectively 6, 7 and 8 days later.No significant differences in dry matter yields, transpiration coefficients and wilting percentages were found between treatments.During the drying cycle leaf water potential ( _l ) decreased concomitantly with decrease in soil water potential ( _s ) with almost constant and similar differences ( _l – _s ) for all treatments despite differences in levels of potentials. The concomitant decrease in leaf osmotic potential () was due partly to dehydration (58%) and partly to increase in leaf solute content (42%) independent of treatment. The part of total osmotic solutes due to K decreased relatively during the drying cycle.Close relationships were found between and _l as functions of relative water content (RWC). Identical curves for the two levels of salt treatment agree with similar concentrations of K, Cl, and ash found for salt treated plants indicating that maximum uptake of macro nutrients may have been reached.During the main part of the drying cycle the turgor potential as function of RWC was higher and decreased less steeply with decreasing RWC in the salt treated than in the non-salt treated plants.In the beginning of the drying cycle additions of KCI lowered the transpiration rates of the salt treated plants resulting in a slower desiccation of the soil and hence an increased growth period. A delay in uptake from a limited soil water supply may be advantageous during intermittent periods of drought.     

Estimating the potential of rainfed agriculture in India: Prospects for water productivity improvements

A detailed district and agro-ecoregional level study comprising the 604 districts of India was undertaken to (i) identify dominant rainfed districts for major rainfed crops, (ii) make a crop-specific assessment of the surplus runoff water available for water harvesting and the irrigable area, (iii) estimate the efficiency of regional rain water use and incremental production due to supplementary irrigation for different crops, and (iv) conduct a preliminary economic analysis of water harvesting/supplemental irrigation to realize the potential of rainfed agriculture. A climatic water balance analysis of 225 dominant rainfed districts provided information on the possible surplus runoff during the year and the cropping season. On a potential (excluding very arid and wet areas) rainfed cropped area of 28.5 million ha, a surplus rainfall of 114 billion m³ (Bm³) was available for harvesting. A part of this amount of water is adequate to provide one turn of supplementary irrigation of 100 mm depth to 20.65 Mha during drought years and 25.08 Mha during normal years. Water used in supplemental irrigation had the highest marginal productivity and increase in rainfed production above 12% was achievable even under traditional practices. Under improved management, an average increase of 50% in total production can be achieved with a single supplemental irrigation. Water harvesting and supplemental irrigation are economically viable at the national level. Net benefits improved by about threefold for rice, fourfold for pulses and sixfold for oilseeds. Droughts have very mild impacts on productivity when farmers are equipped with supplemental irrigation.     

A historical perspective on measurement of soil and plant water status and plant water status

Summary Surrounded by many sophisticated instruments, data acquisition systems and connecting computers, contemporary soil and plant scientists may not fully appreciate what really was known in earlier times and how the science has developed. A short review and a few examples of the growth of measurements and ideas are presented here.     

The potential for monolayers to reduce the evaporation of water from large water storages

In the laboratory, molecularly thick films of compounds such as hexadecanol and octadecanol have been shown to retard the evaporation of water. While such monolayers offer the prospect of an economical solution to the evaporative loss of water from storages there are practical difficulties arising mainly from the short lifetimes of these monolayers on the water surface. This review article describes the relevant laboratory experiments and results, and then discusses the problems that have arisen in field applications. It is clear that better monolayer materials are required and that better methods of monolayer distribution would also be helpful. Although no resolution of these difficulties is available at present it is hoped that a better understanding of the problems will stimulate further research.     

Soil surface water repellency induced by treated wastewater irrigation: physico-chemical characterization and quantification

Irrigation with treated wastewater (TWW) is commonly practiced in Israel to relieve freshwater (FW) shortages. We hypothesized that the organic matter (OM) originating from TWW irrigation alters the physico-chemical properties of the soil, induces water repellency in the soil’s top layer, and consequently alters water distribution in the soil profile. In measurements taken in an avocado orchard on a clayey soil, water repellency was found in TWW-irrigated plots. In addition, smaller wetted surface areas were recorded around the drippers in comparison with FW drippers. Drier zone below soil surface was observed in TWW-emitting drippers. OM extraction from the different plots exhibited differences in quantity and quality of organic substances between TWW- and FW-irrigated soils, with a higher quantity of hydrophobic substances in the TWW-irrigated soil extract.