Managing water in agriculture for food production and other ecosystem services

Agricultural systems as well as other ecosystems generate ecosystem services, i.e., societal benefits from ecological processes. These services include, for example, nutrient reduction that leads to water quality improvements in some wetlands and climatic regulation through recycling of precipitation in rain forests. While agriculture has increased ‘provisioning’ ecosystem services, such as food, fiber and timber production, it has, through time, substantially impacted other ecosystem services. Here we review the trade-offs among ecosystem services that have been generated by agriculture-induced changes to water quality and quantity in downstream aquatic systems, wetlands and terrestrial systems. We highlight emerging issues that need urgent attention in research and policy making. We identify three main strategies by which agricultural water management can deal with these large trade-offs: (a) improving water management practices on agricultural lands, (b) better linkage with management of downstream aquatic ecosystems, and (c) paying more attention to how water can be managed to create multifunctional agro-ecosystems. This can only be done if ecological landscape processes are better understood, and the values of ecosystem services other than food production are also recognized.     

Optimizing competitive uses of water for irrigation and fisheries

Choosing the appropriate reservoir water management strategy can be difficult when the water has multiple uses. This study examines this problem for reservoir managers where water use involves irrigation and fisheries. A stochastic dynamic programming (SDP) model is developed to facilitate reservoir management, using a case study illustration for southern Vietnam. The model includes the response of rice and fish yields to key factors including reservoir water levels, the timing and quantity of water release, and climatic conditions. The model also accounts for variation in rainfall patterns, irrigation requirements, and the demand for low water levels during the fish harvest season. Three production scenarios are examined where the reservoir's water is used for: only producing rice (scenario 1), only producing fish (scenario 2), and producing rice and fish (scenario 3). Key findings are: (1) for scenario 1, adequate water should be released to meet rice growing water requirements and residual water should be stored as a source of water in case of low rainfall, (2) for scenario 2, sufficient water needs to be released prior to the fish harvest to maximize this harvest; and (3) for scenario 3, water should be released prior to fish harvest, but sufficient water should remain to satisfy the water requirements of rice. When the reservoir is managed for joint production of rice and fish, net benefits are 6% greater than when the reservoir is managed solely for rice production. The SDP model developed in this paper could be adapted and applied to other multiple-use resources such as forests, river basins, and land.     

Managing water in rainfed agriculture—The need for a paradigm shift

Rainfed agriculture plays and will continue to play a dominant role in providing food and livelihoods for an increasing world population. We describe the world's semi-arid and dry sub-humid savannah and steppe regions as global hotspots, in terms of water related constraints to food production, high prevalence of malnourishment and poverty, and rapidly increasing food demands. We argue that major water investments in agriculture are required. In these regions yield gaps are large, not due to lack of water per se, but rather due to inefficient management of water, soils, and crops. An assessment of management options indicates that knowledge exists regarding technologies, management systems, and planning methods. A key strategy is to minimise risk for dry spell induced crop failures, which requires an emphasis on water harvesting systems for supplemental irrigation. Large-scale adoption of water harvesting systems will require a paradigm shift in Integrated Water Resource Management (IWRM), in which rainfall is regarded as the entry point for the governance of freshwater, thus incorporating green water resources (sustaining rainfed agriculture and terrestrial ecosystems) and blue water resources (local runoff). The divide between rainfed and irrigated agriculture needs to be reconsidered in favor of a governance, investment, and management paradigm, which considers all water options in agricultural systems. A new focus is needed on the meso-catchment scale, as opposed to the current focus of IWRM on the basin level and the primary focus of agricultural improvements on the farmer's field. We argue that the catchment scale offers the best opportunities for water investments to build resilience in small-scale agricultural systems and to address trade-offs between water for food and other ecosystem functions and services.     

Fate and risks of potentially toxic elements in wastewater-fed food production systems—the examples of Cambodia and Vietnam

Non-treated wastewater is used for irrigation of aquatic food production systems in the peri-urban areas of the major cities in Southeast Asia. This paper complement the knowledge on agricultural soil-based crops irrigated with low quality water, by reviewing the research findings on the wastewater-fed aquatic productions with special focus on heavy metals and other potentially toxic elements (PTEs) in the production systems of Hanoi in Vietnam and Phnom Penh in Cambodia. In Hanoi, sediments in the wastewater exposed rivers of Hanoi were reported to be polluted with PTEs, in particular with Cadmium (Cd). The river sediment had a high retention capacity for PTEs which seems to prevent the transport of PTEs to the wastewater-fed production systems. In Phnom Penh, domestic and industrial wastewater is pumped into the Cheung Ek Lake located south of the city. A major part of the water spinach (Ipomoea aquatica Forssk.) consumed in the city is produced in the lake. The concentrations of some PTEs were elevated at the wastewater inlets to the lake compared to concentrations at the lake outlet and at the control site. Water spinach is by far the major vegetable produced in the wastewater-fed systems in Hanoi and Phnom Penh, but did only contain PTEs in concentrations within or slightly above the concentration range observed for water spinach grown in agricultural soil not exposed to wastewater. PTE concentration in fish grown in wastewater-fed systems in Hanoi and Phnom were low. However, mean PTE concentrations in liver and skin of some fish were high. Consumption of muscle tissue from fish produced in wastewater-fed systems in Hanoi and Phnom Penh resulted in an estimated intake of PTEs amounting to less than 9% of the tolerable intake. It was concluded, that the PTE concentrations in fish and water spinach from Hanoi and Cheung Ek Lake in Phnom Penh constituted low food safety risks for consumers.     

Water harvesting and supplemental irrigation for improved water productivity of dry farming systems in West Asia and North Africa

In the dry areas, water, not land, is the most limiting resource for improved agricultural production. Maximizing water productivity, and not yield per unit of land, is therefore a better strategy for dry farming systems. Under such conditions, more efficient water management techniques must be adopted. Supplemental irrigation (SI) is a highly efficient practice with great potential for increasing agricultural production and improving livelihoods in the dry rainfed areas. In the drier environments, most of the rainwater is lost by evaporation; therefore the rainwater productivity is extremely low. Water harvesting can improve agriculture by directing and concentrating rainwater through runoff to the plants and other beneficial uses. It was found that over 50% of lost water can be recovered at a very little cost. However, socioeconomic and environmental benefits of this practice are far more important than increasing agricultural water productivity. This paper highlights the major research findings regarding improving water productivity in the dry rainfed region of West Asia and North Africa. It shows that substantial and sustainable improvements in water productivity can only be achieved through integrated farm resources management. On-farm water-productive techniques if coupled with improved irrigation management options, better crop selection and appropriate cultural practices, improved genetic make-up, and timely socioeconomic interventions will help to achieve this objective. Conventional water management guidelines should be revised to ensure maximum water productivity instead of land productivity.     

Accounting for water use: Terminology and implications for saving water and increasing production

Scarcity and competition for water are matters of increasing concern, as are potential shortages of food. These issues intersect both within the agricultural sector and across all water using sectors. Irrigation is by far the largest user of water in most water-scarce countries, and is under pressure to reduce utilisation (to release water to other sectors, including the environment) and use water more productively to meet demands for food and fibre.The terminology for such intra- and inter-sectoral analysis must be unambiguous across sectors so that interventions and their impacts are properly understood. Such terminology, based on previous work and debate, is set out. Implications for a better understanding of the scope for improved productivity of water in agriculture are traced, and some examples are given using data from recent research submissions, demonstrating the benefits of precise water accounting.     

Increasing water productivity with improved N fertilizer management

There is continuing debate about the role of water productivity and the potential to increase it in response to significantly increased water demand to meet the future needs for food—estimated to be roughly double that of today by 2050. The debate centers round the relative potential benefits of enhancing rainfed agriculture, improving irrigation and expanding areas of both. All expansion and intensification options will require significantly more water to be used, often in places where the ecosystem impacts of agriculture are already severe. Improvement in water productivity can result from improving the provision and management of the other factor inputs of crop production. There is considerable debate on the ability of other inputs—typically nitrogen—to substitute for water. This paper describes a set of simulations undertaken with well calibrated maize (Zea mays L.) crop model in Decision Support System for Agro-technology Transfer (DSSAT). The simulations investigate the response to nitrogen under rainfed conditions in Florida, and show that neither the transpiration ratio nor the harvest index are constant in practice, and that fertilizer use can enhance water productivity, even in quite high yield conditions and that the transpiration ratio can be increased by N fertilizer application at low levels of crop water use.     

Reuse of drainage water from irrigated areas

Increasing competition for water of good quality and the expectation that at least half of the required increase in food production in the near-future decades must come from the world's irrigated land requires to produce more food by converting more of the diverted water into food. Reuse of the non-consumed fraction ('drainage water') of the irrigation water already diverted is a proven but risky option for better fresh water management. This paper presents an overview of different options for reuse of drainage water and guidelines for its safe use. Criteria for maximum irrigation water salinity to prevent soil deterioration and crop yield reduction, for the maximum concentration of toxic substances and limits for bacteriological water quality are given. Examples of sustainable reuse of drainage water in Egypt, India and the USA are presented. The usefullness of simulation models for the analysis of regional water and salt balances is demonstrated.     

Economic analysis of water harvesting in a mountainous watershed in India

Water management is an essential feature of any project related with overall development of agriculture. The Soan river catchment in the northwest Himalayas, is fed only by rainwater. Hence, a strategy of rainfed agriculture needs to be developed through water conservation and storage techniques. The Soan is an important river from a soil erosion and water management point of view and detailed economic analysis is needed for any proposal to be implemented in the field. The present study was undertaken to propose an economic analysis of water harvesting structures for the Soan catchment. The purpose of the investigation is to control erosion and conserve water to meet the requirements of supplemental and pre-sowing irrigation for major cereal crops in the area and to maximise agricultural productivity. Benefit/cost ratios ranging from 0.41 to 1.33 are obtained for water harvesting structures of different sizes with estimated life of 25 and 40 years respectively, by taking into account different crop return from maize and wheat.     

Irrigation reliability and the productivity of water: A proposed methodology using evapotranspiration mapping

Irrigation is the dominant user of water worldwide, but provision of potable water and water for industry are higher priorities and give higher social and economic returns. Irrigation will continue to lose water to competing sectors and the productivity of irrigation systems (since food demand continues to grow) remains a central issue in water management. Performance assessment of irrigation has traditionally been difficult when based on field measurements of flows, deliveries and depths over large areas. Furthermore, performance measures have shifted from narrow engineering indicators to broader productivity issues of production achieved per unit of water consumed. Remote sensing, applied to the estimation of evapotranspiration (ET) over large areas, provides analysts of irrigation systems with extraordinary new tools for the objective assessment of consumption and production – constituting a quantum leap in the assessment of irrigation system performance. Awareness and utilisation of these tools is spreading, but important areas remain to be “converted” from traditional approaches that rely on an array of estimated parameters. The next challenge for remote sensing will be to map the frontier between the reliability of the irrigation service and the productivity achieved. Reliability provides the inducement for farmers to invest in higher productivity – to the benefit of themselves and society – and understanding better how the individual maximises profits within an uncertain irrigation environment can provide important guidance to managers and system designers.     

菏泽市赵王河和护城河治水保生态对策探讨

赵王河与护城河是菏泽城区两条非常重要的景观河道,由于河流水质污染治理一直不能令人满意,虽然经常换水,但是水质得不到有效保持,管理体制不健全,资金缺乏,缺乏长远规划,专业、高素质管理人才少等问题,导致赵王河与护城河水利风景区不能完全发挥其良好的社会效益、经济效益.针对这些问题,本文通过分析赵王河和护城河现状,有针对性地提出了治水保生态的措施.     

Modernization and optimization of irrigation systems to increase water productivity

Population increase and the improvement of living standards brought about by development will result in a sharp increase in food demand during the next decades. Most of this increase will be met by the products of irrigated agriculture. At the same time, the water input per unit irrigated area will have to be reduced in response to water scarcity and environmental concerns. Water productivity is projected to increase through gains in crop yield and reductions in irrigation water. In order to meet these projections, irrigation systems will have to be modernized and optimised. Water productivity can be defined in a number of ways, although it always represents the output of a given activity (in economic terms, if possible) divided by some expression of water input. Five expressions for this indicator were identified, using different approaches to water input. A hydrological analysis of water productivity poses a number of questions on the choice of the water input expression. In fact, when adopting a basin-wide perspective, irrigation return flows often can not be considered as net water losses. A number of irrigation modernization and optimization measures are discussed in the paper. Particular attention was paid to the improvement of irrigation management, which shows much better economic return than the improvement of the irrigation structures. The hydrological effects of these improvements may be deceiving, since they will be accompanied by larger crop evapotranspiration and even increased cropping intensity. As a consequence, less water will be available for alternative uses.     

Irrigation management under water scarcity

The use of water for agricultural production in water scarcity regions requires innovative and sustainable research, and an appropriate transfer of technologies. This paper discusses some of these aspects, mainly relative to on-farm irrigation management including the use of treated wastewater and saline waters. First, the paper proposes some concepts relative to water scarcity, concerning aridity, drought, desertification and water shortage, as well as policies to cope with these water stressed regimes. Conceptual approaches on irrigation performances, water use and water savings are reviewed in a wide perspective. This is followed by a discussion of supply management to cope with water scarcity, giving particular attention to the use of wastewater and low-quality waters, including the respective impacts on health and the environment as water scarcity is requiring that waters of inferior quality be increasingly used for irrigation. The paper then focuses on demand management, starting with aspects relating to the improvement of irrigation methods and the respective performances, mainly the distribution uniformity (DU) as a fundamental tool to reduce the demand for water at the farm level, and to control the negative environmental impacts of over-irrigation, including salt stressed areas. Discussions are supported by recent research results. The suitability of irrigation methods for using treated wastewaters and saline waters is analysed. Supplemental irrigation (SI) and deficit irrigation strategies are also discussed, including limitations on the applicability of related practices. The paper also identifies the need to adopt emerging technologies for water management as well as to develop appropriate methodologies for the analysis of social, economic, and environmental benefits of improved irrigation management.     

Improving agricultural water productivity: Between optimism and caution

In its broadest sense, water productivity (WP) is the net return for a unit of water used. Improvement of water productivity aims at producing more food, income, better livelihoods and ecosystem services with less water. There is considerable scope for improving water productivity of crop, livestock and fisheries at field through to basin scale. Practices used to achieve this include water harvesting, supplemental irrigation, deficit irrigation, precision irrigation techniques and soil-water conservation practices. Practices not directly related to water management impact water productivity because of interactive effects such as those derived from improvements in soil fertility, pest and disease control, crop selection or access to better markets.However, there are several reasons to be cautious about the scope and ease of achieving water productivity gains. Crop water productivity is already quite high in highly productive regions, and gains in yield (per unit of land area) do not necessarily translate into gains in water productivity. Reuse of water that takes place within an irrigated area or a basin can compensate for the perceived losses at the field-scale in terms of water quantity, though the water quality is likely to be affected. While crop breeding has played an important role in increasing water productivity in the past, especially by improving the harvest index, such large gains are not easily foreseen in the future. More importantly, enabling conditions for farmers and water managers are not in place to enhance water productivity. Improving water productivity will thus require an understanding of the biophysical as well as the socioeconomic environments crossing scales between field, farm and basin.Priority areas where substantive increases in water productivity are possible include: (i) areas where poverty is high and water productivity is low, (ii) areas of physical water scarcity where competition for water is high, (iii) areas with little water resources development where high returns from a little extra water use can make a big difference, and (iv) areas of water-driven ecosystem degradation, such as falling groundwater tables, and river desiccation. However, achieving these gains will be challenging at least, and will require strategies that consider complex biophysical and socioeconomic factors.     

Multiple use of water and water productivity of communal small dams in the Limpopo Basin, Zimbabwe

The history of dam construction in Zimbabwe dates back to the 1920s and since then over 7,000 small dams have been constructed countrywide. Small dams are multipurpose structures used for improving rural livelihoods. The multipurpose nature of these dams has largely gone unquantified in terms of importance of the uses to the community and influence of management practises. The current study made use of a questionnaire among small dam users, key informant interviews, secondary data and observation on four communal dams in the Limpopo basin to establish the uses, volume of water abstracted and water productivity for some uses and the interrelationship between various organisations and the community in the management of small dams. Uses on all dams in order of importance were livestock watering, domestic use, irrigation, fishing, brick making, and collection of reeds used for roofing. Livestock consume on average over 70% of water for consumptive uses. Water productivity in terms of yield per volume unit of water used ranged from 0.025 kg m^?3 for vegetables to 7,575 kg m^?3 for bricks, and monetary values per volume unit of water used were Z$ 389,434 m^?3 for brick making and Z$ 1,874 m^?3 for irrigation. Traditional leadership and the community are pivotal in the management of the small dams, with some organisations giving technical, financial and input assistance. The management and conservation of small dams needs to be well coordinated between the communities, NGOs and government if the full benefits of these national resources are to be realised in the long term.     

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.     

Agricultural water management and poverty linkages

Water is critically important to the livelihoods of more than 1 billion people living on less than $1 a day, particularly for the 850 million rural poor primarily engaged in agriculture. In many developing countries, water is a major factor constraining agricultural output, and income of the world's rural poor. Improved agricultural water management can contribute to poverty reduction through several pathways. First, access to reliable water improves production and productivity, enhances employment opportunities and stabilizes income and consumption. Secondly, it encourages the utilization of other yield-enhancing inputs and allows diversification into high-value products, enhances nonfarm outputs and employment, and fulfils multiple needs of households. Third, it may contribute either negatively or positively to nutritional status, health, societal equity and environment. The net impact of agricultural water management interventions on poverty may depend individually and/or synergistically on the working of these pathways. Improved access to water is essential, but not sufficient for sustained poverty reduction. Investments are needed in agricultural science and technology, policies and institutions, economic reform, addressing global agricultural trade inequities, etc. But how best to match the agricultural water management technologies, institutions and policies to the needs of the heterogeneous poor living in diverse agro-ecological settings remains unclear. This article provides a menu of promising pathways through which agricultural water management can contribute to sustained poverty reduction.     

中国节水灌溉装备与技术发展展望

分别从灌排设施、灌排管理体制和投资政策3个方面,回顾了中国灌溉排水70 a以来所取得的成就.随着灌溉面积增大,灌排设施极大提高了中国粮食产量和农业生产能力;灌排管理体制发生巨大变化,由农民集体管理为主转化为骨干工程国家事业单位管理为主,促进了灌排工程快速发展和良性运行;投资政策有效地服务了水利基本建设.但目前中国依旧存在灌溉用水利用率较低、水肥一体化灌溉农田占比较低和灌溉系统信息化程度较低等问题,与高质量的农业生产发展还有很大的距离.结合国家粮食与生态保障的战略需求,分别从大中型灌区节水改造、水肥一体化节水灌溉装备与技术和喷滴灌、管道输水灌溉和泵站改造方面,提出了中国节水灌溉装备与技术的未来机遇和挑战.为了促进中国节水灌溉行业发展,加强灌排装备的理论研究和自主创新,发展高效、节能和环保的技术和产品,提高产业信息化、智能化和网络化,是实现农业现代化生产建设的必然趋势.     

Crop production functions and the allocation and use of irrigation water

The economically optimal depth of irrigation water to apply depends on the relationship between crop yield and water use. Past research efforts to formulate and to explain the factors influencing irrigated crop production functions have therefore been briefly reviewed. Although it is not possible to obtain a unique relationship, by considering a possible range of functions, and by understanding the factors causing variations in the form of these functions, valuable conclusions can be drawn relating to the optimal depth of water application and the relative magnitude of benefits derived from efficient water management.     

Diagnosing irrigation performance and water productivity through satellite remote sensing and secondary data in a large irrigation system of Pakistan

Irrigation policy makers and managers need information on the irrigation performance and productivity of water at various scales to devise appropriate water management strategies, in particular considering dwindling water availability, further threats from climate change, and continually rising population and food demand. In practice it is often difficult to access sufficient water supply and use data to determine crop water consumption and irrigation performance. Energy balance techniques using remote sensing data have been developed by various researchers over the last 20 years, and can be used as a tool to directly estimate actual evapotranspiration, i.e., water consumption. This study demonstrates how remote sensing-based estimates of water consumption and water stress combined with secondary agricultural production data can provide better estimates of irrigation performance, including water productivity, at a variety of scales than alternative options. A principle benefit of the described approach is that it allows identification of areas where agricultural performance is less than potential, thereby providing insights into where and how irrigation systems can be managed to improve overall performance and increase water productivity in a sustainable manner. To demonstrate the advantages, the approach was applied in Rechna Doab irrigation system of Pakistan’s Punjab Province. Remote sensing-based indicators reflecting equity, adequacy, reliability and water productivity were estimated. Inter- and intra-irrigation subdivision level variability in irrigation performance, associated factors and improvement possibilities are discussed.