Preface: Salinity management in Agriculture: the basis and applications

Agriculture is a human activity that is intimately associated with climate. A major concern in the understanding of the impacts of climate change is the extent to which agriculture will be affected. Thus, in the long term, climate change is an additional problem that agriculture has to face in meeting global and national food requirements while preserving the environment. Climate models predict more extreme weather conditions for decades to come. The agriculture sector will have to deal with larger differences in shortage and excess, compared with the current practice. Therefore, there will be a need to develop adaptations or survival strategies and means for agriculture to become more flexible in its dependence on water and go through extreme climate events. Future number of droughts and flood events are likely to increase with the semi arid regions may face growing water shortage or even water scarcity. Worldwide population growth and rapid urbanization are causing imbalance between water supply and demand. There are two ways to overcome this problem. First by increasing the efficiency with which current needs are met (e.g. more crop per drop) and secondly by increasing the use of saline water resources such as saline agriculture drainage water/brackish groundwater, reclaimed wastewater as well as the conjunctive use of surface and groundwater. The irrigation is most important water consumer. Many heavily irrigated regions of the world are facing a lowering of water tables, land degradation, desertification, salinization and the destruction or degradation of wetlands and aquifers. Bad irrigation practices may enhance salinization specially when irrigation water contains salts or is reused. Salinization affects 25% of the irrigated land in the European Mediterranean. In the particular case of Spain, salinization is widely spread along extensive areas of the Mediterranean coast, mainly in the South East and inland regions. Globally around 43 countries, mostly from arid and semi arid regions, are using saline water for irrigation. The southern Mediterranean countries are using saline water in irrigation purely by necessity, rather than by choice. Bad management of using saline water resources in irrigation could in the long run, seriously affect crop production; deteriorate soil productivity and create serious environmental problems. Semi-arid regions frequently suffer from years of below-average rainfall and severe drought. Studies and field practices by farmers in many regions of the world have shown that water normally classified as too saline for conventional agricultural use can in fact be used to irrigate a wide variety of annual and perennial crops. Plants (trees, crops, fodder, halophytes, etc.) of moderate to high salt tolerance can be irrigated with saline water especially at later growth stages. The long-term success of irrigation with saline water depends largely on the evolution of practical management strategies and the exchange of information among researchers and farmers. Careful integrated management of irrigation water; proper crop selection, taking into consideration rainfall and climate; leaching to control soil salinity; drainage; and amendment applications, if necessary to control sodicity, are the keys to successful management. On the other hand, unsuccessful irrigation and drainage water management could result in an increase of the proportion of salt-affected lands and consequent negative impacts on soil and ground water quality. In the long term, this could lead to an increase in areas of degraded, salinized and unproductive lands. The yield of crops irrigated with saline water could be enhanced substantially, if an additional source of good quality water were available for use at critical times during the season, or for crops that lack salt tolerance but can be grown in a rotation. An alternative approach would be to use the good quality water in a mixture of saline and non-saline water (water blending). The use of saline drainage water for irrigation has the environmental advantages of reducing the non-saline water requirement for salt-tolerant crops and decreasing the volume of drainage water requiring disposal or treatment. In fact, there is no universal approach to achieve salinity control in irrigated agriculture; it varies from country to another. It depends on economic, climatic, social and hydro-geological conditions. Finally, sustainability and success of saline water uses depends on sound implementation and management. Poor planning and management might bring environmental risks, and undesired economic and social consequences. During the planning and management phases, the ecological, social and economic aspects should be considered in order to assure social and economic viability of any reuse activities. There are also a number of social and economic benefits that encourage the use of saline water for agricultural purposes. Using saline water could improve the welfare for local communities, as the use of a saline water resource for irrigation will reduce the stress that exists on conventional freshwater supplies. This is particularly important given the scarcity that is predicted as a result of climate change. Moreover, using saline water is a way to mitigate shortages of irrigation water within local communities and reduce conflict over water resources. Additionally, it might also allow irrigated agriculture to take place in areas where it is currently not possible due to the lack of good quality water. Models can be very useful tools in agricultural water management. Not only can they help in irrigation scheduling and crop water requirements calculation but also, they could be used to predict yields and soil salinization. The latter is particularly a long term, slow process that goes beyond the traditional short term experiments detection. A successful water management scheme for irrigated crops requires an integrated approach that accounts for water, crop, soil and field management. Saline water could be used to irrigate salt tolerant crops under a proper management system. SALTMED model (Ragab, see chapter 18) was developed as an integrated tool to predict yield, salinity and soil moisture profile, leaching requirements and water uptake. Further research will have to give more attention to the following areas: Monitoring of water quality and quantity, as well as soil properties. At present, there is no clearly defined policy and strategy on the use of saline water in irrigation. To formulate this policy and strategy, appropriate monitoring programs are required; Integrated management of water of different qualities at farm level, irrigation systems and drainage basins with the explicit goals of increasing agricultural productivity, achieving optimal efficiency of water use, preventing on-site and off-site degradation and pollution, and sustaining long term production potential of land and water resources; Development and use of mathematical models to relate crop yield to irrigation management under saline conditions so that models can be reliably applied under a wide variety of field conditions; The incorporation of salinity into groundwater flow models to predict the development of not only water logging but also of soil water salinity. Regional agro-hydro-salinity models would be of immense value in planning appropriate water management strategies; Activating the role of policies and institutions in creating demand for technology to ensure the sustainability of irrigated agriculture in saline environment; Conducting a comprehensive and coordinated research on potentials and hazards of the use of saline water for irrigation; Establishing a working relationship between national, regional and international institutions dealing with the reuse of saline water through the formulation of networks; Conducting and fostering a comprehensive multi-disciplinary basic and applied research programs on the sustainable use of saline water in irrigation and related problems and obstacles; Improving the Institutional Capacity Building; Incorporation of environmental, institutional, political and social and economic concerns; Developing general guidelines, setting up a universal strategy and use systemic indicators for assessing, monitoring and evaluating the sustainability of saline water reuse. THE WAY FORWARD The continued increase of domestic and irrigation water demand can only be met through an integrated water management scheme that includes the use of all sources of water including saline waters. Saline water such as brackish water, drainage water, shallow ground water is a potential water source in several countries and there is a wide experience exists for using it in irrigation as part of a fresh water saving practice. The complex interaction of water, soil, plant and climate condition in relation to water salinity should be considered when using saline water in irrigation. Water management strategies should establish when to use saline water in order to minimize the negative impact on environment and soil. The management strategy should include efficient use of water, sustainable and save use of water, suitable irrigation system and suitable crop (salt tolerant level matches the salinity level). Efficient water use would minimize the drainage volume and rising water tables, which are an environmental problem. Monitoring and evaluation programs should be carried out for water quantities and qualities, as well as the soil’s salinity. Socio- economic, institutional, political, ecological and environmental aspects are to be taken into consideration by decision-makers when considering using saline water resources for irrigation. Cost recovery is an essential requisite to ensure the economic sustainability of the use of saline resource. Supporting scientific and research centers and institutions for conducting integrated and applied water research and studies since these centers and institutions are an integral part of the institutional structures responsible for water resource development and utilization. Encouraging the establishment of networks between scientific and research centers on using saline water. Farmer’s participation in the planning and management is a key for the use of saline water in irrigation. Involvement of the farmers in the exercise will close the knowledge gap between farmers and researchers. Further research is needed on integrated water, crop and land resources management. Use of mathematical models should be encouraged to predict long-term salinity impact on soil, plants and the environment. This book covers 5 parts and contains 25 chapters. The first part is dedicated to the concept of integrated management to combat salinity in irrigated agriculture. The second part deals with the aspect of water and salinity which covers issues such as, the salt affected soils (origin and classification), the physical and chemical aspects of the semi arid soils, water quality for irrigation, monitoring soil salinity, green house salinity, modelling of salt transport and statistical techniques to analyze salinity. The third part covers the subject of plant tolerance to salinity. The issues covered are; salt impact on soil and plant, the effect of salt on the physiology and biochemistry of the plant, plant resistance against salinity through biomolucular mechanisms, biosalinity and agriculture production and improving plant tolerance to salinity. Part four covers the Integrated management of soil-water-plant system. The issues covered are; the interaction between salt and fertilizers, evapotranspiration in saline environment, Soil-water-plant management in saline environment, management strategies for using saline water, SALTMED Model application as an integrated tool for water, soil, plant, and N-fertilizer management and using saline water in hydroponic cultivation system. The last part of the book is focused on Drainage requirements for salinity control and land reclamation. The issues covered are drainage system design, biodraiange, land reclamation, land reclamation indicators and Phytoremadiation of salt affected soils. This book is intended to benefit academics, researchers, students, extension services and farmers