It is well known that on a global scale water is probably the most limited resource for agricultural production and directly sensitive to climate variability. Water resources can therefore vary strongly from year to year and within a single year. Extreme precipitation events and floods can be as devastating as droughts (Rosenzweig et al. 2002; Chang 2002), and these extremes could increase under climate change, depending on the region. Extreme precipitation can further lead to nitrogen leaching on sandy soils, which might be accelerated under increasing climate variability in more humid regions (Wessolek and Asseng 2006) and have implications for agricultural land use and management for groundwater recharge harvesting, for example in northern Germany.
However, water shortage and droughts are the most important devastating factors for agriculture and food production because of their large spatial extension, especially in many subtropical regions and developing countries. Over the centuries, mankind in semi-arid and arid regions have therefore developed technologies or systems for water harvesting or irrigation. Nowadays known as traditional methods or indigenous techniques, they are still in use in many parts of the world, not least because they are well adapted to local conditions and are often the only option because of their low costs or inputs. Examples are given in numerous publications such as those listed by Stigter et al. (2005).
The role offarm technologies in water management in developed regions or countries
In many agricultural systems, mostly in better developed countries or regions, new technologies for water management have been successfully introduced and have increased agricultural productivity. For instance, irrigated agriculture in the Mediterranean area was introduced in ancient times and has been improved over time with experience. However, irrigation techniques have been kept in the same way for centuries in most Mediterranean countries. Inefficient flood irrigation systems, for example, can be still found in many areas of Spain and Egypt (El Gindy et al. 2001; Neira et al. 2005). Modern sprinkler and drip-irrigation systems have been introduced at great expense in some Mediterranean European regions such as Spain (MAPA 2005). ttese new techniques significantly reduce water use. As can be seen in Fig. 10.3, the Spanish productivity of irrigated crops, such as maize, has increased in the last 15 years, compared with countries like Egypt, despite the fact that the total production is lower, tte differences between Spain and Egypt may have many causes, but the new engineering irrigation infrastructures that have been introduced in Spain (ANPC 2003) certainly have a strong influence on this yearlyyield increment.
1990 1995 2000 2004
Fig. 10.3. Absolute differences between Egyptian and Spanish maize production (in BT) and yield (in t/ha).
Water availability could well be the most important agricultural constraint in Mediterranean agriculture in the future (Olesen and Bindi 2002; EEA 2005) and in many other agricultural regions worldwide. Adaptation tests by Rosenzweig et al. (2004) for several major agricultural regions worldwide have shown that few regions can readily accommodate an expansion of irrigated land in a changed climate, while others would suffer decreases in system reliability if irrigation areas had to be expanded. Timely improvements in crop cultivars, irrigation and drainage technology and water management are therefore required. Farmers in southern Europe, for example, must realize that techniques such as the "deficit Irrigation" should be considered as an option in the next decades, or irrigated agriculture will become unaffordable (Fereres 2005). Nevertheless, the success of deficit irrigation in a given year depends on weather behavior during that year (Farre 1998), which makes it difficult to introduce it into farming practice, tte only practical solution for the extensive introduction of deficit irrigation and similar techniques to improve irrigation efficiency is through very local assessments, taking into account weather variability (Bastiaansen et al. 2004; Eitzinger et al. 2004; Utset et al. 2004; Utset 2005; Fereres 2005).
As an example of medium- and high-input farming systems, irrigation is being modernised in Spain on a fairly large scale with governmental support (Beceiro, 2003; MAPA, 2005) to replace flooding by sprinkler and by other more efficient technologies. It usually implies large investments and farmers cannot afford them on their own. However, irrigation must not only be kept but also enlarged if the Lisbon Strategy goals are to be met and rural living conditions improved (MAPA 2005).
Moreover, complete sprinkler coverage is very important in terms of personnel savings. Southern European and Spanish agriculture is mainly based on family businesses, tte rural population has dramatically decreased in Europe. Complete coverage combined with automatic control devices therefore allows the manpower effort involved in irrigation to be reduced to a minimum. Furthermore, irrigation advisers in the form of local specialists should be accessible to farmers to accompany modernization, ttese local services must be able to provide help to farmers in dealing with the new available technology, tte irrigation advisers in Spain and other European countries usually have modern laboratories for soil property analysis as well as a relatively dense network of agrometeorological stations and other high-input technologies. Besides, the specialists involved in such advice services could be trained in modern techniques such as simulation modeling tools and remote sensing interpretation.
Irrigation investments include channel designs, water distribution systems and pumping devices, tte engineering effort involved is usually significant, costing several million euros. Complete sprinkler coverage usually involves underground PVC or metal tubes all over the agricultural field. Automatic control devices also need solar cells, modems, computer systems and other related technology. Furthermore, irrigation advice services call for government investment in trained personnel, as well as laboratory infrastructures and technological facilities. Despite the large investment involved in these three potential measures, they can be amortized in few years, particularly in view of the anticipated increase in water prices in Europe as a result of political measures, tte irrigation advice service could also become independent and self-funding in few years. A government-directed effort, providing loans and supporting funds is absolutely essential in the first stage, tte total amount involved is very high, which makes these potential measures affordable onlyby developed countries.
ttere are many examples in Spain and other southern European countries, but we will concentrate here on the results obtained in the irrigation community of Valladolid, Spain, tte community comprises 610 ha, 209 farmers and 383 irrigated fields in Simancas, Geria and Villamarciel, in Valladolid province, central Castille, Spain (41:31N, 4:53W). Maize, sugar beet and alfalfa are the main crops. On-demand pivot and sprinkler irrigation (complete coverage) was recently provided to the farmers, according to the Spanish Plan Nacional de Regadíos, tte investment included an underground pressure-based distribution network, a computer-based automatic open-close control system for the hydrants and on-field control of the used water, which is now being taken into account in the relevant invoices. Flood irrigation is no longer allowed following the modernization investment. Weekly crop water requirements are provided locally by a web service (www.inforiego. org) and by SMS. tte Penman-Monteith daily évapotranspiration calculations are based on a network of agrometeorological stations installed in the last five years all over Castille using European funds.
tte Castilla y León irrigation advice service made a survey of 26 per cent of the local farmers in Simancas-Geria-Villamarciel (Utset et al. 2006a,b). According to the survey, 77 per cent of the farmers take into account the particular season and the crop to manage irrigation. However, 86 per cent do not conduct a water balance to calculate the irrigation supply requirements, ttey recognize they could save more water and they might pay for irrigation advice, particularly considering soil differences and water-table fluctuation levels. TDR-based periodic soil-moisture monitoring is being carried out by the irrigation-advice service in Simancas-Geria-Villamarciel on several fields, providing the farmers with updated information on water use. In particular, the recurrence of soil water content higher than field capacity at deeper depths is an indication of water loss and potential pollution problems. Irrigation productivity calculations are also provided for farmers, ttis service is being supplemented by modeling assessments (Utset et al. 2005), which might help farmers to decide how to manage crop and water in a sustainable way in their respective farms.
The role offarm technologies in water management in developing countries
For many farmers in developing countries, however, these expensive new technologies are not affordable without external support and are therefore not applicable in low-input agricultural systems with weak infrastructure and poor socioeconomic conditions, tte adaptation and use of traditional methods are recommended in these cases (Stigter et al. 2005). Indigenous techniques for agricultural water use in semi-arid regions are known for example from the Incas. Chacras hundidas are sunken pits or basins that allow crops to reach the groundwater table (Golte 1978).
Galerías filtrantes, artificial and complex surface and underground canals to collect groundwater, are also still used in places. Similar systems of ancient underground pipes for the transfer of irrigation water through arid areas can be found in Iran. Ancient surface canal systems and surface tanks over large areas for the transfer, distribution, collection and storage of water from the monsoon periods can be found in India (Das 2001 in Stigter et al., 2005) and Sri Lanka, which also still work effectively and are used for crop production in low-input farming systems. Stigter et al. (2005) reports several examples of traditional and newly adapted effective water use methods in Africa using planting pits with improved soil water storage through the addition of manure, for example.
Beside traditional or indigenous methods, new and low-cost technologies may be still a promising option for low-input farming systems, especially for countries in transition such as India or China. Eitzinger et al. (2005) showed that even simple low-cost technologies could significantly improve irrigation scheduling and crop water use compared with flood irrigation, ttese technologies, based on simple measurements and algorithms to estimate actual évapotranspiration for irrigation scheduling, have still to become more user-friendly, however. Moreover, a basic and stable infrastructure for local companies and technical support should exist or be built up, and this is not the case in many regions of developing countries, especially in Africa (Stigter, personal communication, 2004). ttis could also act as an incentive for technological change to be driven more by environmental objectives and farmer innovations operated through the market as recommended by Norse and Tschirley (2000), among others.
An important management option..." by
"An important management option for low (and all level) input farming systems regarding water resources is the change to crops with better water efficiency, ttis is especially important in regions where pressure on water reserves is increasing owing to human activities, climate change and variability. For example the change from wetland rice to dry land rice or other crops can have enormous effects on agricultural water reserves, as demonstrated in northern China (You 2001).
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