Water and Agriculture - I
Compiled by Dr. Nüvit Soylu
Agriculture has, arguably, been very successful at capturing the major share of the world’s exploitable water resources.Water has unique characteristics that determine both its allocation and use as a resource by agriculture. Agricultural use of water for irrigation is itself contingent on land resources..
In developing countries, irrigated agriculture plays a vital role in contributing towards domestic food security and poverty alleviation.Therefore, achievement of these objectives is dependent on adequate allocations of water to agriculture. Justification of such allocations requires that irrigated agriculture be a cost-effective means of achieving stated political or social objectives, such as food security or poverty alleviation, and that all externalities be taken into account in the pricing mechanism.
Improved allocation of irrigation water is required within the agriculture sectors of developing countries in order to achieve greater efficiency in the use of irrigation water and existing irrigation infrastructure. Reallocation is also required in order to reduce waterlogging and salinization of irrigated land, to decrease the negative environmental impacts and other externalities of irrigation (caused by overextraction of groundwater and depletion and pollution of surface water).
Water provides goods as drinking-water, irrigation water and services as hydroelectricity generation, recreation and amenity that are utilized by agriculture, industry and households. Provision of many of these goods and services is interrelated, determined by the quantity and quality of available water. Management and allocation of water entails consideration of its unique characteristics as a resource.
Water used for irrigation can be pumped from reserves of groundwater, or abstracted from rivers or bodies of stored surface water. It is applied to crops by flooding, via channels, as a spray or drips from nozzles. Crops also obtain water from precipitation. Water infiltrates into the soil, evaporates, or runs off as surface water. Of the water that infiltrates the soil, some is taken up by plants (and later lost through transpiration) and some percolates more deeply, recharging groundwater. This water can be polluted with agrochemicals (fertilizers, herbicides and pesticides), with salts leached from the soil and with effluent from animal waste.
Control or prevent water use.
It is not easy to control or prevent water use. Many uses of water involve the withdrawal of water from the hydrological system (known as 'extractive' or 'off-stream' use). Typically, only a small proportion of the water withdrawn is consumed. Water consumption is exclusive in its use. Consumed water is retained in plants, animals, or industrial products, so it is not available for other uses.
However, most of the water withdrawn is not consumed and it returns to the water system for reuse at a later time and a different location. Water in return flows can reenter the surface water system further downstream, can percolate into aquifers, or evaporate, returning to the hydrological system in gaseous form. Therefore, water withdrawals are not exclusive within a broad perspective on water use, but only within a narrow location- and time-specific context. Water can also be used in-stream without removal from the hydrological system . Uses of water in hydroelectric power generation or boating generally entail little or no consumption of water . But they do affect the location and time at which water is available for consumption by other uses (Young, 1996).
Agricultural Water Use
Irrigation is a vital component of agricultural production in many developing countries. Food production in developing countries is increasing in response to the demands of an expanding population and rising prosperity. Some of this demand will be met by increased productivity of rainfed agriculture, some by increased imports, but irrigated agriculture will be a major contributor.
• Agriculture is the largest user of water in all regions of the world except Europe and North America (FAO, 2002b). In 2000, agriculture accounted for 70 percent of water withdrawals and 93 percent of water consumption worldwide, where consumption refers to withdrawals net of returns flows and evaporation . This is in contrast to industry, which accounted for 20 percent of withdrawals and 4 percent of consumption worldwide in 2000, and household use, which accounted for 10 percent of withdrawals and 3 percent of consumption (FAO 2004 (AQUASTAT-database) FAO, 2002b). The water requirements of agriculture are large relative to water requirements for other human needs. The human body needs about 3 litres of water per day;
• For domestic uses people use approximately 30 - 300 litres of water per person per day;
• To grow their daily food needs people require 3000 litres of water per person per day. (FAO 2003)
Water withdrawals an consumption
However, the agriculture sector is often criticized for high wastage and inefficient use of water at the point of consumption (i.e. at farm level) encouraged by subsidized low charges for water use or low energy tariffs for pumping.
It is often claimed that the charges made for irrigation water, fail to signal the scarcity of the resource to farmers. They result in poor maintenance and consequent inefficient operation of existing irrigation systems, limited capacity for improvements or investment in new infrastructure, and waste of water at the farm level. Furthermore it is claimed that the subsidies provided for irrigation water tend to favour the wealthy and thereby exacerbate inequalities in resource access and wealth distribution in rural areas (De Moor and Calamai, 1997).
Water used for irrigation comes from surface water or groundwater. The use of groundwater for irrigation enables the extension of irrigated area beyond that which surface water alone can support. In addition, it assists with drainage of the soil (by lowering the groundwater table and providing drainage of soil water into tubewells). Groundwater can supplement surface water during periods of low flow, making surface water available for alternative uses. It is also used as a sole source of irrigation water. For example, in India, more than half of irrigated land is supplied with groundwater, providing one-third of the country’s food production (Roy and Shah, 2003).
Groundwater has various advantages over surface water: it can be stored in aquifers for years with little or no evaporative loss; the percolation of aquifer recharge water through the ground attenuates pollution levels (making groundwater particularly suitable as a source of drinking-water, especially in areas with no water treatment facilities); groundwater can be withdrawn near the point of use; and it is available immediately on demand, which enables more timely applications of irrigation water. However, groundwater contains dissolved salts that can be toxic to plants and result in soil salinization. Groundwater can be combined with surface water to dilute salt concentrations to levels suitable for use in irrigation.
Kerry Turner,Stavros Georgiou,Rebecca Clark,Roy Brouwer, Jacob Burke 2004 " Economic valuation of water resources in agriculture" FAO Water Reports 27. Food And Agriculture Organization Of the United Nations Rome, 2004
FAO. 2003a. Unlocking the water potential of agriculture. Rome.
FAO. 2003b. Issue paper for Ministerial meeting on water for food and agriculture, Kyoto, Japan.
FAO. 2003c. World agriculture: towards 2015/2030. London, Earthscan Publications Ltd. Lodon.
FAO. 2004. Water charging in irrigated agriculture: an analysis of internal experience. FAO Water Reports No. 27. Rome.
FAO. 2004. AQUASTAT Web site http://www.fao.org/ag/aquastat.
Roy, D. & Shah, T. 2003. Socio-ecology of groundwater irrigation in India. In Llamas, P. and Custodio, E. Intensive use of groundwater: challenges and opportunities. A.A. Barkema Publications.
Young, R.A. 1996. Measuring economic benefi ts for water investments and policies. World Bank Technical Paper No. 338.
De Moor, A. & Calamai, P. 1997. Subsidizing unsustainable development – undermining the earth with public funds. The Earth Council.