Better water management means a healthier environment
Agriculture can have a significant impact on the environment and on people's health. Inappropriate land and water management can deplete water sources, pollute water systems, contribute to soil infertility and erosion and destroy natural ecosystems.
In many regions, water for irrigation is being pumped out of the ground faster than it can be replenished. In India’s Tamil Nadu state, overpumping in some areas has lowered the water level in wells by 25 to 30 metres in one decade. In northern China, large areas of farmland are threatened by falling water levels owing to the overuse of groundwater.
In addition, much harvested water is wasted -- lost through canal leakage, spillage, seepage and evaporation. Although some of this water does get back into rivers or underground aquifers, excessive losses in irrigation systems affect scheme performances, contribute to excessive water withdrawal and usually increase the negative environmental impacts of irrigation.
Irrigation must be managed carefully to avoid environmental damage, particularly in arid areas. Unless irrigated fields are drained properly, salt builds up in the soil as water evaporates, reducing the productivity of the land and eventually making it infertile.
FAO estimates that poor drainage and irrigation practices have led to waterlogging and salinization of about 10 percent of the world’s irrigated lands. These practices also contribute to the spread of water-borne diseases, such as diarrhoea, cholera, typhoid and malaria.
Raw water extraction from rivers and lakes and the construction of irrigation infrastructure along riverbanks affect fragile ecosystems. Excessive application of pesticides and fertilizers has a direct impact on water quality and people's health.
Finding ways to alleviate these negative environmental impacts is essential to protecting the ecosystems on which agriculture depends.
A variety of simple, affordable techniques can increase food production for small-scale farmers without excessive water withdrawals or damage to the soil.
Water harvesting -- irrigating crops with on-farm runoff -- can significantly improve both yields and the reliability of agricultural production.
And drip irrigation, which directs water only where and when it is needed, is more efficient than flooding fields and using sprinklers. Results from a number of countries show that farmers who switched from sprinkler irrigation to drip systems have cut their water use by 30 to 60 percent. “Spoon-feeding” the optimal amount of water, and sometimes fertilizer, to crops when and where they need it often increases yields at the same time.
Inexpensive, human-powered treadle pumps, which extract irrigation water from shallow aquifers, have increased poor farmers’ productivity in many Asian and African countries. The farmer has full control over the timing and the amount of water pumped which, given the effort involved, is used sparingly. Small motor pumps have also revolutionized small-scale horticulture around cities.
Recycling of treated wastewater for use in irrigation is another option with enormous potential benefits. A city with a population of 500 000 and water consumption of 120 litres per person a day produces about 48 000 cubic metres of wastewater a day. When treated, this wastewater could be used to irrigate around 500 hectares. The nutrients in effluent are almost as valuable as the water itself. Typical concentrations in treated wastewater effluent from conventional sewage could provide all the nitrogen and much of the phosphorus and potassium normally required for agricultural crop production.
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