Irrigation and Salt
This is the VOA Special English AGRICULTURE REPORT.
Irrigation is the watering of land by other than natural methods. Irrigation projects provide water for crops in areas that have long periods of little or no rainfall.
The United Nations Food and Agriculture Organization reports that only seventeen percent of all cropland is irrigated. However, irrigated land provides forty percent of the world's food. Irrigation is said to increase production of most crops by one-hundred to four-hundred percent.
However, F-A-O officials say about ten percent of all irrigated land has been damaged by salt. This is most severe in extremely dry areas. As much as twenty-five percent of the land is affected in these areas.
F-A-O officials say this has become a threat to food security. In the past, the U-N agency said that increasing the use of irrigation could be the answer to feeding the world's people. Now, it warns that rising salt levels in the soil threaten much existing irrigated land.
Salinization is the build-up of salt in the soil. F-A-O officials say salinization reduces productivity and can seriously damage the soil. It warns that salinization is reducing the world's irrigated land by one to two percent each year.
All soil contains some salt. As water wears away rocks and soil, small amounts of mineral salts are carried into rivers and other waterways. If a field has too little water, the mineral salts are not washed away. They remain in the soil.
However, the worst danger to the soil is from too much water. When the ground is too wet, water levels rise. The water evaporates. However, salt remains underground, around plant roots. This interferes with the ability of the roots to take in needed water.
The F-A-O says there are several ways to prevent or reduce salinization. One is for farmers to use just a little more water than the crops need. The extra water can carry salt away from the roots of the plants. Farmers can also build underground pipes or dig deep holes near crops. This can help remove extra water.
Finally, farmers can flood their fields. This can sometimes treat badly salinized land that can on longer be used for agriculture. Adding a lot of water can be costly. But F-A-O officials say it may be a wise economic decision, depending on the value of the land and crops.
This VOA Special English AGRICULTURE REPORT was written by George Grow.