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Washington, D.C. — More than 20 million acres of cropland in Iowa and other Corn Belt states would likely be converted to forests under a congressional plan to reduce greenhouse gas emissions, according to an Agriculture Department analysis released today.
About 59 million acres of land nationwide would be converted to forest by 2050 because of the carbon-offset program, the analysis showed.
The long-term hazards of irrigation are even greater. Investment in irrigation projects pays best in dry areas where evaporation is high. Water is never pure, but has mineral salts dissolved in it. Evaporation will therefore make it saltier still. Rivers flowing through dry or desert areas lose water by evaporation, and become salty. For example, the water in the lower Colorado contains over a ton of salt per acre-foot of water.
Many areas in dry climates have natural brackish or salty lakes, or even dry salt pans. Soils are often laden with lime (calcium carbonate) or salt (sodium chloride), and many sedimentary rocks contain natural salts. Promising irrigation areas thus may have natural salts in rocks or soils that will easily be transferred into fields as soon as irrigation water is applied, and even that water may come from rivers that have become saltier from evaporation along their courses.
As water is used on crops, it spreads out as a thin sheet, exposed to the surface. Much of it may evaporate, making it more saline. It may dry up altogether, leaving a thin layer of salts on and in the soil. Even under normal circumstances, plants absorb moisture from the soil, leaving behind excess salts. Eventually salts build up in the surface soils until they become infertile. Over time, therefore, soils in dry irrigated areas tend to become salinized.
The only way to deal with this problem is to apply enough water so that salt is flushed off or flushed through the soil. The flushing must remove salts from the area altogether, along natural or artificial drainage. In well-drained areas with a dry season and a wet season, natural flushing takes place each year. But in poorly-drained areas, over-watering simply mobilizes the salt while the water table rises to ground level. Capillary action draws the saline water to the surface, where the salt dries out as a surface deposit, and the problem is made worse rather than better. Once the soil is saturated, with water up to the surface, there is no way to leach salts out of the soil, and the fertility of the region is destroyed unless major drainage channels are built to carry away the salt. Even flushing may not be a net environmental plus: flushing simply delivers salt somewhere else, perhaps to downstream users, or into groundwater supplies. Flushing also leaches away soil nutrients with the salts.
After the wave of Moslem expansion broke over Mesopotamia, the Abassid Caliphate was based on Baghdad from 762 AD until its demise in 1258. Existing irrigation schemes were renovated and greatly extended in very large projects. Abassid engineers drew water from the Euphrates at five separate points, and led it in parallel canals across the plains, watering a huge area south of Baghdad. This system provided the basis for the enormously rich culture of Baghdad, which is still remembered in legend (Scheherezade, the Caliph of Baghdad, and the Arabian Nights) as well as history. But it required a lot of physical maintenance, and there was a lot of salinization in the south. As central government began to fail in the 12th century (mostly from extravagant overspending), the canals became silt-choked, the irrigation system deteriorated, and the lands became more salinized. The deathblow to the system was natural: massive floods about 1200 AD shifted the courses of both the Tigris and the Euphrates, cutting off most of the water supply to the Nahrwan Canal and wrecking the whole system. The Abbasids were too weak (or bankrupt) by now to institute repairs, and the agricultural system collapsed. By the time the Mongols under Hulagu devastated Iraq and Baghdad in 1258 AD, they were finishing off a society that was already a wasteland. Iraq has remained a desert for more than 600 years.
When food was plentyful the civilzation grew but when the irrigation needed for it destroyed the land and the water it destroyed the civilzation and turned them into deserts.
Look at what is happening in California with water and ask yourself if they need to shut down some farms there. They are turning that place into a desert.