Some farm lands contain too much water for the growth of farm crops; for example, bottom lands which are so low that water falling on the surface cannot run off or soak down into the lower soil. The result is that the spaces between the soil particles are most of the time filled with water, and this checks ventilation, which is a necessary factor in soil fertility. This state of affairs occurs also on sloping uplands which are kept wet by spring water or by seepage water from higher lands. Some soils are so close and compact that water falling on the surface finds great difficulty in percolating through them, and therefore renders them too wet for profitable cropping during longer or shorter periods of the year. Nearly all such lands can be improved by removing the surplus water through drains. (See Chapter XXV.) Percolation and ventilation of close compact soils can be improved by mixing lime and organic matter with them. NOT ENOUGH WATER In some sections of the country, particularly the arid and semi-arid sections of the West, the soil does not receive a sufficient supply of rain water for the production of profitable yearly crops. These soils are rendered unfertile by the lack of this one all important factor of fertility. They can be made fertile and productive by supplying them with sufficient water through irrigation. The crop-producing power of some lands is lowered even in regions where the rainfall is sufficient, because these lands are not properly prepared by tillage and the addition of organic matter to absorb and hold the water that comes to them, or part of the water may be lost or wasted by lack of proper after-tillage or after-cultivation. This state of affairs is of course improved by better preparation to receive water before planting the crop and better methods of after-cultivation to save the water for the use of the crop. LOSS OF SOIL WATER Aside from what is used by the crops the soil may lose its water in the following ways: Rain water which comes to the soil may be lost by running off over the surface of the land. This occurs especially on hilly farms and in the case of close, compact soils. Water may be lost from the soil by leaching through the lower soil. Water may be lost from the soil by evaporation from the surface. The soil may lose water by the growth of weeds which are continually pumping water up by their roots and transpiring it from their leaves into the air. HOW SOME FARM OPERATIONS INFLUENCE SOIL WATER Plowing and soil water. One of the first effects of deeply and thoroughly plowing a close, compact soil, is that rain will sink into it readily and not be lost by surface wash. In many parts of the country, especially the South, great damage is done by the surface washing and gulleying of sloping fields.