Irrigation erosion

Irrigation is important to global food production. About 15% of cropland (1) and 5% of food production land, [Fl] which includes rangeland and permanent cropland (2), are [F2] irrigated. However, irrigated land produces more than 30% of the world's food (3), which is 2.5 times as much per unit area compared with nonirrigated production (1). In the U.S., approximately 15% of the harvested cropland is irrigated; however, almost 40% of the total crop value is produced on irrigated land (4). Although sprinkler- and drip-irrigated areas are increasing, most of the world's irrigated land uses surface or flood irrigation. The countries with the large irrigated areas are India (59,000,000 ha), China (52,580,000 ha), U.S. (21,400,000 ha), and Pakistan (18,000,000 ha) (2). These countries account for 55% of the world's irrigated land; all other countries have less than 10 million ha each of irrigated land (2). About 50% of the irrigated land in the U.S. is surface irrigated (5), although 95-99% of the irrigated land in India, China, and Pakistan is surface irrigated (6). Soil erosion from irrigated fields has been discussed previously (7, 8); this article focuses on unique aspects of irrigation-induced soil erosion that are important when managing and simulating soil erosion on irrigated lands. Soil erosion mechanics can be divided into three components: detachment, transport, and deposition. Water droplets and flowing water detach soil particles; flowing water then transports these detached particles downstream; deposition occurs when flowing water can no longer transport the soil particles because flow rate decreases as water infiltrates or as rill slope or roughness changes. Some particles are deposited within a few meters although others are transported off the field with runoff water. These mechanisms are the same for surface irrigation, sprinkler irrigation and rainfall; however, there are some systematic differences between irrigation and rainfall erosion and especially between surface irrigation and rainfall