Reference-and-Education It takes a notoriously long amount of time for soil to be made. Under normal agricultural conditions it usually takes between 200 and 1,000 years for one inch of topsoil to be formed. There are estimates that, dependent on where it is happening in the world topsoil is currently being lost sixteen to three hundred times faster than it will take for it to be replaced. Many negative environmental impacts are a result of either land being converted to agricultural use or of the misuse of fertilizers and pesticides. By 1990, approximately 38% of the roughly 600 million acres of the world’s cropland had been degraded because of the poor agricultural practices that had gone on over the years. Although some of the land was only partially degraded a substantial amount was severely damaged. Much of the land was so damaged that it was either completely taken out of production or its productive capacity was greatly diminished. Since 1990 soil has continued to be lost to severe soil degradation to the tune of 2 to 2 1/2 million acres per year. And, in the long run, when soil degrades less food can be grown. There are a number of reasons that degradation occurs. The best known reason is soil erosion. Approximately 67% of topsoil is washed away by water. The wind accounts for the balance. Farmland is often physically degraded due to mechanical tilling. Mechanical tilling can lead to soil crusting and compaction. If crops are repeatedly grown without any adequate fallow periods, soil gets damaged. When agricultural chemicals are over applied they can kill the beneficial organisms within the soil and deplete soil of its nutrients. When water is not properly managed on irrigated cropland, degraded farmland is a common result. Salt levels often build to toxic levels in soil that is inadequately drained and consequently waterlogged. Approximately 10% to 15% of all the irrigated land in the world now suffers, to some degree, from salinization and waterlogging. Consequently, productive capacity in the world is now being significantly threatened. Ironically, the total production of food throughout the world has actually increased over the years. However this is because of the increased use of fertilizer and higher densities of crops, It is just a matter of time before the results of soil degradation caused by these processes becomes irreversible throughout the world. It is already happening in some parts of the world. Losses from soil erosion in Africa are approximately 8%. Data from a number of studies indicate that soil degradation may have caused more than a 20% loss in productivity in a number of Middle Eastern and Asian countries. About the Author: 相关的主题文章: