A survey by the U-S Department of Agriculture shows soil erosion from wind and water on Iowa farmland dropped 21-percent from 1992 to 1997. The Natural Resources Conservation Service conducts the survey every five years. Spokesman Corry Brockman says the downside is that the amount of farmland lost to development is increasing.Brockman says the annual rate of land development has increased 400 percent in the last 10 years.Brockman says the state can’t afford to let up in its conservation efforts.He says the use of conservation methods has other benefits such as increasing the amount of forestland in the state.The amount of forestland in the state has increased five-and-a-half percent between 1992 and 1997.