In the united states, unwise land-use practices lead to annual losses of topsoil by wind and water totaling

4 Billion Metric tons

Explanation:

Mismanagement of arable land is a major factor that leads to the loss of top fertile soil layer that can support the growth and development of crop plants. The studies have reported that unwise land-use practices lead to annual losses of topsoil by wind and water totaling 4 Billion Metric tons.

Therefore, there is alot of focus now adays on conservation of soil and arable land that can also prevent soil erosion and help in growth of more crops and increase agricultural productivity.

Studies have also reported that proper management practices of soil can help in lowering the soil erosion by 100 to 5 tonnes/ hectare/year.

In the promotion of this efforts, during 1930s there were  220 million trees  planted in United States as a strategy to lower soil erosion due to water and wind.

Hope it help!

b. the carbon cycle ensures living things have a source of hydrogen