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3. flat shelves that are cut into a hillside
6. ___ can be conserved in many different ways
7. ___ plowing: insead of plowing up and down the slope of the hill, farmers plow furrows across the slope
12. ___ supports plant andanima life and can be polluted
15. The ___ in soil are naturally removed by plants
16. farmers may plant grasses between rows of other crops
17. farmers can plant ___ crops on the sae land in ___ years
18. the preservation or protection of natural resources, including soil
19. ____ containing one or more nutrients can be added to soil to replace nutrients used up by previous crops

1. a period of severe dust storms and drought that devastated the American and Canadian prairies during the 1930s
2. soil can be polluted by ___ placed in the ground
4. ___ flows swiftly down hills and ca carry away rich topsoil
5. is th addition of harmful materials to soil, air, or water
8. can also pollute soil
9. where there are ___, the wind is less likly to blow away topsoil
10. ___ may pass laws to stop the pollution of soil
11. a country that is well known for terracing
13. The plants use the ___ to grow and build their body parts
14. A mixture of bits of rock and once living parts of plants and animals