About ____ of U.S. cropland is irrigated.

a. 13
  b. 16
  c. 19
  d. 22

a. River flooding
  b. Ponding
  c. Degraded water quality

a. clay
  b. lead
  c. concrete
  d. plastic

a. land grading
  b. certain tillage practices
  c. berms

a. root oxygen deprivation
  b. tillage problems
  c. lack of available water
  d. delayed planting

In irrigating saline soil, the amount of water to be applied in excess of that needed to wet the root zone
  of the plant is called the ____ requirement.

a. flooding
  b. saturation
  c. leaching

a. control wetlands
  b. need to be employed on all agricultural fields
  c. make otherwise difficult soil productive
  d. are tools used only by growers