Context: From the 1950s on, many areas of the Great Plains have become productive crop-growing areas because of extensive irrigation on large landholdings. The United States is a major exporter of agricultural products. The southern portion of the Great Plains lies over the Ogallala Aquifer, a huge underground layer of water-bearing strata dating from the last ice age. Center pivot irrigation is used extensively in drier sections of the Great Plains, resulting in aquifer depletion at a rate that is greater than the ground's ability to recharge.

Question: around when did the great plains become productive for crop growing
Answer: 1950s

Question: what is the large underground layer of water in the great plains called?
Answer: Ogallala Aquifer

Question: what type of irrigation is used in the great plains?
Answer: Center pivot irrigation

Question: When was the last ice age?
Answer: Unanswerable

Question: In what decade did center pivot irrigation get invented?
Answer: Unanswerable

Question: In what decade did aquafier depletion begin to outpace the ground's ability to recharge?
Answer: Unanswerable

Question: In what country was center pivot irrigation invented?
Answer: Unanswerable