Final answer:
The 'wide open spaces and a long growing season' refer to the Corn and Wheat Belts in the United States, known for their fertile soil and agricultural productivity, fitting the context of the 16-letter phrase.
Step-by-step explanation:
Wide open spaces and a long growing season are characteristic features of the Corn and Wheat Belts in the United States. The phrase "wide open spaces and a long growing season" refers to the agricultural regions east of the 100th meridian, notably the Corn Belt. In this region, characterized by flat lands and conducive climate, farmers grow corn and soybeans.
The long growing season and adequate summer rainfall, along with deep, fertile topsoil of the former tallgrass prairies, now transformed into cropland, typify the Corn Belt, making it an ideal agricultural hub. This area's description fits the context of the 16-letter phrase you are seeking, which identifies this region's agricultural productivity.