Final answer:
The question focuses on the agricultural practices of temperate grasslands in North America, particularly the cultivation of wheat west of the 100th meridian due to drier conditions and the growth of corn and soybeans in the more humid and fertile Corn Belt.
Step-by-step explanation:
The primary subject matter of the question concerns temperate grasslands and their agricultural uses, particularly the cultivation of crops such as corn, wheat, and soybeans in relation to geographic and climatic conditions. The temperate grasslands, known as prairies in central North America and as steppes in Eurasia, experience pronounced annual temperature fluctuations with suitable conditions for plant growth in spring, summer, and fall. These areas support the cultivation of different crops based on soil productivity and moisture availability. Farmers west of the 100th meridian in the United States, situated in the drier half of the country, typically plant wheat because the dry conditions are less favorable for moisture-demanding crops like corn and soybeans. Conversely, in the more humid east, especially in the Corn Belt centered on Iowa, corn and soybeans thrive due to the fertile soil conditions of the former tallgrass prairie and more abundant rainfall. The use of center-pivot irrigation is also a key element in facilitating agriculture in these drier regions by efficiently providing water to crops.