Final answer:
Farm subsidies were changed in the 1970s to decrease government spending, increase prices of agricultural products, and encourage larger-scale commercial farming.
Step-by-step explanation:
In the 1970s, farm subsidies were changed for several reasons. One of the reasons was to decrease government spending on agriculture. The government aimed to reduce the excess supply of farm commodities and increase their prices. Another reason was to encourage larger-scale commercial farming by providing support to farmers. These changes were implemented through programs such as subsidies for not planting certain acres and livestock slaughter.