Final answer:
The Incas innovated with terrace farming to efficiently grow crops in the steep Andean mountainsides, which supported their large population by providing benefits like improved irrigation and prevention of soil erosion.
Step-by-step explanation:
The Incas used terrace farming as their innovative agricultural technique to grow their crops. This practice involved cutting out flat areas into the steep mountainsides, creating a series of steps or terraces that allowed for more efficient use of the limited arable land in mountainous regions. Terrace farming was a vital adaptation that enabled the Incas to cultivate enough food for their substantial population. The terraces provided numerous benefits, such as improved irrigation, prevention of soil erosion, and the creation of micro-climates that supported the growth of a diversity of plants. Notably, this allowed the cultivation of their main staple, corn, alongside a variety of other crops, thus sustaining a large population estimated between 4 million and potentially up to 40 million inhabitants. In addition to agriculture, the Andean people also maintained a diverse economy which included animal husbandry and trade with regions that had different climates and resources.