Agriculture in the prehistoric Southwest
After the Hohokam disappeared, Spanish explorers of the 16th century noted the use of canal irrigation in only two areas of the Southwest: eastern Sonora, primarily practiced by the Opata and Lower Pima, and among the Pueblos of northern New Mexico. Irrigation by the Opata and Pueblos had different objectives. In Sonora, with a long growing season, two crops of maize a year were grown in river valleys. The spring crop during the dry season was dependent upon irrigation; the summer and fall crop during the rainy season utilized irrigation to supplement rainfall. The necessity of irrigation probably required a high level of social organization. In New Mexico, with only one crop of maize per year possible, irrigation was supplemental and the lesser dependence on irrigation implies less social organization than in Sonora.
Irrigation in Brazil
Brazil has always been considered a country rich in water. However, Brazil's hydro-climatic regions and irrigation systems vary widely. In the South, frosty conditions in winter have limited irrigation mainly to summer flooding of lowlands for rice production. In the milder Southeast, irrigation in winter has made double-cropping possible. Winter wheat, peas, or beans are rotated with rainfed summer crops, including cotton. Local water shortage occurs in some small watersheds in the Southeast and South where irrigation development and water consumption for industry and municipal use have been relatively uncontrolled. The large size and level terrain of farms in the vast cerrado areas of the Center-West are well suited to center-pivot and self-propelled irrigation systems, which have expanded rapidly in the last few years.