The agricultural practices of the Native Americans inhabiting the American Southwest, which includes the states of Arizona and New Mexico plus portions of surrounding states and neighboring Mexico, are influenced by the low levels of precipitation in the region. Irrigation and several techniques of water harvesting and conservation were essential for successful agriculture. To take advantage of limited water, the southwestern Native Americans utilized irrigation canals, terraces (trincheras), rock mulches, and floodplain cultivation. Success in agriculture enabled some Native Americans to live in communities that numbered in the thousands as compared to their former lives as hunter-gatherers in which their bands numbered only a few dozen.

Maize (corn), the dominant crop, was introduced from Mesoamerica and cultivated in the present-day Southwest U.S. by 2100 BCE at the latest. Non-migrant cultures based on farming developed afterwards, including the Hohokam, Mogollon, Ancestral Puebloans, and Patayan.

The environmental challenges of agriculture in the Southwest resulted in the demise or evolution of many once-successful agricultural societies, but they left behind impressive archeological evidence of their existence. Some agricultural cultures, such as the Pueblos of the United States and the Yaqui and Mayo of Mexico, were durable and survive into the 21st century.

Earliest agriculture

Indigenous people in the Southwest likely began domesticating local plants, such as native grasses and weedy annuals, over 5000 years ago. Later, Mesoamerican crops like squash and maize were introduced to the region between 3000 and 2000 BP. Other introduced crops, including amaranth, the common bean, and cotton, appeared between 800 BC and AD 300. As the lower America crops were introduced, the people developed agricultural practices to incorporate them into their economies, taking into account the climate and conditions of their land.

Geographer William E. Doolittle describes the diverse geography of the Southwest by categorizing its agricultural landscape into two types: "the floodplains of low-lying desert streams, with deep and fertile soils that are highly localized" and "upland slopes where rainfall may be sufficient but soils are thin and of poor quality". Despite the limitations of the land, Doolittle observed that agriculture was quite intensive for many early farmers, who modified the landscape with durable irrigation systems and check dams to support the growth of various cultivars.Doolittle, p. 388 The prehistoric people of the Southwest developed various agricultural techniques and technologies to manage water retention for crop growth, including diverse field designs like runoff agroecosystems and terraces, lithic-mulch soils, and waffle gardens.

Among the crops introduced to the Southwest, maize emerged as the most important and widely grown. The earliest evidence of maize cultivation in the Southwest dates from about 2100 BCE. Small, primitive maize cobs have been found at five different sites in New Mexico and Arizona. These sites encompass a wide climatic range, from the Tucson basin in the Arizona desert, at an elevation of 700 m (2300 ft), to a rocky cave on the Colorado Plateau at 2200 m (7200 ft). This variation suggests that the primitive maize grown in these areas was already adapted for growth in both hot, dry climates and short growing seasons.Merrill, William L. et al, "The Diffusion of Maize to the Southwestern United States and its Impact." Proceedings of the National Academy of Sciences of the United States of America. Vol. 106, No. 50 (December 15, 2009), pp. 21019–21020

Maize reached the Southwest via an unknown route from Mexico. Its diffusion was relatively rapid. One theory is that the maize cultivation was carried northward from central Mexico by migrating farmers, most likely speakers of a Uto-Aztecan language. Another theory, more accepted among scholars, is that maize was diffused northward from group to group rather than migrants. The first cultivation of maize in the Southwest came during a climatic period when precipitation was relatively high. Although maize cultivation spread rapidly in the Southwest, the hunter-gatherers living in the region did not immediately adopt it as their primary source of nutrition, but rather integrated maize cultivation as one element, initially a minor element, in their foraging strategy. Hunter-gatherers usually exploit a broad spectrum of food sources to minimize risk in the event that one or more of their principal sources of food fails.Merrill, et al, p. 21024

Pre-agricultural hunter-gatherer bands were typically small, comprising only 10–50 members, although several bands joined on occasion for ceremonies or mutual cooperation. As maize cultivation became more important, communities became larger and more settled, although hunting and gathering wild foods remained important. Several of the agricultural towns in the Southwest, such as Casa Grande and Casas Grandes plus Pueblo and Opata settlements may have had populations of 2,000 or more at the peak of their influence. Many more people lived in smaller satellite settlements of 200 to 300 people each, or in isolated settlements.

Maize cultivation in the Southwest predates by many centuries maize cultivation in the eastern United States which has a much more favorable climate for agriculture.

Crops

Southwestern farmers probably began experimenting with agriculture by facilitating the growth of wild grains such as amaranth and chenopods and gourds for edible seeds and containers. The earliest maize known to have been grown in the Southwest was a popcorn variety with a cob only about one or two inches long. It was not a very productive crop. More productive varieties were developed by Southwestern farmers or introduced from Mesoamerica. Beans and squashes were also introduced from Mesoamerica, although the drought-resistant tepary bean was native. Cotton, presumably cultivated, is found at archaeological sites dating about 1200 BC in the Tucson basin and evidence of tobacco use, and possibly cultivation, occurs at about the same time. Agave, especially Agave murpheyi, was a major food source of the Hohokam and was grown on dry hillsides where other crops would not grow. The early farmers also consumed and possibly facilitated the growth of cactus fruit, mesquite bean, and species of wild grasses for their edible seeds.Diehl, Michael W. "Early Agricultural Period Food Provisioning and Foraging." Archaeology Southwest, Vol. 23, No. 1, Winter 2009, p. 12

Tools

Southwestern Indians did not have draft animals or metal tools. Planting was done with a sharpened, fire-hardened stick, a tool that is now known as a dibble stick. Hoes and shovels were made of wood and the shoulder bones of buffalo and other large animals. Mussel shells, pottery, and rocks were also used as planting and digging tools. Indians did not customarily fertilize their field with organic matter, but rather relied on crop rotation, fallowing, and silt deposit from rainwater runoff. Fire was sometimes used to clear and fertilize land with ash. They transported water in large pottery jugs for hand watering of garden plots.

Water management

Agriculture at the lower elevations of the Southwest is difficult without irrigation as precipitation is sparse and unreliable. Higher elevations, about , may have greater precipitation but also have cooler temperatures, shorter growing seasons, and less fertile soils. In either case agriculture was a challenge. The agricultural strategies used by ancient Southwestern farmers included: "seed selection, fallowing fields, planting in different locations, staggering the times of plantings, and maintaining separate plantings of different corn and bean varieties."

Canal irrigation

The Las Capas site near Tucson features the earliest irrigation system, dating to 1200 BCE, found in the United States. The network of canals and small fields, each about in size, covers more than indicating a sizable community of people with the organization to undertake substantial public works project. Also found at the site are tobacco pipes, the oldest smoking pipes yet found. This site may have supported 150 people. Corn grown at Las Capas was similar to today's popcorn. Archaeologists speculate that the kernels were popped and then ground into meal to make tortillas."Ina dig reveals early irrigation practices." Pima Pinal 12 May 2009. https://www.tucsonlocalmedia.com/news/pima_pinal/ina-dig-reveals-early-irrigation-practices/article_09d25c60-b96b-5d5a-b2b4-a2a813dbbabe.html

The Las Capas people were probably the forerunners of the Hohokam, the most accomplished farmers of the Southwest. The Hohokam lived in the Gila and Salt river valleys of Arizona between the first century and 1450 CE. Their society bloomed about 750 CE, probably as a result of their agricultural success. The Hohokam constructed a vast system of canals to irrigate thousands of acres of cropland. Their main canals were as much as 10 m (10 yards) wide, four m (4 yards) deep, and extended across the river valleys for as much as .Doolittle, William E. "Agriculture in North America on the Eve of Contact: A Reassessment" Annals of the Association of American Geographers, 82(3), 1992, p. 389 At the peak of their culture in the 14th century, the Hohokam may have numbered 40,000 people."Immigrants and Population Collapse in the Southern Southwest" Archaeology Southwest, Vol 22, No. 4, Fall 2008, p. 1

The sudden disappearance of the Hohokam between 1400 and 1450 CE is a puzzle. Archaeologists speculate that maintenance of the canals was difficult and sediment accumulated over the centuries. Farmers were forced to abandon old canals and move further from the river, increasing the technological challenge to farming. After a thousand years of success, the Hohokam were unable to sustain their intensive agricultural economy. They disappeared from the archaeological record and when Spanish explorers reached the Gila and Salt valleys in the 16th century, they were only sparsely populated by the Upper Pima and Tohono O'odham (Papago) Indians, the likely descendants of the Hohokam.Doolittle, pp. 389–390

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.Doolittle, p. 389

Trincheras

Trincheras (Spanish for trenches or fortifications) are rock walls or terraces built on hillsides by pre-historic Indians. Trincheras are common throughout the Southwest. They date back to near the beginning of Southwestern agriculture. By about 1300 BCE, at Casas Grandes, in Chihuahua, early farmers constructed hilltop fortresses and trincheras on hillsides, public works that required considerable labor and organization which implies a settled and numerous community.Merrill et al, p. 21,024