4.1 Soils and water
What are soils?
Soil is made of a combination of minerals, organic matter, and sediment. These three ingredients are combined in different amounts and travel long distances around the globe through gravity and the movements of glaciers, water, and wind. Soils store water and nutrients that plants use to flourish.
How does soil gain water?
Water is delivered to the soil in two ways:
- The Earth’s water cycle: precipitation in the form of rain, snow and ice. In the Southwest, the most important weather events that deliver water to the soil are winter snowstorms and summer monsoon rains.
- Water management: Humans capture and store water from the water cycle and spread it on the soil using irrigation systems.
This video from The Monsoon Project describes the importance of the North American Monsoon to the Southwest.
How does soil lose water?
Soils lose water through a process called evapotranspiration. This means that the sun and the wind cause soil to lose moisture through direct evaporation and through plant tissues.
Breaking this term into two parts clarifies this definition:
- Transpiration — plants sweat out and lose water they have received from the soil
- Evaporation — the soil loses water due to the wind and the sun
To slow this process, farmers often use a technique called mulching. Mulch is:
- A material that is spread over a planting area to protect the soil from the effects of the wind and the sun.
- A layer of insulation that traps moisture and shades the soil, which slows evaporation.
- Carbon-based materials such as straw or dry grass clippings.
Pueblo farmers, such as the Hopi, use dust and sand as a mulch; they cover the moist soil that holds their seeds with a thick layer of sand and dust.
Why do some farmers apply irrigation water to their soil?
Some farmers irrigate because:
- They are replacing the water that their plants and soils have lost due to evapotranspiration.
- Some plants require more water than the environment has to offer; the farmers apply irrigation water to make up for water that does not arrive in the form of rain and snow.
Some modern farmers do not apply irrigation water to their soil:
- Hopi farmers who have vast direct-precipitation corn fields.
- Farmers in the Western states who have large direct-precipitation crop farms.
Many Hopi farmers and other farmers in the Southwest do not use irrigation systems; the keys to their success are understanding weather patterns, caring for their soil, planting drought-resilient seeds, and having faith in natural cycles.
“Dry-farming in the high desert … relying only on precipitation and runoff water, requires an almost miraculous level of faith and is sustained by hard work, prayer, and an attitude of deep humility.”
— Wall and Masayesva 2004:436
How do direct-precipitation farmers decide where to place their gardens and fields? Why is this decision so important?
Choosing the location of a garden is called site selection. It is important to direct-precipitation farmers because the chosen site must be able to capture and hold water delivered by the water cycle, making it drought resilient.
These are features that Hopi farmers of today look for—and that ancestral Pueblo farmers probably also looked for—when searching for a drought-resilient site.:
- Geography: Rainfall and snowmelt that drains off of a mesa or cliff will collect and flow into drainages, washes, arroyos, and canyons. Where these features become less narrow and widen into sandy slopes, Pueblo farmers expect water and good soil to collect because it is washed down with the floodwaters. This mouth or opening is also a place where they traditionally built check dams—rows of low rock walls to slow down the movement of runoff water.
- Garden slope: North-facing slopes have less direct exposure to sunlight and lower soil temperature, and therefore less water is lost to evaporation.
- Indicator plants: The appearance of certain plants in early spring give information, or indicate, to Hopi and other direct-precipitation farmers about the best locations for a garden/field, how deep to plant and how much space to leave between plants. Farmers combine these indications with practice, experience, and knowledge of the land. Some examples of plants that indicate these conditions are:
|Good soil moisture||
|Deep, well-drained soil||
- Soil moisture depth: deep, soft soils allow natural reservoirs of water to collect and be held deep in the soil.
- Soil color: darker colors often mean higher amounts of decomposed organic matter and nutrients in the soil. In the Southwest, this means dark red-brown.
- Large, open planting area: the area must be large enough that clumps of seeds can be planted with wide spaces between them (2–3 adult paces/steps or 4–6 feet between clumps.) This spacing allows little soil-moisture reservoirs to be created between clumps, providing long-term moisture.
Soil moisture is especially important to maize growth at planting (for germination), at tasseling/silking (for best chances at pollination), and during grain fill (to get ears completely covered with kernels).
When a normal amount of snow and rain does not arrive, this is called a drought.
How do Pueblo farmers respond to drought?
The Hopi use the agricultural knowledge gained through their ancestral direct-precipitation farming practices. They want to ensure their crops will continue to be drought-resilient into the future. To survive drought, direct-precipitation farmers must know a lot about their soil and their seeds. Ancestral Pueblo farmers might have responded to drought by:
- anticipating the possibility that it could arrive any year and preparing for it by saving seeds from plants that can survive drought.
- using the site-selection factors listed above to decide whether or not a site would be drought-resilient.
- meeting these site requirements by planting in multiple locations.
- using clumps of plants, twigs, or brush at the edge of the planting area or placing small upright stone slabs around seedlings as a windbreak to decrease evapotranspiration.
- covering holes that contain seeds with loose topsoil to act as a dust mulch.
Do other direct-precipitation farmers use any of these same practices?
Yes, though some farmers emphasize knowing the soil through soil testing:
- First, farmers learn what is in their soil to determine what kind of soil they have.
- Second, farmers find out how much water their soil can hold. If the soil receives more water than it can hold, much of the extra water will drain away. Water that is wasted in this way is called runoff; it leads to erosion, when soil is carried away by the runoff.
Soils in the PFP gardens
Pueblo Farming Project researchers used data from the USDA and local soil analysis to characterize the soils in the gardens on Crow Canyon’s campus in southwestern Colorado. The map below displays the soils on Crow Canyon’s campus. Click a soil to learn more information about it!