Yuma Ag and You: Giving our soils the R&R they need

Bobbi Stevenson-McDermott      March 27, 2016 publication

March brings many changes to the Yuma County farmlands. Gone are the rows and rows of colorful produce with varied leaves, shapes and sizes. These are replaced with wide green expanses of wheat, rows of cotton plants, fields of Sudan grass, acres of wonderfully strange looking seed crops: artichokes, onions and broccoli. In addition there are fields of beans and peas that are being grown for the dried seed market. Not to be left out, cantaloupes, honeydew and watermelons are growing rapidly for harvest starting in late May.

The soils in Yuma County are actually in a rest and rebuilding stage from April to August. After the intense activity of the produce season with its field traffic of feet, tractors and harvest equipment, the soil becomes compacted with the soil particles squeezed together, eliminating passage ways for water and air. The spring/summer crops have larger root systems that help to open up the closed passages, allowing the soil to become more porous. This is important because plants need as much air as water and recreating the soil structure is vital to the soil health.

The organic matter that desert soils so desperately needs is also added during this resting period. With food safety a major goal, all manures used in the fields are composted to kill harmful bacteria and reduce the amount of viable weed seed. Manures are often applied after the harvest of the rotation crop and worked into the soil. Desert soils, unlike the Midwest or Eastern soils, have less than one half percent organic matter in them. In contrast, the dark, rich soils of the East and South may contain as much as 7 to 10 percent organic material, the largest portion being dead plant parts, then living roots and last living molds and bacteria. Organic matter in the soil changes the amount of nitrogen available to plants, changes the amount of other available nutrients, changes the way the soil sticks together (soil aggregation or structure); and changes the number and type of organisms present in the soil.

Tillage is a major cause of the loss of organic matter in desert soils. Tillage disturbs the soil and brings organic matter that is inside soil particles in contact with microorganisms which decompose it. Yuma County farmers are constantly working to use new technologies to reduce the amount of soil disturbance in their farming operations. As with any business, the changing farming methods must make economic sense.

Another important characteristic of adding organic matter to soils is that it acts as a sponge when the soil is irrigated. This allows more water and nutrients to be available to the crop roots.

The type of roots that the summer crops have also greatly influence the soil during this rest and rebuilding time of the year. Crops that are considered in the grass family have fibrous root systems opposite of a taproot system. It is usually formed by thin, moderately branching roots growing from the stem. The network of roots does not grow as branches of the primary root but consists of many branching roots that emerge from the base of the stem. If you examine the roots of Bermuda grass, another rotation crop, the large amount of roots available for opening the soil can be seen.

Giving our Yuma soils the R & R they need each year, insures that next year’s produce crops will be growing in healthy, refreshed soil, vital to our amazing fruit and vegetable crops.