   Verde Valley Soils - February 14, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County There is little that we can do to change our soil over the long-term. For example, if you have a sandy loam, you will never convert it into a clay or visa versa. We can significantly improve our soil's ability to produce a crop in localized areas through intensive composting, deep digging, rock removal, etc. However, without continuous inputs, most of our laborious improvements go by the wayside and the soil quickly reverts back to its natural state. The point of this column is not to plunge you into a hopeless state. Rather, it is to learn about our local soils to better understand them and make our feeble efforts more fruitful. The best agricultural soils lay on the terraces above the floodplains along the Verde River and it tributaries. These soils are often deep, well-drained, fine sandy loams. If they are not currently growing a crop, then someone almost certainly has farmed them at sometime between 600 AD and the present. These lands are also vulnerable to periodic flooding. These soils are usually alkaline (7.9 to 8.4 or higher). If these lands have been fallow, then mesquite trees may be present. Once cleared, these soils are excellent for irrigated pasture, crops, and orchards. Moving up off the river and creek bottoms, we usually find low hills and benches. Some of these areas can be very stony. You may see some large rock outcrops. This tells you the soil is likely to be very shallow. In the Cornville, Lake Montezuma, and Rimrock areas, you will find limestone. In Sedona, you may find red sandstone. Around House Mountain, the rock may be dark basalt. Each of these different areas often has native soils that are well suited to rangeland habitat. With ample work, they can be improved for crop production. If rocks are abundant and soils are shallow, then consider raised beds or other intensive methods for vegetable or flowerbeds. Mesa tops can have relatively flat expanses with moderately developed soils. For the most part, these soils have the same limitations as the low hills and benches. In some places you may find moderately developed soils formed from basalt. Many times these soils have high clay content which swells when moist and shrinks as it dries. These soils are recognizable by deep cracks during dry periods. Soil scientists describe these soils as "vertisols". These soils severely limit woody plant growth because roots are severed as shrinkage occurs. Grasses often predominate on these soils. Caliche is a common soil problem in the Verde Valley. Caliche is a cemented soil layer that is found between 6 and 12 inches deep. It forms when calcium carbonate is leached from the upper soil layers and becomes concentrated in the subsoil. Our limited rainfall only caries the calcium carbonate to a limited depth. Over thousands of years, the concentration of this material cements soil particle, gravel, and rocks together in an impermeable layer we call caliche. When planting trees and shrubs, you must break a hole through the caliche layer to allow irrigation water to drain. On a large scale, it can be deeply ripped by a bulldozer to break it up. Moderate sized rocks can be removed and used to build walls and other structural improvements. Soil texture can also offer unique challenges. Sandy soils have abundant air but they are limited by their ability to hold moisture. Clay soils have the opposite problem: too much water and too little air. Annual flower and vegetable crops are demanding on soil resources and success can be greatly increased through the addition of well-rotted compost (not raw wood chips or uncomposted mulch). Compost benefits soil in many ways. It helps bind soil particles together to improve structure. It adds essential plant nutrients in readily available forms. It improves soil water holding capacity and aeration. Biological activity is also increased. To a limited extent, compost also helps acidify our alkaline soils. Large quantities are required due to our warm summers and alkaline soils, which cause compost to break down and volatilize quickly. Everyone that gardens should be composting kitchen and garden waste. The University of Arizona Cooperative Extension has publications and information on horticulture and composting. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. The Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/. |