Arizona consistently produces the highest yields and quality of crops found anywhere. This is a testimony to not only the skill of Arizona farmers and the capacity to irrigate and produce crops in the desert but also to the productive soils that we are fortunate to have in this region. Soils are commonly considered to serve as the foundation of agriculture (Parikh and James, 2012) and that is certainly true in Arizona.
Many people think Arizona is composed of nothing but rocks and sand. While we do have an abundance of rocks and sand in Arizona, this region also has many areas with soils that are geologically young, with high natural fertility, and extremely productive if provided with sufficient water and good management.
Most Arizona crops are produced on alluvial soils that are formed from the deposits of sediments from periodic flooding of rivers and streams over thousands and millions of years. The alluvial soils used in Arizona crop production vary tremendously across the state and the entire desert Southwest. They vary in texture, depth, and structure. Our crop production capacities in this region are supported by the irrigation water and these incredible soil resources.
A great example of the rich alluvial soils of this region can be found in the lower Colorado River valleys including Mohave Valley, AZ; Parker Valley, AZ; Palo Verde Valley, CA; Imperial Valley, CA; Bard Valley, CA; Yuma Valley, Arizona; and the lower Gila Valleys of Arizona. The alluvial sediments that have formed the soils we encounter in the lower Colorado River system are estimated to have been deposited to several hundred meters (several thousand feet) in depth in the current river channel approximately 4.63 to 4.80 million years ago (Crow et al., 2021 and Kimbrough et al., 2015). These sediments are geologically “young” in contrast to the ancient crystalline rocks at the bottom of the Grand Canyon, often referred to as the “Vishnu Basement Rocks” that are 1,680 – 1,750 Ma (1.68 – 1.75 billion (b) years ago), (Crow, et al., 2021 and Mathis and Bowman, 2018).
In 1941, Dr. Hans Jenny from the University of California – Berkeley, published Factors of Soil Formation: A System of Quantitative Pedology. [Pedology is the scientific study of soils and their weathering profiles, including the formation, nature, ecology, and classification of soil.] This book is a classic and fundamental piece of work in the study of soil science due to Jenny’s capacity to translate the basic concepts into a quantitative scientific framework through a rigorous definition of the soil system and its genesis, including the identification and separation of dependent and independent variables.
Jenny described soil formation as a function of five factors: climate, biota (plants and animals), relief (topography), and parent material, all operating together over time (Figure 1).
Alluvial soils tend to be highly variable both horizontally across the landscape and vertically down through the soil profile. This can sometimes present challenges in field-level management for crop production, particularly when soil types change within a given field or relatively small area, which is rather common.
Figure 1. Hans Jenny and the factors of soil formation, 1941.
We commonly find that soil formation will vary tremendously across a landscape with natural soil variation across the landscape in both the horizontal and vertical dimensions with the distinct organization of soil horizons (Figures 2 and 3).
It is important to recognize soil variability in a crop production system because different soil types will have unique physical and chemical properties that can affect things like soil-water holding capacity, drainage, leaching capacities, soil fertility, and plant root development.
The United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) has conducted extensive soil surveys across the United States for each state by county. Soil surveys can be accessed on-line at the following site: https://websoilsurvey.nrcs.usda.gov/app/
A broad map selected from NRCS Soil Survey of the Yuma area graphically depicts both the alluvial nature and variability of the soil resources commonly encountered in this area. https://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx
It is important to recognize the importance and high value of these natural soil resources that our agricultural systems are developed and dependent upon and be alert to the natural variability associated with the alluvial soils in this region.
Figure 2. Natural variation of soils across a landscape
Figure 3. Layers of soil, basic organization of soil horizons.
Figure 4. Soil volume, soil texture, and water holding capacity
relationships. Source: Kansas State University Agronomy Department, Soil
Laboratory Manual.
References:
Crow, R.S., J. Schwing, K.E. Karlstrom, M. Heizler, P.A. Pearthree, P.K. House, S. Dulin, S.U. Jänecke, M. Stelten, and L.J. Crossey. 2021. Redefining the age of the lower Colorado River, southwestern United States: Geology, v. 49, p. 635–640, https://doi.org/10.1130/G48080.1
Jenny, H. 1941. Factors of Soil Formation: A System of Quantitative Pedology. McGraw-Hill Book Company. New York and London.
https://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf
Kimbrough, D.L., M. Grove, M., G.E. Gehrels,, R.J. Dorsey, K.A. Howard, O. Lovera, A. Aslan, P.K. House, and P.A. Pearthree. 2015. Detrital zircon U-Pb provenance of the Colorado River: A 5 m.y. record of incision into cover strata overlying the Colorado Plateau and adjacent regions:
Geosphere, v. 11, p. 1719–1748, https://doi.
org/10.1130/GES00982.1.
Kansas State University Agronomy Department, Soil Laboratory Manual: Soil and water relationships. https://kstatelibraries.pressbooks.pub/soilslabmanual/chapter/soil-and-water-relationships/
Mathis, A. and C. Bowman. 2018. Telling Time at Grand Canyon National Park. United States Department of the Interior, National Park Service.
Parikh, S. J. and B.R. James. 2012. Soil: The Foundation of Agriculture. Nature Education Knowledge 3(10):2
https://www.nature.com/scitable/knowledge/library/soil-the-foundation-of-agriculture-84224268/#
I am seeking samples of downy mildew on lettuce from around Yuma County to support the Michelmore Lab and their ongoing efforts to help characterize the downy mildew populations of the United States. The Michelmore Lab has led the charge on a survey of Bremia variants since 1980 and has been instrumental in demystifying the gene-for-gene nature of lettuce resistance to downy mildew.
Their group invites growers across the United States to submit downy mildew infected plant samples, which are then used to culture the Bremia on live host plants. The team then inoculates a panel of lettuce varieties carrying known resistance genes to determine the race of each isolate they receive. Identifying which races occur in which specific fields is essential to guiding the breeding of new resistant cultivars and maximizing the effectiveness of host-based genetic disease management. The data obtained from these tests are also used to designate new Bremia races through the International Bremia Evaluation Board.
Your contribution will help breed better lettuce for Yuma. This means less breakdown of resistance in the field, and better yields for Yuma growers. To facilitate these submissions the Yuma Plant Health Clinic will be setting up a separate drop-off point and submission sheet for downy mildew sample submissions in the same hallway we use for standard plant diagnostic submissions. The drop-off point will be clearly labelled and consist of a chest-style refrigerator and printed copies of the submission form. It is vital to keep these samples cool so they remain viable for future inoculations, so please place your samples inside of the refrigerator before you leave.
Shipping will be handled by the clinic. All we ask is that you fill out the submission form as completely as you can. An example of the questions that are asked in that form so you can prepare ahead of time can be found HERE .With the advent of low-cost computing systems that can identify and locating crop and weed plants in real-time, there’s been an explosion in the interest, investment and development of technologies for robotic/automated weed control. A quick internet search will reveal over 50 companies or university research groups working in this space. You are probably familiar with many of these as they are domestically based and have been discussed in previous articles, but there are also numerous efforts being made in Europe that may be of interest. One of these is highlighted here. In future articles, I’ll discuss additional technologies.
Andela Techniek & Innovatie1 is a Dutch company who appears to be making good progress with an innovative robotic weeding machine (Fig. 1). The solar powered device spans 29.5 feet and is equipped with 12 robotic delta arms for removing in-row weeds (Fig. 2). A camera-based imaging system is used to differentiate crop plants from weeds and provide coordinates of targeted weeds to the delta arms. Each delta arm is equipped with an end-effector that uses heat to kill the weed when it comes into contact with it. A company video showing the device operating in carrot and onion crops can be found by clicking here or on the images below.
Stay tuned!
Fig. 1. Andela Techniek & Innovatie1 solar powered robotic weeding machine. (Photo credits: Andela Techniek & Innovatie)
Fig. 2. Delta arms and end effector of Andela Techiek &
Innovatie1 robotic weeding machine. (Photo credits:
Andela Techniek & Innovatie)
The IPM team frequently receives questions from our friend PCAs in Yuma regarding possible injury with herbicide combinations. A recent inquiry was about the addition of Prowl (pendimethalin) to Prefar herbicide preplant.
We found in our archives an evaluation that was done in 2002 by Barry Tickes from Arizona Cooperative Extension that addressing this question. The evaluation was located on 8th Street and the Levee in Yuma CO and included the following treatments: Dacthal at 10 and 12lb, Prefar at 6qt alone and with the addition of 0.5pt Prowl. All treatments were applied in 20 gallon/A spray volume as a 50% band on 42-inch beds. The plot size for this experiment was 600 ft. x 8 beds. Immediate incorporation was done with sprinkler irrigation. The results reported are in the following table:
|
Herbicide |
Rate |
Phyto (%Stunting) |
Control: Nettleleaf Goosefoot |
Control: Groundcherry |
|
1. Dacthal |
10lb |
0 |
95 |
90 |
|
2. Dacthal |
12lb |
0 |
95 |
95 |
|
3. Prefar |
6qt |
0 |
30 |
0 |
|
4. Prefar+Prowl |
6qt+0.5pt |
20 |
50 |
0 |
|
5. Untreated |
-- |
0 |
0 |
0 |
|
|
|
|
|
|
As can be seen the addition of 0.5pt of pendimethalin to 6qt of bensulide produced 20% stunting in this case.
