Arizona agriculture utilizes ~ 70% of the water in this state and generates a strong and productive industry. Arizona agriculture generates more than $23B in sales as well as directly and indirectly supporting more than 138,000 Arizona jobs and employing more than 162,000 unique workers. Arizona ranks among leading states in the production of lettuce, spinach, broccoli, cauliflower, cantaloupe, honeydew melons, durum wheat, and other commodities. Arizona is an important area for the seed production of many crops that are used across the U.S. and worldwide. Many Arizona counties rank in the top 1% of all U.S. counties in terms of crop and livestock production (Murphree, 2018).
In response to the Colorado River (CR) water shortage and the current reductions in CR allocations to Arizona via the Central Arizona Project (CAP), which is primarily impacting agricultural irrigation districts in central Arizona, there is an increasing level of scrutiny on agricultural uses of Arizona water. This of course is accentuated with the recognition that agriculture utilizes ~ 70% of the Arizona water supply.
In the irrigation districts along the mainstem of the CR, there is a common adage of “First in use, first in right.” This is a fundamental aspect of the “law of the river”, which is an amalgam of the various laws, agreements, and rulings on the governance of CR water. Therefore, it is important for us to consider and prepare the positive case that can be made for the good stewardship of water resources provided by Arizona agriculture.
One common area of criticism that is directed towards Arizona crop production systems, is the use of surface and flood irrigation systems. The alternative irrigation methods that are commonly advocated for use instead of flood irrigation are methods such as drip irrigation, micro-irrigation systems, sprinklers, etc. Each of these are good irrigation methods and advantageous under the appropriate conditions. However, a good case can be made for the very efficient use of flood irrigation systems, particularly with high-flow turnouts and dead level (or very nearly so) basins for irrigation. When properly managed, these types of flood irrigation systems can be very efficient.
When we know the area to be irrigated, the flow rate of water in the irrigation delivery ditch, and the amount of water needed; then we can determine the proper time or duration for an irrigation event. If we can get fast and uniform coverage of the field to be irrigated, apply the proper volume of water to replenish the plant-available water supply to the soil, then cut off the flow of irrigation water into the field; we can do a very good job of delivery for high water-use efficiency.
To facilitate the process of managing individual irrigations for optimum efficiency, the Irrigator’s Equation can be used to estimate the depth of water applied or time (duration) of an irrigation event.
Q x t = d x A
Where: Q = the flow rate, in cubic feet per second (cfs);
t = the set time or total time of irrigation (hours);
d = the depth of water applied (inches) and
A = the area irrigated (acres).
With an understanding of the dominant soil type in the field being irrigated and the level of soil-water depletion at the time of irrigation, we can estimate the amount or depth of water needed to replenish the soil profile of plant-available water to support the crop and prevent water stress.
In managing crop fields and irrigations, we recognize that soil textures vary in terms of water holding capacities and it is important to understand the dominant soil textures in the field, not only on the surface but also through the depths of the soil profile through the effective rooting depth of the crop, Tables 1 & 2.
Collectively, we can manage surface or flood irrigation systems efficiently. In the crop production arena, it is important to communicate these points effectively.
Table 1. Soil texture and water holding capacity.
2. Depths to which the roots of mature crops will deplete the available water supply when grown in a deep permeable, well-drained soil under average conditions.
Source: Chapter 11, "Sprinkler Irrigation," Section 15, Natural Resources Conservation Service National Engineering Handbook
References:
Murphree, J. 2018. Arizona Agriculture is 23 Billion Dollars Beautiful, Arizona Farm Bureau.
https://www.azfb.org/Article/Arizona-Agriculture-is-23-Billion-Dollars-Beautiful
This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Meerkat’ was seeded, then sprinkler-irrigated to germinate seed Jan 13, 2025 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2 backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae)was first observed in plots on Mar 5 and final reading was taken on March 6 and March 7, 2025. Spray date for each treatments are listed in excel file with the results.
Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft2areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2area of bed was approximately 144. The percentage were then changed to 1-10scale, with 1 being 10% infection and 10 being 100% infection.
The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided most effective control against the disease include Orondis ultra, Zampro, Stargus, Cevya, Eject .Please see table for other treatments with significant disease suppression/control. No phytotoxicity was observed in any of the treatments in this trial.
At last week’s 2nd AgTech Field Demo: Automated Weeding Technologies, there were some practice fields that had extremely high weed pressure. It was a unique situation and company reps from the three commercial automated in-row companies participating in the Field Day wanted to test their machines to see how they would perform. We were all impressed at how well they worked in the challenging conditions –large weeds, high density (Fig. 1). Some crop plants were mistakenly removed, but not many. They also performed well in celery plots that were similarly heavily infested with weeds (Fig. 2).
It was readily apparent that image-based crop/weed differentiation using artificial intelligence and pattern recognition algorithms has come a long way in the last several years. In the past, when leaves of adjacent plants overlapped or crop plants and weeds were similarly sized, automated weeding machine imaging systems were not able to reliably detect crop plants and weeding performance was poor.
Our studies on automated in-row weeding machine performance (Lati et al., 2016) have confirmed the logical result that labor savings for follow up hand weeding operations are significant in fields where weed pressure is high as compared to where it is low. If you have a heavily infested field, it might be worth investigating the use of an automated in-row weeding machine. I was impressed at how well today’s machines work.
References
Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.
Fig. 1. Representative image of cultivating performance of three commercial
automated in-row weeding machines (right) operated in heavily weed infested
lettuce (left). Photo taken 5 days after treatment. Machines included Stout AgTech
Smart Cultivator, FarmWise Titan FT-35 and K.U.L.T. Kress iSelect.
Fig. 2. Celery cultivated using an automated in-row weeding machine (left) and a standard cultivator (right).
Weeds are a problem year after year even where they have been diligently controlled. A major reason for this is that weed seeds continually move into fields by irrigation water, wind, equipment, contaminated seed and other means. Controlling weeds on irrigation ditch banks can greatly help to reduce weed seed movement into fields.
The EPA regards non-crop areas as those that are not dedicated to crop production. Although crops are not normally grown on irrigation ditch banks, these areas should not be managed as non-crop. Several very broad spectrum and long lasting herbicides are registered for non-crop areas which include roadsides, industrial sites, fence rows, around structures, railroads etc.. Irrigation ditch banks should be considered separately because of their proximity to crop fields and irrigation water and the potential for herbicide movement into sensitive areas.
It is important to read the label carefully and only use those products that are specifically allowed for use on ditch banks. Some products are restricted to drainage ditch banks or dry ditches. Some can be used only above the water line and some can only be used for non-irrigation ditch banks Because most ditches here are used for irrigation, this can be confusing. The definition of a ditch however, can include an open trench or natural channel. It can also include ditches that are not in use for long periods of time. Some labels specify how long this non-use period should be. Some herbicides that have been used on ditch banks in the past are now restricted from this use because of groundwater contamination or off target movement that has occasionally occurred. Do not assume that products that were used for ditch banks in the past can still be used. Even very old products like MSMA can no longer be used for irrigation or drainage ditches. The following summarizes how some of the more common products that have been used on ditches can be used although the product labels should be read for more complete directions. There are several broad spectrum herbicides that are registered for “Non-Crop” sites but that are retricted from use on irrigation ditches. These include Bromacil,Triclopyr,Imazapyr,Thiazapyr Flumioxyzin,Imazomox,Topamezone,Valpar and others.
