Irrigation efficiency has been receiving a lot of attention in recent months, particularly with the Colorado River system water shortages that we have been experiencing. There are several ways to define irrigation efficiency. The primary definitions for irrigation efficiency include water conveyance and delivery systems, agronomic, economic, and environmental efficiencies.
Water Conveyance and Delivery System Efficiency
In the desert Southwest we have the benefit of good engineering and infrastructure with the highly developed systems of dams, primary and secondary canals, pumps, laterals, and ditches that move water from rivers and groundwater supplies to areas of need, which are often managed by irrigation districts.
Our ability to move water from the original source to the field is a critical aspect of managing water resources and there is an “efficiency” consideration associated with that. This level of efficiency is largely a function of system engineering design, maintenance, and management.
Economic Efficiency
Economic efficiency is often considered to be the primary factor defining the financial sustainability of a farming operation. Water is a crop input and the costs associated with irrigating a crop include the costs of the water and delivery (pumps, equipment, maintenance, labor, etc.). Water is consistently the most expensive and critical input provided to a crop in Arizona and the desert Southwest. Economic efficiency essentially considers the “return on the investment” and profitability of irrigating a crop.
Environmental Efficiency
Considerations of irrigation efficiency from an environmental perspective is very broad and encompassing and it can include a combination of factors previously discussed (water conveyance systems, agronomic, and economic considerations). Environmental efficiency of an irrigation system is the product of the overall stewardship of water as a natural resource with multiple considerations for beneficial use.
Agronomic Irrigation Efficiency
Agronomic (crop and soil) considerations are centered on our ability to provide irrigation water for the sustainable production of a crop in the field. The three primary demands for crop water management include: 1) providing water for seed germination and stand establishment, 2) providing irrigation water to match crop-consumptive water use, and 3) sufficient irrigation water to leach soluble salts from the root zone so that the soils can support crop production in a sustainable manner (Figure 1).
Agronomic efficiency at the field level focuses on the crop water demand (CWD) through crop consumptive use, often referred to as the crop evapotranspiration (ETc), which is the combination of evaporation and transpiration from the crop. Total crop water demand should also include the leaching requirement (LR), which is dependent upon the crop and salinity of the irrigation water.
Agronomic efficiency can be estimated by considering the difference between total crop water demand, CWD and the volume of irrigation water applied (IWA).
The Leaching Requirement (LR) can be estimated by use of the following calculation:
Where:
ECw = salinity of the irrigation water, electrical conductivity (dS/m)
ECe = critical plant salinity tolerance, electrical conductivity (dS/m)
This is a good method of for the LR calculation that has been utilized extensively and successfully in Arizona and the desert Southwest for many years. We can easily determine the salinity of our irrigation waters (ECw) and we can find the critical plant salinity tolerance level from open access tabulations of salinity tolerance for many crops (Ayers and Westcot, 1989). Additional direct references are from Dr. E.V. Maas’ lab at the University of California (Maas, 1984: Maas, 1986; Maas and Grattan, 1999; Maas and Grieve, 1994; and Maas and Hoffman, 1997).
Estimating Field Level Irrigation Efficiencies
The focal point of any irrigation system, from the regional, district, farm, and field levels is to provide water to produce a crop. The crop is the centerpiece of the entire operation. Therefore, it is entirely appropriate to consider irrigation efficiency at the field level in agronomic terms, by use of Equation 2.
We need three factors to estimate agronomic field level irrigation efficiency for a crop: 1) crop evapotranspiration (ETc), 2) the crop and field leaching requirement (LR), and 3) a measure of the irrigation water applied (IWA) to the field in question.
To determine crop evapotranspiration (ETc) we need a good reference evapotranspiration (ETo) measurement for the field site in question. Reference evapotranspiration (ETo) values multiplied by an appropriate crop coefficient (Kc) can provide very good estimates on actual crop evapotranspiration (ETc) rates as shown in the following equation:
Reference Evapotranspiration (ETo)
The Arizona Meteorological Network (AZMET) is a system that provides both historical and real-time weather information that can be used to track reference evapotranspiration (ETo) measured at a standardized and properly calibrated weather station site. Reference evapotranspiration values can be obtained daily from AZMET for the nearly 30 sites in Arizona, including several sites in the Yuma area and the lower Colorado River Valleys.
Very importantly, the AZMET data is of a very high quality and the integrity of the system has been very well managed for over 36 years, first under the direction of Dr. Paul Brown and now with Dr. Jeremy Weiss. This information is valuable in crop water and irrigation management.
Crop Coefficients (Kc)
The appropriate crop coefficient (Kc) values are specific for each crop species and stage of growth. We commonly use crop coefficient (Kc) values that are provided in the publication “Consumptive Use by Major Crops in the Desert Southwest” by Dr. Leonard Erie and his colleagues, USDA-ARS Conservation Research Report No. 29. Crop coefficients from the publication FAO 56 “Crop Evapotranspiration-Guidelines for Computing Crop Water Requirements-FAO Irrigation and Drainage Paper 56” (Allen et al., 1998) are also sometimes used. Reference information for Kc values can be obtained in these publications for common crops grown in this region.
Example: Irrigation Efficiency Calculation
If we consider an example lettuce crop irrigated with water that has ECw = 1.1 dS/m and the total seasonal crop consumptive use (ETc) = 30 inches
Using Equations 1-3, an overall estimate of field level irrigation efficiency can be made. From Equation 2 we can estimate the leaching requirement (LR).
ECw = 1.1 dS/m and ECe (lettuce) = 1.3 dS/m
LR = 1.1 dS/m / (5 X 1.3) – 1.1 = 1.1/5.4 = 0.20 = 20% leaching requirement
LR = 30 X 0.2 = 6.1 ~ 6 inches
Thus, CWD = 30 + 6 = 36 inches total
For this example, we can assume: 40 inches of irrigation water was applied (IWA).
Therefore: Agronomic efficiency (from Equation 1) = 36/40 = 0.9 = 90% efficiency
Note: If the LR were not included in the total CWD, efficiency would be: 30/40 = 75%
That is an important difference and distinction to understand and demonstrate.
Irrigation efficiency has always been a major concern in the agriculture of the desert Southwest, and it always will be. The increased levels of attention being given to irrigation efficiency is good and it is important to recognize there are many factors associated with improvements in irrigation efficiency.
Figure 1. Soil-water balance and plant relationships in a crop production system.
References
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9), D05109.
Ayers, R.S. and D.W. Westcot. 1989 (reprinted 1994). Water quality for agriculture. FAO Irrigation and Drainage Paper 29 Rev. 1. ISBN 92-5-102263-1. Food and Agriculture Organization of the United Nations Rome, 1985 © FAO.
https://www.fao.org/3/t0234e/t0234e00.htm
Erie, L.J., O.A French, D.A. Bucks, and K. Harris. 1981. Consumptive Use of Water by Major Crops in the Southwestern United States. United States Department of Agriculture, Conservation Research Report No. 29.
Maas, E.V. 1984. Crop tolerance to salinity. California Agriculture, October 1984. https://calag.ucanr.edu/archive/?type=pdf&article=ca.v038n10p20
Maas, E.V. 1986. Salt tolerance of plants. Appl. Agric. Res., 1, 12-36.
Maas, E.V. and S.R. Grattan. 1999. Crop yields as affected by salinity, Agricultural Drainage, Agronomy Monograph No. 38.
Maas, E. V., and Grattan, S. R. (1999). Crop yields as affected by salinity, agricultural
drainage, Agronomy Monograph No. 38, R. W.
Maas, E. V., and Grieve, C. M. 1994. “Salt tolerance of plants at different growth stages,” in Proc., Int. Conf. Current Developments in Salinity and Drought Tolerance of Plants. January 7–11, 1990, Tando Jam, Pakistan, 181–197.
Maas, E. V., and Hoffman, G. J. (1977). “Crop salt tolerance: Current assessment.”
Frost and freeze damage affect countless fruit and vegetable growers leading to yield losses and occasionally the loss of the entire crop. Frost damage occurs when the temperature briefly dips below freezing (32°F).With a frost, the water within plant tissue may or may not actually freeze, depending on other conditions. A frost becomes a freeze event when ice forms within and between the cell walls of plant tissue. When this occurs, water expands and can burst cell walls. Symptoms of frost damage on vegetables include brown or blackening of plant tissues, dropping of leaves and flowers, translucent limp leaves, and cracking of the fruit. Symptoms are usually vegetable specific and vary depending on the hardiness of the crop and lowest temperature reached. A lot of times frost injury is followed by secondary infection by bacteria or opportunist fungi confusing with plant disease.
Most susceptible to frost and freezing injury: Asparagus, snap beans, Cucumbers, eggplant, lemons, lettuce, limes, okra, peppers, sweet potato
Moderately susceptible to frost and freezing injury: Broccoli, Carrots, Cauliflower, Celery, Grapefruit, Grapes, Oranges, Parsley, Radish, Spinach, Squash
Least susceptible to frost and freezing injury: Brussels sprouts, Cabbage, Dates, Kale, Kohlrabi, Parsnips, Turnips, Beets
More information:
Keeping up to date with the latest developments in automated weeding machines is challenging. It’s a very fast-moving space with significant private and public investment. At the 2023 Southwest Ag Summit “Innovations in Weed Control Technologies” breakout session, university experts and cutting-edge innovators will provide updates on the latest advances in high precision smart spot sprayers, towed automated weeders and autonomous weed pulling robots (agenda below). The session will be held TOMMOROW Thursday, February 23rd from 9:30-11:30 pm at Arizona Western College in Yuma, AZ.
As I mentioned in the last newsletter, we’ll also be demoing our band-steam applicator for controlling soilborne diseases and weeds at the Southwest Ag Summit Field Demo Day (Fig. 2). It is simpler in design and has a higher capacity steam generator as compared to our first prototype. This will increase travel speed and thereby work rate. The event is scheduled for TODAY, Wednesday, February 22nd from 10:00 am – 4:30 pm.
For more information about the Southwest Ag Summit, visit https://yumafreshveg.com/southwest-ag-summit/.
Hope to see you there!
Fig. 1. “Innovations in Weed Control Technologies” breakout session agenda at
the 2023 Southwest Ag Summit. Session will be held Thursday, February 23rd at
Arizona Western College, Yuma, AZ.
Fig. 2. Band-steaming demo plots prior to planting in preparation for the 2023
Southwest Ag Summit Field Demo Day, February
22nd (https://yumafreshveg.com/southwest-ag-summit/).
We published this booklet last July. Please let us know what you think by responding our five questions in the link provided below, email marcop@ag.arizona.edu and let us know if you like to receive a free of the booklet!
The method for identification presented is not by using a dichotomous key or answering complicated questions about the species. The idea is to leaf through the booklet and find images that match plants you see in the field. If there are unusual characteristics, we note them in our comments for each weed. Here is a link to the guide in PDF format: HERE
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: CEW moth counts remain at low levels in all areas, well below average for this time of year.
Beet armyworm: Trap increased areawide; above average compared to previous years.
Cabbage looper: Cabbage looper counts decreased in all areas; below average for this time of season.
Diamondback moth: DBM moth counts decreased in most areas. About average for this time of the year.
Whitefly: Adult movement beginning at low levels, average for early spring.
Thrips: Thrips adult counts reached their peak for the season. Above average compared with previous years.
Aphids: Aphid movement decreased in all areas; below average for late-March.
Leafminers: Adults remain low in most locations, below average for March.
