- Author: Gerry Spinelli
- Author: Michael Cahn
Determining how long to run your irrigation system can be challenging because typical recommendations on how much water to apply are expressed in units of inches (or feet) of water depth. Knowing the application rate of your irrigation system will allow you to convert these recommendations into the time (hours) to operate the irrigation system.
The application rate is the depth of water that the irrigation system applies during a period of time, and is typically expressed in units of inches per hour (in/hr). An application rate of 0.27 in/hr means that when the system is operated for one hour it will apply 0.27 inches of water to the field; if it is operated 45 minutes, 0.2 inches (0.27 in/hr × 45 min ÷ 60 min/hr) are applied and so on.
Note that the application rate is independent of the number of acres irrigated. In other words, an irrigation system would have the same application rate on a one-acre or a five-acre block. For raised bed crops such as vegetables and strawberries, the application rate includes the area of both the furrows and the bed tops.
Determining the application rate of drip systems
The variables determining the application rate of drip systems are: 1. bed width, 2. number of drip lines per bed, and 3. flowrate of the drip tape. The flow rate of the tape (also referred to as the discharge rate) corresponds to a specific pressure, usually 8 or 10 pounds per square inch (psi). The flow rate of the drip tape is usually specified on the label of the tape roll (Fig. 1) and is often expressed in units of gallons per minute per one hundred feet of tape (gpm/100 ft).
Figure 1. Examples of a drip tape label with flow (discharge) rate information.
Some tape manufacturers provide the discharge rate of the emitters and the emitter spacing rather than the flow (discharge) rate of the tape. The discharge rate of the emitters is usually expressed in units of gallons per hour (gph). To calculate the tape flow rate from the emitter discharge rate, use the following equation:
Tape discharge rate (gpm/100 ft) = Emitter discharge rate (gph) × 20 ÷ emitter spacing (inches) [1]
Example (from Fig. 1): emitter discharge rate = 0.16 gph; emitter spacing= 8 inches
Tape discharge rate (gpm/100 ft) = 0.16 gph × 20 ÷ 8 inches = 0.40 gpm/100 ft
The application rate of a drip system can be determined from the tape flow rate (gpm/100 ft), bed width (inches), and number of drip lines using the following equation:
Application rate (inches/hour) = tape flow rate (gpm/100 ft) × number of tapes × 11.55 ÷ bed width (inches) [2]
Example: tape flow rate = 0.45 gpm/100 ft; bed width = 48 inches; 2 drip lines per bed
Application rate = 0.45 gpm/100 ft × 2 drip lines × 11.55 ÷ 48 inches = 0.22 inches per hour
Table 1 also summarizes application rates of some common drip system configurations for strawberry. The application rate of the drip system can be estimated by finding the row with the flow rate that is closest to the tape that you use, and then reading the application rate under the bed and drip line configuration used at your farm.
Table 1. Application rate (in/hr) of drip systems for common drip tape flow rates and bed widths in strawberry.
Determining the application rate of solid-set and hand-move sprinkler systems
To estimate the application rate in sprinkler systems (aluminum hand-move pipes) one needs to know the spacing of the lateral lines, the sprinkler nozzle size and pressure at which the system is operated. For hand-move sprinklers, the distance that the sprinkler line is moved between irrigation sets is the lateral line spacing. Pressure can be measured at the sprinkler nozzle using a with a pitot tube fitted with a pressure gauge. Alternatively, a gauge or Schrader valve can be added to a riser so that the pressure can be measured on the lateral line. Discharge rate of sprinkler heads will increase with higher pressures and larger nozzle sizes. Most manufacturers provide data on discharge rate for each sprinkler head model. Table 2 shows the range of discharge rates for the Rainbird 20JH model.
Table 2. Discharge rates of Rainbird 20 JH sprinkler heads at varying nozzle sizes and pressures.
From the discharge rate, lateral pipe spacing, and discharge rate, the application rate for a sprinkler system can be estimated using the equation:
Sprinkler application rate (inches/hr) = discharge rate (gpm) × 96.3 ÷ [lateral spacing (ft) × head spacing (ft) [3]
Example: Sprinkler head = Rainbird 20JH with 7/64 inch nozzle operated at 45 psi; lateral spacing = 40 ft; head spacing = 30 ft.
From Table 2 the discharge rate of the sprinkler head = 2.63 gpm.
Sprinkler application rate (inches/hr) = 2.63 gpm × 96.3÷[30 ft ×40 ft] = 0.21 inches/hr
Alternatively, Table 3 can be used to estimate the application rate of an irrigation system using the Rainbird 20JH sprinkler heads.
Table 3. Application rates for sprinkler systems using Rainbird 20 JH heads at varying pressures, nozzle sizes, and lateral and head spacings.
Using the application rate to determine how long to irrigate
The application rate can be used to determine how long to irrigate a crop from estimates of crop water use. For an average year in the Pajaro Valley, a strawberry crop needs one inch of water during a typical week in August and about 28 inches for an entire crop cycle. A grower with an application rate of 0.22 inches/hour will need to irrigate four and a half hours (1 inch ÷ 0.22 in/hr = 4.5 hr) during a week in August and a total of 127 hours (28 in ÷ 0.22 in/hr = 127 hr) during the entire season.
Summary
Accurately estimating the application rate of an irrigation system requires precise knowledge of the discharge rate of the drip tape or sprinkler nozzle. Over time, nozzles become worn and drip emitters clog, or the pressure of the system may not be operated at the specifications of the manufacturer. The best way to accurately know the application rate is to directly measure it in the field. For direct measurements of the application rate, schedule an on-site irrigation evaluation with the RCD of Santa Cruz County at: 831-464-2950, info@rcdsantacruz.org.
- Author: Michael D Cahn, Ph.D.
The California Irrigation and Management Information System (CIMIS) operates and maintains more than 145 weather stations throughout California. The CIMIS program is funded by the California Department of Water Resources. Most stations are located on or near agricultural land, and provide measurements of reference evapotranspiration (ETo), which can be used to estimate how much water to apply to crops. Hourly, daily, and monthly averages of data are available through the CIMIS web site (http://www.cimis.water.ca.gov). The website includes an option to automatically email data from selected stations on a daily or weekly schedule. In addition to ET data, CIMIS stations record precipitation, relative humidity, air and soil temperature, solar radiation, wind speed, and dew point. Besides irrigation management, weather data can be used for plant disease forecasts, for calculating insect and crop degree-days, and for determining wind speeds during spray operations. Water management agencies use historical reference ET data to determine pumping demands, and to estimate future ground water supplies using mathematical computer simulation models.
The Central Coast region currently has 16 active CIMIS stations (Table 1). Stations are located in Monterey, San Benito, Santa Cruz, Santa Clara counties. The newest station is #252 (Figure 1), located near Soledad CA on the east side of the Salinas Valley. CIMIS is a cooperative program, requiring collaboration between a local entity to provide land, maintain the site, and provide periodic servicing of the station. In some cases, stations are owned by the CIMIS program, but in many situations the weather stations are purchased through grant funding obtained by a local agency. Funding for station 252 was from a proposition 84 grant administered by the Coastal Conservation and Research Inc. The installation of the station was a partnership among Monterey County Resource Conservation District, UC Cooperative Extension (Monterey County), Dole Food Company Inc., CIMIS, Monterey Bay National Marine Sanctuary, and the Central Coast Wetlands Group (CCWG). Because CIMIS stations need to be sited on well-watered grass to provide accurate estimates of reference ET, funds from this grant were also used to establish 2-acres of grass surrounding the weather station and to install an underground sprinkler system.
Table 1. CIMIS stations located in the Central Coast region.
Figure 1. CIMIS station 252 located near Camphora-Gloria Rd, Soledad CA.
Even if a ranch has a private weather station, CIMIS data can still be useful. Many private weather stations are not instrumented to monitor ET or are not sited on a well-watered reference crop. Frequently private weather stations are located near a building, parking lot, or tree that can confound micro-climatic measurements. Over time instrumentation on weather stations can malfunction and record inaccurate data. The CIMIS system uses both an automated and manual quality assurance program to flag data that appear inaccurate or outside the normal range. CIMIS staff also service and check that the instruments are working properly. Additionally, CIMIS data are archived so that historical data can be accessed by users. CIMIS weather station data also contributes to Spatial CIMIS, a hybrid ET product that uses weather station and satellite data to provide reference ET estimates at approximately a 1-mile resolution. Spatial CIMIS reference ET data are also available through the CIMIS website.
During the past decade, significant progress has been made in adding new CIMIS weather stations or revitalizing old stations with improved site maintenance on the Central Coast. In addition to the Soledad station, Station 209 was established in West Watsonville, Station 211 was installed in Gilroy, and Station 210 was located in the Carmel Valley. Permanent grass was planted at station 129 in Pajaro and also at station 214 in South Salinas. Although progress has been made to increase the number and accuracy of CIMIS stations, weather stations are still lacking in some important Central Coast growing regions. Closer to the coast, the Castroville (#19) and North Salinas (#116) Stations are no longer reporting reference ET because the sites do not have sufficient grass cover to accurate measure ET. Also, the Green Valley road station (#111), which represents a warmer zone of the Pajaro valley no longer reports reference ET data due to insufficient grass cover at the site.
Having reliable long-term weather data from the main growing regions on the Central Coast is becoming more important for our region. As water demands continue to increase on the Central Coast, the agriculture community is under increased pressure to demonstrate efficient irrigation practices. Online irrigation scheduling tools such as CropManage and the Satellite Irrigation Management Support (SIMS), use CIMIS data to help growers quickly determine crop water needs. These tools can also help growers justify water needs of their crops. To comply with the Sustainable Groundwater Management Act (SGMA), water management agencies will need accurate reference ET data for developing ground water extraction plans. My hope is that through partnerships among local and state agencies, private land owners, and grower groups, we can add new or revitalize existing CIMIS stations so that all growing regions on the Central Coast have accurate weather data.
- Author: Michael D Cahn, Ph.D.
Agricultural Order Public Scoping Meeting
Monday, August 7th 9 am – 11:30 am
Monterey County Agriculture Conference Room
1432 Abbott St.
Salinas CA
The current Agricultural Order which regulates water quality for irrigated agriculture on the Central Coast will expire on March 8, 2020. Ahead of this deadline, The Central Coast Regional Water Quality Control Board (CCRWQCB) staff must develop a new Agricultural Order. Water Quality Control Board members and staff will be hosting several listening sessions where attendees will have the opportunity to share their perspective and experiences regarding the pros, cons, and ideas for potential improvement of the Ag Order. Discussion topics will include the structure of the Ag Order, such as tiering and enrollment, as well as monitoring and reporting requirements.
The current agenda is:
1. Current Agricultural Order Staff will present a summary. Public will have the opportunity to comment on the current Ag Order structure, including enrollment; tiering; electronic notice of intent form; annual compliance form.
2. Water Quality Monitoring Public will have the opportunity to comment on the surface water and groundwater monitoring requirements; cooperatives conducting monitoring such as the Preservation Inc.'s Cooperative Monitoring Program and the Central Coast Groundwater Coalition.
3. Total Nitrogen Applied Public will have the opportunity to comment on the total nitrogen applied requirement.
5. Tier 3 Ranch Requirements Public will have the opportunity to comment on Ag Order requirements for tier 3 ranches, including individual surface water discharge monitoring; irrigation and nutrient management plan reporting; water quality buffer plans.
6. Missing Requirements Public will have the opportunity to comment on the requirements they deem are necessary but currently not in the Ag Order.
A quorum of Central Coast Water Board members may be present; however, the Central Coast Water Board will not be taking any action at the scoping meeting.
The meeting will be conducted in English, Spanish translation will be provided for attendees sharing a comment in Spanish.
Esta reunión se va a llevar a cabo en inglés, pero va a haber traducción al español disponible para aquellas personas que quieran dar testimonio en español.
If you cannot attend this meeting, there will be another opportunity in Watsonville at the Public library on August 15th. Please see the attached flyers for more information.
/h3>Flyer Spanish
Flyer English
- Author: Laura Tourte
- Author: Richard Smith
- Author: Jeremy Murdock
- Author: Daniel A Sumner
Studies that examine crop production and harvest costs, as well as capital costs and net returns, can be helpful to growers in making production decisions, preparing budgets, and evaluating production loans. Cost and return analyses can also assist growers in considering risk and in determining the potential profitability of a crop. Two recently completed studies estimating costs and returns for Central Coast wrapped iceberg lettuce and fresh market bunched broccoli are now available at https://coststudies.ucdavis.edu. Titled Sample Costs to Produce and Harvest Iceberg Lettuce 2017 and Sample Costs to Produce and Harvest Broccoli 2017, these studies were a collaborative effort that included UC Cooperative Extension farm advisors, local growers and industry, and UC Agricultural Issues Center economists and researchers.
Each study begins with a narrative that describes how the costs and returns were calculated. Following this text, an in-depth analysis of the estimated production and harvest costs are presented in a series of tables. Per acre costs are shown for land preparation, fertilization and pest management practices, and material inputs and labor, all of which fall under the category cultural costs. Harvest practices and costs are also detailed. Cash or business overhead costs are estimated, and include items such as land rent, insurance, food safety and regulatory programs. Finally, non-cash or investment costs are discussed and included in each study. Table 1 summarizes per acre costs for iceberg lettuce and broccoli. Greater detail on the sequence of operations and costs contained in each broad cgory can be found in the studies.
Monthly cash cost tables are presented in each study, which can be helpful in managing cash flow and understanding when production loans may be needed. In addition, the tables can be used to evaluate months with peak labor demands and assist with scheduling.
A ranging analysis is also included in each study, which estimates net returns per acre above operating, cash, and total costs for several alternative yield and price combinations. For lettuce, net returns are calculated for yields ranging from 600 to 1,200 cartons per acre (24 film wrapped heads weighing 42 pounds) and prices ranging from $9 to $17 per carton. For broccoli, net returns are estimated using a yield range of 550 to 850 cartons per acre (14 bunches weighing 21 pounds) and prices ranging from $8 to $13.10 per carton. Tables 2 and 3 below contain a selection of the estimated net returns above total costs for lettuce and broccoli.
At the lower yields and prices for iceberg lettuce (table 2), growers operate at a net loss per acre. As yields and prices improve, however, there is potential for a modest positive net return per acre. Growers of bunched broccoli operate at a net loss per acre regardless of yield or price scenario (table 3). The loss is smaller as yields and prices improve. Though net returns to growers can vary substantially from crop to crop and depend on many production and market conditions, the results from both studies—most notably for bunched broccoli—show that there is currently substantial pressure for growers to increase net returns. To improve profitability, growers may use different pack types and market strategies. High labor costs and low product prices, at least in part, help explain the results shown here. An expanded analysis can be found in each study.
Although technology has begun to play a larger role in the production and harvest of fresh market crops than it has in the past, a reliable and productive labor force is still critical to bring a crop to market. Labor costs are discussed and calculated for each crop, with hourly wages set at $21.85 for equipment operators, $17.80 for irrigators, and $16.90 for field workers. These rates include overhead costs of 41 percent. Irrigation, weed management, and harvest are prominent “high cost” labor practices.
New minimum wage and overtime laws that were passed in California in 2016 will have significant implications for agriculture. Although wage rates used in the studies are already higher than the minimum wage shown below for 2017, tables 4 and 5 provide information on the phase-in schedules for the new laws.
As table 4 indicates, minimum wage will steadily increase each year, reaching a $15 base wage per hour by 2022. Table 5 shows that the overtime law will gradually decrease the number of hours employees can work on a weekly basis before overtime wages are required. Prior to its passage agricultural workers could work up to 10 hours per day or 60 hours per week without overtime wages; by 2022 the requirement will be lowered to 8 hours per day or 40 hours per week for employers with 26 or more employees. The overtime law may change wages and scheduling of work in complicated ways as it is phased in.
The full impact of the two new laws on prevailing agricultural wages is not yet clear. But the studies recognize that growers may already pay wages that are different than those used to calculate the lettuce and broccoli costs, and that agricultural wages are currently in flux. The studies also note that growers may choose to use a farm labor contractor or the H-2A guest worker visa program to employ workers and assure a reliable supply of labor.
Vegetable and other cost and return studies for this area, and for other regions in California, are updated periodically, and are always available at https://coststudies.ucdavis.edu. Questions about these or other studies can be directed to either Laura Tourte or Richard Smith at UC Cooperative Extension.
- Author: Timothy K Hartz
- Author: Richard Smith
The factors controlling cadmium (Cd) uptake by leafy greens, particularly spinach, have been the focus of intensive study since 2014. By far the largest influence is the soil test Cd level (Fig. 1A). Coastal soils vary from in total Cd content from less than 0.5 PPM to more than 8 PPM; across this range spinach Cd concentration varies by at least a factor of 10. This is the reason why spinach should not be grown on soils of very high Cd content, at least not without some remediation effort to reduce Cd uptake by the crop. However, if one looks at the relationship between soil and spinach Cd concentrations over a narrower range of soil Cd content it becomes clear that factors other than soil Cd content affect spinach Cd uptake (Fig. 1B). Among those factors is the concentration of chloride (Cl) in the soil.
In soils of neutral to alkaline pH like those of coastal California, much of the Cd in the soil is precipitated in compounds of low solubility, or adsorbed on the surface of soil minerals; this reduces the plant availability of soil Cd. Chloride has been shown to enhance the solubility (and therefore, the plant availability) of soil Cd; in this regard Cl is different from the other common anions in the soil (sulfate or nitrate). The main factors governing the amount of Cl in soil are the Cl concentration of irrigation water, and the degree of leaching for salinity control.
To determine how significant an influence soil Cl can be on spinach Cd uptake a pot trial was conducted in 2016. A loam soil with a total Cd content of 1.5 PPM was used. Large pots containing approximately 7 pounds of soil were seeded with ‘Tambourine' spinach seed. Different Cl treatments were imposed by watering the pots with one of four levels of irrigation water Cl concentration. The irrigation water Cl concentrations evaluated were 1, 4, 7 and 10 milliequivalents per liter (meq/L), equal to approximately 35, 140, 250 and 360 PPM Cl. For context, irrigation water on the central coast typically ranges between 1-7 meq/L, occasionally higher. These solutions were made by adding Cl to a low Cl concentration water. A mixture of sodium and calcium chloride was used to maintain a reasonable cation balance. All pots were germinated with the low Cl water, with the different Cl treatments beginning 7 days after seeding. Watering was controlled to ensure at least 10% of applied water leached from the pots, to maintain a relatively constant soil Cl concentration over the trial period. The spinach was allowed to grow for approximately a month, and then the entire vegetative biomass was harvested, oven-dried, ground and analyzed for Cd concentration. The experimental design of the trial was a randomized complete block, with 4 replicate pots per irrigation Cl treatment.
Spinach Cd concentration increased linearly with increasing irrigation water Cl concentration (Fig. 2). The slope of the regression line showed that each meq/L increase in irrigation water Cl corresponded to a 0.025 PPM increase in fresh tissue Cd concentration. This suggested that irrigation water quality can be a potentially significant factor in spinach Cl uptake. All other factors being equal, a field irrigated with water containing 7 meq/L Cl (250 PPM) may produce spinach with a Cd concentration more than 25% higher than if lower Cl irrigation water was used. These results may actually understate the effect of Cl. In this trial all treatments were germinated with low Cl water, meaning that the initial Cl status of the soil was low across treatments; it may have been well into the growth cycle before soil Cl concentrations fully reflected the treatment differences. In a commercial field situation, irrigating with high Cl water would set a baseline of soil Cl concentration at a relatively high level, affecting the crop from germination onward.
We realize that growers often do not have a choice of irrigation wells to use on a particular field. Where a choice of irrigation water exists, using the lower Cl water would minimize spinach Cd uptake. More broadly, it seems appropriate to use irrigation water Cl concentration as one factor in the determination of which fields to use for spinach production.