- Author: Michael Cahn
- Contributor: David Chambers
- Contributor: Noe Cabrera
Growers will need to implement best management practices that reduce nitrate leaching losses on the Central Coast to comply with Agricultural Discharge Order 4.0. The use of drip irrigation has allowed many growers to be efficient with both water and nitrogen fertilizer. Fertigating through the drip system allows for spoon feeding nitrogen in amounts matching the pattern of crop N uptake, and to place fertilizer in the root zone. Tools like the soil nitrate quick test and the online irrigation and nutrient management platform, CropManage, can help farm managers accurately determine the right amount of fertilizer to apply to satisfy crop N requirements without jeopardizing production.
Once the right amount of fertilizer to apply is determined, it is important that irrigators have the tools that they need to accurately inject the correct volume into the drip system. Fertigation trailers usually consist of a nurse tank that can hold a maximum volume of 500 to 1000 gallons of fertilizer and is equipped with a small gas or electric pump used to inject liquid fertilizer into the drip system. Often irrigators rely on markings on the side of the nurse tank to determine the volume of fertilizer that they are injecting. These markings are usually not accurately calibrated nor have fine enough graduations to precisely measure out fertilizer volume. Furthermore, tank markings can be hard to read, especially if the trailer is not level.
An accurate flowmeter could increase the precision of metering fertilizer into a nurse tank or for measuring the volume of fertilizer injected into the drip system. Using a flowmeter for metering fertilizer would also facilitate tracking the volume of fertilizer applied to each crop by either noting the meter readings or by interfacing the flowmeter to a datalogger that can keep records of the applications.
We evaluated the accuracy of three models of flowmeters designed for metering liquid fertilizer: 1. Banjo FM100 meter, 2. Dura-meter, and 3. Blue White F-1000 (Fig. 1). Each model relied on a different mechanism to monitor fertilizer volume. The Banjo meter measured flow using a magnetic sensor, while the Dura-meter used a nutating disk, and the Blue white meter used a small propeller. The accuracy of the flowmeters was tested using 25 gallons of either water, ammonium nitrate (20% N), or urea-ammonium nitrate (32% N). A testing manifold was set up in the UCCE Monterey greenhouse that pumped a calibrated volume of each fluid through the flowmeters using an electric diaphragm pump. Five or more test runs were made for each meter and fluid. The average volume measured and standard deviation from the mean volume was calculated.
All three models of flowmeters tested accurately measured water and fertilizer volumes (Table 1). Measurement errors were generally less than ±2% of the true volume. The Dura-meter which uses a nutating disk to measure volume was the most accurate flowmeter of the three models and had an overall average absolute error of -0.2 gallons per 25 gallons measured, and a coefficient of variation of ±0.3%. The Blue White meter, which uses a paddle wheel to measure volume, was least accurate and had an overall absolute error of 1 gallon per 25 gallons measured and a coefficient of variation of ±1.3%. The type of liquid metered affected the accuracy of the Dura-meter least compared to the other two meters tested.
Table 1. Accuracy of flowmeter measurements of water and two types of liquid fertilizer (AN20 and UAN32).
Although the Dura-meter was most accurate of the three flowmeters, it did require an initial calibration before testing began. The other meters could not be manually calibrated. The nutating disk mechanism directly measures volume of a liquid which may explain why the Dura-meter was not affected by the density of the liquid tested. Both the paddle wheel and the magnetic sensor mechanisms on the Blue-White and Banjo meters, respectively, indirectly estimate the volume of the flowing liquids. Another advantage of the Dura-meter was that it was the cheapest of the three meters when the tests were conducted. Another version of the Dura-meter can be used to turn off an injection pump when a specified volume of fertilizer has been injected. This version is available as part the auto batch system (Dura-ABS™). The Banjo meter is also available in a model (MFM100) the can output an electrical pulse proportional to flow rate so that volume of fertilizer injected can be recorded on a datalogger.
Conclusions
Three commercially available flowmeters were demonstrated to accurately measure fertilizer. Either of these meters could help irrigators more accurately apply the intended volume of fertilizer to a crop as well as verify and maintain records of the fertilizer volumes used to grow each crop. Depending on the practices of the growing operation it may be more efficient to install the meters on either the nurse tank trailer or the main fertilizer tank. If the nurse tank is used for injecting fertilizer at several fields during the day, then installing the meter on the trailer would be logical, but if the nurse tank is only filled for a single field at a time, the flowmeter could be installed on the main fertilizer tank.
- Author: Michael Cahn
- Contributor: David Chambers
- Contributor: Tom Lockhart
- Contributor: Noe Cabrera
Minimizing suspended sediments in irrigation runoff is desirable for several reasons. For growers reusing tailwater for watering their crops, they must assure that the water has minimal food safety risks by testing it for generic E coli and/or treating it with chlorine. The concentration of free (or reactive) chlorine is reduced when tailwater contains a high concentration of suspended sediments. Treating a large volume of tailwater with chlorine can be a significant expense over a season so it is important to be able to remove as much of the suspended sediments as possible before treatment.
A second reason is that water quality regulations under Agriculture discharge Order 4.0 requires tailwater discharged into public water ways to not be toxic to aquatic organisms. Pesticides that strongly bind to soil, such as pyrethroids, are carried on the suspended sediments in runoff which can cause toxicity to aquatic organisms that live in creeks and rivers downstream from farms. Also, particulate forms of N and P which bind with the suspended sediments pose a water quality risk to receiving waterbodies such as the sloughs and wetlands along the coast. Both nutrients can spur algal blooms which reduces dissolved oxygen available to fish and other aquatic organisms.
In a previous article we discussed a new approach to using Polyacrylamide (PAM), an inexpensive polymer molecule for reducing soil erosion, to treat sprinkler water. This practice uses a specialized applicator (Fig. 1) to condition water flowing from a well with PAM. An advantage of this method is that the cartridges in the applicator release a small amount of PAM (1 to 2 ppm) into the irrigation water, which flocculates soil particles that could potentially become suspended and transported in runoff. Field tests using a prototype version of this applicator resulted in about 90% less suspended sediment in the tailwater when treated with PAM compared to untreated irrigation water.
Auger ditch applicator
A second approach we developed for reducing suspended sediment in runoff is to use a smart applicator that can automatically apply dry PAM to the runoff water flowing in farm ditches. This type of applicator is suspended on a platform above a ditch and uses a hopper filled with dry PAM and an auger system controlled by an electric motor and small computer to drop PAM down a tube into the flowing runoff (Fig. 2). A weir and float mechanism located upstream are used to monitor the flow rate of the runoff so that the computer can adjust the frequency that PAM is applied. A video at this link demonstrates how the auger applicator operates.
Field testing of the ditch applicator
A yearlong study at a commercial farm showed that the ditch applicator was effective in removing 98% of the suspended sediments transported in runoff (Table 1, Fig. 3). Based on the total runoff measured in a single drainage ditch during the 2022 season (21.5 acre-feet), an estimated 106 tons of sediment were removed (Fig. 4).
Turbidity in the runoff was reduced by more than 99%, and Total P and N were reduced on average by 89% and 60%, respectively, during the season (Table 1, Figs. 5 and 6). These reductions in nutrient load, suspended sediment, and turbidity could greatly improve water quality in water bodies downstream from farms that discharge irrigation runoff.
Table 1. Average concentration of N, P, and sediments carried in irrigation runoff before (upstream) and after (downstream) treatment with the PAM ditch applicator (April – October 2022). Average of 32 paired grab samples from 3 farm ditches. Downstream locations varied from 300 to 500 ft downstream from the PAM applicators.
Ditch applicator vs well applicator
Although more effective at reducing suspended sediment in runoff than the well applicator, the ditch applicator required more maintenance. PAM needed to be added to the hopper once or twice per week during the irrigation season, and sediment that settled in the ditches had to be cleaned out periodically using a backhoe. Also, removed sediment had to be spread back in the fields. The well applicator only required periodic refilling of the cartridges with PAM, and minimizes the amount of sediment that settles out in the drainage ditches.
PAM effects on chlorine requirement
To evaluate the effect of PAM on the quantity of chlorine needed to treat runoff, we performed a laboratory assay on samples of sprinkler runoff collected upstream and downstream of one of the ditch applicators. The turbidity of the upstream (untreated) and downstream samples (PAM treated) was 2276 and 9.5 NTU, respectively. The electrical conductivity of the runoff samples was 1.35 dS/m and the pH was 8.4 before adding chlorine. The main factors evaluated in the assay were sodium hypochlorite concentration and acidification with 10% sulfuric acid. Presumably, acidifying the runoff to a pH of 6.5 should increase the concentration of the more reactive form of chlorine, hypochlorous acid which is more effective as a microbial disinfectant. Residual free chlorine concentration of the treatments was evaluated 2 and 4 hours after adding 12.5% sodium hypochlorite at concentrations ranging 12.5 to 31.3 ul per liter of runoff (100 to 250 ul of 12.5% NaOCl per L of water).
The laboratory assay showed that reducing suspended sediment concentration using PAM increased the efficacy of chlorine treatment of runoff. The free chlorine concentration for PAM treated runoff was more than twice the concentration measured in the untreated runoff for all sodium hypochlorite concentrations evaluated after 2 hours and more than three times the concentration after 4 hours (Fig. 7). Free chlorine concentration in the PAM treated runoff was more than 2.5 ppm two hours after treatment at the lowest concentration of chlorine evaluated (12.5 ul/L) but was less than 0.5 ppm in the untreated runoff. To attain similar chlorine efficacy as PAM treated runoff, untreated runoff would require twice as much sodium hypochlorite (25 ul/L). These chlorine requirements would correspond to 26 and52 gallons of 12.5% sodium hypochlorite to treat and acre-foot of runoff with and without a PAM pretreatment, respectively.
Acidification of the runoff to a pH of 6.5 with sulfuric acid increased the free chlorine concentration in the PAM treated runoff at the highest concentration of sodium hypochlorite (31.3 ul/L) after 4 hours. Acidification did not have a significant effect on free chlorine concentration for the other treatments.
Summary
Both versions of the dry PAM applicators (well and ditch) show promise for greatly reducing soil erosion, as well as helping improve water quality and the efficacy of chlorine for treating tail water reused for irrigation. By considerably reducing the concentration of suspended sediment in irrigation runoff, chlorine can be more effective as a disinfection agent, and better control E. coli and other microbial pathogens that could potentially cause public health risks.
Acknowledgments: We greatly appreciate assistance in fabricating the prototype PAM applicators from RayFab. This project was funded by the California Leafy Green Research Board.
Further reading
- Author: richard smith
Sample costs to produce and harvest the following commodities are now complete:
- Romaine hearts
- Film wrapped iceberg lettuce
- Broccoli – bunched 14's
- Broccoli – crown cut
The cost studies are now posted on-line at the UC Davis Cost Studies website (https://coststudies.ucdavis.edu/en/ ). The studies were conducted by Laura Tourte, Emeritus Farm Management Farm Advisor and Richard Smith, Emeritus Vegetable Crops Farm Advisor, along with other researchers at UC Davis and here locally. The cost studies are the result of interviews and important contributions from a sizeable number of growers and other agricultural representatives and includes an overview of the growing costs for the industry. New technologies such as one-use drip tape and automated thinners are included in the evaluations as well as the current price increases for fuel, labor, fertilizers and pest management. In addition, new regulatory costs are also included. Specific prices are included in the tables and more nuanced costs are discussed in the narrative sections of the studies.
- Author: Richard Smith
Richard Smith, Joji Muramoto, Tim Hartz and Michael Cahn
UCCE Emeritus Farm Advisor, Extension Specialist, Emeritus, Extension Specialist and Irrigation and Water Resources Farm Advisor.
The winter of 2023 had the highest rainfall years in the last 25 years. The high rainfall resulted in flooding onto farmland along the main branch of the Salinas River in both January and March. The flood waters disrupted planting schedules as well as inundated established plantings resulting in a disruption to the beginning of the vegetable production season.
The river also deposited a layer of sediments in flooded fields (Photo 1). The sediments came from several sources: river sediments from as far away as San Luis Obispo County; sediments from side channels; and soil sediments scoured from upstream farms. Several growers and industry personnel have asked what is the composition of these sediments? In April after the flooding had subsided, we collected samples at river crossings from San Lucas to Salinas. The layer of sediment left by the flood waters tended to curled up as it dried out and were easy to collect. Any field soil was brushed from the bottom of the sediments and they were sent to the UC Davis Analytical Laboratory for analysis.
Tables 1 and 2 have analysis of the sediments collected. The data in the table is arranged with sites from south to north; the two side channels, Arroyo Seco and Monroe Canyon are listed separately. Monroe Canyon is the drainage that comes from the west side of Hwy 101 just south of the intersection of Hwy 101 and Central Avenue north of King City; it cuts through a large section of the Monterey shale formation that contains elevated levels of cadmium.
The San Lucas, Arroyo Seco and Monroe Canyon samples are coarser indicating that they were transported by rapid water movement, while the rest of the samples are dominated by silts and clays, indicating that they were transported by slower moving water. In general, there is a good correlation between the clay content of the sediments and nutrient and organic matter content. Higher nutrients in the silt and clay sediments include total nitrogen, calcium, magnesium, sulfate, zinc and iron. The sediments are generally fertile which may indicate that they are at least partially composed of soil eroded from farmed fields farther upstream. Sediments that are low in phosphorus likely originated from non-farmed or vineyard areas.
The elevated cadmium levels measured in sediments from the Arroyo Seco and Monroe Canyon indicate that these side channels carried sediments from the Monterey shale formation which has naturally high levels of cadmium into the Salinas River. Presumably these sediments originating in the Monterey shale formation are transported to areas further downstream by flood waters.
Photo 1. Sediments deposited in a field along the Salinas River
Table 1. Analysis of river sediment samples from locations from San Lucas to Salinas and two side channel locations.
Table 2. Analysis of river sediment samples from locations from San Lucas to Salinas and two side channel locations.
- Author: Kirsten Pearsons
I have received a handful of calls this season with concerns about “trash bugs,” a catch all term for various soil invertebrates. These soil invertebrates include root maggots, springtails, bulb mites, and symphylans, all which will happily feed on decomposing plant debris, i.e., trash. If given the opportunity, trash bugs will feed on seedlings and transplants, but high pressure can usually be avoided by allowing plant debris to fully breakdown before planting the next crop. A long enough pause between plant debris and seedlings acts as a sort of field-level host-free period, allowing trash bug populations to drop before planting.
Why does it feel like we have more trash bugs this season?
We had an unseasonably cool, wet spring. Under these conditions, crop debris from the fall was breaking down much slower than usual. With the compressed start to the season, folks have been eager to plant into fields as soon as possible, so many were likely planting into fields with higher-than-optimal plant debris.
By mid-April, daily temperatures were starting to get more back to normal, so why are we still dealing with more trash bugs? From talking with a handful of growers and PCAs, the slow start to the season has set back the whole planting schedule. To try and bring things back to schedule as close as possible, folks are still pushing the limit on how quickly they turn around fields for the next crop. A perfect storm for trash bug pressure.
Which trash bug am I dealing with?
A diverse group of pests can cause stunting and stand loss, so accurate pest ID is critical for successful management.
Root Maggots (seedcorn maggots or cabbage maggots, Delia spp.)
Root maggots are the larvae of small grey flies. The adult flies are commonly caught on sticky cards that are deployed for monitoring thrips and aphids.
Seedcorn maggot, Delia platura, seems to be the primary culprit that I have come across that is stunting brassicas. Seedcorn maggots tend to hit fields within a week or two after planting, causing patchy stands and stunted seedlings. Closely related cabbage maggots tend to hit fields a few weeks after planting and can continue to cause damage as plants mature.
To scout for root maggots, pull up stunted plants (see picture #1 below) and check roots for small, yellowish-white maggots (less than ¼ of an inch long). They can be easy to miss when they're all tangled up in the roots (picture #2). If scouting is delayed, you may also find the brown pupa (picture #3). With seedcorn maggots, timing a reactive control (i.e., insecticide application) can be tricky since the damage may go unnoticed until the maggots have already pupated and left the field.
|
From left to right: #1 broccoli stunting caused by root maggot feeding; #2 maggot tangled up in the roots of a broccoli plant; #3 root maggot pupa found next to a stunted broccoli plant. |
Springtails and soil mites
Pest springtails and soil mites are trickier to identify, since non-pest species are common in healthy soils. The one species of springtail that has been identified as an occasional pest of lettuce and brassicas is Protaphorura fimata, while the main pest mites are bulb mites (Rhizoglyphus spp., Tyrophagus spp.). Both P. fimata and bulb mites are small and whiteish while non-pest species are often larger and more colorful.
|
Clockwise from top left; Protaphorura fimata, the springtail species that can be a pest (Photo Credit: Shimat Joseph, previous UC IPM Advisor); non-pest springtails (note that these springtails are more colorful and have long antennae); a predatory soil mite (not a pest); and two bulb mites (Photo Credit: Jack Kelly Clark, UC IPM). |
Symphylans
Symphylans look like small (less than ½ an inch), white centipedes. Since symphylans are fast and mobile, you will be more likely to catch symphylans in action if you dig around stunted plants that are near healthy looking plants. If you readily find symphylans just by digging, the symphylan pressure is probably high enough to cause economic damage.
Lower symphylan densities can be harder to observe, so you may want to try bait-trapping with potato or beet wedges if you suspect symphylans but cannot find any by digging around stunted plants. The bait-trapping method can also be used to scout for springtails.
For more on the identification, scouting, and management of these pests, be sure to reference the UC IPM Pest Management Guidelines:
https://ipm.ucanr.edu/agriculture/cole-crops/
https://ipm.ucanr.edu/agriculture/lettuce/
Related blog posts from past entomology advisors:
Root maggots:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9804
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4301
Symphylans:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18819
Springtails:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16769
Bulb Mites:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13271
