- 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: Michael D Cahn
- Author: Richard Smith
Tuesday, February 21;
7:55 a.m. to 12:15 p.m.
1432 Abbott St, Salinas CA
Habrá traducción al Español
Free Workshop + Pizza!
7:55 Introduction
8:00 Tuning up your drip irrigation system: pressure regulation, system design, and scheduling.
Michael Cahn, UCCE Irrigation Advisor, Monterey County
8:30 Basics of pumps, pump tests, and variable frequency drives
Bill Green, Education Specialist, Center for Irrigation Technology, CSU Fresno
9:05 Practices for improving soil health and its broader impacts
Richard Smith, UCCE Weed and Vegetable Advisor, Monterey County
9:35 How to Maximize Cover Crop Benefits and Credits in Ag Order 4.0 and Beyond.
Eric Brennan, Research Horticulturist, USDA ARS
10:05 Break
10:20 Strategies for factoring in nitrate in irrigation water in nutrient management plans
Michael Cahn, UCCE Irrigation Advisor, Monterey County
10:40 Status of the Third Party Program for Ag Order 4.0
Sarah Lopez, Executive Director, Central Coast Water Quality Preservation Inc.
11:00 Getting organized for AgOrder 4.0
Jillian Flavin and Caroline Webster, Environmental Scientists, Central Coast Regional Water Quality Control Board
11:30 On Farm Experiences: Improving irrigation and Nutrient Management (Grower Round Table Panel) Karen Lowell USDA-NRCS Moderator (Mark Mason, Huntington Farms, Sergio Casillas, D'Arrigo Bro., Salvador Montes Christensen and Giannini, Eric Morgan, Braga Fresh)
12:15 Adjourn (free Pizza Lunch)
CCA continuing education credits have been requested. Pre-registration encouraged but not required.
For more information, contact Michael Cahn @ 831-759-7377, email: mdcahn@ucdavis.edu
The University of California prohibits discrimination or harassment of any person in any of its programs or activities. (Complete nondiscrimination policy statement can be found at http://ucanr.org/sites/anrstaff/files/107734.doc). Inquiries regarding the University's equal employment opportunity policies may be directed to Affirmative Action Contact and Title IX Officer, University of California, Agriculture and Natural Resources, 2801 2nd Street, Davis, CA 95618, (530) 750-1397; titleixdiscrimination@ucanr.edu.
2023 UCCE irrigation and nutrient meeting final
- Author: Michael D Cahn
- Author: Richard Smith
2018 UCCE Irrigation and Nutrient Management Meeting
Monterey County Agricultural Center
1432 Abbott Street, Salinas, CA
Tuesday, February 13
7:45 a.m. to 12:30 p.m.
7:45 Registration (Free)
8:00 Update on the Ag Order for the Central Coast.
Chris Rose, Senior Environmental Scientist, Irrigated Lands Regulatory Program Manager, Central Coast Water Board
8:30 Soil nitrogen dynamics in long-season vegetable crops
Richard Smith, Vegetable Crops Farm Advisor, Monterey County
9:00 Fall application of high C:N ratio amendments to immobilize soil nitrate
Joji Muramoto, Associate Researcher, Dept. of Environmental Studies, UCSC
9:30 On-farm trials evaluating the fertilizer value of nitrate in irrigation water
Michael Cahn, Irrigation and Water Resources Advisor, Monterey County
10:00 Break
10:30 On-farm management practices for mitigating insecticides in irrigation run-off
Laura McCalla, Department of Environmental Toxicology, UCD, Granite Canyon Laboratory
11:00 Microbial food safety risks of reusing tail water for production of leafy greens
Anne-laure Moyne, Staff Research Associate, Food Science and Technology Dept., UCD
11:30 Update on seawater intrusion in the Salinas Valley Aquifer
Howard Franklin, Senior Hydrologist, Monterey County Water Resources Agency.
12:00 Conclusion and Pizza Lunch
3.5 CCA & 0.5 DPR continuing education credits have been requested
- Author: Michael D Cahn, Ph.D.
Tomorrow we will host the 2016 UC Irrigation and Nutrient Meeting at the Agricultural Center in Salinas CA. We also have a field meeting following a pizza lunch to discuss the use of cover crops in strawberries. 4.5 hours of Certified Crop Adviser educational credits will also be available. This year we will include a panel discussion about how growers are implementing practices to better manage water and nitrogen fertilizer as well as a presentation on the sustainable groundwater management act. Please see the agenda below:
2016 Irrigation and Nutrient Management Meeting
Agricultural Center 1432 Abbott Street, Salinas, CA
Wednesday, February 17
7:45 a.m. to 1:45 p.m.
4.5 CCA Credits applied for
7:45 Registration
8:00 Summary of N use of crops in Region 3 and current water quality regulations
Chris Rose, Central Coast Regional Water Quality Control Board
8:30 Fertilizer value of N in irrigation water
Michael Cahn, Irrigation and Water Resources Farm Advisor, Monterey County
9:00 Field studies on N and water management (broccoli and spinach)
Richard Smith, Vegetable Crops Farm Advisor, Monterey County
9:30 Denitrification beds for removing nitrate from tile water
Tim Hartz, Vegetable Specialist, UCD
10:00 Break
10:30 Potential for increasing groundwater recharge on agricultural land
Toby O'Geen, Soil Specialist, Dept of Land, Air and Water Resources, UCD
11:00 Groundwater Sustainability Act – Where are we headed in Monterey County
Stephanie Hastings: Brownstein, Hyatt, Farber and Schreck Law Firm
11:30 Panel discussion on Grower implementation of BMP's
Salvador Montes, Christensen and Giannini; Manual Mercado, River Valley Farms;
Eric Morgan, Morgan Consulting
12:00 Conclusion and Pizza Lunch
Afternoon Session:
12:45 Field trip to see conservation practices
1:45 Conclusion
- Author: Michael D Cahn
CropManage Workshop: Hands-on training
Monterey County Agricultural Center Conference Room
1432 Abbott St, Salinas CA 93901
Thursday, April 2nd 2015
(8:30 am – 12 pm)
We will offer a hands-on training to learn in depth about the features of CropManage, a free online decision support tool for water and nutrient management of coastal crops. In addition to head and romaine lettuce, CropManage now supports broccoli, cauliflower, cabbage, and strawberries.
Considering that the drought is continuing into a 4th year, and nutrient management continues to be linked to water quality regulations, efficiently using water and nitrogen fertilizer is a high priority for Central Coast growers. CropManage can play an important role in providing quick decision support on water and nutrient management on a field-by-field basis.
This training will provide an opportunity to learn how to use CropManage for improving the efficiency of your farming operations or for adding value to your consulting services. We will provide in depth hands-on training so that you can learn step-by-step how to navigate and use CropManage for assisting with fertilizer and water management decisions and record keeping. Wi-Fi internet access is available at our conference room so please bring a laptop or tablet computer so that you can follow along as we tour through the features of the software. There should be sufficient time to answer questions as we cover the following topics:
Agenda:
8:30 – 9:00 Registration and Refreshments
9:00 – 9:30 Introduction and update on CropManage
9:30-10:15 Getting started with CropManage
10:15 (Break)
10:30 – 11:15 Strategies for using CropManage for decision support and record keeping
11:15- 11:45 Advanced features and interfacing sensors with CropManage
11:45-12:00 Discussion of new features or changes needed.
To keep the group size manageable so that we can provide individual help, we would like to limit the workshop to 30 participants. If you have attended previous workshops and or feel proficient in using the on-line tool, then you are welcome to just attend the second half of the workshop (10:30-12 pm). Whether or not you plan to attend the entire or part of the workshop, please RSVP in advance by sending an email to larriaga@ucdavis.edu or mdcahn@ucdavis.edu with the subject heading “CropManage workshop” and let us know the number of participants in your group. We will email you a confirmation. Thank you, and I hope to see you soon.
Respectfully,
Michael Cahn, Irrigation and Water Resources Advisor
Certified Crop Adviser CEU hours requested (1.5 hrs irrigation management, 1.5 hrs nutrient management)
