- Author: Richard Smith
- Author: Michael Cahn
On April 15th, the Central Coast Regional Water Quality Control Board (CCRWQCB) finalized and approved Ag Order 4.0. The new rulings affect several aspects of agricultural production such as buffer areas and discharge of pesticides to water ways. In this article we will focus on the impacts of Ag Order 4.0 on the use of nitrogen (N) fertilizers.
New targets and limits on the use of N fertilizer are calculated using the A minus R metric. In this scenario, “A” is N applied to the crop in the form of fertilizer (Afertilizer), N in irrigation water (Airrigation), N supplied by compost (Acompost) and N mineralized from organic fertilizer (Aorganic fertilizer). “R” is N removed from the field by the crop (Rharvest), scavenged during the winter fallow by cover crops or immobilized by high-carbon compost (Rscavenge), N removed by denitrification bioreactors (Rtreated), N sequestered in woody plant biomass (Rsequestered), or other unspecified forms of N removal from fields (Rother). Although AgOrder 4.0 outlines 3 pathways to compliance, pathway 1 is most likely the one that most ranches would use unless the wells have very high nitrate-N concentrations (> 40 ppm N). A - R is not to exceed the targets or limits shown in Table 1 for pathway 1 compliance. The A-R is calculated over the growing season on a land acre basis. If two or more crops are grown on the same physical acre, each crop contributes to the value for the year. Below is a discussion of each component of the A-R metric.
Table 1. A-R regulatory schedule
|
Regulatory Status |
A-R Limit Lbs N/ac/year |
Compliance Date (as of Dec. 31) |
|
Target |
500 |
2023 |
|
Target |
400 |
2025 |
|
Limit |
300 |
2027 |
|
Limit |
200 |
2031 |
|
Limit |
150 |
2036 |
|
Limit |
100 |
2041 |
|
Limit |
50 |
2051 |
The “A” side of the equation:
Afertilizer is the amount of N fertilizer added to grow the crop. The actual units of N in lbs/A are used in this calculation.
Airrigation is the amount of N contained in the irrigation water that is taken up by the crop. For most vegetable and berry crops grown on the central coast the volume of water that must be accounted for in this calculation is equivalent to the volume used by the crop for evapotranspiration (ET). For crops where less water is applied than ET, the volume of applied water can be used in the calculation. To calculate Airrigation use the equation:
Airrigation = water volume (inches) x nitrate-N concentration of water (ppm N) x 0.227
The factor 0.227 converts the units inches x ppm N to lbs of N/acre.
For example, if a lettuce crop uses 7.3 inches for ET, and is irrigated with water that has a 37 ppm N concentration, the Airrigation would be:
7.3 inches x 37 ppm N x 0.227 = 61 lbs N/acre
Acompost is the amount of N provided by compost. Given that the amount of N that is mineralized by the compost depends on the carbon to nitrogen (C:N) ratio not all the N in the compost becomes available. This fact is recognized in the Ag Order as follows:
For compost with a C:N ratio of <11, the amount of N in the compost is multiplied by 0.10, and for composts with a C:N ratio of >11 the amount of N in the compost is multiplied by 0.05. Only this amount of N is added to the A side of the equation. These discount factors were an important change made by the Regional Board staff to reflect the actual quantity of N provided by compost and to avoid a disincentive to the use of composts, a key soil health practice.
Aorganic fertilizer is the amount of N that is mineralized during the cropping system. The amount of N mineralized depends upon the C:N ratio of the material and the CCRWQCB is using the regression curve in a recent paper published by Lazicki et al (2020) to determine the amount of N mineralized. For instance, a material like 4-4-2 has a C:N ratio of 7.3 (29% C/4% N) and has a discount factor of 0.39 (Table MRP-3 in Attachment B). This means that if 100 units of N are applied as 4-4-2, the amount mineralized from this material and that is attributed to the A side of the equation is 39 lbs/A (100 lbs x 0.39). This discount factor acknowledges the fact that not all N in organic fertilizer mineralizes during the cropping season and was an important correction made to Ag Order 4.0.
The “R” side of the equation:
Rharvest is the amount of N that is removed from the field in the harvested product. The amount of N removed in the harvested product is calculated by a removal coefficient composed of the percent moisture multiplied by the percent N of the crop. This coefficient is then multiplied by the net pounds of product harvested from a field to determine lbs N/A removed. We have been working on a project developing N removal coefficients for a number of vegetable commodities. Table 2 shows data for full term romaine lettuce. Note that percent solids and nitrogen values observed in our evaluations vary significantly and that the mean value has a notable degree of variability which affects the estimate of N removed by the crop. Regardless of the variability, the important point to recognize is that the removed N is modest in relation to the amount of N applied. Figure 1 shows total fertilizer N to lettuce for a large number of vegetable operations in our area. It becomes evident that growers face some major challenges in complying with the application limits as the limits ratchet down over the next several years.
Table 2. Example of calculation of removal coefficient for a full-term romaine crop.
|
Component |
Mean |
Minimum |
Maximum |
|
Solids |
5.69% (0.0569) |
4.65% (0.0465) |
7.51% (0.0751) |
|
Nitrogen |
3.15% (0.0315) |
2.33% (0.0233) |
3.97% (0.0397) |
|
Removal Coefficient |
0.00178* |
0.00147 |
0.00243 |
|
Romaine yield (lbs) |
30,000 |
30,000 |
30,000 |
|
Crop R value (lbs N/ac) |
54 |
44 |
73 |
* 0.0569 x 0.0315 = 0.00178
Rscavenge is the amount of N that is captured by by cover crops or immobilized by high-carbon compost during the winter fallow period. The CCRWQCB agreed to credit non-legume winter cover crops with 97% of their N content that meet the following criteria: 1) are grown for ≥ 90 days during the winter fallow period, 2) accumulate more than 4,500 lbs/acre of dry biomass and 3) have a C:N ratio of ≥ 20 when incorporated into the ground. N scavenging credits granted for cover crops are helpful, but do not remove any of the current logistical barriers to using of cover crops in intensive vegetable systems. However, given that non-legume cover crops routinely contain 100 to 150+ lbs N/acre, as N application limits ratchet down, cover crop use may be incentivized to some degree.
High-carbon composts were also included in the Rscavenge category. This practice is still being researched to fully understand how much N can be immobilized. Growers already use compost (typical C:N ratio of 10-12) but could substitute high-carbon compost (C:N ratio of >30) which can quickly facilitate its use. Currently, high-carbon compost has been granted a credit of 30 lbs N/acre in Ag Order 4.0. However, once the research on this practice is completed, this practice may be granted greater credits as warranted on the R side of the equation.
Rtreat is the quantity of N removed from tile drainage and irrigation runoff by denitrification bioreactors or constructed wetlands. This practice can be implemented in the northern part of Monterey County where high nitrate tile drain water impacts the surrounding sloughs and creeks. The bioreactors vary in size and sophistication, from sunken beds filled with wood chips to highly engineered portable treatment systems.
Rsequestered is the quantity of N that is captured in the woody plant tissue of perennial crops. This form of N removal is relevant to vineyards and orchards in our area and does not impact the vegetable industry.
Rother is the quantity of N removed from the field in other, unspecified ways. One form of N removal not addressed in Ag Order 4.0 is the gaseous loss of N by denitrification from soil. This is a topic that needs further research. Two studies done on the Central Coast showed that in sandy soils with drip irrigation, there is little nitrous oxide or dinitrogen loss (2-4 lbs N/acre/crop). However, an earlier study of celery and lettuce production fields in the 1980s showed that on heavier soil with furrow irrigation gaseous N losses ranged from 18 to 37 lbs N/acre. Further research is needed to understand denitrification rates more fully in coastal vegetable production.
What options does the industry have moving forward?
Basically, a timer has been started by Ag Order 4.0. The first dates are targets of 500 lbs N/acre/year 2 years from now and 400 lbs N/acre/year in 2025 (four years). Starting in 2027 the targets become limits ratcheting down to 300 lbs N/acre/year. In scenarios that we and others have run, the 300 lbs N/acre/year limit will become very challenging for growers to comply with in typical double cropped production. There are basically three key practices that will provide the most improvements in N use efficiency: 1) measuring residual soil nitrate and adjusting fertilizer applications accordingly, 2) accounting for the nitrate in irrigation water as part of the N budget, and 3) improving irrigation efficiency to help maintain residual soil nitrate in the active rootzone of crops. A concerted focus on these three practices will require a commitment from the decision makers at each farming operation. Farming operations have differed in their approach to the pending water quality regulations. Some have taken a proactive approach and are farther along on the learning curve. It is important to make attempts to begin implementing these practices and see what is possible for your operation given the crop mix, soil types, and nitrate levels in the irrigation water. The good news is that there is still time. To begin implementing these practices, it is important to start small to gain the needed knowledge base in efficient N and water management practices. Working with knowledgeable people will be essential.
Other options that can help fine tune fertilizer applications and reduce the risk of cutting fertilizer rates are various nitrogen technologies such as nitrification inhibitors and controlled release fertilizers. In studies that we have done, there is clearly a benefit to the use of some of these materials, but again, there is a learning curve to obtaining the benefits that they can provide. Nitrapyrin (a nitrification inhibitor commonly used in the corn belt) was registered on lettuce and brassicas in 2019 and has not been widely used yet by the industry, but it along with other materials, deserves greater evaluation.
In addition to improving in-season N use efficiency, implementation of practices to minimize nitrate losses during the winter fallow period is needed. Cover crops are a key practice for reducing leaching losses during the winter and finding opportunities for their use will become more important in the next several years. The credits given cover crops on the R side of the equation can help growers achieve compliance with Ag Order 4.0 as the A – R limits are reduced to less than 300 lbs N/acre/year.
In summary, the finalization of Ag Order 4.0 will have a significant impact on how vegetables are grown on the Central Coast in the coming years. There is a window of opportunity to experiment on how to address limits that will be applied to the use of N fertilizers. Now is the time to make the decisions needed to address this new reality. Please do not hesitate to reach out to us for help or advice.
- Author: Michael D Cahn
CropManage Hands-On Webinar
Co-sponsored by:
Pajaro Valley Water Management Agency and
Resource Conservation District of Santa Cruz County
When: Tuesday, May 4, 2021, 9:00 AM-12:00 PM
Where: Virtual Meeting via Zoom (link and instructions will be emailed to registrants)
Hosts: Michael Cahn, Advisor, UCCE Monterey and Andre Biscaro, Advisor, UCCE Ventura
Registration fee: $20
A limited number of registration waivers are available in case of financial difficulties. If interested, please email anrprogramsupport@ucanr.edu to discuss before registering. Registration fees do not apply to Pajaro Valley Growers.
Join us for this hands-on webinar to learn to use CropManage to support irrigation and nutrient management decisions and record-keeping. Para el formulario de registro en español, vaya aquí.
What is CropManage?
CropManage is a free online decision support tool for water and nitrogen management. Based on in-depth research and field studies conducted by the University of California, CropManage provides real-time recommendations for efficient irrigation and fertilizer applications—while maintaining or improving overall yield.
Who should participate?
Vegetable and berry growers, ranch managers, other farm staff, and technical service providers are welcome. The webinar is for both new and current CropManage users.
How to prepare?
As this is a participatory webinar, please join via computer or tablet so that you can follow along and participate in the exercises. Two screens will work better so participants can follow the webinar and use CropManage at the same time.
Each participant will need a user account for CropManage. Please set up a free user account at cropmanage.ucanr.edu before the webinar.
Continuing Education
Certified Crop Advisers (CCA) 2.5 hours of CE units have been approved
Contacts for More Information
Logistics & Registration: Rachel Palmer, anrprogramsupport@ucanr.edu, or 530-750-1361
Course Content: Michael Cahn, mdcahn@ucanr.edu; Farm Advisor, UCCE Monterey County
Para obtener más información en español, comuníquese con Sacha Lozano al 831-224-0293
- Author: Michael D Cahn
- Author: David Chambers
Tensiometers are useful for monitoring soil moisture in vegetable and row crops so that plants are not over-watered nor become water stressed. As the name implies, tensiometers measure soil moisture (water) tension, otherwise referred to as matric water potential. Soil water tension is essentially a measure of the force that plants need to exert to suck water from the soil pores into the roots. A high tension means that the soil is dry and a plant needs more energy to extract water from the soil compared to when the soil is moist. Tensiometers function without batteries and wires, although they can be interfaced to dataloggers by adding a pressure transducer. Also, the readings are not affected by soil texture, temperature, and salinity unlike many electronic soil moisture sensors.
A previous article published in this blog described how to build a tensiometer from PVC parts and ceramic cups that can be purchased from a supplier in California. The design results in a dependable and inexpensive tensiometer that can be built by anyone comfortable using a few hand tools. The most challenging step was gluing the cup to the end of the PVC shaft using epoxy cement which can sometimes result in a vacuum leak if the bond is weak. Since publishing this article, we have built and used more than a hundred of these tensiometers and can suggest some modifications to the original design and a few other words of wisdom. For example, we observed that the PVC “T” can crack if the gauge is threaded too tightly or during cold weather conditions which can cause the plastic to contract, so we suggest using a different type of “T” and not to over thread the gauge. We have also collaborated with a supplier of the ceramic cups, SoilMoisture Equipment Corporation, whose engineers have developed a cup that can be bonded to the PVC shaft using standard PVC cement and primer rather than a specialized epoxy (Fig. 1). This improvement greatly reduces the time required to build the tensiometer which is why we call it the “ten-minute tensiometer.” Once you have some experience, you will probably need less than 10 minutes to assemble one of these tensiometers from the parts shown in Fig 2.
Materials needed:
Ceramic cups
Vender: SoilMoisture Equipment Corporation, Santa Barbara CA (805-964-3525, www.soilmoisture.com)
Part Number Y2630C, Dimensions: 0.875 inch OD x 2.75 inch length
Cost: $25 ea. Note that this is a new part that must be special ordered.
Vacuum gauge
Vender: Zoro.com/Grainger.com
Part Number 4FMK3, Description: ¼ inch MNPT 2 inch diameter test vacuum gauge
Weblink: https://www.zoro.com/zoro-select-vacuum-gauge-test-2-in-4fmk3/i/G0040792/?q=4FMK3 Cost: $18.99 ea.
#1 size rubber stopper
Vender: Grainger.com
Part Number 8DWU6, model RST1-S, Description: 24 mm neck, bottom diam. = 14 mm. Top diam. = 20 mm.
Weblink: https://www.grainger.com/product/GRAINGER-APPROVED-Stopper-8DWU6?internalSearchTerm=Stopper%2C+24mm%2C+Black%2C+PK52&suggestConfigId=8&searchBar=true&suggestConfigId=8&searchBar=true&suggestConfigId=8&searchBar=true&suggestConfigId=8&searchBar=true
Cost: $18.55 / 52 pieces
Schedule 40 PVC pipe (½ inch diameter)
Vender: irrigation supply or hardware store
Sand paper (60 or 80 grid)
Vender: hardware store
½-inch PVC “T”
Vender: irrigation supply or hardware store
Description: ½ inch Female slip x ½ inch Female slip T. Note that this T replaces part number 402-072 from Spears Inc., which we found to sometimes split during cold periods. Also, the previous part was often not in stock.
PVC bushing
Vender: irrigation supply or hardware store. Description: ½-inch PVC Male slip x female ¼” thread bushing.
PVC cement (gray) and purple primer (Fig. 3)
Vender: irrigation supply or hardware store. Note that the gray cement provides a stronger bond than the clear product.
Gas pipe thread sealant (white or blue paste type)
Vender: irrigation supply or hardware store
Painters masking tape
Vender: hardware store
Petroleum Jelly (Vasoline)
Vender: pharmacy. A coating of petroleum jelly improves the seal between the rubber stopper and PVC tube.
Rubber gloves
Vender: hardware store, paint store, etc. Description: Nitrile disposable gloves to protect hands from PVC primer and glue.
Tools needed:
- PVC saw
- Miter box
Procedures
- Cut PVC pipe sections in the following lengths
1 foot depth tensiometer: top shaft = 4 inches*, bottom shaft = 17 inches
2 foot depth tensiometer: top shaft = 4inches, bottom shaft = 30 inches
We advise first cutting the bottom shaft about 1-inch longer than indicated above using the miter box or an electric miter saw to assure that the cut at the lower end is at a 90-degree angle (Fig. 4). The ceramic cup will fit crooked on the end of the shaft if the cut deviates from 90- degrees. After assuring that the cup fits well, the top end of the shaft can be cut to the exact length.
*Note that the top shaft can cut shorter than 4-inches so that when the tensiometer is installed in the field it has a lower profile to the ground, thereby reducing chances of being hit by tractor implements.
- Check that the ceramic cup fits into the bottom of the PVC shaft and is aligned straight. Sand the neck of the cup and/or the interior walls of the PVC shaft if the cup cannot be inserted at least half-way into the PVC. Be careful not to over-sand the cup or the fit between the neck and the PVC shaft will be loose and not bond well when glued. The fit between the neck of the cup and the PVC should be very tight such that a lot of force is needed to insert the cup into the bottom of the PVC shaft. If the cup is not in alignment with the PVC shaft, then recut the end with the miter box at a 90-degree angle and recheck the fit.
- Wrap the bottom of the PVC shaft and the top of the ceramic cup with painter's tape to prevent cement from coating the outside of the ceramic cup (Fig. 5).
Fig. 5 Painter’s tape will protect the outer surface of the ceramic cup from becoming coated with cement and primer.- In a well-ventilated location, apply PVC primer to both the interior of the PVC shaft and the outside of the PVC top of the ceramic cup. Then apply gray PVC glue to both surfaces, and push the parts together, and hold in place for about 30 seconds to 1 minute (Figs. 6-9). Tip: slightly twist the parts by about 30-degrees immediately after gluing to assure a good bond before the cement begins to set.
Fig. 6. Coat the PVC portion of the cup with primer and then PVC gray cement
Fig. 7 Coat the inside of the bottom of the shaft with primer and PVC gray cement.
Fig. 8 Insert the cup into the shaft.
Fig. 9 After inserting the cup into the shaft immediately twist the cup about 30-degrees and hold in place for 1 minute while the cement sets. Wipe off any excess cement. - Next glue the top and bottom shafts and the bushing into the ½ inch, PVC slip “T” using the PVC primer and cement. After inserting each of these parts into the T, slightly twist them and hold in place for about 30 seconds while the cement sets (Figs 10-12). Also cover the non-glued areas with painter's tape to prevent the outside from becoming covered with primer and cement.
Fig. 10 Add primer to the interior of the “T” and the outside edges of the shafts and bushing. Then coat both surfaces with PVC cement.
Fig. 11 Hold the parts in place for at least 30 seconds after gluing so that the cement can set.
Fig. 12 The “T” shown with the bushing and upper and lower shafts connected.- Coat the ¼ inch male threads of the gauge with pipe thread sealant and hand screw on the vacuum gauge. Tip: do not over tighten or the PVC “T” may crack.
- Fill the tensiometer fully with degassed distilled water. The water can be degassed by boiling it and allowing it to cool.
- Coat the lower end of the rubber stopper with a thin film of petroleum jelly and insert into the top end of the tensiometer with a light twist to firmly seat the stopper (A loose stopper is the main cause for vacuum leaks).
Conclusion
So that is it—the tensiometer is ready for testing and installation (Fig. 13). Hopefully, it did not take too long to build and with practice one should be able to assemble these tensiometers in 10 minutes or less. Please visit our previous blog article on how to test and install tensiometers in the field. Please let us know if you have any questions or feed back.
- Author: Michael D Cahn
The rain situation was beginning to look dire for our region before last week, with most major storms passing to the north of Monterey county. However, the storms that occurred last week were generated by an atmospheric river that was focused on the southern part of Monterey County. Cumulative depths recorded at CIMIS weather stations along the valley showed increasing amounts moving south in the valley with almost 9 inches recorded at the King City CIMIS weather station (station 113) (Fig. 1). Also 8.3 inches were recorded at San Antonio and Nacimiento Reservoirs, where before these storms less than an inch of rain had fallen since October.
This one weather event was able to significantly increase the water stored in Nacimiento reservoir and helped the situation in San Antonio (Fig. 2.) Nacimiento water storage increased from 21% to 41% between January 23 and February 3, and San Antonio increased from 16% to 20% capacity. In combination, water stored in the two reservoirs increased from 133,778 acre-ft to 216,858 acre-ft, representing 64% more water compared to before the storm events. Total capacity of the two reservoirs is 712,900 acre-ft, so water stored in the reservoirs at this point in the season is still at 30% of maximum capacity.
Our region usually receives a few atmospheric river events each winter, most of which usually pass too far north or south to greatly impact the Salinas Valley reservoirs. This first major rain event of the season was a direct hit for the reservoirs. Hopefully, more rain will be coming in the upcoming weeks.
The other benefit of this last storm was that by mostly passing over the southern part of the county, debris flows were minimized in the burned areas.
If you want to keep track of the reservoir storage as we proceed through the winter visit the link at Monterey County Water Resource Agency website.
- Author: Michael Cahn
- Author: Richard Smith
Tuesday, February 23;
7:55 a.m. to 12:00 p.m.
Habrá traducción al Español
Registration Cost: $10
Registration Link: https://ucanr.edu/survey/survey.cfm?surveynumber=32769
7:55 Introduction
8:00 Woodchip bioreactors for removal of nitrate and pesticides from tile drainage.
Pam Krone-Davis, California Marine Sanctuary Foundation
8:30 Nitrogen mineralization from organic fertilizers and composts
Daniel Geisseler, UC Davis
9:00 Improving the efficiency of drip germination of lettuce and weed control.
Michael Cahn and Richard Smith, UC Cooperative Extension
9:30 Using weather-based irrigation scheduling for optimizing red cabbage production.
Lee Johnson, NASA Ames Research Center-CSUMB
10:00 Break
10:15 Update on Ag Order 4.0.
Matt Keeling, Central Coast Regional Water Quality Control Board
10:45 Development of N removal coefficients for vegetables on the central coast
Richard Smith, UC Cooperative Extension
11:15 New approaches for using Polyacrylamide (PAM) for mitigating sediment and pesticides in irrigation runoff.
Michael Cahn, UC Cooperative extension
11:45 Using high-carbon compost for reducing nitrate leaching during the winter.
Richard Smith, UC Cooperative Extension
12:00 Adjourn
CCA & DPR continuing education credits have been requested
