Over the last several months, a team from UC Cooperative Extension has been conducting trials with wheat growers to better understand nitrogen (N) management under local conditions. The trials are funded by the CDFA Fertilizer Research and Education Program and demonstrate practices that UC Small Grains Specialist, Mark Lundy, has been investigating for several years, namely the use of N-rich strips in the field, a soil nitrate (NO₃^-) quick test, handheld canopy reflectance devices, and drone imagery. The N-rich strips serve as zones of soil N adequacy, and the soil NO₃^- quick test, canopy reflectance devices, and drone imagery serve to characterize differences between the zones of N adequacy and the rest of the field. Our trials implement these practices across variable soil and climatic conditions so that we can extend the information across wheat-growing regions of the state. Integral to these trials is identifying growers who are interested and able to shift at least half of their seasonal N budget from a pre-season to an in-season N application. Our goal is to help growers and consultants learn and implement these practices to guide nitrogen fertilization in wheat, for economic and environmental efficiency outcomes.

At the Delta location on Tyler Island, we are trialing these practices on high organic matter soils. The field has two different soil types: Gazwell mucky clay and Rindge mucky silt loam. The Gazwell series is characterized as having approximately 11 percent organic matter in the top foot of soil, and the Rindge series has approximately 18 percent organic matter in the top foot of soil. The grower's pre-plant aqua ammonia application provided approximately 60 pounds of N per acre, and the wheat was planted on November 15^th. After planting, we flagged off three zones for the N-rich strips – two in the Gazwell soil and one in the Rindge soil. Each strip was 90 feet wide by 180 feet long. (While, in practice, N-rich strips do not need to be this large, we made ours this large so that we could also make observations from satellite imagery.) We took soil samples and performed the soil NO₃^- quick test (described below). On November 25^th, we applied urea to the N-rich strips at a rate of approximately 62 pounds of additional N per acre. We timed our application ahead of a storm in the following days (approximately 0.5 inches, according to the Staten Island CIMIS station).

The soil NO₃^- quick test is performed in the field and provides a quick, inexpensive estimate of nitrogen availability in the soil. We performed the quick test just after planting to establish baseline conditions and then again each time we used the canopy reflectance devices and collected drone imagery, which we started at tillering (Feekes 2-3, Figure 1, see below). For the quick test, it is important to get representative soil samples, staying away from field edges and from the borders of the N-rich strips. We collected and aggregated several subsamples from the top 12 inches, from both inside and outside the N-rich strips. The soil was mixed with a calcium chloride solution, and then the test strips were dipped into the soil-water solution. The color on the strip is compared to the color chart on the bottle. In an organic soil, we consider a test strip reading of 10 ppm and above to be adequate soil N, and in a mineral soil, a test strip reading of 20 ppm and above would be adequate. (This is due to the higher bulk density of a mineral soil compared to an organic soil.) The quick test reading is not the same as what a lab would determine for the same sample. Mark and his team are preparing an online tool that will convert the quick test reading to the lab-equivalent value of NO₃^--N and the fertilizer equivalent in pounds of N per acre, based on soil type. We would expect to see higher soil NO₃^- in the N-rich strips compared to the surrounding field unless heavy rainfall resulted in leaching. (Consider the benefits of only leaching N from small plots rather than the entire field!) For fertilizer decision-making, the quick test readings are best considered in combination with plant reflectance measurements (see below). On their own, however, they do provide an estimate of nitrogen fertilizer equivalency that is available to the crop.  

We have used Greenseeker NDVI devices and drone imagery to characterize canopy color of the N-rich strips and the surrounding field (Figure 2, see below). NDVI stands for normalized difference vegetation index and is a measurement of green vegetation that picks up differences that the human eye cannot detect. It allows us to make inferences about canopy cover and plant N status, and when considered with soil NO₃^-  status, we can have even more confidence in our fertilization decisions. For example, if soil NO₃^- differs between the N-rich strips and surrounding field, and we observe a difference in canopy reflectance, then we have confidence – based on previous years of research – that the crop will respond to additional N fertilizer. If we don't see a difference in canopy reflectance, we would recommend postponing application of additional fertilizer and continue monitoring, or we would recommend adjusting the application to account for the available soil N. At tillering, we started sampling for soil NO₃^-  and canopy reflectance on 14-day intervals. In February, we started seeing slight differences in Greenseeker canopy reflectance between the N-rich strips and the surrounding field, but the differences were not evident in the drone imagery. There was no rain on the horizon at that time and no opportunity to apply additional N. By early-March, the grower made the decision not to apply additional N this year, and we, in UCCE, needed to reduce activities due to the Covid-19 outbreak. We will, however, harvest the trial to determine whether there are yield or quality differences between the N-rich strips and the field.

In the future, I will use this blog to extend further information about the trial, including data for the Delta site. More immediately, the research team will be producing a series of weekly articles in the month of May that will be posted to the UC Small Grains Blog to provide more in-depth information on each of the practices. We will also be creating videos to demonstrate how to implement these practices. Consider subscribing to both blogs to be notified of new content.

Figure 2. Drone image of a field in Solano County where N-rich strips are implemented. (Photo courtesy of Mark Lundy and Taylor Nelsen, UC Davis.)

As you all know, national, state, and local agencies have been implementing various measures to reduce the rate and risk of community spread of COVID-19. Many California counties, businesses, and school districts have implemented remote working protocols, and the state has issued a shelter-in-place order, with some exceptions for essential services.

Protective measure are being taken by the UC Division of Agriculture and Natural Resources (ANR) and the local Cooperative Extension offices. This week, all UC ANR county offices, research and extension centers, and statewide programs are implementing telecommuting protocols. Starting today, all UC ANR employees are instructed to work remotely, with some exceptions for designated essential on-site staff and academics. 

Being mindful of official guidance concerning social distancing, San Joaquin County Cooperative Extension functions through April 7th are canceled. This directive also includes all volunteer-led youth or adult programming, meetings, or gatherings. Our office may close depending on County directives.

During this telecommute status, I am still available to assist you with questions that arise on-farm. Please do not hesitate to reach out to me via email. I advise not stopping by the office. My goal is to maintain my research program as planned, and I will rely on this blog and my website for extending information. Thank you for your cooperation and understanding.

Weeds are important pests of California rice systems, and weed management can account for roughly 17 percent of total operating costs, according to a UC cost of production study. Integrated weed management uses cultural and chemical practices and considers the following:

• Prevention (e.g. using certified seed, equipment sanitation, maintaining roads and levees)
• Cultural practices (e.g. land leveling, crop rotation, tillage, winter flooding, drill-seeding)
• Fertilizer placement and management
• Water management
• Monitoring
• Herbicides

Herbicides are important tools; however, resistance can occur when products are not rotated, or when diverse chemistries are not available.

In 2019, in cooperation with Corteva Agriscience, I conducted a trial to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl). Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Corteva Agriscience anticipates California rice registration in 2020, with the product being available for use in 2021. Previous trials have shown that Loyant provides good control of broadleaf weeds (e.g. ducksalad, redstems), smallflower umbrella sedge, and ricefield bulrush. It has some activity on Echinochloa species (e.g. barnyardgrass, watergrass). More data was needed, however, in drill-seeded systems. The objective of the trial was to assess the efficacy and crop tolerance of Loyant for weed control in drill-seeded rice in California.

The trial took place in the Delta region on a Kingile muck soil. This soil classification is characterized as having upwards of 40 percent organic matter in the top foot of soil. On high organic matter soils in the Delta, the typical practice is drill-seeding. Water-seeding, which is the typical practice in the Sacramento Valley, is not successful in the Delta because the soil particles can float and move too easily, causing seed to get buried too deeply and germinate poorly.

For a full report on this trial with methods and crop injury data tables, please see my website. Treatments are described in Table 1 below. We observed slight to noticeable leaf curling in the Loyant treatments at 14 days after treatment (DAT), but this had disappeared by 21 DAT. We observed no stunting or stand reduction with any of the treatments; nor did we observe any differences in heading. All treatments had similar weed control with the exception of the Prowl-only treatment, which had statistically higher weed counts. Loyant does not control sprangletop, so sprangletop was the weed most commonly observed. We found no differences in yield or seed moisture at harvest (Table 2 below), and we observed no lodging. Yield averaged 8965 pounds per acre across treatments, and seed moisture averaged 13.7 percent.

In summary, the purpose of this trial was to learn the efficacy and crop tolerance of Loyant (florpyrauxifen-benzyl) for weed control in drill-seeded rice. We observed slight leaf rolling with the Loyant treatments a couple weeks after treatment, but those symptoms were gone by the third week after treatment. We observed Loyant to have good activity on the Echinochloa species but not on sprangletop, which was expected based on previous company trials. We observed Loyant treatments to have similarly low weed counts compared to the grower standard practice, and no significant differences in yield among the treatments. Tank mixes will be needed to manage sprangletop. The results indicate that Loyant could be used in drill-seeded rice herbicide programs, providing a different chemistry for herbicide resistance management.

This information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.

Table 1. Rice herbicide treatments.

Happy New Year! We are entering "meeting season". The new year brings several opportunities for continuing education.  

1. UC Cooperative Extension will host the SJC and Delta Field Crops Meeting on Friday, January 10, 2020 from 8:00am to 12:00pm. The meeting location is the Cabral Agricultural Center in Stockton (2101 E. Earhart Ave., Stockton, CA 95206). Please see this previous post for the agenda, or open the attachment below. We will offer continuing education credits for DPR licensing (2), CCA certification (3.5), and nitrogen management (1.5). Light refreshments will be provided.

2. UC Cooperative Extension will host five meetings for rice growers. The meeting details are as follows:

Richvale:     Monday, Jan. 13, 8:30am, Evangelical Church, 5219 Church St., Richvale

Willows:      Monday, Jan. 13, 1:30pm, Glenn Co. Office of Education, 311 South Villa Ave., Willows

Colusa:       Tuesday, Jan. 14, 8:30am, Colusa Casino Resort, 3770 Hwy. 45, Colusa

Yuba City:   Tuesday, Jan. 14, 1:30pm, Veterans Hall, 1425 Veterans Memorial Circle, Yuba City

Woodland:   Wednesday, Jan. 15, 1:30pm, Norton Hall, 70 Cottonwood St., Woodland

Doors open at 8:00am, and meetings start at 8:30am at Richvale, Colusa, and Woodland. Doors open at 1:00pm, and meetings start at 1:30pm at Willows and Yuba City. DPR and CCA continuing education credits will be offered. For the program, please visit the UC Rice Blog.

3. San Joaquin County Farm Bureau and the Ag Commissioner's Office will host Spray Safe on January 27, 2020. The event takes place at the Cabral Agricultural Center in Stockton. Registration begins at 7:30am, with lunch concluding at 12:50pm. Please see the registration flyer and agenda here. 

4. The California Chapter of the American Society of Agronomy will hold its annual Plant and Soil Conference on February 4-5 in Fresno, California. Program information and registration are available from the conference website. Session topics include nitrogen management, drip irrigation, and cover cropping, among others. DPR licensing, CCA certification, and nitrogen management continuing education credits will be offered.

UCCE farm advisors will be hosting local meetings for other crops, like tomatoes, almonds, and cherries. Please see our calendar for details.