In a previous blog post, I introduced a project about using nitrogen (N) rich reference zones in wheat. The goal of the project is to show how N-rich reference zones can be used to guide N fertilization in small grains, to increase crop productivity and N use efficiency. This is a three-year project funded by the CDFA Fertilizer Research and Education Program, and UCCE has implemented several demonstration sites, including a site in the Delta. As we move into the 2021-22 wheat season, I wanted to provide an update on the project and share that we have published case studies about the Delta site. The purpose of the case studies is to describe how local conditions influenced how we used N-rich reference zones to guide N management.

The N-rich reference zone is a small area within a field where extra N fertilizer is added at the beginning of the season. This extra fertilizer ensures that the reference zone will not be N-limited after planting. Reference zones are most useful to growers who can apply the majority of their seasonal N budget during or after the tillering stage of growth. Previous work has shown that in-season N applications can improve yield and/or protein under some conditions. When a grower is determining whether and how much N fertilizer to add in-season, measurements from both the reference zone and the broader field are compared to understand whether the broader field is sufficient in plant-available N.

We have used a soil nitrate quick test (SNQT), handheld canopy reflectance devices, and drone and satellite imagery to evaluate the N status of the reference zones and the broader field. The SNQT is performed in the field and provides a quick, inexpensive estimate of nitrogen availability in the soil. The proximal and remote sensing allow us to see differences in green vegetation that the human eye cannot detect. We collect data from both the N-rich zones and the broader field, and then we can evaluate N sufficiency in the field relative to the N-rich zone. Our team has also developed a N Fertilizer Management Tool, which can help with in-season N fertilizer decision making.

At the Delta location on Tyler Island, we have trialed these practices on high organic matter soils. In the 2020-2021 wheat season, we found that the additional fertilizer in the N-rich zones did not improve wheat yield at this site. We did find, however, that in-season N fertilizer improved wheat protein by about 0.5 percent. More details can be found in the case study.

Implementing N-rich reference zones allows growers to get real-time knowledge to inform N fertilizer management in small grains. This information can help them make fertilizer applications when increased yield and/or protein benefits are likely and avoid them when they are not. Please visit the UC small grains website for more information about N management practices and to read case studies from other statewide demonstration sites. Don't hesitate to reach out to me if you would like more information on how to implement N-rich zones in your fields this season.

I am pleased to announce the following two meetings:

1. UC Cooperative Extension and UC Davis will host a Healthy Soils Program Workshop on compost. The meeting will take place on Tuesday, October 26th from 9:00am to 12:30pm (BBQ lunch provided). The meeting will take place at Rominger Brothers Farm (28800 Co Rd 29, Winters, CA). Presentations topics include how to acquire compost, different types of compost and how it can improve soil health, and nitrogen management in tomato systems receiving compost. At the end of the workshop, there will be a compost spreading demonstration. Attendance is free, but registration is required. Continuing education credits will be offered (0.5 of N management for ILRP program; 0.5 NM and 1.0 SW credits for CCAs). The agenda is available from the registration page.

2. UC Cooperative Extension will host an online workshop on Using N-rich Reference Zones to Guide N Management in Small Grains. The workshop will take place on Thursday, November 4th from 2:00-4:00pm. Presentation topics include how to implement N-rich reference zones, online N management tools, and case studies from local sites. Attendance is free, but registration is required for anyone requesting continuing education. Continuing education credits (2.0 of N management) will be offered for the ILRP program. The agenda is pasted below, and the meeting link is here.

Thanks for your interest in UC Cooperative Extension programming.

 

Agenda: Using N-rich Reference Zones to Guide N Management in Small Grains

2:00 - 2:15 Overview of concepts and tools related to utilizing N rich reference zones to guide N management in California small grains. (Mark Lundy, UC Davis/UCCE)

2:15 - 2:30 Introduction to The Nitrogen Fertilizer Management Tool for California Wheat and other web tools for optimizing N management in California small grain crops (Taylor Nelsen, UC Davis)

2:30 - 2:35 Questions and Discussion

2:35 - 4:00 Case Studies: Using N-rich reference zones to guide N fertilizer management in diverse California environments. Presentations will discuss specifics of implementing N rich reference zones and using UC decisions support tools to make in-season N fertilizer decisions. 

• Yolo County irrigated site N rich case study (Mark Lundy, UC Davis/UCCE)
• Yolo County rainfed site N rich case study (Konrad Mathesius, UCCE)
• Kings County N rich case study (Nick Clark, UCCE)
• Sacramento County Delta N rich case study (Michelle Leinfelder-Miles, UCCE)
• Siskiyou County N rich case study (Giuliano Galdi, UCCE)
• Colusa County N rich case study (Sarah Light, UCCE)
• Wrap-up discussion and survey

UC Cooperative Extension will host the annual Delta field meeting on Thursday, September 30th from 10:00-11:30am, on Tyler Island in Sacramento County. The agenda is pasted below and attached. In addition to providing information on the annual field corn variety trial, this year's agenda includes presentations on nitrogen management in corn and wheat. The attached version of the agenda includes a map and directions to the field site. We have applied for CCA and CDFA INMP continuing education credits. The University is attentive to the ongoing Covid-19 pandemic. Please monitor yourself for Covid-19 symptoms before coming to the event, and do not come if you are experiencing symptoms. While this meeting is outdoors, we will be following University safety precautions for in-person events. Please practice social distancing, or wear a mask if within 6 feet of another person. Thanks for your interest in UC Cooperative Extension programming, and we hope to see you in the field! 

Agenda:

10:00am     Field corn variety evaluation – preliminary results, Michelle Leinfelder-Miles, UCCE, SJC/Delta

10:15am     Variety traits for the Delta, Seed company representatives

10:30am     In-season nitrogen management in wheat, Michelle Leinfelder-Miles, UCCE, SJC/Delta

10:45am     Development of site-specific nitrogen fertilization recommendations for annual crops, Suzette Turner and Daniel Geisseler, UC Davis

11:00am     Viewing of field plots

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.)