- Author: Michelle Leinfelder-Miles
- Contributor: Mark Lundy
- Contributor: Taylor Nelsen
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 15th. 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 25th, 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.)
The Delta trial was on a Rindge muck soil, characterized by over 20 percent organic matter in the top foot of soil. Approximately 56,000 acres in the Delta have the Rindge classification (USDA-NRCS). Over the course of the season, the site received approximately 11.5 inches of rain, and the site was not otherwise irrigated. (Precipitation data is from the Staten Island CIMIS station.) The previous crop in the field was triticale during the 2016-17 season.
The results from the 2017-18 Delta trial are summarized in table form for wheat and triticale. The top-yielding wheat varieties were WB 7566 (4.6 tons/ac; 11.7% protein), LCS 12SB0224 (4.5 tons/ac; 11.6% protein), and UC Patwin 515 (4.2 tons/ac; 12.9% protein), and the top-yielding triticale varieties were WB Pacheco (5.9 tons/ac; 11.1% protein), NS Trical 115T (5.2 tons/ac; 9.3% protein), and NS Trical 158EP (4.8 tons/ac; 9.6% protein). Of note, there was volunteer triticale from the previous year that grew in the plot. We ended up only harvesting one replicate (of four) where we rogued the triticale by hand.
Since environmental conditions vary from location to location and year to year, we advise making variety decisions based on aggregated data. For example, the Delta trial had very wet conditions in 2016-17 when California received record-setting rainfall. While conditions in 2017-18 were closer to “normal”, we still suggest reviewing three-year summaries when making variety decisions. The results for the Delta tend to align better with those from the Sacramento Valley compared to the San Joaquin Valley. Thus, the Delta results are incorporated into the three-year summaries for the Sacramento Valley, available for wheat and triticale.
Over the past two years, the UC Davis team has developed web tools that allow us to view some of the trial data in a more interactive way. There are two websites – one with the multi-year summary data and another that summarizes each trial individually. We suggest using these interactive tools on a computer, rather than a phone.
Please let us know if you have questions about the trials or the web tools.
The meeting showcased the UC Davis wheat and triticale variety testing program for the Delta, and presentations were given by UC Cooperative Extension and USDA-NRCS scientists. UCCE Grains Specialist, Mark Lundy, demonstrated a soil nitrate quick test and how it can be used in small grains fertility programs. UCCE Cropping Systems Specialist, Jeff Mitchell, described tillage research taking place at the UC Westside Research and Extension Center and demonstrated how no-till plots had better soil aggregation and tilth than conventionally tilled plots. USDA-NRCS Director, Margaret Smither-Kopperl, described winter and summer cover cropping trials at the Plant Materials Center in Lockeford, CA.
Additionally, Brenna Aegerter and I described an upcoming cover cropping trial that we will conduct on Staten Island. We were awarded a CDFA Healthy Soils Program grant with our farm advisor colleagues in the Sacramento and San Joaquin Valleys – Sarah Light, Amber Vinchesi, and Scott Stoddard – along with Jeff Mitchell and Will Horwath at UC Davis. On Staten Island, we will trial legume cover cropping versus no cover cropping treatments for soil health properties, greenhouse gas emissions, and grain yield from 2018-2020.
The trial will take place in a field that is in small grains (wheat and triticale) rotations, with soil classification Valdez silt loam. Cover cropping will take place in the summer months following the small grains harvest. Initial soil sampling will take place after wheat harvest and subsequent tillage. We will take baseline soil samples, measuring bulk density, pH, salinity, total C and N, aggregate stability, infiltration, and active C (a measure of the carbon available as an energy source for soil microbial communities) in the top foot of soil. At deeper depths, we will also test bulk density and total C. We will soil sample each fall, at the end of the cover crop season, to evaluate changes in soil properties over the three years. Greenhouse gas (N2O and CH4) monitoring will allow comparative evaluations of cumulative emissions between the soil management systems. Small grains yields will also be determined.
We look forward to this trial and will share results as we have them. We want to thank Dawit Zeleke and Morgan Johnson at The Nature Conservancy's Staten Island, Margaret Smither-Kopperl and Valerie Bullard at the USDA-NRCS Plant Materials Center, and Tom Johnson at Kamprath Seed for their collaboration on this trial.
For more information on UCCE or USDA-NRCS programs, please visit the following blogs and websites:
I have received a couple inquiries from Pest Control Advisors about wheat that is showing leaf tip yellowing and burning (Fig. 1). Their suspicion is frost injury, and with the weather we have experienced over the last several weeks, their suspicion is likely true.
There isn't a hard-fast rule of when frost injury will occur because several factors influence its occurrence and severity. The factors include the temperature but also the duration of cold exposure, the plant growth stage, and the growing conditions. The UC Small Grains Production Manual (see page 101) states that injury may occur with temperatures at or below 35⁰F and that even just a couple hours of exposure is enough to cause injury.
Below (Fig. 2), I present temperature data from the last month from a few local CIMIS stations. Remember that in early-February, daytime highs were getting above 70⁰F. By mid-February, however, minimum temperatures were low enough to cause frost injury, and hourly data (which I am not showing but is available from the CIMIS website) shows that temperatures below 30⁰F often spanned several hours over many nights in late-February.
The plant stage of development is critically important to how a crop may be injured from frost and how it may overcome injury. At tillering, leaf yellowing and tip burning will be the obvious symptoms. At this stage, however, yield impact will likely be slight, if any. That is because the growing point of the tillers is close to the soil and protected from the cold. When warmer weather resumes, the plants may be able to continue tillering, particularly in thin stands where there is space to fill, and overcome the injury. In the jointing stages, in addition to the leaf yellowing and tip burning, some leaf or stem lesions may be apparent. There could be moderate impacts on yield if the growing points of the tillers have been injured. Look for a chlorotic or dead leaf in the whorl. Also, try splitting the stem with a razor blade at the growing point. This picture from Texas A&M University shows how to do this. If the growing point (at the arrow) appears white, brown, or water-soaked, then there has been frost injury. Once the crop gets into the reproductive stages of growth, it becomes more sensitive to injury with bigger repercussions for yield, but luckily, I think most of the fields in our region aren't yet to these later stages of development.
Keep in mind that there are field and other growth conditions that may lessen or worsen the severity of frost. Low parts of the field where cold air settles will likely show more injury. Fields that were planted earlier in the fall, or earlier-maturing varieties, that are in a later stage of growth will likely show more injury. Crops that have had good moisture and nutrient conditions may also show more injury. With one of the inquiries I received, the field had been fertilized about a month ago, and given the warm daytime temperatures we had at that time, those plants were likely resuming growth and probably got hit by the frost all-the-more. Crops that have been moisture stressed, however, may have been hardened and not show as much injury.
So, what now? Again, growers and consultants with crops in the jointing stages who are seeing leaf tip yellowing may wish to split some stems to observe whether there has been injury to the growing points. If this has occurred, there is nothing that can be done to “save” those tillers, but it might provide some insight into potential yield impact. If stem lesions appear, be on the look-out for disease infections but also lodging later in the season. Unfortunately, the most telling symptom will appear after heading when grain doesn't fill. Don't hesitate to reach out to me or your local farm advisor if you have questions about frost injury.
- Author: Michelle Leinfelder-Miles
- Contributor: Mark Lundy
- Contributor: Nicolas George
Fall has arrived, and for many crops, this means that it is harvest season. For small grains, however, the season starts anew. The UC Davis small grains variety evaluations are conducted across the state, including a site in the Delta. The results of last year's evaluations are now available, and we invite you to take a look as you prepare to plant your new crop.
To understand trends over time, we suggest reviewing the 3-year summaries, which are available from the link “Yield and Protein Summary” for common wheat and triticale. These summaries indicate which varieties performed consistently well over time. For these summaries, the Delta is grouped with other Sacramento Valley locations. The data indicated that the varieties performed similarly between the Sacramento Valley and the Delta, compared to the San Joaquin Valley and the Delta. This is probably due to similar climatic considerations, like rainfall and temperature. The 3-year summaries rank the varieties for both yield and protein. In the future, rather than tables, the research team will develop an online tool to assist with variety selection that will take both yield and protein into account. Stay tuned for more information on this tool.
Keep in mind that disease ratings are important considerations. Disease ratings are found here, where “S” indicates susceptible varieties and “R” indicates resistant ones. Additionally, some of these varieties are in initial stages of testing, so not all of them are commercially available. Look for whether the variety is “released”, which is indicated on the data tables.
Barley and durum wheat were also evaluated at certain locations but not in the Delta. We will continue trialing small grain varieties in the Delta in 2018.