- Author: Konrad Mathesius
Join us next week for a workshop that will cover some basic wheat fertilization strategies and focus on how to use the Nitrogen Fertilizer Management for California Wheat Webtool.
Yolo County: Wednesday, October 11th 2023, 9 a.m. – 11:00 a.m.
70 Cottonwood Street, Woodland, CA
Register: click here
Given the high cost of Nitrogen (N) fertilizer and a tendency to apply the majority of N prior to planting, growers stand to potentially leave a lot of money on the table by failing to optimize their N-management in small grain systems. For example, early, heavy rains last year flushed a lot of nitrate out of the soil profile before wheat could take it up during the rapid growth phase. In-season applications provide an opportunity to take account of the water year, and the crop status before deciding on a season-long N fertilizer budget.
The Nitrogen Fertilizer Management Webtool for California Wheat offers in-season insight on whether and how much N to apply given the seasonal conditions. While the use of the webtool is pretty straightforward, we have found that it is helpful to offer workshops to help CCAs and growers become more familiar with its use. These two-hour trainings offer an introduction to principles of N-management in wheat and use/ interpretation of the webtool.
Agenda Below:
YOLO COUNTY
Small Grains Nitrogen Management Webtool Training
Wednesday, October 11th 2023, 9 a.m. – 11:00 a.m.
70 Cottonwood Street, Woodland, CA
Please RSVP using QR code or click here
Presented by:
Konrad Mathesius, UCCE Agronomy Advisor, Yolo, Sacramento, and Solano
Who should attend: CCAs and other crop consultants specializing in crop nutrient management.
Growers, Ag Industry, and the general public are also welcome
8:40 a.m. Registration, light refreshments
9:00 a.m. Welcome and Introduction
9:10 a.m. Principles of N fertilizer use in California small grains
9:40 a.m. Measuring field data pre-plant and in-season
N-rich reference zones
Soil sampling for nitrate
10:00 a.m. Soil nitrate quick test demonstration and data interpretation
10:15 a.m. Webtool example and case studies
10:25 a.m. Webtool walkthrough
10:45 a.m. Crop Consultant/ CCA forum, survey, feedback, troubleshooting, and discussion
11:00 a.m. Adjourn and Lunch, Please RSVP using the link or QR code above.
CE Credits
CCA: 2 (pending)
INMP/Cures: 2 (pending)
- Author: Mark Lundy
- Author: Konrad Mathesius
Recent UCCE research has illustrated the value of in-season applications of nitrogen (N) fertilizer, particularly applications made at the early vegetative growth stages. This is typically the stage of growth when N demand from the crop is increasing rapidly, the soil is beginning to warm up, and microbial metabolism and associated mineralization/transformations of the various forms of N are increasing. Over a wide range of California conditions and across multiple seasons, applications of N fertilizer at this stage of growth have been shown to increase grain yield and protein and improve fertilizer use efficiency relative to equivalent amounts of N applied pre-plant. Therefore, a strategy that prioritizes in-season applications of N fertilizer over pre-plant applications is a good starting point for getting the most out of your N fertilizer.
The decision to save the majority of your N budget for an in-season application also creates an opportunity to determine whether and how much N fertilizer to apply during a topdress application with more precision. N-rich reference strips are a relatively simple way to determine the need for N in a site-specific manner at the time of the topdress application. This approach has been used with some success in other parts of the US, but is not typically used here in California. Combining a N-rich reference strip with simple tools that measure the soil nitrate status and the relative crop N status via canopy and leaf sensors is the best way to make a precision N topdress decision with confidence.
UCCE agronomists are interested in assisting growers with implementing N-rich reference strips in the coming season. The general principles for using N-rich reference strips to inform N management in wheat are as follows:
1) For a given N fertilizer budget, consider applying 1/3 of the N budget pre-plant and saving 2/3 of the budget for an in-season topdress application.
2) During the pre-plant application, make a double or triple pass across the field in an area(s) that will be generally representative of the entire field (see below). For example, if your pre-plant field rate is 50 lb/acre N, make a triple pass in one or two strips so that the pre-plant application in the N-rich strip is 150 lb/acre N.
3) At the early vegetative growth stage (tillering), measure the plant-soil environment in representative areas of both the N-rich reference strip and the larger field.
- Soil nitrate-N concentration in the top foot is the best predictor of crop response to N fertilizer applications at this stage of growth. Soil nitrate can be determined via a lab value or with less precision but greater speed by using a soil nitrate quick test.
- Canopy greenness as measured by NDVI can indicate whether the crop canopy is currently showing signs of N-deficiency relative to the reference strip. The Trimble Greenseeker is an example of an easy to use and relatively inexpensive NDVI meter.
- Tissue N concentration of leaf samples taken from both the N-rich area and the larger field can also indicate whether the main crop is N-deficient relative to the reference strip. Leaf chlorophyll meters such as the atLEAF chlorophyll meter return values that are closely correlated to tissue N concentrations and provide information on the spot. Tissue analysis from a lab would also be a suitable approach that would produce similar information as a chlorophyll meter.
4) Each of these tools/tests can help to detect differences in N status that are not obvious to the eye. By comparing the values in the reference strip to the values in the broader field, the need for and quantity of the topdress N application can be specified with more confidence. Because each of the above indicates N status from a different scale of the plant-soil continuum, a precision management decision can be made with the greatest degree of confidence when the full suite of measurements are taken. Nevertheless, each of these measurements can provide useful and actionable information on their own.
Because residual soil N, rainfall and rotation effects can differ from year-to-year and field-to-field and soil type can differ both within and across fields, the N-rich strip helps to correct for some of these site- and year-specific differences. It also serves as a local calibration point for the tests and devices used to measure N availability. In addition, UCCE research has produced algorithms in a research context that can inform whether and how much N to apply based on values obtained following steps 1-3.
We are keen to apply and validate these in on-farm settings and are looking for cooperators willing to try out this approach in the coming season. We can assist in implementing N-rich strips and taking in-season measurements on a limited number of fields. If you are interested in setting up a N-rich strip in the coming season and would like to discuss further, please reach out to Konrad Mathesius in the Woodland UCCE office or Mark Lundy at UC Davis.
- Author: Jordon Wade
“Soil health”, as both a term and a concept, has been gaining traction in the last few years. The National Resource Conservation Service (NRCS) has defined soil health as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans”. Generally, soil health is considered to be the intersection of soil physical, chemical, and biological factors. Each soil will have differing levels of health within these three areas. Some of these constraints are inherent to a soil due to differences in the geologic material that it was formed from, but each individual soil can be optimized for agronomic performance by using management strategies that will improve the health of an individual soil.
In recent years, one area of soil health that has received a lot of attention is the biological component. Researchers are diving into the complexity of soil microbiology and looking for ways to translate these complex, micro-scale interactions into reliable, actionable recommendations for growers to use. These recommendations are usually going to be adjusted using results from commercial soil test labs. One biologically-based test that has been increasing in popularity in recent years is respiration, or the production of CO2 by soil microbes, after an air-dried soil is rewetted. Measuring CO2 production rates is a quick, inexpensive method to estimate soil microbial community size and activity level, as well as the availability of carbon to those soil microbes. For these reasons, respiration can serve as one useful tool in the toolbox for assessing soil health. However, translating these respiration measurements into a recommendation for growers has proved difficult.
One proposed use of respiration is to predict the inherent ability of a soil to supply nitrogen to a crop. The breakdown of soil organic matter into plant available forms of nitrogen, a process known as mineralization, is largely controlled by soil microbial activity, so a measure of microbial activity (e.g. respiration) has the potential to predict this process. If nitrogen mineralization can be predicted prior to planting, nitrogen fertilizer recommendations can be reduced, resulting in decreased fertilizer costs for growers and decreasing the potential for adverse environmental effects.
Funded by CDFA's Fertilizer Research and Education Program (FREP), UC Davis researchers Jordon Wade, Martin Burger, and Will Horwath sought to test the ability of respiration to predict nitrogen mineralization in California's diverse cropping systems. The study used soils from four distinct regions—Yolo County, San Joaquin County, Fresno/Kern Counties, and Monterey County—and two differing management strategies—fields receiving a winter cover crop and those not receiving a cover crop. A suite of common commercial test lab indicators were used to predict N mineralization.
The ability of our soil tests to predict a soil's N mineralization potential was very low. Respiration was able to predict nitrogen availability in cover cropped fields better than in non-cover cropped fields, although neither was a particularly strong relationship. Combining biological and chemical tests did improve the predictive ability, but the relationships were still weak. Additionally, they were inconsistent in their accuracy across growing regions. There is a potential to use N fertilizer rate trials to calibrate these tests for an individual field or set of fields, but large-scale recommendations at this time would likely be inaccurate.
While respiration may not be able to predict a specific outcome (such as N availability), it has been shown to be correlated with increased yields in corn (both grain and silage) and processing tomatoes in California agricultural systems. Together, these findings suggest that measuring respiration does have limited agronomic utility, but that its ability to predict specific outcomes is uncertain.