- Author: Michelle Leinfelder-Miles
UC Cooperative Extension and UC Davis will host a Healthy Soils Program field meeting on compost. The meeting will take place on Thursday, July 28th from 10:00am to 11:30am. The meeting will take place off of S. Landi Road, on Roberts Island in the Delta. Presentation topics include how to acquire compost, different types of compost, how compost can improve soil health and mitigate greenhouse gas emissions, and how to apply for cost-share funding. The meeting location is where we are trialing different rates of green waste compost application for potential soil health and alfalfa yield benefits. Preliminary results will be described. Attendance is free, and registration is not required. Continuing education credits will be offered (CCA and N management applications pending). The agenda is pasted below, and a downloadable version is attached. Thanks for your interest in UC Cooperative Extension programming, and we hope to see you later this month!
Agenda
2022-7-28 Meeting Agenda FINAL
- Author: Michelle Leinfelder-Miles
Over the last few years, I have been working on a project to characterize a suite of soil health properties in alfalfa receiving full and deficit irrigation. Soil health has been described as the ability of soil to function and is characterized by biological, chemical, and physical soil properties that are sensitive to changes in management. The idea for this project developed after the 2012-2015 drought when water shortages and regulatory curtailments meant that growers had to make tough decisions on how to apply scarce water resources. Some growers opted to cut irrigation to alfalfa since it is a deep-rooted crop that can scavenge water and nutrients from the soil profile. (See this recent blog post by UC Alfalfa and Forage Specialist Dan Putnam, and Farm Advisor Rachael Long on the resiliency of alfalfa during drought.) I had a hunch, however, that while alfalfa may be adapted to survive drought conditions, soil health properties might be negatively impacted because water is essential to life in the soil, facilitates nutrient movement and availability, and influences soil physical characteristics, among other things. Fortunate for me, there was a research trial at UC Davis where I could test this idea.
I view alfalfa as a model crop for studying soil health under restricted water conditions because practices like crop rotation and tillage do not occur over the four or more years of an alfalfa stand. Therefore, those practices would not confound the results. From this experiment, we are learning how imposing varying levels of deficit at different stages of the cropping season impact soil properties, which will help us optimize deficit irrigation strategies for alfalfa. Additionally, the deficit treatments serve as a proxy for drought and could potentially demonstrate how prioritization of water uses during drought may impact soil conservation outcomes.
Data analysis is ongoing, but preliminary results suggest that soil health may not be resilient under deficit irrigation or drought, even if alfalfa is. When the trial began in Spring 2019, there were no differences in rootzone salinity among treatments, which averaged 0.41 dS/m. After two cropping seasons where deficits were imposed, the 60 percent ETc treatment with the water cut-off toward the end of the season (CT) resulted in significantly higher rootzone salinity down to the 36-inch depth (Figure 2). The salinity in that treatment was higher than even the 40 percent ETc treatment that had the sustained deficit (SD) throughout the entire season. In other words, it appears that the timing of the deficit is more important than the amount of deficit, and applying water throughout the season – even if the amount is severely reduced – appears to mitigate salinity build-up in the rootzone. Of note, salinity is not high enough to be problematic at this site. The overall ECe of the soil is low, and water quality is generally good at this location. I would expect, however, that in locations where soil and/or water has higher salinity to begin with, then deficit irrigation that includes a water cut-off could be problematic.
There will be a lot more information to come about this project in the near future, but the salinity information seemed timely to share given our current water year. In addition to Dan, Isaya, and Umair, I want to acknowledge Daniel Geisseler (UC Nutrient Management Specialist), Will Horwath (Professor of Soil Biogeochemistry), and graduate student Veronica Suarez Romero who have helped on soil nitrogen and carbon testing. I also want to acknowledge the South Delta Water Agency for financial support of the project.
- Author: Michelle Leinfelder-Miles
Soil health has been described as the ability of soil to function and is characterized by biological, chemical, and physical soil properties that are sensitive to changes in management. Studies have shown that reducing tillage, increasing rotational crop diversity, and employing cover crops during the fallow season can improve soil health characteristics. In turn, improvements in soil health may enhance various soil functions, like improving crop productivity, reducing input costs, and buffering plant health from living and non-living stresses.
Over the last year and a half, I have been working on a project to characterize a suite of soil health properties in alfalfa receiving full and deficit irrigation. When I was developing the project, I had two hunches. The first was that alfalfa production may improve certain soil health characteristics. Alfalfa provides soil coverage for several years. Alfalfa is also a deep-rooted crop that can scavenge water and nutrients deep in the soil profile. Additionally, alfalfa has been shown to provide a nitrogen benefit to subsequent crops. For reasons like these, I hypothesized that certain soil health characteristics might improve over the years of an alfalfa stand.
My second hunch, however, was that deficit irrigation could negatively impact soil health properties. In recent years, California alfalfa production has received negative press for water usage that exceeds that of other crops. Alfalfa does represent an important footprint in California's agricultural water use. Alfalfa has a high water demand (i.e. crop evapotranspiration, ETc) that is directly related to yield. All else being equal, as ETc increases, alfalfa yield also increases up to maximum ETc. Studies conducted by UC Alfalfa and Forage Specialist, Dan Putnam, have demonstrated, however, that alfalfa is resilient under water deficit conditions. While alfalfa may be resilient under deficit irrigation, water facilitates soil microbe functioning and nutrient availability. Therefore, I also hypothesize that soil health may degrade under deficit irrigation. This is critical knowledge to develop not only for deficit irrigation strategies but also in the event of drought, where growers may be asked to sacrifice crop irrigation for water transfers to other uses. Such knowledge could demonstrate how prioritization of water uses may impact soil conservation outcomes.
This project is being conducted at UC Davis on a Yolo silt loam and was initiated in Spring 2019. The treatments, which are replicated four times, are: 1) full irrigation (100 percent ETc), 2) full irrigation at the beginning of the season with a sudden cutoff toward the end of the season (60 percent ETc), 3) gradual deficit where each irrigation imposes restriction (60 percent ETc), and 4) more-severe gradual deficit (40 percent ETc). The treatments are applied using overhead irrigation – an 8000 series Valley 500 feet, four span linear-move system. The site allows us to observe soil characteristics under different levels of deficit, imposed at different stages of the cropping season. Soil sampling occurs twice each year – in the spring before irrigation begins and in the fall after the last irrigation. We are testing a comprehensive nutrient analysis, organic matter, total carbon and nitrogen, salinity, compaction, bulk density, N mineralization, and particulate organic carbon.
This project is ongoing, but we have interesting preliminary results. One example is with particulate organic carbon. Particulate organic carbon (POC) is a biological indicator of soil health because it is the fraction of soil organic matter that is readily available as an energy source for soil microorganisms. Though not statistically significant (Fig. 1, P = 0.066), there is a trend for the higher irrigation rates – and sustained irrigation throughout the season – to have higher POC. Between the two irrigation treatments providing approximately 60 percent of ETc, the third treatment which provides a sustained deficit throughout the season tends to have higher POC than the 60 percent ETc treatment that has a sudden cut-off of water about two-thirds of the way through the season. These results suggest the importance of water in sustaining soil biological activity.
Likewise, there is a similar trend for higher irrigation rates and sustained irrigation through the season to result in lower soil compaction readings (Fig. 2, P = 0.2691). At the 6-inch depth, the full irrigation rate trended toward having the lowest compaction, followed by the 60 percent sustained deficit treatment. All treatments, however, had average readings below 300 psi, which is the pressure above which root growth is believed to be constrained.
These are preliminary results. We will soil sample again this fall, and hopefully again next spring and fall, to see if these trends continue. I want to acknowledge my UC Davis collaborators on this project: Dan Putnam, Isaya Kisekka, Daniel Geisseler, Umair Gull, and Veronica Romero. I also want to acknowledge the South Delta Water Agency for funding support.
Figure 1. Average particulate organic carbon (top 12 inches) across four irrigation treatments and three seasonal readings (Spring 2019, Fall 2019, Spring 2020).
Figure 2. Average soil compaction at 6-inch depth across four irrigation treatments and three seasonal readings (Spring 2019, Spring 2020, Summer 2020).
- Author: Michelle Leinfelder-Miles
- Contributor: Brenna J. Aegerter
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:
UC Sacramento Valley Field Crops Blog
- Author: Michelle Leinfelder-Miles
A consultant recently brought in some alfalfa plants to get another opinion on why growth was resuming slowly this spring. The field is located in Merced County and is a sandy loam soil. The field is in its fifth year, is glyphosate-tolerant, and has traditionally produced high-quality hay. About 5 acres of a 40-acre field are affected.
There are many reasons why growth may resume slowly this spring. The obvious reason, of course, is that we received a lot of rain this winter. With that rain has come associated problems from cool, anoxic (lack of oxygen) soil conditions. A previous blog article describes things to look for in alfalfa fields where there was standing water this winter, and how to diagnose problems as the weather warms and soil dries out. In this particular example, the consultant assessed soil conditions by augering down about four feet. He did not observe excessive moisture, even down to four feet, and generally, we would presume fairly good drainage from a sandy loam soil. He also sent samples to the lab for chemical analysis. The soil analysis indicated an acceptable pH (7.6), low salinity (EC 0.5-0.8 dS/m), adequate soil phosphorus (12 ppm), and marginal to low potassium (45 ppm). Despite the low potassium, no potassium deficiency symptoms have been observed on the leaves. The grower applied turkey manure to the field in the fall but did not have it analyzed, so we do not know its fertility characteristics. Additionally, the grower applied herbicides in the fall. There has been some concern that the affected acreage is reacting poorly to the herbicides; however, when herbicide damage has occurred, we would generally expect to see the damage over the entire treated acreage, and that is not the case in this field.
Earthworms do not feed on roots, but rather, ingest the soil and its microorganisms, mixing the soil as they feed. A recent California Agriculture article discusses how soil biodiversity contributes to soil health, defined as soil functionality. Earthworms certainly are a component of soil biodiversity, and their presence often relates to beneficial soil physical and chemical characteristics. While the jury is still out on what might be causing the slow spring growth of this alfalfa field, I think we can rule out these little, white orbs.