- Author: Jeffrey P Mitchell
April 12, 2024
The UC ANR CASI Center hosted five members of the Soil Health Institute's US Regenerative Ag Cotton Program in the San Joaquin Valley on April 11th and 12th, 2024. The Soil Health Institute (SHI) is a non-profit organization based in Morrisville, NC that conducts research and extension education related to soil health management. Five SHI members, Diana Bagnall, David Lamm, Jessica Kelton, Emily Ball, and Nate Looker, took part in the two-day tour of six San Joaquin Valley farms and the California Cotton Ginners and Growers Associations. San Joaquin Valley farmers who hosted the SHI members included Mark Borba of Borba Farms in Riverdale, CA, Mark McKean of McKean Farms also in Riverdale, Tony Azevedo of Stone Land Company in Stratford, CA, Cannon Michael and Derek Azevedo of Bowles Farming in Los Banos, Gary and Mari Martin of Pikalok Farms in Mendota, and Gary Smith of Ingleby Farms in Burrel. Roger Isom, President of the CCGGA in Fresno, also hosted the SHI guests.
SHI requested help from CASI with the cotton tour and discussions that took place as an effort to expand their national Regenerative Ag Cotton Program to California in 2024. The tour provided excellent opportunities for SHI to learn about California cotton and to make connections with leading cotton farmers in the San Joaquin Valley who may become part of the baseline soil sampling project that SHI is looking to conduct with cotton producers this year.
In addition to the farmers who generously hosted the SHI guests, several other local California folks including Cary Crum, Kimber Moreland, Rob Roy, Jacob Wright, and Olivia Peters helped CASI's Jeff Mitchell in sharing information about California cotton systems.
- Author: Help Desk Team
Perhaps you've seen them. You're digging into the soil to plant something and as you dig you run across a few earthworms. Most of us have heard from childhood that worms are good for the soil. You may also be aware of vermiculture, or worm composting, using worms to help turn organic waste into nutrient rich compost for the soil. When you see earthworms in your garden, what does their presence suggest about the soil health? Should you add more?
Earthworms and Wigglers
The earthworms you typically see in your garden are considered "migratory" which means they will travel to find the habitat best suited to their success. They tend to cluster in the top 6 to 8 inches of soil around the roots of plants where they feed on decaying material and the fungi and other organisms that live there. As they travel through the soil, they drag leaves and other litter down into their burrows where soil microorganisms also begin digesting the material. These worms can tolerate colder temperatures through the winter months when they burrow deeper into the soil.
Earthworms need a light airy soil and rely on decaying organic material for nourishment. Introducing these earthworms to an inhospitable environment such as heavy clay, or compacted and/or dry soil, will result in them either leaving or dying. Where they flourish, however, they are important in mixing the dead surface litter with the main body of the soil. If you regularly add compost and a layer of mulch to your garden to improve the soil you may find the worms 'magically' appear, attracted to the habitat you are creating. In turn their constant burrowing and feeding activities help mix and distribute organic matter throughout the soil, improve soil aeration and water penetration, promoting a healthier root environment for your plants. Their excrement, known as castings, is richer in nitrogen, potassium carbon, sulfur, and other minerals than the rest of the soil, and acts as a natural fertilizer.
There is a second type of worm which lives close to the soil surface in areas of abundant organic material. These worms, including the popular species red wigglers, reproduce rapidly and thrive in warm, crowded conditions. They are less likely to survive in your garden environment, particularly during cold weather. Instead, these worms are ideally suited to worm bins, and you will usually find them for sale for use in vermiculture. In a bin they can rapidly break down food scraps and other organic waste materials, and their castings also act as a natural fertilizer when collected and added to garden soils. Think of these worms as composting specialists.
A Note of Caution
There is a type of worm known as a jumping worm, an invasive species capable of harming native forests which has been seen in California and many other states. It is recognizable by a milky-white band wrapping all around its body near the head. When disturbed, jumping worms have been known to throw themselves into the air and thrash around. It is very difficult to eliminate these worms once established, so make sure to check new mulch, compost, and potting soil for the worms, as well as soil in nursery pots. Because they live close to the surface their castings are often visible as a coffee-ground-like substance on the soil. Don't use these worms for fishing, vermiculture, or gardening. You can learn more about jumping worms at https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=56929.
The Bottom Line
Should you add worms to your garden soil? Ultimately, it's a chicken and egg situation. Do earthworms create healthy soil or are they attracted to healthy soil? Few valid studies have been done to link the presence of earthworms with improved plant growth. However, both plants and earthworms need temperatures between 60°F and 100°F, water (but not too much or too little), oxygen, and a soil that isn't too acidic, basic, or salty. It's clear the conditions that are good for plants are also good for earthworms, and improving your soil by regularly adding compost and mulch ends up supporting a thriving community of both healthy plants and earthworms.
Help Desk of the UC Master Gardeners of Contra Costa County (RDH)
- Author: Trina Kleist, UC Davis
One more reason to adopt sustainable cultivation
California wheat farmers could both maintain their yields and improve soil health by growing annual wheat without tilling the soil year after year.
This could be one more encouragement to farmers to adopt a sustainable practice commonly called conservation tillage, no-till or minimum-till cultivation, impacting how we grow a grain that supplies about 20 percent of the calories and protein for people around the world.
A new study, by a team led by Mark Lundy, University of California Cooperative Extension specialist in UC Davis' Department of Plant Sciences, offers new insight for decades-long discussions around soil conservation, sustainable agriculture and climate-warming emissions related to growing our food. The study has been published in the journal Soil and Tillage Research. For the first time, researchers have shown that annual wheat that is not tilled each year is better for stashing carbon in the soil than perennial wheatgrass, while still yielding more crop in Central California.
Previous studies have looked at annual wheat that is tilled each year, annual wheat that is not tilled, and a cousin species, perennial intermediate wheatgrass (trademarked Kernza), which also is not tilled. But until now, no one has looked at all of the benefits and trade-offs together. Most importantly, “no one has ever controlled for tillage,” Lundy said. “And, no one has compared annual wheat to perennial intermediate wheatgrass over multiple years in a Mediterranean climate, which is what we have in California.”
This study also is unique because it delves into the deeper question of what is going on in the soil that drives the different results for carbon there. Soil carbon reflects various processes linked to plant activity and soil health. Measuring the different forms of soil carbon may also signal whether a farming system is accumulating carbon in the soil over time – a plus for reducing climate-warming gases in the atmosphere.
“Measuring soil carbon is complex and nuanced,” said Kalyn Taylor, the lead author on the paper. “We started this experiment because we wanted to know whether and how plant activity and tilling or not tilling would affect the carbon story belowground in California's climate.”
“When we started this study, we thought the crop being perennial or annual would drive the differences in carbon storage in the soil,” Lundy added. Specifically, they had expected perennial wheatgrass would lead to more carbon in the soil because of its deeper, better-established root system. “But that's not what we found,” he went on. “What we found was, it was the lack of tillage, plus the level of productivity of common annual wheat, that made the difference in soil carbon here in California.”
Soil carbon in annual vs. perennial grain
In 2017, Lundy, then-graduate-student Taylor, UC Davis Professor Emeritus Kate Scow and others on the team started measuring different forms of soil carbon in test plots at Russell Ranch, west of campus. Plots were planted with annual wheat that was tilled each spring, annual wheat that was not tilled and perennial intermediate wheatgrass (Kernza) that also was not tilled.
Each year, the researchers measured the carbon present in the soil, the amount of soil organisms (which have carbon in their bodies) and the amount of material the plants created.
At the end of three growing seasons, they found that land planted with no-till, common, annual wheat had the highest amount of soil organisms, measured as biomass, of the three treatments.
The researchers also found soil carbon is more likely to remain stable in the no-till, annual plots, compared to both tilled wheat and wheatgrass.
In addition, the no-till, annual wheat produced plant material more consistently than the perennial wheatgrass across the three years, which saw variation in rainfall.
“Overall, annual wheat grown without soil disturbance or tillage had both higher productivity and higher potential for storing carbon in the topsoil than perennial wheatgrass in our Mediterranean climate,” Lundy said.
Related research
“No-till annual wheat increases plant productivity, soil microbial biomass, and soil carbon stabilization relative to intermediate wheatgrass in a Mediterranean climate,” is online now and will be published in the January 2024 edition of Soil and Tillage Research.
The team also found that tilled annual wheat vs. Kernza stores total carbon at different depths in the soil profile and hosts distinct soil fungal communities, primarily in the root zone and topsoil: Taylor, K., Samaddar, S., Schmidt, R., Lundy, M. and Scow, K., 2023. Soil carbon storage and compositional responses of soil microbial communities under perennial grain IWG vs. annual wheat. Soil Biology and Biochemistry, p.109111.
Previous work comparing the perennial grain known as intermediate wheatgrass (trademarked Kernza) to annual wheat had not distinguished the extent to which soil health benefits are a function of the perennial nature of the crop. Read the story here.
This story was originally published on the UC Davis News site.
/h3>/h3>/h3>- Author: Michelle Leinfelder-Miles
- Author: Radomir Schmidt
The term ‘soil health' has become a common term in agricultural research and management. While most of us are familiar with testing soil for chemical properties, like nutrients, salinity, and pH, soil health also considers soil physical characteristics – like compaction, aggregation, and water infiltration – and biological characteristics – like soil respiration, active carbon, and nitrogen mineralization.
These properties influence the soil's ability to function, and enhancing these properties can improve soil functioning to grow crops and produce ecosystem services. We often relate soil health to management practices like crop rotation, cover cropping, reducing tillage, and adding compost because these have been shown to increase soil functioning in agricultural landscapes. They are also some of the practices that are financially incentivized by the CA Department of Food and Agriculture Healthy Soils Program.
There is a regulatory framework for diverting green waste from landfills to make compost. In 2014, AB 1826 was passed in California, which required businesses to recycle organic wastes and jurisdictions to set up organic waste recycling programs to divert green waste from landfills. In 2016, AB 1383 established organic waste reduction targets (75% reduction by 2025, compared to 2014). The bill also required jurisdictions to do education and outreach. Green waste diversion is expected to reduce greenhouse gas emissions by 4 million metric tons per year and increase food recovery by 20 percent. Agricultural land could serve to receive green waste compost recovered by this regulatory framework.
Our project objectives were to learn whether green waste compost improves soil nutrient status or other soil health characteristics, whether it improves alfalfa yield or quality, or if its application affects greenhouse gas emissions from the system. Alfalfa was chosen for this study because it has a large footprint on the state's agricultural landscape and because it has a high phosphorus (P) and potassium (K) nutrient need which compost could help supply. Also, as a ‘high-traffic' crop, alfalfa soils can have poor physical traits (e.g. compaction, water infiltration), which could potentially be ameliorated with compost.
The study was conducted on commercial farms in Yolo and San Joaquin (SJ) counties. The Yolo site had a mineral soil with high clay content (approximately 50 percent clay), and the SJ soil was a mucky clay with high organic matter (approximately 8 percent). We are comparing two green waste compost rates (3 and 6 tons per acre) to the untreated control. Compost applications were annually (2020-2022) surface-applied in the fall/winter ahead of rain.
Our preliminary results indicate no statistically significant differences in total carbon and nitrogen among treatments (Fig. 2). There is a trend, however, for compost to increase carbon at the Yolo site, which is inherently low in organic matter. An interesting observation about the SJ site, where the soil is inherently low in K, is that the compost increased soil K (statistically significant, Fig. 3). The compost analysis showed that the product was roughly 1 percent K. Therefore, the 3-ton compost rate should have added approximately 50 lb of K per acre, and the 6-ton rate approximately 100 lb of K per acre. Based on the amount of change in soil K and the compost analysis, the compost was likely what contributed to the increase in soil K. This appears to be translating into higher tissue K (Fig. 3), and in turn, higher yields (though neither tissue K nor yield are statistically higher than the control, Fig. 4).
Greenhouse gas emissions have not differed among treatments (Fig. 5), indicating that the carbon that is added by the compost is not being respired from the system. There are higher CO2 emissions at the SJ compared to the Yolo site, which we attribute to the inherently higher carbon of the SJ soil. Additionally, we have observed that the soil acts as a methane sink. This is noteworthy because methane is a more potent greenhouse gas than CO2.
Based on our experiences working on this project, we have the following guidance for growers interested in applying green waste compost. While green waste compost is a relatively cheap input, transport cost can be high. In 2021, we estimated that material plus hauling cost was approximately $27/ton and spreading was an additional $10/ton. The highest demand for compost is in the fall. To ensure availability, growers should aim to purchase compost in the spring or summer and store it on-site until fall. Ordering the compost in spring or summer also tends to result in a higher quality product delivered (i.e. less trashy). Timing compost application can be a challenge (i.e. after all harvests but before soil gets too wet), so having the compost already on-site may help in getting it applied more readily. We still have more data to analyzed for this project, so more information will be forthcoming. We want to thank the growers in Yolo and San Joaquin counties for collaborating with us on this project.
- Author: Linda Carloni
What are cover crops?
Cover crops are plants used for improving soil in the off-season. These are frequently called green manure to emphasize their multiple benefits to the soil. Using cover crops is actually an ancient technique; references to them are found in Chinese manuscripts from 3,000 years ago and as well as in Greek and Roman writings.
Benefits of cover crops
- Improve the physical properties of the soil, helping it form a crumbly structure.
- Increase the soil's organic material. This helps feed the soil microbes that improve the soil, and keeps nutrients from washing out of the soil, releasing them slowly instead.
- Protect the soil surface, keeping it from blowing or washing away.
- Improve water retention, water infiltration and drainage.
- Break up compacted soil and hardpan. (Legumes like vetches, clovers and beans, mustards and annual grasses are great at this!)
- Provide habitat and food for beneficial insects.
- Allow for an increase in earthworm populations, if the soil is left undisturbed for 5 to 7 months.
- Legumes increase nitrogen in the soil available for plants can use.Kinds of cover crops
Type of cover crops
Winter cover crops can be divided into three types, commonly used together:
- Legumes - commonly vetches, clovers, beans (bell or fava). Legumes actually add nitrogen to the soil. Legume roots are symbiotically associated with root-zone (rhizobial) bacteria. These bacterial threads enter the plant through the root hairs, multiply, enter the main part of the roots and then rupture. The bacteria then can enter the root cells, which enlarge into nodules. In these nodules, the bacteria can grab nitrogen from air in the soil and convert it into a form plants can use (ammonium). This is commonly called “fixing” nitrogen. In return, the legume gives the bacteria carbohydrates, protein, and oxygen. When the top of the cover crop is cut, the nodules remain in the soil and release their nitrogen, which is then available for uptake by plants. Legumes also have large tap roots that can break up the soil.
- Annual grasses - commonly barley, oats, cereal rye. These are sometimes considered “nurse” plants. They germinate fast and provide cover and soil-holding while the slower legumes start up. Grasses provide soil organic matter even as they grow because they commonly slough off dying roots and grow new ones. Because they have a lot of biomass above ground, they also provide a lot of carbon material when cut down.
- Miscellaneous - mustards (white, brown, black and field), phacelia, radishes such as daikon. Mustard leaves gather and store existing nitrogen from the soil, keeping it from washing out, and contribute it back in usable form when worked back into the soil. Legumes do this as well, in addition to their “fixing” capabilities described above. Keeping nutrients in the top layer of soil is particularly a problem in sandy soil.
Cover crops by function
Adding organic material to soil |
Annual grasses like barley, oats or rye, which provide a lot of carbon material. Daikon radish also produces a lot of biomass. |
Increase nitrogen |
Legumes (esp. vetch, clover and bell beans). Fava beans work well too, but their seeds tend to be more expensive. |
Breaking up compacted soil and hardpan |
Plants with large or deep roots such as daikon radish, chicory, mustards and legumes. |
Holding nutrients in the soil so they don't leach out |
Mustards, radishes and legumes. |
Protecting the soil from erosion and suppressing weeds |
Grasses, mustard, and radish. |
Attracting beneficial insects |
Mustards and radish, which may unfortunately also attract undesirable insects such as cucumber beetles and stink bugs. |
Chart adapted from UC Master Gardeners of Marin County, https://marinmg.ucanr.edu/EDIBLES/COVERCROPSETC/
- Mixes. Many gardeners use a blend designed for use as a soil-building cover crop. Blends generally have legumes for adding nitrogen and annual grasses to produce lots of biomass to add to the soil. Other species may be useful as well for particular needs, as outlined in the table above. Something that flowers (maybe a clover?) is a nice addition.
Planting
- In Alameda County, cover crops can be seeded in late September to mid-November. Spreading a light but even sprinkling of seeds should be sufficient. The goal is to get at least 8 to 10 cover plants per square foot.
- Not much soil prep is needed. The easy first step: take the existing plants off the surface and irrigate well. After a few days, scatter the cover crop seeds on the surface then rake them in well with quick short strokes in one direction to cover them with soil. Use a rake with rigid tines, not a leaf rake. Mulch with straw or leaves, water well again, and it's planted. (Note: never use diseased or infested leaves as mulch; put them in your green bin for municipal composting.)
- Until it starts to rain, provide irrigation. After the rains start, check periodically to make sure the crop is growing and not wilting. Some irrigation may be needed throughout the winter if it's very dry.
Cutting down and incorporating into the soil
- Cover crops in Alameda County may be cut down between late February and early April.
- There are two schools of thought on the time to cut down the crop. For a quick result, cut the cover crop down when it first begins to flower, the plant matter will still be succulent and the crop will decompose quickly to provide nitrogen to the soil. If you have time, for additional benefit you can wait to cut down until half to full bloom and the crop will add also additional organic matter to the soil. This technique is better for gradually improving soil that needs help, but you may not be able to replant as soon.
- Whenever a legume crop is cut, it is important to keep the root material in the ground. Just remove the tops. This will disturb the plant enough that the nodules on the roots of the legumes slough off within three days to a week. This releases the nitrogen in the nodules into the soil. When the soil is dug to plant, it's easy to pick out any nodule-less root materials that have not decomposed.
- There are two techniques for getting the cut plant materials back into the soil. The first is to chop them up and immediately dig them into the soil. If the beds are large, this can mean a lot of digging. At least three to five weeks are then needed for the plant material to decompose enough for replanting. The alternative is to take the cut plant tops, chop them up and put them into a compost pile with a source of carbon (dead leaves, straw, etc.) When the compost is ready, return it back to the cover crop bed. How long it takes to make the compost depends on many factors. Composting in a Hurry. Composting Basics. If you want to replant immediately, you can instead add compost that you have purchased or made previously.
- When you aren't growing anything, the bed should be mulched, not left bare. Compost, non-diseased and non-infested leaves (green or brown), straw, and arborist-sourced wood chips are excellent mulches for this.
Using cover crops to improve the soil in your veggie plot takes a minimum of work while both the gardener and the soil rest and rejuvenate through our rainy season.
Resources:
- Comprehensive resource for home gardeners and the principal source for this post: Choosing and Using Cover Crops in the Home Garden and Orchard, Center for Agroecology and Sustainable Food Systems (CASFS)
- Great summary of benefits and drawbacks of cover crops from the UC Marin County Master Gardeners
- Cover crop information from UCANR SAREP (Center for Sustainable Agriculture Research and Education Program)
- Information on Tansy Phacelia, which has been used widely in Europe as a cover crop, but can attract problematic pests in California, particularly the Lygus bug, a hard-to-control pest of strawberries, tomatoes and other crops.
Alameda County Master Gardeners Help Desk:
This blog post is brought to you by the Help Desk of the Master Gardeners of Alameda County.
Have a gardening question? We'll help. You can reach us by:
- Emailing acmg@ucanr.edu. Please include a photo of the problem, if you can, plus your name, phone number, and city and a description of the problem.
- Using our online form: https://surveys.ucanr.edu/survey.cfm?surveynumber=16371
By phone, during our office hours, 10am to noon Wednesday and noon to 2pm Thursday: 510-670-5645. At other times, please leave a message and we'll return your call during our office hours - In person at our Hayward office, during our office hours, only by appointment.
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