- (Public Value) UCANR: Promoting economic prosperity in California
Alli Rowe-Fish and Ben Faber
Cover crops offer an important opportunity to build soil health in avocado orchards. A cover crop is a crop seeded or encouraged as natural plant cover as an investment in soil fertility and not as a cash crop. Most cover crops are grasses, legumes, brassicas or a mixture and serve to protect bare soil while improving soil physical, chemical, and biological properties.
Benefits of cover crops
Perennial systems, trees in the ground for long periods of time, are unable to harness the benefits of crop rotation that include improved nutrient cycling, soil tilth, soil physical properties, weed and pest suppression, and erosion control. By cycling cover crops, growers of tree crops can mimic crop rotation on a portion of the land surface and maximize benefits in an orchard system.
The benefits of cover crops in California avocado orchards include:
- Improved soil structure;
- Reduced soil compaction;
- Reduced soil erosion from wind and rain;
- Increased soil organic matter content;
- Improved nutrient cycling;
- Weed suppression;
- Creation of habitat for pollinators and beneficial insects;
- Improved water infiltration
- Improved soil moisture storage
- Increased soil aeration
- Disease suppression.
California will continue to experience increased intensity and duration of drought and heat stress days. These environmental conditions dramatically impact fruit set and viable production of avocados. Improving soil health builds resiliency to climatic conditions and allows farmers to continue to grow in the face of climate change. A specific consideration is improved water infiltration achieved by cover cropping in orchards. The enhancement in soil structure due to the presence of varying depths of roots allows for precipitation to infiltrate rather than run off. By keeping precious precipitation on the orchard property, growers become more resilient in the face of drought and heat. Improved infiltration by rain water can improve salt leaching and reduce salt stress on the tree.
Selecting a cover crop
The main consideration in selecting a cover crop is to identify the purpose and objectives for its use. Table 1 identifies specific goals and considerations for cover cropping. Most avocado growers in California will opt for a winter cover crop to harness winter rains to avoid irrigating. Therefore, the following selections are geared towards winter cover crops and do not go into detail for summer cover cropping.
Cover crop mixes may be more expensive than single species covers such as only a brome or a medic, but satisfy multiple purposes in one planting and often see successful establishment and growth rates. They may provide better cover, weed suppression, and biomass, especially during drought or other non-optimal growing conditions. In addition, mixes supply multiple nutrients and benefits beyond a single species. For example, a mix that includes triticale, faba bean, and daikon radish sees the benefit of soil stabilization and infiltration from all three species, increased carbon content from the triticale, nitrogen fixation from the faba bean, and reduced soil compaction from the radish.
In selecting a cover crop, it is critical to consider any pests that may be encouraged with certain species. For example, many avocado growers are constantly battling gophers in young orchards. Gophers love clover varieties, so if you already have more gophers than you can handle, consider choosing a cover crop mix that does not contain clovers. There does not appear to be an increase of ground squirrel activity with covers (https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1020&context=vpc17).
Table 1. Cover Crop Categories and Considerations
Seeding timing
The timing of cover crop seeding will vary based on location and operational goals. However, flexibility is key for getting cover crops seeded at the right time to maximize winter rainfall for good establishment. Many cover crop seed companies will recommend seeding in fall, October or November. In Central and Southern California, that time frame tends to be hot, dry, and windy – not ideal conditions to seed a cover crop. The best time to seed would be right after the first rains come to loosen the soil and provide a bit of moisture. The key to success lies in watching the weather and being able to jump on a window between early rain events.
Frost can be a consideration for many avocado growers in Central and Southern California. Early establishment of tall cover crops can increase risk of frost exposure and should be avoided. To get around frost issues, seeding later in the fall and early winter can delay growth of the cover crop until the frost prone days have passed. This may mean seeding in early January to ensure minimal growth during January and February when frost may be a concern. As the weather warms in March, cover crops can take off and build biomass without posing a risk to tree health.
Termination strategies
Winter cover crops are generally terminated nearing the last rainfall events so they do not compete with trees for irrigation water. Termination strategies vary based on type of cover crop and availability of equipment. Cover crops can be terminated by mowing, tillage/disking, grazing, or simply allowing them to dry up if they are low growing. Leaving cover crop residue on the surface protects the soil from wind erosion, acts as a natural mulch to suppress weed seedlings, and releases nutrients to the soil as it decomposes. The downside to leaving residue on the surface is the retention of moisture which could provide habitat for slugs and snails. Incorporating cover crop residue immediately after termination speeds up the decomposition time, increasing nutrient release into the soil. This should only be considered in young or=chards where root damage would not occur due to incorporation. This, however, requires the right equipment and relatively flat terrain, which is not representative of most California avocado operations. Grazing is an effective termination strategy to remove high biomass cover crops. However, it is important to consider GAP and NOP food safety regulations by ensuring animals are not in the orchard within 90 days of harvest.
Triticale and Lamb Hass
- Author: Ben Faber
The avocado lace bug (Pseudacysta perseae, family Tingidae) occurs in the Caribbean, French Guyana, Mexico, and southeastern United States. As of 2006, in California it occurs only in San Diego County. Also known as the camphor lace bug, this pest feeds on certain plants in the family Lauraceae. Hosts are the avocado fruit tree (Persea americana), other Persea species such as red bay (P. borbonia), and camphor tree (Cinnamomum camphora), which is grown as a landscape ornamental and commercially for its aromatic extracts.
Recently, Dr. Mark Hoddle from UC Riverside presented an update on the bug and its potential for spread in California. Hoddle is a biocontrol specialist who has done extensive work on this pest, as well as many other pests that afflict plants in this state. Here him:
And while you are at, you might check out the numerous other videos on file at UC IPM's "Ask The Ag Experts" website.
photo: Avocado lace bug, Pseudacysta perseae, adults, nymphs, and eggs under black excrement.
Photo by David Rosen.
- Author: Ben Faber
The redbay ambrosia beetle, Xyleborus glabratus, and its fungal symbiont, Raffaelea lauricola (Rl), were introduced into Port Wentworth, Georgia, USA, in infested wood packing material from Asia during 2002. This insect-disease complex, commonly called laurel wilt (LW), affects trees in the Lauraceae family and spreads through natural areas by redbay ambrosia beetle movement and anthropogenic movement of infested wood products (e.g., firewood, wood-turners wood, and BBQ smoke-wood). Plant hosts of the redbay ambrosia beetle-Rl complex include at least ten native lauraceous woody species (e.g., redbay [Persea borbonia] and swamp- bay [P. palustris]) in Florida, as well as non-native species such as camphor (Cinnamomum camphora), avocado (P. americana), and potentially California bay (Umbellularia californica). By February 2010, redbay ambrosia beetles were detected in a natural area 21 miles (33.7 km) north of the south Florida avocado production area (125 sq. miles; 324 sq. km) in Miami-Dade County. In 2011, the first confirmed swampbay tree to succumb to LW was documented in this natural area, and by 2012 LW was detected in a commercial avocado grove in Homestead, Florida.
Now everything we know about this disease that affects avocados and other laurel relatives is at one website - articles, videos, webinars, maps. Check it out: https://trec.ifas.ufl.edu/faculty/dr-crane-lw-ab-website/lw-ab/
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- Author: Ben Faber
For quite some time, farmers and researchers have been focusing on how to bind carbon to soil. Doing so makes food crops more nutritious and increases yields.
However, because carbon is converted into CO2 when it enters the atmosphere, there is a significant climate benefit to capturing carbon in soil as well.
Too much carbon finds its way into the atmosphere. Should we fail to reverse this unfortunate trend, we will fail to achieve the Paris Agreement's goal of reducing greenhouse gas emissions by 40 percent by 2030, according to CONCITO, Denmark's Green Think Tank.
As such, it is important to find new ways of sequestering carbon in soil. This is where a team of researchers from the University of Copenhagen and the Technical University of Munich enter the picture.
In their new study, they argue for the potential of simply allowing agricultural crop residues to rot in fields.
"Fragments of dead plants in soil are often considered as fast food for microbes and fungi. But our study demonstrates that plant residues actually play a more significant role in forming and sequestering carbon in soil than what was once thought," explains Kristina Witzgall, a PhD Candidate at the Technical University of Munich and the study's lead author.
In the past, researchers mainly focused on carbon storage in the surfaces of minerals like clay. However, the new results demonstrate that plant residues themselves have the ability to store carbon, and perhaps for longer than once supposed.
This is because a number of important processes take place directly upon the surface of these plant remains.
"We demonstrate that agricultural crop residues are absolutely central to carbon storage and that we should use them in a much more calculated way in the future. Plant residues make it possible for carbon, in all likelihood, to be stored in soil for roughly four times longer than if they aren't added," states Carsten Müller, the study's co-author and an associate professor at the University of Copenhagen's Department of Geosciences and Natural Resource Management.
Fungi and soil clumps store carbon
To understand how plant residue sequesters carbon, it is important to know that plant tissue already contains carbon absorbed by plants from the atmosphere via photosynthesis. As plant matter rots, carbon can be transferred into the soil in a number of ways.
"Our analysis shows that plant residues, as they interact with fungi, play a surprisingly large role in carbon storage. As fungi fling their white strands around plant fragments, they 'glue' them together with the soil. The fungi then consume the carbon found in the plant matter. In doing so, they store carbon in the soil," explains Carsten Müller.
In addition to fungi, the researchers' analyses also show that the soil structure itself determines the amount of carbon that can be stored.
"When soil is glued together in large hard lumps by the stickiness of bacteria and fungi, plant residues are shielded from being consumed by bacteria and fungi, which would otherwise eat and then emit some of the carbon as CO2 into the atmosphere," says Kristina Witzgall.
She goes on to say that while carbon can be stored in soil from weeks to a thousand years, the usual duration is about 50 years.
Reducing CO2 in the future
The method of leaving crop residues like stalks, stubble and leaves to rot is not unheard of when it comes to enhancing agricultural land.
However, deploying rotten plants as a tool to store carbon should be taken more seriously and considered as a strategy to be expanded, according to the researchers behind the new study.
"The fertile and climate-friendly agricultural lands of the future should use crop residue as a way of sequestering carbon. We will also be conducting experiments where we add rotten plant matter deeper into the soil, which will allow carbon to be stored for even longer periods of time," says Carsten Müller.
If we work to create better conditions for carbon sequestration in soil, we could store between 0.8 and 1.5 gigatonnes of carbon annually. By comparison, the world's population has emitted 4.9 gigatonnes of carbon per year over the past 10 years.
All in all, the researchers' findings can be used to understand the important role and promise of crop residues for carbon storage in the future.
However, Kristina Witzgall goes on to say that a variety of initiatives are needed to increase carbon sequestration, such as crops that can absorb atmospheric carbon and the restoration of lost forests.
Read the whole story: https://www.nature.com/articles/s41467-021-24192-8
Images:
Scanning electron microscopy (SEM) images of the interface of plant litter (POM) and soil minerals, where soil minerals are (a) attached to the litter surface (scale bar = 100 µm) and (b) enmeshed with fungal hyphae and extracellular polymeric substances (EPS; scale bar = 10 µm). Similar images were obtained from at least 10 independent locations in each soil texture.
- Author: Ben Faber
1 to 20 of 47,867 Full-Text results on Avocado
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47,867 full text articles and books on avocado. The digital world brings more avocado information to you. In the case of avocado, 47,867 citations with full text. You want links to loquat? Same thing, but only 20,379 citations. This is what you get when you go to the HathiTrust Digital Library. This is a collaboration among a lot of different academic institutions to make these obscure, but still valuable sources of information available to all.
Check it out. It's not just fruit trees, but gobs of other publications on a range of topics
A bibliography on the avocado (Persea americana Miller)
Published
1950
Author
Condit, Ira J. b. 1883.
A bibliography on the avocado (Persea americana Miller) [by] Ira J. Condit
Published
1939
Author
Condit, Ira J. b. 1883.
Between separation and integration : the avocado sector in California and Mexico, 1911-2011 / by Maria Michaela Burke Gould
Published
2011
Author
Gould, Maria Michaela Burke.
How to-- : Calavo avocado recipes
Published
1969
Leaflet University of California, Division of Agricultural Sciences no.2251 1975
Published
1975
Annual report of the California Avocado Association for the year .. 1915-1916
Published
1916
Author
California Avocado Association.
Annual report of the California Avocado Association for the year .. 1917-1919
Published
1919
Author
California Avocado Association.
Bulletin - University of Florida, Agricultural Experiment Stations no. 605A
Published
Author
University of Florida. Agricultural Experiment Station.
Annual report of the California Avocado Association for the year .. 1915-1920
Published
1920
Author
California Avocado Association.
The avocado : its insect enemies and how to combat them G.F. Moznette
Published
1922
Author
Moznette, G. F. 1890-
Yearbook of the California Avocado Society for the year ... 1917
Published
1917
Author
California Avocado Society.
The avocado : its insect enemies and how to combat them G.F. Moznette v.1261(1922)
Published
1922
Author
Moznette, G. F. 1890-
Special report on maturity standards for avocados.
Published
1958
Author
California. Legislature. Joint Committee on Agriculture and Livestock Problems.
Farmers' bulletin c.1 no.1261
Published
Author
United States. Department of Agriculture.
Yearbook of the California Avocado Society for the year ... 1916
Published
1916
Author
California Avocado Society.
The California avocado industry / Robert W. Hodgson
Published
1930
Author
Hodgson, Robert W. 1893-1966.
[Records and briefs of the United States Supreme Court]. flo
Published
Avocado diseases George A. Zentmyer ... [et al.].
Published
1965
Annual report of the California Avocado Association for the year .. 1920-21
Published
1921
Author
California Avocado Association.
Avocado pests / Walter Ebeling, Roy J. Pence
Published
1953
Author
Ebeling, Walter, 1907-
