- Author: Ben Faber
The more different the root architecture, the greater potential to store more carbon
The greater the diversity of the rooting network, the greater diversity of pores
It's not just the biomass that stores the carbon, it's the diversity of the pores
So plant a greater diversity of plants to increase stored soil carbon
EAST LANSING, Mich. -- Alexandra Kravchenko, Michigan State University professor in the Department of Plant, Soil and Microbial Sciences, and several of her colleagues recently discovered a new mechanism determining how carbon is stored in soils that could improve the climate resilience of cropping systems and also reduce their carbon footprints.
The findings, published last week in the scientific journal Nature Communications, reveal the importance of soil pore structure for stimulating soil carbon accumulation and protection.
"Understanding how carbon is stored in soils is important for thinking about solutions for climate change," said Phil Robertson, University Distinguished Professor of Plant, Soil and Microbial Sciences, and a co-author of the study. "It's also pretty important for ways to think about soil fertility and therefore, crop production."
The study was conducted through the MSU Great Lakes Bioenergy Research Center, funded by the U.S. Department of Energy, and the Kellogg Biological Station Long-term Ecological Research program funded by the National Science Foundation, or NSF, and it was supported by NSF's Division of Earth Sciences.
Over a period of nine years, researchers studied five different cropping systems in a replicated field experiment in southwest Michigan. Of the five cropping systems, only the two with high plant diversity resulted in higher levels of soil carbon. Kravchenko and her colleagues used X-ray micro-tomography and micro-scale enzyme mapping to show how pore structures affect microbial activity and carbon protection in these systems, and how plant diversity then impacts the development of soil pores conducive to greater carbon storage.
John Schade, from the NSF Division of Environmental Biology, said the results may transform the understanding of how carbon and climate can interact in plant and soil microbial communities.
"This is a clear demonstration of a unique mechanism by which biological communities can alter the environment, with fundamental consequences for carbon cycling," Schade said.
"One thing that scientists always tend to assume is that the places where the new carbon enters the soil are also the places where it is processed by microbes and is subsequently stored and protected," Kravchenko said. "What we have found is that in order to be protected, the carbon has to move; it cannot be protected in the same place where it enters."
Scientists have traditionally believed soil aggregates, clusters of soil particles, were the principal locations for stable carbon storage.
Recent evidence, however, shows that most stable carbon appears to be the result of microbes producing organic compounds that are then adsorbed onto soil mineral particles. The research further reveals that soil pores created by root systems provide an ideal habitat where this can occur.
Of particular importance are soils from ecosystems with higher plant diversity. Soils from restored prairie ecosystems, with many different plant species, had many more pores of the right size for stable carbon storage than did a pure stand of switchgrass.
"What we found in native prairie, probably because of all the interactions between the roots of diverse species, is that the entire soil matrix is covered with a network of pores," Kravchenko said. "Thus, the distance between the locations where the carbon input occurs, and the mineral surfaces on which it can be protected is very short.
"So, a lot of carbon is being gained by the soil. In monoculture switchgrass the pore network was much weaker, so the microbial metabolites had a much longer way to travel to the protective mineral surfaces," explained Kravchenko.
Robertson said the research may prompt farmers to focus on plant diversity when attempting to increase soil carbon storage.
"We used to think the main way to put more carbon in soil is to have plants produce more biomass either as roots or as residue left on the soil surface to decompose," Robertson said.
"What this research points out is that there are smarter ways of storing carbon than such brute force approaches. If we can design or breed crops with rooting characteristics that favor this kind of soil porosity and therefore that favor soil carbon stabilization, that would be a pretty smart way to design systems that can build carbon faster."
Nick Haddad, director of the Kellogg Biological Station Long-term Ecological Research program, said research that builds from these findings will continue to discover ways to improve the sustainability of agricultural ecosystems and landscapes.
"Long-term research shows surprising ways that a diversity of plants can benefit the microbes needed for a resilient agricultural system," Haddad added.
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- Author: Ben Faber
WASHINGTON, June 26, 2019 – USDA's Natural Resources Conservation Service (NRCS) and the University of California at Davis Soil Resource Laboratory today announced the release of the iOS and Android SoilWeb app, version 2.0. The app now has a cleaner and more modern interface with GPS-location-based links to access detailed digital soil survey data (SSURGO) published by the NRCS for most of the United States. The newly updated SoilWeb smartphone application is available as a free download on Google Play and Apple App Store .
“SoilWeb reached a new milestone this year when it was integrated with Google Maps and designed to scale across any device, desktop, tablet or smart phone,” said NRCS Chief Matthew Lohr. “SoilWeb app is a portable interface to authoritative digital soil survey data from NRCS, giving users access to practical detailed scientific soil information on the go.”
The SoilWeb app provides users with information relating to soil types that are associated with their location. The images are then linked to information about the different types of soil profiles, soil taxonomy, land classification, hydraulic and erosion ratings and soil suitability ratings. Identifying soil types is important to understanding land for agricultural production purposes and determining flooding frequencies and suitable locations for roads or septic tanks. SoilWeb provides gardeners, landscapers and realtors with information relating to soil types and how to optimally use the soil. Although soil survey information can be used for general farm, local, and wider area planning, a professional onsite evaluation may be needed to supplement this information in some cases.
“SoilWeb is a great way to understand the landscape you live in,” said Anthony O'Geen, UC Davis Professor and Cooperative Extension Specialist in the Department of Land, Air and Water Resources. “Producing food, constructing structures and maintaining landscapes all depend on this little understood, but critical outermost layer of the earth's crust, the soil.”
The app gives access to valuable scientific data through modern technology. All the soil information in SoilWeb was collected from the National Cooperative Soil Survey, organized by the NRCS, and accesses soil survey information the agency has been collecting since the 1890s. The resulting database, the largest such in the world, makes it possible for soil scientists to generate specialized maps using computer-aided techniques.
O'Geen developed SoilWeb with NRCS Soil Scientist Dylan Beaudette, in 2010 when Beaudette was a Ph.D. student at UC Davis. The app was a popular download, but by 2017 was no longer in compliance with requirements set by Apple and Google. Frequent users of SoilWeb had to rely on the web-based version from 2017 to June 2019. Any users with the older version on their phone can do a simple update to access the newest version. The app is a product of a 14-year partnership between NRCS and UC Davis College of Land, Air and Water Resources.
- Author: Ben Faber
- Author: Elizabeth Grafton-Cardwell
- Author: Barbara Alonso
The summer issue of Citrograph has just been released, and our outreach project has been featured. Written by Sara García-Figuera, the article discusses our approach for educating citrus stakeholders, researchers, media and the general public about the nationwide technologies being developed to combat the devastating citrus disease – huanglongbing (HLB). Read more about all the tools available to growers and the general public at http://www.citrusresearch.org/uncategorized/citrograph-summer-2019/#more-8369 (pages 28-30)
/span>- Author: Ben Faber
Nick Sakovich, Emeritus Farm Advisor
Dry Root Rot has menaced growers in Ventura County for many years. In the ‘50's and ‘60's it seemed most prevalent on older orange trees. A few years after the wet winter of 1968-69, dry root rot became an increasing problem among citrus trees of all ages. At that time, most of the damaged trees were on sweet rootstock (susceptible to Phytophthora), and growing in fine-textured soils or soils with poor drainage. A few years after another wet winter/spring (of 1983), dry root rot again reared its ugly head, but this time predominately on young lemons.
The disease is caused by the fungus, Fusarium solani. This fungus is most likely present in all citrus soils in California. It is a weak pathogen in that by itself it will not attack a healthy tree. However, experiments conducted in the early 1980's by Dr. Gary Bender, showed that when seedlings were girdled, root invasion occurred. In the field, the fungus can infect trees once gophers have girdled the roots or crown. A Phytophthora infection will also predispose trees to Fusarium, as will asphyxiation. Therefore, the mere presence of the fungus in the orchard soil will not lead to the disease.
Description
Fusarium is a soil borne fungus that invades the root system. Once infected, the entire root will turn reddish-purple to grayish-black. This is in contrast to a Phytophthora infection which, in many cases, will attack only the feeder roots, but when larger roots are infected, only the inner bark is decayed and it does not discolor the wood. In addition, when observing the cross section of a dry root rot infected trunk, a grayishbrown discoloration in the wood tissue can be observed.
Dry root rot is a root disease, but symptoms of the root decline are seen above ground. They are similar to any of the root and crown disorders such as Phytophthora root rot, oak root rot fungus (Armillaria) and gophers. The trees lack vigor, leaves begin to turn yellow and eventually drop (especially in hot weather) causing twig dieback. Finally, the foliage will become so sparse that one will be able to see through the canopy of the tree. A period of two to three years may pass from the time of invasion until noticeable wilt. Many times, the tree will collapse in the summer, after a period of prolonged heat. In the case of dry root rot, the collapse is so rapid that the tree dies with all the leaves still on the tree. When looking for symptoms of dry root rot, keep an eye out for symptoms of other maladies as well — Phytophthora, oak root rot fungus and gophers being the most prevalent.
As mentioned previously, in order for Fusarium to infect a tree, there must be a predisposing factor such as girdling from gopher feeding. However, since many trees collapse from dry root rot without any apparent predisposing factor, there are obviously other factors which we have yet to identify. Therefore, in 1998, a grower survey was developed, along with intensive soil and leaf sampling, to attempt to identify as many new predisposing factors as possible. They might be elements in the soil, either deficiencies or excesses, or specific cultural practices such as irrigation patterns or fertilizer practices. Twenty orchards were identified from which 20 soil and 20 leaf samples were taken in diseased areas and another 20 soil and 20 leaf samples were taken from adjacent healthy areas. The owners or managers of the properties were given a questionnaire to complete regarding a variety of cultural operations. The objective was to identify those factors that would correlate well to trees becoming infected with dry root rot.
Survey Results
Soil analysis - The following laboratory procedures were conducted to see if there was any correlation between the disease and either deficiencies or toxicities of these elements or
conditions: sodium, boron, salt level, pH and soil type (sand, loam, clay). For these elements or conditions, no correlation was found. It would appear that for our sampling sites, these conditions, whether favorable or not (toxic or deficient), did not play a major role in predisposing the tree to dry root rot.
Leaf analysis - The following elements were analyzed for their concentration within the leaf: nitrogen, potassium, phosphate, manganese, magnesium and zinc. Of these, three correlations were found. Zinc and manganese levels were substantially higher in diseased trees. The third correlation showed a potassium deficiency in diseased trees. However, we do not believe that dry root rot is caused by elevated levels of zinc or manganese, or by potassium deficiency, but rather are a result of the disease. Unfortunately, it seems that we have still not identified any elements in leaf analysis that truly correlates and points to a predisposing factor for disease development.
Grower survey - The grower survey included questions on planting site (location, wind, previous crop, fumigation etc.), trees (source, type, rootstock, etc.), and cultural practices (irrigation, fertilization, gophers, history of Phytophthora, water quality, etc). Through statistical analysis it was found that the healthy and diseased sites were significantly different with reference to three conditions or situations: 1.) The presence of Phytophthora in an orchard will increase the chance of those trees succumbing to dry root rot. 2.) Orchards that have been fumigated have a less likely chance of succumbing to dry root rot. 3.) Balled vs. Container Plants -- growers were asked if their trees were balled or container
grown nursery plants. Healthy sites were significantly more likely to have been planted with balled trees (73% vs 33%). The results of this analysis were not strong, but rather they
suggest that there is a relationship between the disease and the type of tree planted - balled or container grown - and suggesting in favor of a balled tree for a healthy orchard.
Control Measures – What Works and What Does Not
Early experiments conducted by Menge, Ohr and Sakovich showed that the following circumstances or operations do not influence the incidence of this disease: fungicidal treatments, wounding the tap root at time of planting, sandy versus clay textured soils, spring versus fall planting and soil mounding.
- In choosing your nursery tree, the choice of rootstock is not important in that, as far as we know, all rootstocks are susceptible to this disease. However, since Phytophthora is a major component in dry root rot development, choosing a rootstock like sweet orange would certainly put those trees in a high risk category. We recommend that growers use Phytophthora resistant rootstocks like C35 or Citrumelo.
- According to the survey, it would be advantageous to fumigate before planting. Methyl bromide, although expensive, is the best fumigant as it is a complete biocide. If one chooses not to fumigate, the alternative would be a number of fungicide/nematicide applications to the newly planted trees. Generally speaking, this may work well with trees planted on a rootstock like Citrumelo or C35.
Phytophthora. Publications written in the 1970's, and again noted by our survey, showed that Phytophthora is a major culprit in the dry root rot complex. To control dry root rot, it is essential that the Phytophthora, when present, be controlled. This can be accomplished by fungicidal treatments, and by the proper application and timing of irrigation water. Overwatering creates a favorable environment for the multiplication of the Phytophthora fungus.
Gophers. It is well known that gopher damage provides entry points for Fusarium. Controlling gophers is an important factor in reducing the potential of infection by Fusarium.
Control
We presently have no direct control for dry root rot. To control the disease, we must control the predisposing factors such as gophers, Phytophthora, poor drainage and over-watering. If the predisposing factor(s) cannot be identified for a given diseased orchard, it will indeed be difficult to control the disease. Two things are certain though: 1.) There are no chemicals to date which will control this disease; and 2.) Presently, there are no rootstocks resistant to the disease.
Hear the latest on DRR with Akif Eskalen – a Webinar, July 24
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30658
- Author: Ben Faber
Newly Improved Thrips Key
The online Lucid Key, Thrips of California (https://keys.lucidcentral.org/keys/v3/thrips_of_california/Thrips_of_California.html), that identifies native and pest thrips resident in California, along with potentially invasive species not yet present in California, has been updated.
The revised version, Thysanoptera Californica (https://keys.lucidcentral.org/keys/v3/thrips_of_california_2019/), has been produced to overcome technical problems arising from Java software and to incorporate new information and images, together with some additional potentially invasive thrips species. Information pages are provided to 300 thrips species in 108 genera, with the identification system discriminating 249 species. Of these species, 40 are as yet unrecorded in California but are potential invaders, whether interstate or from overseas.
Remember, if you have one or many of these insects, there is always an "s" at the end of their name. One thrips is a thrips, three thrips are thrips.