- Author: Sonia Rios
The University of California Cooperative Extension is hosting free workshops for citrus grove owners, managers and farmers. The workshop will provide an overview of proper Asian citrus psyllid (ACP) scouting techniques from University of California research entomologists Dr. Monique Rivera. Attendees will have the opportunity to practice psyllid scouting techniques in blocks of trees known to host ACP.
- No cost to attend this event
- Strongly encouraged to bring a hand lens (a loaner hand lens will be provided if needed).
- 1.5 of “other” DPR Continuing Education Hours will be given.
- Further details on workshop location will be provided to registrants by email 48 hours prior to the event.
Space is limited, please register at: http://ucanr.edu/survey/survey.cfm?surveynumber=25658
October 2, 2018, 9-11 AM
If you have any questions, please contact:
951-683-6491 EXT 224
The latest Topics in Subtropics quarterly is out. Check it out. And subscribe for further editions. And check out the archive of past editions.
Topics in Subtropics
The U.C. Cooperative Extension Farm Advisors have combined to publish this quarterly combined newsletter. It will emphasize citrus and avocado, but will also discuss the minor subtropicals.
|Volume 17, Summer 2018 (763KB)||
TOPICS IN THIS ISSUE
One good idea from a meeting can make all the difference of whether that was a meeting worth going to or not. One idea, that's all it takes to make a big difference back at the ranch. A lot of times the good idea comes from the people you meet there. Sometimes it comes from the speaker's presentation. Sometimes the idea comes to you while processing something you've just heard.
Whatever. I just went to a meeting organized by the Ventlecura County Farm Bureau where there were several speakers and numerous vendors. Lots of good ideas popped up on nutrients and water management. The practices were for the general grower audience, not specifically for citrus or strawberry growers. Meetings can often be focused on a given crop like the CA Avocado Society or Index Fresh avocado meetings. That doesn't mean a lemon or a flower grower couldn't learn from avocado practices. They can. Cross fertilization is good. And this Farm Bureau meeting was a good meeting.
Coming up October 4 and 5, is the annual CA Avocado Society meeting. This starts off with a field tours on the first day, then settles down to a lecture room style on Friday. This should be a good chance to meet other growers, see some interesting field practices and hear some good talks. It will be a good meeting.
Reno, NV (Sept 10, 2018): Scientists from the Western Regional Climate Center (WRCC) at the Desert Research Institute (DRI) in Reno, Nev. are pleased to announce the release of a long-awaited update to a climate mapping tool called the California Climate Tracker.
"One really significant change between the old and new versions of the California Climate Tracker is that in the previous version, you weren't able to look at archived maps," said Daniel McEvoy, Ph.D., Assistant Research Professor of Climatology at DRI and member of the Climate Tracker project team. "Now you can say for example, 'I want to see what the 1934 drought looked like,' and go back and get the actual maps and data from 1934. You can also look at graphs of the data and see trends in temperature and precipitation over time."
In addition to providing historical and modern data for regions across California, this easy-to-use web-based tool can be used to produce publication-quality graphics for reports, articles, presentations or other needs. It can be accessed for free by anyone with a standard web browser and an internet connection.
"The California Climate Tracker was initially designed and developed for use by the California Department of Water Resources, but we hope it is also useful to a much broader community of water managers, climatologists, meteorologists and researchers in California," McEvoy said.
Low-severity wildland fires and prescribed burns have long been presumed by scientists and resource managers to be harmless to soils, but this may not be the case, new research shows.
According to two new studies by a team from the University of California, Merced (UCM) and the Desert Research Institute (DRI), low-severity burns - in which fire moves quickly and soil temperature does not exceed 250oC (482oF) - cause damage to soil structure and organic matter in ways that are not immediately apparent after a fire.
"When you have a high-severity fire, you burn off the organic matter from the soil and the impact is immediate," said Teamrat Ghezzehei, Ph.D., principal investigator of the two studies and Associate Professor of Environmental Soil Physics at UCM. "In a low-severity fire, the organic matter doesn't burn off, and there is no visible destruction right away. But the burning weakens the soil structure, and unless you come back at a later time and carefully look at the soil, you wouldn't notice the damage."
DRI researcher Markus Berli, Ph.D., Associate Research Professor of Environmental Science, became interested in studying this phenomenon while visiting a burned area near Ely, Nev. in 2009, where he made the unexpected observation that a prescribed, low-severity fire had resulted in soil structure damage in the burned area. He and several colleagues from DRI conducted a follow-up study on another controlled burn in the area, and found that soil structure that appeared to be fine immediately after a fire but deteriorated over the weeks and months that followed. Berli then teamed up with Ghezzehei and a team from UCM that included graduate student Mathew Jian, and Associate Professor Asmeret Asefaw Berhe, Ph.D., to further investigate.
Soil consists of large and small mineral particles (gravel, sand, silt, and clay) which are bound together by organic matter, water and other materials to form aggregates. When soil aggregates are exposed to severe fires, the organic matter burns, altering the physical structure of the soil and increasing the risk of erosion in burned areas. In low-severity burn areas where organic matter doesn't experience significant losses, the team wondered if the soil structure was being degraded by another process, such as by the boiling of water held within soil aggregates?
In a study published in AGU Geophysical Research Letters in May 2018, the UCM-DRI team investigated this question, using soil samples from an unburned forest area in Mariposa County, Calif. and from unburned shrubland in Clark County, Nev. to analyze the impacts of low-severity fires on soil structure. They heated soil aggregates to temperatures that simulated the conditions of a low-severity fire (175oC/347oF) over a 15-minute period, then looked for changes in the soil's internal pore pressure and tensile strength (the force required to pull the aggregate apart).
During the experiment, they observed that pore pressure within the soil aggregates rose to a peak as water boiled and vaporized, then dropped as the bonds in the soil aggregates broke and vapor escaped. Tensile strength measurements showed that the wetter soil aggregates had been weakened more than drier soil samples during this process.
"Our results show that the heat produced by low-severity fires is actually enough to do damage to soil structure, and that the damage is worse if the soils are wet," Berli explained. "This is important information for resource managers because it implies that prescribed burns and other fires that occur during wetter times of year may be more harmful to soils than fires that occur during dry times."Next, the research team wondered what the impact of this structural degradation was on the organic matter that the soil structure normally protects. Soil organic matter consists primarily of microbes and decomposing plant tissue, and contributes to the overall stability and water-holding capacity of soils.
In a second study that was published in Frontiers in Environmental Science in late July, the UCM-DRI research team conducted simulated burn experiments to weaken the structure of the soil aggregates, and tested the soils for changes in quality and quantity of several types of organic matter over a 70-day period.
They found that heating of soils led to the release of organic carbon into the atmosphere as CO2 during the weeks and months after the fire, and again found that the highest levels of degradation occurred in soils that were moist. This loss of organic carbon is important for several reasons, Ghezzehei explained.
"The loss of organic matter from soil to the atmosphere directly contributes to climate change, because that carbon is released as CO2," Ghezzehei said. "Organic matter that is lost due to fires is also the most important reserve of nutrients for soil micro-organisms, and it is the glue that holds soil aggregates together. Once you lose the structure, there are a lot of other things that happen. For example, infiltration becomes slower, you get more runoff, you have erosion."
Although the research team's findings showed several detrimental effects of fire on soils, low-severity wildfires and prescribed burns are known to benefit ecosystems in other ways -- recycling nutrients back into the soil and getting rid of overgrown vegetation, for example. It is not yet clear whether the negative impacts on soil associated with these low-severity fires outweigh the positives, Berli says, but the team hopes that their research results will help to inform land managers as they manage wildfires and plan prescribed burns.
"There is very little fuel in arid and semi-arid areas, and thus fires tend to be short lived and relatively low in peak temperature," Ghezzehei said. "In contrast to the hot fires and that burn for days and weeks that we see in the news, these seem to be benign and we usually treat them as such. Our work shows that low-severity fires are not as harmless as they may appear."
The study, "Soil Structural Degradation During Low?Severity Burns," was published on May 31, 2018 in the journal AGU Geophysical Research Letters and is available here: https:/
The study, "Vulnerability of Physically Protected Soil Organic Carbon to Loss Under Low Severity Fires," was published July 19, 2018 in the journal Frontiers in Environmental Science, and is available here: https:/