- Author: Ben Faber
For centuries, the prevailing science has indicated that all of the nitrogen on Earth available to plants comes from the atmosphere. But a study from the University of California, Davis, indicates that more than a quarter comes from Earth's bedrock.
The study, to be published April 6 in the journal Science, found that up to 26 percent of the nitrogen in natural ecosystems is sourced from rocks, with the remaining fraction from the atmosphere.
Before this study, the input of this nitrogen to the global land system was unknown. The discovery could greatly improve climate change projections, which rely on understanding the carbon cycle. This newly identified source of nitrogen could also feed the carbon cycle on land, allowing ecosystems to pull more emissions out of the atmosphere, the authors said.
"Our study shows that nitrogen weathering is a globally significant source of nutrition to soils and ecosystems worldwide," said co-lead author Ben Houlton, a professor in the UC Davis Department of Land, Air and Water Resources and director of the UC Davis Muir Institute. "This runs counter the centuries-long paradigm that has laid the foundation for the environmental sciences. We think that this nitrogen may allow forests and grasslands to sequester more fossil fuel CO2 emissions than previously thought."
WEATHERING IS KEY
Ecosystems need nitrogen and other nutrients to absorb carbon dioxide pollution, and there is a limited amount of it available from plants and soils. If a large amount of nitrogen comes from rocks, it helps explain how natural ecosystems like boreal forests are capable of taking up high levels of carbon dioxide.
But not just any rock can leach nitrogen. Rock nitrogen availability is determined by weathering, which can be physical, such as through tectonic movement, or chemical, such as when minerals react with rainwater.
That's primarily why rock nitrogen weathering varies across regions and landscapes. The study said that large areas of Africa are devoid of nitrogen-rich bedrock while northern latitudes have some of the highest levels of rock nitrogen weathering. Mountainous regions like the Himalayas and Andes are estimated to be significant sources of rock nitrogen weathering, similar to those regions' importance to global weathering rates and climate. Grasslands, tundra, deserts and woodlands also experience sizable rates of rock nitrogen weathering.
GEOLOGY AND CARBON SEQUESTRATION
Mapping nutrient profiles in rocks to their potential for carbon uptake could help drive conservation considerations. Areas with higher levels of rock nitrogen weathering may be able to sequester more carbon.
"Geology might have a huge control over which systems can take up carbon dioxide and which ones don't," Houlton said. "When thinking about carbon sequestration, the geology of the planet can help guide our decisions about what we're conserving."
MYSTERIOUS GAP
The work also elucidates the "case of the missing nitrogen." For decades, scientists have recognized that more nitrogen accumulates in soils and plants than can be explained by the atmosphere alone, but they could not pinpoint what was missing.
"We show that the paradox of nitrogen is written in stone," said co-leading author Scott Morford, a UC Davis graduate student at the time of the study. "There's enough nitrogen in the rocks, and it breaks down fast enough to explain the cases where there has been this mysterious gap."
In previous work, the research team analyzed samples of ancient rock collected from the Klamath Mountains of Northern California to find that the rocks and surrounding trees there held large amounts of nitrogen. With the current study, the authors built on that work, analyzing the planet's nitrogen balance, geochemical proxies and building a spatial nitrogen weathering model to assess rock nitrogen availability on a global scale.
The researchers say the work does not hold immediate implications for farmers and gardeners, who greatly rely on nitrogen in natural and synthetic forms to grow food. Past work has indicated that some background nitrate in groundwater can be traced back to rock sources, but further research is needed to better understand how much.
REWRITING TEXTBOOKS
"These results are going to require rewriting the textbooks," said Kendra McLauchlan, program director in the National Science Foundation's Division of Environmental Biology, which co-funded the research. "While there were hints that plants could use rock-derived nitrogen, this discovery shatters the paradigm that the ultimate source of available nitrogen is the atmosphere. Nitrogen is both the most important limiting nutrient on Earth and a dangerous pollutant, so it is important to understand the natural controls on its supply and demand. Humanity currently depends on atmospheric nitrogen to produce enough fertilizer to maintain world food supply. A discovery of this magnitude will open up a new era of research on this essential nutrient."
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UC Davis Professor Randy Dahlgren in the Department of Land, Air and Water Resources co-authored the study.
The study was funded by the National Science Foundation's Division of Earth Sciences and its Division of Environmental Biology, as well as the Andrew W. Mellon Foundation.
Photo: The stuff that makes leaves green
- Author: Roger Baldwin, Ryan Meinerz, Gary Witmer and Scott Werner
Baldwin and Meinerz are UC Davis and Witmer and Werner are USDA/APHIA/Wildlife Services-National Wildlife Research Center
Voles are short, stocky rodents that often cause extensive girdling damage to a variety of tree and vine crops throughout California. Vole management is often quite challenging given how numerous they can be in a given area. In more recent years, effective management has often relied on some combination of vegetation removal, exclusion using trunk protectors, and rodenticide application. Vegetation removal is a great tool for reducing numbers in a field, but doesn't always eliminate all problems in an area. Plus, vole population size tends to ebb and flow from low to high densities; when densities are high, vegetation removal is often insufficient to reduce girdling damage.
Exclusion through the use of trunk protectors can be a good way to reduce girdling damage as well. However, trunk protectors should be buried at least 6 inches below ground to keep voles from tunneling underneath the protectors. This substantially increases the amount of labor required to protect trees and vines. Ultimately, this approach is only cost effective if high levels of damage are anticipated.
Rodenticide applications are also frequently used to knock down vole populations. However, rodenticide applications are generally not allowable within an orchard or vineyard during the growing season, thereby eliminating the use of one of the most effective vole management tools when it is most needed. Clearly there is room for a new tool to be added to the proverbial IPM toolbox when it comes to managing voles in orchard and vine crops.
Chemical repellents are one such tool that could be considered. Historically, repellents have not proven overly effective for field application against voles. However, recent laboratory testing of anthraquinone indicated that even low concentrations of this chemical were effective at reducing grain consumption by voles. Furthermore, anthraquinone has proven effective as a bird repellent. Anthraquinone is a post-ingestive product that causes animals that consume the product to become ill, thereby making it less likely that the animal will consume the product again during a subsequent feeding event. This kind of repellent is ideally suited for trunk application given that the repellent can easily be applied to the portion likely to be consumed by the vole. If effective, minimal girdling damage should be observed. A repellent application also has the added advantage in that it can easily be paired with vegetation management to hopefully further reduce girdling damage when compared to using either one of these approaches alone. Therefore, we set up a study to test the potential impact that a combination of vegetation management and anthraquinone applications would have on girdling damage by voles to young citrus trees. We also tested the longevity of anthraquinone to determine if long-term repellency following field application was likely. We tested this impact during both spring (characterized by a cool-wet weather pattern) and summer (characterized by a hot-dry weather pattern) seasons to determine if weather impacted potential girdling damage.
We found that anthraquinone was in fact highly repellent following trunk application, with a >90% reduction in girdling damage observed following application regardless of the season when it was applied. Anthraquinone exhibited substantial longevity, with no increase in girdling damage observed for the entire summer (5 weeks) and spring (6 weeks) sampling periods. This clearly indicates substantial repellency for anthraquinone applications, with repellency to last for at least two months, and likely for much longer given that we observed no upward trend at all in girdling damage at the end of our study period.
When combined with anthraquinone treatments, the removal of vegetation completely eliminated all girdling damage during summer. However, we did not observe this same collective impact during spring. That said, the inclusion of vegetation management with anthraquinone applications is likely warranted given our understanding of the need for multiple management strategies to maintain the long-term effectiveness of rodent management programs.
These results clearly indicate effective repellency of voles following anthraquinone applications, but at this time, anthraquinone is not registered for use against any mammalian species. We are hoping to gauge the interest of growers for the registration of this repellent against voles in orchard and vine crops. This is where we need your help. We have developed a very short survey (will take less than 3 minutes to complete) to gauge this interest. Please take this very quick survey to assist in this effort:
- Author: Ben Faber
The California Avocado Commission is pleased to announce the availability of ProGibb LV Plus Plant Growth Regulator Solution (gibberellic acid) for use on avocados in California under a Special Local Needs (SLN) registration effective March 27, 2018. ProGibb has been shown to effectively increase fruit size and set when applied at the cauliflower stage of bloom.
ProGibb LV Plus can be applied from the ground or by air. Ground applications should be made by mixing 12.5 fluid ounces of product in 100 gallons of water per acre. Aerial applications should be made by mixing 12.5 fluid ounces of product in 75 gallons of water per acre. Only one (1) application is allowed per year.
The restricted entry interval (REI) is 4 hours, and the preharvest interval (PHI) is 0 days, so ProGibb LV Plus can be used with minimal disruption to harvesting and other grove management activities.
Please note:
- A copy of the SLN Label must be in the possession of the user at the time of application.
- The signature of the County Agricultural Commissioner or their designee must be obtained prior to the use of ProGibb LV Plus.
- This SLN is only valid for the ProGibb LV Plus product manufactured by Valent BioSciences Corporation. Generic gibberellic acid products may not be used under this SLN.
The California Avocado Commission wishes to thank Dr. Carol Lovatt, University of California Riverside, for her many years of dedicated research that made this registration possible. We also thank the many growers, PCAs, and pesticide applicators who participated in the research trials.
If you have any questions about this SLN registration and the use of ProGibb LV Plus, please consult with your local PCA or you may contact Tim Spann at tspann@avocado.org.
Photo: Cauliflower stage of flowerr
/span>- Author: Sonia Rios
The roof rat (Rattus rattus, also known as a citrus rat, fruit rat, black rat, or gray rat) is an introduced species of rat native to southern Asia. It was brought to America on the first ships to reach the New World. This is the same species that carried the bubonic plague around the world and is the reservoir host for murine typhus, which is a disease that is transmitted by fleas. This primarily nocturnal vertebrate is a pest in citrus, nut orchards and other tree crops. In citrus, it builds leaf and twig nests in trees or it can nest in debris piles, thick mulch pile on the ground, or in shallow burrows under the tree. In livestock feed yards and barns, roof rats often burrow and hide under feed bunks or in the hay bales. Adult roof rats range from 12-14 inches long (30-36cm) and weigh 5-10oz. (150-250g) (UC IPM 2017). The large, sleek rat has a pointed muzzle and hairless scale-covered tail that can be longer than the body and head combined.
DAMAGE
A rats gnawing can cause some serious damage to just about anything, electrical wires, wooden structures, and they tend to not be picky about which agriculture crop to invade. Roof rats often feed on citrus, avocados, and other fruits, sometimes leaving hollow fruit skins hanging on the tree. In tree crops, they can girdle limbs or stems, leading to mortality to part or all of a tree. After harvest, they damage fruit and nuts in bins by chewing them and leaving excrement. This can cause major esthetics damage to fruit and become a food safety issue. Since rats are active throughout the year, and mostly at night, this can be a challenge to growers and can become infestation because of their quick gestational period of 3 to 4 weeks.
MANAGEMENT
Cultural Control
Because roof rats are such good climbers, swimmers, and hitchhikers it is hard to completely exclude them from your grove or orchard. Fruit trees should be isolated, not touching fences, overhead wires, or the scaffolds or branches of other trees. Roof rats will run along fence stringer boards or support poles, phone and cable TV wires, and tree branches to reach your fruit tree. Lower branches of the tree should never touch the ground. Reducing shelter and nesting opportunity sites of rats is crucial. Eliminate debris and woodpiles and store materials neatly off the ground. Thin and separate non-crop vegetation around orchards, such as weeds and remove dead wood from fruit trees, especially in citrus and avocado (UC IPM 2017). A low-hanging skirt of drooping branches give the rats additional access routes and provides them with protective cover while feeding. It's best to prune tree skirts so that the ground under them is open and visible. This lack of cover makes the rats uncomfortable and more susceptible to predators such as snakes and birds of prey.
Sanitation is also an important component to an IPM program. Use or remove all fallen fruit, do not leave any fruit behind, as the roof rat is an opportunist and will take advantage of the mess left behind.
Monitoring and Treatment Decisions
According to the UC IPM guidelines, the use of elevated bait stations containing 0.005% diphacinone*-treated oats (sold at some county agricultural commissioner's offices) is highly effective at controlling roof rats in orchards. Secure bait in a bait station before placing in trees on limbs 6 feet or more above the ground. Placing the bait in a secure bait station will prevent bait from dropping to the ground and creating a hazard for non-target species. Bait can only be applied during the non-bearing season, so growers must take a proactive approach to managing problematic rat populations (UC IPM 2017).
Trapping
Rat-sized snap or wooden box traps placed in trees are also effective, although a more time-consuming control option. Do not use glue board traps outdoors, as birds, lizards, and other non-target wildlife may be trapped. Rats are wary, tending to avoid baits and traps for at least a few days after their initial placement. Fasten traps to limbs and bait them with fruit or nut meats, but do not set the traps until after bait is readily eaten. Be aware that certain types of rat baits for use inside buildings (such as sticky traps) are not labeled for use outdoors in orchards; these are hazardous to wildlife and should not be used.
Preventative care, sanitation and scouting for rat's nests or damage is the easiest way to stop a problem before it becomes a problem. For more information regarding the roof rat, please visit the UC IPM website: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74106.html.
Baiting *Be sure to identify the species of rat present to avoid killing non-target or protected species.*
- Author: Sonia Rios, Julie Pedraza and Ben Faber
Firefighters from all over the country worked around the clock to put out fires throughout the state of California. Fires could be devastating to growers and, in some ways, they could be beneficial by reducing populations of weeds and unwanted vegetation. However, after the loss of vegetation after a fire, growers have to prepare for the next possible disaster- mudslides, debris flow and flashfloods. Vegetation that once secured soil and gravel, preventing erosion on mountain and hill slopes is no longer there. Instead the waxy residue from burnt plant debris has formed into a baked waxy layer that prevents water from infiltrating more than a few inches into the soil, creating a water-proof surface layer. When a significant amount of rainfall occurs after a fire, it becomes an environment for a mudslide.
According to Randy Brooks, author of the article “After the Fires: Hydrophobic Soils,” during a fire, burning plants release gases from waxy plant substances that permeate through the soil pore space, coating soil particles with a hydrophobic substance, thus repelling water. Over time, the wax-like, hydrophobic layer that has formed a few inches below the soil could persist in repelling water causing damage years later. Orchard trees with shallow roots can be destroyed and/or develop weakened root systems if a mudslide occurs post-fire. As rain continues to fall, large chunks of topsoil can break loose and slide down sloped landscapes. In some cases, mud and debris can exceed 35 mph, causing massive damage and major mudslides.
Rapid moving mudslides can enter into infiltration basins, irrigation canals, and reservoirs moving silty-clay sand suspension sediment that could clog pumps and irrigation lines creating an expensive problem for growers.
Erosion in Orchards Post-Fire
Post-fire rains result in the transport of fertile soil particles into downstream waterways. These sediments can carry unwanted pesticides and nutrients that adhere to them. Erosion problems can include water pollution, loss of soil quality, increased flooding, impairment of stream ecosystems, decreased groundwater storage, release of carbon, slope failures, degradation of habitat and loss of species, damage to downstream lands and properties. Not to mention the amount of time and costs associated with addressing these issues.
Preventable Management Practices
Orchard floor management can include anything from the addition of soil amendments to changes in tillage practices. One way to minimize soil erosion is to implement management practices that improve soil structure. Soil structure is the arrangement of mineral particles into aggregates. A well-structured soil having stable aggregates can easily accommodate infiltrating water that decreases runoff and reduces erosion. In addition, stable aggregates resist particle detachment, prevent the formation of crusts, and are less susceptible to compaction. Light tillage where possible can break up the hydrophobic topsoil layer post-fire, followed by planting a cover crop, such as a grass or a forb can prevent soil erosion and be a moderate barrier in the event of a mudslide.
Mature avocado groves have high soil organic matter (SOM) due to leaf mulch and fine rootlets that die and decompose in the shallow soils. Soil organic matter promotes good soil aggregation and stable aggregates. The form of SOM that binds soil particles together into aggregates is called humus, which consists of highly decomposed organic material. Humus results from the breakdown of mulches, roots and any amended organic materials like compost or other supplemental mulches.
Periodic application of organic materials is a proven method for improving the water-infiltration capacity of certain soils: those that suffer from weak structure due to low organic matter content.
In many situations it is neither practical nor feasible to add soil amendments as an erosion control practice. Cover crops are an excellent alternative to reduce soil erosion. They protect the soil from raindrop impact, prevent the formation of surface crusts, increase infiltration rates, and intercept sediment-rich runoff. Cover crops are also a great source of SOM. Critical aspects to consider are nutrient and water competition with crops, cost of additional water for irrigation, shade tolerance, crop height, and maintenance practices such as mowing.
Like most management practices, cover cropping has disadvantages, too. All cover crops use water, some are invasive, some serve as habitat for pests, some can increase the potential for frost damage, and they may be costly to establish.
Management practices are ever changing for prevention and protection of orchards every year especially against fire and mudslides. Being informed and assessing the situation post-fire adds value to how we can evaluate the cost of protecting orchards and economically prepare fields from mudslides damages.