- Author: Linda Chalker-Scott
- Author: Jim Downer
Washington State University and UCCE Ventura County, respectively
Healthy Soils Workshop
February 19, 9am – 11am
University of California Cooperative Extension Office
669 County Square Drive Suite 100
Ventura, CA 93003
CDFA's Healthy Soils Program is opening and will be accepting applications on a rolling basis. Join us to learn about exciting changes to the grant opportunity, how to apply, and how to get technical assistance for your grant.
This event is free and open to anyone interested in soil health practices. Please share with your networks! We are also putting together a field day to discuss healthy soils practices in early March.
To RSVP and save your spot please follow the linkhttp://ucanr.edu/survey/survey.cfm?surveynumber=29382
**If you cannot attend but want to learn more, please contact
technical assistance provider near you**
- Author: Linda Chalker-Scott
- Author: Jim Downer
Washington State University and UCCE - Ventura County, respectively
Horticultural myths, found extensively in print and online resources, are passed along by uninformed gardeners, nursery staff, and landscape professionals. Occasionally myths are so compelling that they make their way into Extension publications, used by Master Gardeners as educational resources. In this article we deconstruct seven widespread gardening myths by way of reviewing research-based literature. We also provide scientifically sound alternatives to these gardening practices and products. Our hope is to arm Extension educators with the educational resources necessary to battle misinformation that ranges from the merely useless to that which is actively damaging to soils, plants, and the surrounding environment.
Home gardeners and landscape professionals are a rapidly growing audience for extension educators as they seek science-based information to support their activities. However, many are not familiar with current research and cannot assess whether the information they find in print, on the internet, or through social media is accurate. In addition, some products and practices are meant for agricultural production, not for maintaining home gardens and landscapes. The combination of misinformation and misapplied information means that this audience risks damaging their plants and soils through overuse of fertilizers, misuse of pesticides, and poor management practices.
The field of urban horticulture, including arboriculture, is expanding with new insights about plants and soils in residential and public landscapes. However, there are few Extension educators who have an academic background in environmental horticulture and may be as confused as the public about what constitutes sound, science-based recommendations.
The authors of this article are state Cooperative Extension educators and researchers with many years of experience in translating science for use by home gardeners and landscape professionals. Our goal is to assist other Extension educators by providing reliable information for them to share with the gardening and landscaping public.
The purposes of this literature review article are:
- to identify some common beliefs homeowners and landscape professionals have about managing landscape plants and soils;
- to provide a brief, science-based explanation on why these beliefs are not accurate;
- to provide links to published, peer-reviewed information that supports the explanation and can be distributed to clientele; and
- to suggest strategies based on current and relevant applied plant and soil sciences for managed landscapes.
And here is the article:
Garden Myth Busting for Extension Educators: Reviewing the literture on Landscape Trees
- Author: Mark Battany
Published on: July 18, 2019
Irrigation frequency and volume
One fundamental decision that a grower needs to make is how frequently to irrigate a vineyard; either applying small amounts of water frequently, or larger amounts of water less frequently. This choice determines how large the soil "flower pot" is that supports the vines, while also having implications for nutrient availability, salinity conditions and potential limitations on water infiltration. Changing from frequent small irrigations to infrequent large irrigations, either as an ongoing practice or as a one-time event, may lead to unanticipated outcomes and thus should ideally be done after ensuring that the conditions are adequate for this practice. For this reason it can be beneficial to evaluate the soil and water quality conditions at a site before making large changes in irrigation practices. Factors to consider include the potential depth of the rootzone, the presence of any layers in the soil which may cause infiltration problems, the salinity of the irrigation water, and the potential nutrient conditions affected by changing the wetted soil volume.
Root zone depth
If applying a large volume of irrigation water, the soil needs to have the capacity to store this water while providing adequate porosity conditions allowing gas exchange for proper root function. The soil depth to bedrock needs to be considered; if this depth is shallow in areas of the vineyard, this can lead to poor performance with large irrigations if they result in ponded water above the bedrock or large variations in total available soil water due to varying soil depths.
Most of our vineyards are located on deeper alluvial soils where shallow bedrock is not a concern. For a given rooting depth, finer-textured soils with their relatively high water holding capacity can store more water and thus be irrigated with larger volumes less frequently, while coarse-textured soils with their lower water holding capacity generally need to be irrigated with smaller amounts more frequently. Grapevine roots can grow very deeply in the soil, more so if that is where available water is found; however a vine which has developed mostly shallow roots from a history of shallow irrigation may not be able to take advantage of recently applied deeper soil moisture until it has developed the roots to do so.
Less permeable layers
Common throughout the Central Coast are different types of low-permeability layers in soils which can impede the movement of water, resulting in ponding or saturated conditions above the restrictive layer with negative impacts on any roots in that zone. These less permeable layers may not have been been given much attention until well after a vineyard has been planted, for example when mature vines are observed to suffer stress in heavy rainfall years or with a change to longer duration irrigation in the summer. A thorough evaluation of a site prior to planting should include an assessment of the deeper soil conditions to identify any potential restrictions on the movement of water or penetration of roots. Sites which have such conditions that cannot be corrected are not good candidates for applying large volumes of irrigation water in the summer, if doing so results in water saturation of the active root zone.
Impermeable layers can exist due to a variety of physical and/or chemical conditions in the soil. A hardpan can be formed naturally in the soil due to the gradual compaction and cementing together of soil particles. Agricultural practices of using moldboard plows and heavy equipment can also create hardpan conditions.
A clay lens is a horizontal layer of clay in between soil layers; this clay can be an effective barrier to both water movement and root penetration. These clay lenses can occur below the depths which can be effectively corrected with tillage, leading to perched water tables which can be particularly troublesome by preventing deeper drainage.
Another type of textural barrier occurs in a stratified soil, when a fine-textured soil horizon overlies a coarse-textured horizon. Water does not flow downward out of the fine-textured horizon and into the coarse-textured horizon until the former is fully saturated with water. This may seem counter intuitive, because we generally associate coarse soils with good drainage; in reality this stratified condition results in water-logging of the fine soil layer when large amounts of irrigation are applied. With small volumes of irrigation this fine soil layer may be wetted enough to support the bulk of the vine roots; a subsequent change to a large volume of irrigation can saturate this same soil and negatively affect root function.
Figure 5. A stratified soil, with a finer textured layer overlying a coarser textured layer. The roots are all in the finer textured layer, because moisture rarely passes to the coarse texture below. A heavy irrigation will saturate the fine texture layer, impacting root function.
A less-permeable layer can also be due to variations in soil structure where the cation exchange capacity of the deeper soil is dominated by magnesium, while the surface horizon has more calcium, typically from the historic additions of lime or gypsum amendments. The greater calcium content of the surface horizon creates a more porous and stable soil structure that allows for good water penetration, whereas the higher magnesium content of the deeper soil results in a very dense, massive soil structure with much less ability to infiltrate water.
Chemical weathering of the soil can also form low-permeability layers over thousands of years. An example are the "calcic" (also known as "caliche") soil horizons which are formed by rainfall dissolving the naturally occurring lime in the upper soil horizons, which then moves downwards where it precipitates out of solution (becomes solid) again at a deeper depth. Because the precipitation of the lime occurs within the existing soil pores, this process gradually clogs these soil pores and creates a barrier to water movement and root penetration.
The above types of restrictive layers may exist in current vineyards, and they can be very difficult or impossible to alter with the vines in place. These restrictive layers are more effectively addressed during the vineyard development phase, when deeper tillage is possible. Some conditions such as the presence of highly stratified layers can be very difficult to correct and require the use of very large equipment, which will forever alter the natural state of the soil.
Figure 8. Tandem D8H crawlers pulling a large slip plow to thoroughly mix a stratified soil near Santa Maria. The result has been described as a "blended" terroir. Photo by Frank Laemmlen, retired Farm Advisor.
Such extensive deep tillage may not be desirable or feasible for a variety of practical and philosophical reasons; in that case the irrigation management needs to be adapted to the presence of these soil barriers to water movement. Lighter, more frequent irrigation can avoid problems due to deeper restrictive layers. Alternatively, applying irrigation more broadly by increasing the number of emitters per vine (two 1/2 gph emitters instead of one 1 gph emitter for example) can increase the wetted soil volume while avoiding the potential deeper problem layers if applied volumes remain small. A heavy summer irrigation which results in the extended saturation of the soil horizon containing the most active roots can result in vine collapse and death, but the same soil conditions during the winter will not impact the vines in the same manner; thus applying large irrigations to soils during the winter to increase their water storage can be more successful than during the summer when roots are active and the vine root water uptake is at its maximum. This type of winter irrigation is more useful in dry regions where rainfall is limited, and may not be suitable for areas that receive heavier precipitation.
Soil salinity considerations
Another factor to consider when determining the irrigation frequency is the potential for soil salinity to impact vine growth. Groundwater quality throughout the Central Coast is highly variable; sites with relatively poor-quality irrigation water, particularly those having rootstocks susceptible to salinity, need to take this into consideration when choosing their irrigation frequency. To understand why, consider this example: after applying irrigation, assume that the electrical conductivity of the soil water is the same as the irrigation water. As the soil water is consumed by root uptake and evaporation, the volume of soil water is reduced but most of the salts remain behind in the soil water. As a result, the concentration of salts in the remaining soil water gradually increases as the volume of soil water decreases. This adds an additional stress on the vines, an osmotic stress, which reduces the vine's ability to take up the remaining soil moisture. We can minimize this osmotic stress by increasing the frequency of irrigation, which ensures that at least a small volume of the soil is maintained at a higher water content and therefore a lower salinity level. With higher frequency irrigation, the vines won't experience the same degree of increasing salinity stress towards the end of the irrigation cycle as they would between large, infrequent irrigations. This characteristic of high-frequency drip irrigation to maintain a lower osmotic stress is what has permitted successful crop production where conventional irrigation would not be feasible due to the poor quality irrigation water.
The choice of whether we are growing the vines in a "big pot" or a "small pot" has important implications for nutrient management as well. When a larger volume of soil is wetted with irrigation, this can increase the total amount of soil nutrients which are available to the vines; this can be good or bad, depending upon the situation.
As the soil dries out over the summer and early fall, the most active roots will be in the volume of soil wetted by irrigation. If this soil volume does not contain sufficient nutrients, then deficiencies can occur. A common example is potassium; it can exist in adequate quantities in the drier soil outside the wetted volume but is not readily available to the roots under these dry soil conditions. This is an example of an induced deficiency, where the nutrient is present, but conditions do not permit its uptake by the vine. This condition is typically addressed by fertilizing with the nutrient in the wetted soil volume, generally by fertigation. Increasing the wetted soil volume can allow the vines to access nutrients which previously were not as accessible such as the potassium example above. It may also increase the availability of other nutrients, for example nitrogen which had leached below an earlier shallow root zone. An increased level of available nitrogen may lead to excessive vegetative growth, thus these deeper nutrient levels may need to be evaluated before increasing the soil wetted volume.
Figure 10. A raisin grape vineyard in Argentina with excessive nitrogen fertilizer; the resulting extremely dense canopy had almost no light penetration and very little ventilation, resulting in a total crop loss due to powdery mildew. This image was taken during the daytime.
Prior to making major changes in the irrigation frequency and amounts at a site, the soil and rooting conditions should be evaluated to predict whether or not such changes might have any negative effects on the growth of the vines. The factors involved are relatively straightforward but can be difficult to evaluate due to the need to dig deeply in the soil, and often at multiple locations if there is much variability at the site. Making this effort can help predict what types of changes may occur due to alternations in the irrigation patterns, and help identify situations beforehand that could result in undesired outcomes.
Videos of water movement in soils
Water Movement in Soils, a classic 1959 video produced by Washington State University has some excellent demonstrations of how water moves in soils; some key examples:
A coarse soil layer underlying a fine soil layer:
A clay layer (which will behave similarly to a hardpan layer or a strong calcic horizon):
A more recent video from the University of Arizona has similar demonstrations of water movement in stratified soils:
A historical perspective on hardpan soils
For a history of local farmers dealing with hardpan soils on the Central Coast a century ago, see the earlier blog article: The rise (and demise) of the UC Experiment Station at Paso Robles
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.