- Author: Anne Schellman
Do I need to test my garden soil?
The short answer is, “no.” Although many gardening magazines and websites advise gardeners to “test” their soil, it's unnecessary unless you suspect a major problem such as lead contamination or excess salts.
For a list of soil laboratories located in Stanislaus, Merced, Fresno, and Merced Counties, visit https://cemerced.ucanr.edu/ClimateSmartAg/HSP/SoilTest/Soil_Testing_Laboratories_in_Fresno_Madera_Merced_and_Stanislaus_Counties/
I think I have bad soil; nothing grows! What should I do?
The most common reason gardeners have trouble with soil is compaction, which results in poor drainage. This is often caused by compaction from heavy machinery or foot traffic. To improve soil, Master Gardeners recommend adding 4-6” of compost and mixing it into the soil. This is best done when soil is not wet. Since compost is an organic material that breaks down, continue to add it each season.
I think there are diseases in my soil, what should I spray?
Should I add manure to my vegetable garden soil?
Manure is a great addition to prepare your soil for a vegetable garden. However, it's best to use composted manure and to incorporate it into the soil several weeks before you plant. If fresh manure is used, plants may turn yellow due to the high concentration of salts.
How often should I fertilize my fruit trees?
Fruit trees work hard to produce a crop and do benefit from applications of fruit tree fertilizer in spring. Always follow the instructions on the package and never apply more than is recommended.
Have a soil, fertilizer, or other question topic we didn't answer?
Our Master Gardeners are available on Wednesdays from 9:00 a.m. to noon in person or by phone (209) 525-6802. You can also drop off a sample during business hours and we will get back to you, or fill out this survey (you can also attach photos if needed):
http://ucanr.edu/ask/ucmgstanislaus A Master Gardener will get back to you within 5 days of your request.
UCCE Stanislaus County Master Gardeners
3800 Cornucopia Way Ste A
Modesto, CA 95358
If you live in another county in California, you can find your local Master Gardener program by using this link https://mg.ucanr.edu/FindUs/
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- Author: Lynn Wunderlich
Over the years as Farm Advisor here (gosh, 19 years this October) my job has changed in many ways with the times. Recently, I have answered more and more inquiries from those who own a parcel and are wondering about agricultural development or those who are looking to purchase. The foothills, it seems to me, are becoming impacted by a growing California population and those who may be priced out of other locations and seek a rural lifestyle.
But the "what can I grow?" question, as I call it, is more complicated to answer than some anticipate. The key is to not have any preconceived notions (this isn't the Valley nor is it the North Coast) and to be open to exploring the opportunities, and challenges, the foothill landscape offers. The foothills are kind of like Nebraska, whose new slogan is "Honestly, it's not for everyone" (true!)
The first step to evaluating a property's suitability for agricultural development is to understand the natural resources that parcel offers. The most important: soils, water, microclimate. Enter an amazing resource...the Natural Resource Conservation Service (NRCS) Web Soil Survey! I recently received word that after 12 (or more) years of work, the Calaveras and Tuolumne county soil series maps have been added to our NRCS database and included in the Web Soil Survey (WSS). Calaveras and Tuolumne had been the only 2 California counties for which the soils were not mapped previously. This work, led by our local Tuolumne county NRCS office headed by Theresa Kunch and her team of soil scientists, represents a wonderful resource for anyone interested in land, for any reason.
Last fall I asked Andrew Brown, NRCS Soil Scientist and one of the staff in the Sonora office, to help me explain local
Whenever I get the "what can I grow on my property?" question, I encourage the landowner to dig a soil pit to get a good look at their soils, BEFORE they plant. Soil depth, texture and percent rock (some of the foothill soils have alot of rocks!) all contribute to a soil's water holding capacity. Soil is, in some ways, a key to water, and water is a limiting factor in agricultural productivity. Understanding the soil will help greatly with planting decisions, such as spacing, rootstock, and soil amendments.
Take a look at the soil survey map available online, then go out and dig your pits. Using the WSS may not be easy the first time around, although there are excellent instructions (begin by defining your AOL "area of interest") on the web page. I also really like the UC Davis California Soil Web Resource app, created by our UCANR Toby O'Geen and his lab and is newly updated for use on a mobile phone or tablet. I just bookmarked it on my phone homepage, for easy access when I'm out in the field. Check it out!
- Author: Steven A. Tjosvold
Since a plant has a limited volume of soil to find and absorb nutrients, special attention has to be taken to make sure container soils have adequate nutrient concentrations through the entire crop cycle. Thus a supply of nutrients and other amendments must be added before planting and nutrients are applied either as a liquid feed or slow release form of nutrients to meet crop demand Two of the most important chemical properties of soils that can affect the pre-plant and feeding regimes will be considered here: pH and the cation exchange capacity (C.E.C).
Many container soils contain a large proportion of organic components, for example peat, bark, or coir. Organic components have unique chemical properties that express themselves when they sit in the soil solution, and these properties affect pH and C.E.C. Fig 1.
The acidity—the H+-- of organic amendments derives from carboxyl groups attached to long chain polymers. In water, these carboxyl groups dissociate to make a weak acid. Roots are sensitive to low pH, and many nutrients are not absorbed by plants at low pH values. Fig 2.
Thus, the pH must be raised to achieve satisfactory growth. This is most easily accomplished by replacing H+ with Ca2+. Since calcium is required for plant growth, too, this is a particularly favorable solution to the problem. Pre-plant amendments of calcium in the form of lime (CaCO3) or dolomitic- lime are added. Fig 3.
Both clay particles and organic matter have negative surface charges (seen above in Fig 1) that attract cations (positively charged ions) such as potassium (K+), ammonium (NH4+), sodium (Na+), calcium (Ca++), and magnesium (Mg++) and therefore act as a reservoir for holding these nutrients. The electrostatic interaction between cations and negatively charged particle surfaces such as soil particles is called cation exchange capacity (C.E.C.). C.E.C is used to quantify the reservoir of cations that can be held by soils. High C.E.C. soils can hold a large reservoir of nutrients and could be fertilized less often than a soil with low C.E.C.
In general, cation exchange capacity is related to particle size—the smaller the soil particle, the greater the cation exchange capacity. This is because of the large surface to volume ratio of smaller particles; the increased surface area increases the binding possibilities. Here are examples of common organic components and their C.E.C. values. Even coir or peat cannot be relied on to hold enough nutrients to finish a typical nursery crop, so liquid feed or slow release fertilizers are still necessary. Fig 4.
Inorganic components have limited impact on C.E.C. and pH. Fig 5.Calcined clay's modest C.E.C. can be explained by its fine pores and increased surface area. Rockwool was one of the first products used exclusively in soil-less culture of greenhouse roses and tomatoes in the 1980's. With its negligible C.E.C. , feeding at nearly every irrigation was very important. The other inorganic components also have negligible C.E.C. and are primarily used to increase air-filled porosity of a soil mix.
Next: Soil components and their properties
Figures and tables adapted from: Management of Container Media by Richard Evans, UC Davis, for the class, ENH 120.
- Author: Steven A. Tjosvold
In the last post, I showed that irrigation should occur when half of the available water in the container is used. That amount of water is what evaporated from the soil surface and the plant extracted (transpiration), collectively called evapotranspiration (ET). You might think that the total ET accumulated from the last irrigation would also be how much water is needed to fill the soil completely back up with water. In some way it is like your car's fuel tank, the volume of available water is analogous to the capacity of the fuel tank. You're supposed to refuel when the fuel tank is half full, and at that point you fill it up with a half of a tank. That's where the analogy ends though. Actually some adjustments are still needed, especially when applying this to the entire irrigated crop. More water than a “half a tank” needs to be applied to compensate for the salinity in the irrigation water and the inefficiency of the irrigation system. First, let's look at the salinity component.
The concentration of salts in the soil solution is a result of the added fertilizer nutrients and the salts in the raw irrigation water. Salinity in solutions are measured by how well they pass an electrical current, the electrical conductivity (E.C.). Many of the ions, from added fertilizer salts, such as ammonium, nitrate, and potassium will be absorbed in large part by the plant. But not all will be absorbed. These ions and others are mostly selectively taken up by the plant and not just drawn into the plant passively with the water pulled in by transpiration. Many of the other salts are taken up at low rates or excluded all together. As a result, the concentration of these salts may accumulate, that is, if there is no leaching. Fig 1.
Salt accumulation in the soil is ameliorated by leaching, which is applying enough water so that some water drains from the pot. The leaching fraction can tell us how much extra water to apply. It is the ratio of the volume of water leached (the water that runs out of the bottom of a pot) to the volume of water applied (the total amount of water applied to a pot). The proper leaching fraction depends on the E.C. of the irrigation water applied (E.C.A) and the E.C.- sensitivity of the crop . Most crops tolerate a leachate EC (E.C. L ) of 6 dS/m to 9dS/m while salt sensitive crops tolerate 3 dS/m. So, recommended leaching fractions are given in the table below. In the middle of the ranges, you can see that the leaching fractions are in the 0.2 to 0.25 range, which means, in this case, that about another 20 or 25% water needs to be added to the water applied to the crop. (The exact amount is explained in the handout). Fig 2.
Surveys of nursery practices indicate that most commercial growers leach excessively. Although this prevents salt accumulation in container media, excessive leaching wastes water and fertilizer and may contaminate groundwater or surface water.
Irrigation systems are imperfect. Some sprinklers or emitters put out more water than average and others apply less than average. To meet the needs of plants that receive less than average amounts of water, growers must supply excessive amounts to other plants. Measuring the uniformity of irrigation systems gives growers two important pieces of information. It provides a measure of how good the system is. In many cases, there are simple steps that can be taken to increase uniformity (for instance, using better nozzles, repairing leaks, and eliminating sources of large pressure drops). Second, the measured irrigation uniformity gives growers a way to decide how much more water needs to be applied to compensate for the inefficient system. Irrigation systems can be evaluated in the field, and an efficiency value can be determined called the distribution uniformity (D.U.). (Measuring D.U. is explained in the handout). Drip irrigation systems are usually very efficient, usually with a D.U. of around 0.9 (A D.U. of 1.0 is perfect). Sprinkler systems are less efficient, with a D.U. between 0.4 and 0.9, and hand watering efficiency is usually unpredictable but usually is not efficient. Fig 3.
In conclusion, the total amount of water that needs to be applied to a crop is equal to the total evapotranspiration since the last irrigation plus the extra water needed to compensate for the salinity in the irrigation water and the lack of uniformity of the irrigation system. Fig 4.
Attached is a really nice article from Richard Evans that gives some examples to increase your understanding of irrigation efficiency, water quality and their impact on the total amount of irrigation water applied.
Next: Container Soil Chemical Properties
Handout