David Doll3 CommentsOctober 18, 2015Salinity

Salinity Management for Fine Textured Soils

AUTHORS NOTE: The following article discusses salinity management considerations for FINE TEXTURED SOILS (e.g. loams, silts, and clays). This is a follow-up to the previous article, “Salinity Management for Sandy Soils.” For the most part, this article describes issues with the WEST SIDE of the San Joaquin Valley. NOT ALL SOILS ARE THE SAME. Please note that the following guidelines may need site-specific adjustments. Starting with the soil, we often use the term cation exchange capacity (CEC), which is the amount of cations (positively-charged ions like sodium, magnesium, calcium, potassium, etc.) that can bind to the soil particle surface. In fine textured soils across the State, CEC values can be very high, with values ranging between 15-40 meq/100 g of soil. Generally, sandy loams are in the teens through 20s, and silts and clays are in the 30s to 40s. This CEC value is important as it indicates the amount of cations the soil particles can hold. The higher the CEC, the more cations that stick to the soil, preventing them from entering the soil water (soil water is the amount of water that is held between soil particles – it is what the tree drinks), reducing salt exposure to the roots of the tree. Regardless of the CEC, once the soil is saturated with cations, the excess will stay within the soil water. As soil salinity increases, the tree’s roots salt exposure is increased. High soil salinity affects the osmotic movement of water, and this impacts the tree roots’ uptake of water (e.g. essentially making the tree work harder for water), leading to eventual toxicity. Salt toxicities within fine textured soils can vary based on the element involved. Chloride toxicity can occur rapidly, showing up within a year or two when applying poor quality water. This is due to chloride being an anion, and due

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Allan Fulton2 CommentsSeptember 21, 2015Soil

Understanding and Applying Information from a Soil Test, Part 3: Secondary Plant Nutrients: Calcium (Ca), Magnesium (Mg), and Sulfur (S)

Written by Allan Fulton, Farm Advisor, Tehama County and Roland D. Meyer, Extension Soils Specialist Emeritus This article (Part 3) discusses the use of soil tests to evaluate levels of the secondary nutrients calcium (Ca), Magnesium (Mg), and sulfur (S) in orchard soils.  It is a follow up to a series of articles on intrpretation of soil sampling results. These nutrients are considered secondary because while they are essential to crop development, seasonal crop uptake is usually lower than for the primary nutrients N, P, and K but considerably higher than the micronutrients zinc (Zn), iron (Fe), Manganese (Mn), copper (Cu), boron (B), and chloride (Cl). Calcium and Magnesium Plant uptake, cation adsorption and desorption in soil, leaching from rainfall and irrigation, and weathering of minerals all contribute to the concentration of water soluble Ca and Mg available to meet tree nutritional needs.  Water soluble cations are determined from the saturated paste extract soil test procedure while the exchangeable cations are determined with the ammonium acetate procedure.  Also important are the concentrations of exchangeable (non-water soluble) Ca and Mg which help to promote favorable soil structure.  Soil chemistry is in a constant state of change attempting to reach equilibrium between the soluble and non-soluble (exchangeable and mineral) phases.  The May 2009 newsletter discussed this dynamic process.  Calcium and magnesium share similar chemical properties in soils.  Both Ca and Mg are “double positively charged (divalent) cations in the soil-water phase and on soil cation exchange sites.  Calcium is adsorbed to soil exchange sites preferentially and more strongly than Mg.  When Ca and Mg are abundant in the soluble phase tree roots absorb these nutrients by mass flow.  If Ca and/or Mg are less abundant or limited by soil moisture, uptake occurs more slowly through diffusion. Table 1 provides ranges of exchangeable

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David Doll6 CommentsSeptember 29, 2014Salinity, Soil

Fall soil sampling for salinity management

The harvest season is winding down, and in the next few weeks many orchards will be receiving their last irrigations. After the final irrigation of the season, growers should conduct soil sampling to determine any potential issues with sodium, chloride, or boron. These salts are “imported” onto the farm through fertilizers and soil amendments, with the largest amount coming through irrigation water. There are several videos online that go through the procedure of collecting a soil sample. Here is a link to an article containing this series. When soil sampling for salinity management, varying depths of soil must be collected to determine where the salts have accumulated. Suggested depths are in one foot increments (down to four five feet), but 18 inch increments may also be used. If dealing with soil infiltration issues, it may be of value to sample the top 6″ to determine if there is a soil imbalance.

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