Calcareous soils have often more than 15% CaCO3 in the soil that may occur in various forms (powdery, nodules, crusts etc…). They are relatively widespread in the drier areas of the earth. California is notable for its young soils, that is, soils that have a relatively high level of nutrients because low rainfall means that natural productivity has not been leached out. The potential productivity of calcareous soils is high where adequate water and nutrients can be supplied. Water is the most limiting input to making California soils productive.
The high pH associated with these soils, though, is not the level of calcium present. It is the carbonate in the soil or the bicarbonate associated with the waters found in those soils which controls the pH. The high pH then controls the availability of iron, zinc, manganese and copper. These nutrients need to be added as foliars or soil applied, or better yet, the soil pH needs to be dropped to around 7 to make these nutrients available.
Recently someone asked if replacing the calcium with potassium would change the pH. No, it won't. The carbonate needs to be removed. Calling it a calcareous soil confuses people about what caused the high pH. The carbonate or bicarbonate needs to be removed with acidification, it turning it into CO2 gas. This is done with urea sulfuric acid or sulfuric or sulfurous acid. There are actually magnesium dominated soils in the San Luis Obispo area that have high pHs due to carbonates. They are carbonateceous.
I am frequently asked if I can recommend a book on Soils. And yes, I can. It is Soils: An Introduction by Michael Singer and Donald Munns. The sixth edition recently came out so there's a lot of older used copies floating around on the wed for under $10. This book takes a different tack on describing soils. Instead of tacking the tack of a chapter on Nitrogen another on Calcium etc., it weaves a story of how all the parts are related.
It is more than just the confusion about the effects of phosphonates, but also how to spell the words associated with the P atom. Phosphorus with an ending in “us” is the element we know as P, while Phosphorous with a “ous” ending is the adjective of P. So an acid containing Phosphorous acid is written H3PO3 while phosphoric acid is H3PO4. These are both strong acids and can hurt and cause damage if splashed on the skin. When either is reacted with calcium or potassium hydroxide, a salt is formed which is less dangerous to users, but as with any chemical can be misused.
The salt formed from Phosphorous acid is called calcium phosphite or calcium phosphonate depending on what naming system is used to describe it. Whereas when these bases are reacted with phosphoric acid, the result is calcium or potassium phosphate. These salts are relatively benign in contact with skin. Labels on containers often call phosphorous acid, “soil applied” whereas the phosphite forms are called “leaf applied”. The “soil applied” when applied to a leaf can cause damage, whereas, the leaf applied is much less likely to cause damage to both plant and applicator. It can be applied to the soil, as well. It's much safer to use the leaf applied in either application technique.
The phosphites are often registered as fertilizers, but they have little nutrient effect. Most of their effect is to boost the plant's immunity to Phytophthoras and pythiums. This is called fungistasis and the material is called a fungistat. They don't act as a fungicide when normally applied to kill these organisms.
So you can see there is a lot of confusion in the phosphorous world. Knowing the proper spelling, pronunciation and use is note only good grammar, it makes good farming.
To read more, see:
There are few documented cases of phosphorus (P) deficiency in tree crops in California.
When we think about space missions, we tend to look toward the stars to planets like Mars where robotic rovers roam, gathering data and sending it back to Earth. Rarely do we think about missions closer to home. But a view of Earth from 426 miles above is helping us monitor droughts, predict floods, improve weather forecasts and assist with crop productivity. This year, the National Aeronautics and Space Administration (NASA) launched a new satellite called SMAP (Soil Moisture Active-Passive) with the help of a team that included U.S. Department of Agriculture (USDA) hydrologist Susan Moran at the Agricultural Research Service's (ARS) Southwest Watershed Research Laboratory in Tucson, Arizona, and physical scientist Wade Crow and hydrologist Thomas Jackson at ARS's Hydrology and Remote Sensing Laboratory in Beltsville, Maryland. ARS scientists played a key role in designing and implementing SMAP—an orbiting observatory that measures the amount of water in the top layer of the soil everywhere on Earth. SMAP gathers soil moisture data that can help track diseases and famine, predict weather and climate patterns, assist emergency workers' response to natural disasters and let farmers know what crops to plant. “We've seen impressive advances in our ability to produce crops on a given area of soil, but have also retained susceptibility to climate events, particularly droughts that occur when there is inadequate soil water for crops,” Crow says. “The idea is to better predict and monitor droughts so they don't turn into food crises, and soil moisture is the most direct and earliest indication of drought.” SMAP provides the best global view of soil moisture to date, Crow says. Therefore, it has the potential to help monitor global food production. It's the best soil moisture sensor ever deployed due to its resolution, accuracy, global coverage and repeat time. Before the satellite was launched, volunteer users around the world could put SMAP's simulated data to use, Moran says. “We wanted to make sure our products would be as good as possible and easy to access. In return, these users provided feedback on how SMAP could help them.” Early users included those in agriculture, weather, human health, emergency response and military readiness. Data were used to monitor droughts, predict floods and even to predict the water supply in New York City, Moran says. “Some used the data to predict large regional dust storms that affect the health of millions of people in Saharan Africa and throughout the Middle East,” she adds. “In Germany, the data were used to map sea ice in hopes of improving maritime navigation, and at Texas A&M University, researchers looked at the impact of hurricanes on power outages.” SMAP will release the first data products to the public in August. To learn more, go to http://smap.jpl.nasa.gov/. - See more at: http://blogs.usda.gov/2015/04/07/usda-nasas-global-view-of-earths-soil-holds-many-benefits/#sthash.okw1NTAN.dpuf
- Author: Jim Wolpert - UC Davis
Soil Moisture Sensors
Jim Wolpert, University of California, Davis
Soil Moisture Content
The quantity of water in soil is called the soil moisture content. After rainfall or irrigation, some water drains from the soil by the force of gravity. The remaining water is held in the soil by a complex force known as surface tension and varies depending on the amount of sand, silt, and clay. Sands, with larger particles and smaller total surface area, will hold less water than clays, which have much smaller particles and larger total surface area. The drier the soil, the greater the surface tension, and the more energy it will take for a plant to extract water.
Vineyard managers often measure soil water content as a guide to determine their irrigation timings and amounts. There are several methods for monitoring soil water content. Correlating these methods with actual inches of moisture per foot of soil is very complicated (see Recommended Links) but at the very least can help a grower to identify patterns of water use, depth of irrigation, and soil water content trends over time.
A tensiometer, as its name implies, is a device for measuring soil moisture tension. The design is a simple tube with a porous cup at the lower end and a vacuum gauge on top. The tube is filled with water, sealed airtight, and placed in soil. As soil dries, water is pulled from the porous cup into the soil, creating a vacuum and causing the gauge to move. As soil continues to dry, more water is pulled out and the suction increases. As soil re-wets after a rain or irrigation, water moves back into the cup and the suction decreases. Installing tensiometers in soil requires attention to detail to obtain accurate readings (see Recommended Links for installation downloads).
Tensiometers are usually placed as a pair with the shorter tube positioned in the middle of the rooting zone (e.g., 18 inches deep) and a longer tube positioned near the bottom of the rooting zone (3 to 4 feet deep). Growers can use the difference between the two tubes to monitor water usage and determine the effective depth of irrigation. At least two stations (two tubes per station) are recommended per field, or more depending on soil variability.
Tensiometers have the advantage of being inexpensive, and easy to install, maintain, and read. They are better in fine-textured soils where good contact can be made between the porous cup and the soil. They do not work well in coarse sands where good contact may not be possible. Because the gauges are aboveground, the units are prone to damage by vineyard equipment.
Electrical Resistance Blocks
Electrical resistance blocks are also known as gypsum blocks or soil moisture blocks. They are simple devices with two electrodes embedded in a block of gypsum or other similar material. When blocks are buried in soil, water moves into or out of the block, depending on the moisture of the soil, changing the resistance between the two electrodes. Like tensiometers, gypsum blocks are cheap and easy to install. They are usually installed in at least two stations per field, at two depths, and must be installed correctly to provide accurate readings. Some block designs perform better under wet soil conditions and some correct for soil temperature. The meter used to read the blocks can be moved from field to field, but is specific to the block design (i.e., it is not a simple ohm meter). The wires aboveground are much less prone to damage by equipment compared to tensiometers.
A neutron probe uses a radioactive source for measuring soil moisture. A tube, usually made of PVC or aluminum, is installed in soil to a depth of interest and the radioactive probe is lowered into soil to measure soil moisture at as many depths as desired. The probe emits fast neutrons that are slowed by water in the soil in a way that can be calibrated to the soil water content. The probe has a significant advantage, especially for perennial crops, because access tubes are easy to install and relatively permanent. Another advantage is the reading accounts for a spherical area about 10 inches in diameter, much greater than other methods. The major limitation to this method is the probe itself; it is expensive and the presence of a radioactive source triggers requirements for operators to be trained and licensed in handling, storage, and use. In some production regions, service providers are available, usually at a fixed cost per access tube for a growing season.
Di-electric sensors measure the di-electric constant of soil, a characteristic that changes with changing soil moisture. A common method is called time domain reflectometry, or TDR. The theory behind how this method works is too complicated to be discussed here. The advantage of these types of systems is that they are designed to be left in place and provide continuous readings of soil moisture. The disadvantages are that the units are expensive and read soil moisture only a very small distance from the unit.
All measures of soil moisture suffer from the same limitation — the value of the information is dependent on the extent to which the soil where the measurements are taken reflects the rest of the field. Where soil variability is high, growers must exercise caution in relying too heavily on relatively few measurements.
Irrigation of Winegrapes, University of California
Irrigation Basics for Eastern Washington Vineyards, Washington State University
Reviewed by Ed Hellman, Texas AgriLife Extension and Eric Stafne, Mississippi State University