SACRAMENTO, Calif. (AP). 11 January 2011. An expert says small changes in agricultural irrigation practices could eliminate wasteful water use. Delta Watermaster Craig Wilson says in a report being presented to the State Water Resources Control Board next week that California should crack down and aggressively enforce the state’s ban on wasteful water use.
The Los Angeles Times reports Tuesday that Wilson proposes broader enforcement of the state Constitution’s “reasonable use” doctrine rather than current case-by-case enforcement. Wilson says serious water savings would be realized if agriculture used water more efficiently. He urges the state board to convene a summit, create an enforcement unit and streamline enforcement procedures. read more
Sorry, I can’t help it… I see water penetration problems due to poor soil structure wherever I go and I have to stop and take pictures…. and the problem has certainly gotting worse and worse in recent years.
I stopped a took this photo last week [Friday 23 April 2010] after a light rain. The soil is very sandy… probably a sandy loam, but after just a light rain, the water is standing in the lower areas. This condition is very indicitive of poor soil structure from using snow-melt water for years, which has led to this serious problem. Not only does the water not move down into the soil well, oxygen can’t move into the soil very well, and of course, the root system is suffering, too. If you have any problems with your crops like this, contact us… we can help improve your production and profit. Like the Men’s Wearhouse guy, we guanantee it… Dr. B.
This week I visited a wholesale nursery grower in the Sebastopol, California area.
They had very high levels of bicarbonate in their irrigation water (above 220 ppm [3.6 meq/L]). Because of the high bicarbonate levels, many of the plants were showing severe iron deficiency symptoms (iron chlorosis). High bicarbonate levels in the soil and/or irrigation water can lead to iron deficiency in crops and other plants.
Chlorosis is generally a symptom of cellular iron (Fe) deficiency that results from a limited availability of apoplastic Fe in the leaf. However, it is often not necessarily associated with a deficiency of soluble iron in the soil solution, or a decrease in Fe uptake by the roots. An elevated bicarbonate concentration of the soil has been identified as a major factor for the induction of chlorosis in various crops/plants. Bicarbonate-induced chlorosis is caused by transport of bicarbonate into the stele that leads to an alkalinization of the xylem sap and, in turn, of the leaf apoplast. Symptoms of iron deficiency develop at a high apoplastic pH due to a repression of Fe3+ reduction, which is a prerequisite for iron uptake by mesophyll cells.
With irrigation water, levels of bicarbonate + carbonate above 3.0 meq/L are considered harmful; also because of calcium in the soil that is precipitated out as lime as the soil dries (see the Bicarbonate in Irrigation Water (part 1), posted yesterday).
If you have any questions about high bicarbonates or iron deficiency, or any other problems with your soils or irrigation water, contact us and we can help. Dr. B.
Bicarbonate + Carbonate: Irrigation water that contains levels of bicarbonate plus carbonate (especially above 3.0 meq/L (183 ppm) [combined]) are considered very harmful for two primary reasons. Reason #1: Bicarbonates and carbonates will combine with calcium to form lime (CaCO3) when the water evaporates. This results in several negative consequences: (1) when free lime forms, any available beneficial calcium will be precipitated out, further compounding problems of not having enough calcium in the soil (most soils in California, Washington, Oregon and the rest of the western United States fall into this category); and (2) bicarbonate itself is the most toxic anion that exists in relation to plant health (more on this tomorrow, which is “Reason #2”).
To compensate, the addition of calcium to the irrigation water (e.g., in the form of solution-grade anhydrite or gypsum) will help a lot with any calcium precipitated out as lime. Also, an acid (e.g., N-pHuric or sulfuric) can also be added to the water to neutralize the bicarbonates and carbonates, maintaining an optimum water pH of approximately 6.5.
Also ♫: 100-ppm of anything in the irrigation water amounts to 270 lbs. per acre-foot of water. Many crops may use 2.5 acre-feet of water. If, for example, your irrigation water contained 350 ppm bicarbonate (very common in California), you could deliver an astounding 2,363 lbs. of bicarbonate per acre into your soil. Each pound of bicarbonate ties up one pound of soluble calcium. Reason to give bicarbonates in irrigation water serious attention. If you have high bicarbonates and/or water penetration or soil structure problems, contact us and we can help you. Dr. B.
This photo was taken yesterday 15 March 2010 east of Lodi, California. No… the chardonnay vineyard has not been irrigated [it’s a drip irrigation system], and there hasn’t been excessive amounts of rain, either. Yet, the entire bottom half of the vineyard is under water… a serious anaerobic condition for the vines. We are seeing more and more serious water penetration problems like this, and the primary problem is irrigation water that is snow-melt runoff contributing to serious soil structure issues. This soil condition can easily be corrected, but without help, the vineyard and the grapes are in serious trouble. If you have a water penetration problem like this, call us… we would gladly talk to you about our services and how we can help your crops, whether it be grapes, almonds, vegetables or field crops, …or something fun like pussytoes (Antennaria plantaginifolia) or red undies (Begonia sinensis)… we can help you do a better job with your production.
Toxicity of Gypsum: Some other folks are still teaching about “gypsum toxicity.” Facts:
1. There has to be approximately 20,000 ppm Ca2+ in the soil for calcium toxicities to exist…
2. There has to be approximately 800 ppm SO42- in the soil for sulfur toxicities to exist.
Both are extremely rare in productive, agricultural soils, even soils where gypsum has been applied in extreme excess.
Solubility of Limestone vs. Gypsum:
The other gypsum myth I have heard is that as soil pH conditions reach values near 7.0, agricultural limestone becomes is a better choice for adding calcium to the soil rather that gypsum or anhydrite. First of all, agricultural limestone is always 150 times less soluble than gypsum or anhydrite under any conditions. Gypsum/anhydrite is never in any soil reaction (pH) or oxidation/reduction condition any less soluble than this.
However, note that all soluble soil calcium becomes insoluble at pH values near 8.0 So at these pH values, calcium is basically nonexistent in the soil for promoting good soil structure, and as an essential plant nutrient. This is why we need to keep the soil pH values for most soils in California and the west at pH values about equal to 6.4.
Much more on this subject later….
And please write me with your gypsum/anhydrite/limestone questions…
I have written and lectured a lot about the benefits and uses of gypsum products in the past [see the publications tab to your left]. Gypsum [and its more concentrated and prevalent form, anhydrite] remains the “miracle” amendment…it has been documented by many scientists as having over 40 (yes, forty!) beneficial uses in production agriculture. Now, as time moves on, I’ll talk more about the benefits and uses, and dispel many myths about gypsum usage vs. that of agricultural limestone, etc…. . For now, here are some quick facts about “gypsum.”
There are two calcium sulfate minerals found on earth: the first is called gypsum. The chemical formula for gypsum is (CaSO4·2H2O). The second/much more prevalent calcium sulfate mineral on earth, is anhydrite (CaSO4)…almost identical to gypsum, but sans the two molecules of water. By nature, gypsum with its associated two water molecules is 21% water, and 79% solids. Calcium sulfate in the pure anhydrite form (no water) is 29.4 percent calcium (Ca) and 23.5 percent sulfur (S), while pure gypsum with its water associated in the molecular structure (CaSO4·2H2O) is approximately 23.3 percent Ca and 18.5 percent S. However, agricultural anhydrite and gypsum, as a soil amendment/conditioner/fertilizer usually has other impurities, so grades are approximately 22 percent Ca and 17 percent S for a decent quality product.
There has been some serious confusion concerning the solubility of calcium sulfate products. The fact is: both anhydrite and gypsum are indeed water soluble, and both essentially have the same solubility: 0.205 grams per 100 grams water (2003-2004 CRC Handbook of Chemistry and Physics). This has also been verified by many field trials by Soil Scientists [including myself], worldwide farmers and others. The solubility of 0.205 grams per 100 grams water equates to:
0.205 grams/100 grams water = 0.0171 pounds per gallon
= 5,575 pounds per acre foot water (325,850.58 U.S. gallons)
Therefore: the maximum solubility of anhydrite or gypsum in one acre-foot water ≈ 23.8 milliequivalents per liter (or 5,575 pounds per acre foot water [or basically 12″ of rainfall will dissolve approximately 2.8 tons of agricultural gypsum/acre)
Gypsum and anhydrite are the neutral salts of a strong acid and strong base and do not increase or decrease acidity. Dissolving gypsum and anhydrite in water or soil results in the following reaction: (CaSO4·2H2O) = Ca2+ + SO42- + 2H2O. They add calcium ions (Ca2+) and sulfate ions (SO42-), but do not add or take away hydrogen ions (H+). Therefore, they do not act as a liming or acidifying material. The Ca2+ ions simply interact with exchange sites in soil and sulfate remains dissolved in soil water.
More on gypsum this coming Monday March 8. Please send me your gypsum, limestone and other questions…