Calcium and calcium chloride in agriculture: crop-use checks
Calcium chloride is used on cherries against rain-induced cracking: 0.5–1.0 % CaCl2 has proven effective at reducing splitting with proper application and timing. A non-ionic wetter/spreader should improve effectiveness.
Before buying calcium chloride, name the crop and the problem you want to solve. For cherries, match the product and the spray plan to rain cracking and nothing else.
What the cherry evidence addresses
Rain-induced cracking is direct osmotic water absorption through the fruit cuticle and skin. Calcium chloride lowers the osmotic potential of the water on the fruit surface and so slows water entry. Fruit coatings do not reduce internal-water cracking, so surface salts and coatings address only the rainwater route.
Timing and fruit coverage matter
The salt must reach the fruit surface while it is still dry. It is water-soluble, so it needs re-application after a rain event, and it can leave a residue on the fruit that may require postharvest washing.
Before you book the spray, check three things: whether the fruit will still be dry at application, what rain is forecast, and how the packing line washes fruit.
Cultivars differ in cracking susceptibility, and cherries become more susceptible as they mature. Drying the fruit with airblast sprayer fans or helicopter rotor wash shortly after rain also reduces losses.
Lime, gypsum and calcium chloride do different jobs
Calcitic and dolomitic lime have the same acid-neutralizing value at equivalent rates. Calcitic lime contains calcium carbonate only; dolomitic lime is a mixture of calcium and magnesium carbonates with at least six percent magnesium.
Gypsum, also known as land plaster, is calcium sulfate with 23 % Ca and 18 % S. It cannot be used as a liming material because it cannot neutralize soil acidity. Applied to acid soil below pH 5.5 it can harm certain crops by displacing soil aluminum, which is toxic to plant roots.
Before applying gypsum, get a crop-and-soil recommendation, especially on acid soil.
Compare liming materials by calcium carbonate equivalent
The calcium carbonate equivalent (CCE) relates all liming materials to CaCO3, which is set at 100. Dolomite has a neutralizing value of 109, slag 86. Many state laws require liming materials to have a purity of 90 % or greater.
Before ordering lime, get the local lime recommendation, and ask the supplier for the neutralizing value and the particle-size analysis of the actual material. Compare liming value separately from calcium content: a high calcium figure does not tell you how much acidity the material neutralizes.
Fineness decides how fast limestone reacts, because the reaction rate depends on the surface area in contact with the soil.
Ferrous sulfate (ferrous sulphate) in agriculture: nutrient and crop-use checks
Iron chlorosis is the plant's inability to extract enough iron from the soil. In Utah it is the most common micronutrient problem of ornamentals, shrubs, vines, small fruits and trees, and the presence of lime in the soil is the most important predisposing factor.
Identify why the plant cannot get iron before you choose an iron source: buying iron does not fix a soil that locks it up.
Where ferrous sulfate works and where it does not
Soil incorporation of inorganic compounds such as iron sulfate is not effective in most Utah soils; it gives good results on turf. Iron sulfate leaves rust-colored spots on pavement when misapplied.
Foliar sprays give the most rapid but temporary response: chelated iron or 0.1 % ferrous sulfate, with a spreader-sticker. Green spots appear on the leaves a few days after spraying, and repeated applications are needed as new foliage appears. Applications are avoided when fruit are present because staining may occur.
When you ask about a foliar job, include the surfaces next to the plants (paving, walls) and the market quality of the fruit.
Chelated iron compounds consist of an organic molecule that binds iron and makes it more available to plants. EDDHA works on raspberries when the soil pH exceeds 7.5, whereas other chelates are effective only between pH 7.2 and 7.5. They must be placed in the root zone in spring, and in most cases treated every year. No single iron product has proven consistently successful.
When someone proposes a chelate, ask which chelating compound it is and what evidence supports it for your pH and soil, then compare that with foliar and soil options for the same site.
In Colorado, soil application of iron fertilizers has not been economically feasible on a field scale.
Soybean iron deficiency
A tolerant variety is the first line of defense against iron deficiency chlorosis (IDC) in soybean.
Soil nitrate in the field increases IDC, and the severity increases on waterlogged soils, especially when soils are cold. The more bicarbonate in the soil, the more IDC occurs.
Map the affected parts of the field, choose a tolerant variety first, and only then assess iron-chelate options for those areas.
Organic production
Synthetic micronutrients, including iron sulfates, are allowed on an organic farm only when the deficiency is documented by soil or tissue testing or another verifiable method approved by the certifying agent. Micronutrients made from nitrates or chlorides are not allowed, and they may not be used as a defoliant, herbicide or desiccant. All substances used on organic operations must be approved by the certifying agent. Details are in the organic input checklist.
On an organic farm, write down the deficiency and get the certifier's approval before buying or applying an iron product.
Symptoms and what aggravates them
Leaves are yellow, light green or white with distinct green veins. In severe cases the leaves may be entirely white and the margins scorch and die during hot periods.
Chlorosis is exaggerated by excessive soil moisture, soil salinity, high phosphorus, high copper, manganese and zinc, low or high soil temperature, large additions of organic matter, and inefficient root function caused by nematodes or fungal pathogens. Frequent irrigation in heavy clay soils or cold temperatures often results in a persistent deficiency of iron. If chlorosis persists for several years, individual limbs or the entire plant may die.
Symptoms change with the season and the weather, so make a useful record: note which leaves you looked at, the date, how severe it was, and whether the same plants were affected before. If yellowing comes back after a foliar response, look at drainage and wet spots and use the site's history before repeating the treatment.
Iron-efficient plants
The best control of iron chlorosis is the selection of iron-efficient cultivars; neighborhood plants show which are adapted to local soils. Some species obtain iron from alkaline soils, whereas others cannot be grown successfully in native high-pH soils.
Keep your spray records in one place. Free to start.
If replacing plants is on the table, ask which locally adapted cultivar or species is recommended and why, and consider the planting space, the soil and what the planting is for, before committing to repeated iron inputs.
Magnesium sulfate (magnesium sulphate) in agriculture: diagnose the need and compare sources
In Minnesota, magnesium deficiency has only been observed on very acid soils, usually sandy loam, loamy sand or sand, and is not likely until soil pH drops below 5.5.
Sources and their magnesium content
Dolomitic limestone is the most cost-effective method for applying needed Mg; it contains 8–10 % Mg and must be broadcast and incorporated before planting. A combined potassium sulfate and magnesium sulfate fertilizer contains 11 % Mg, 22 % S and 22 % K2O, and serves as a Mg source when there is no desire to increase soil pH.
Choose the source by both things at once: how much magnesium the field needs and what you want to happen to soil pH.
Irrigation water can contain a substantial amount of Mg2+ that is readily available to a crop; a soil test detects any such Mg not used by the crop.
Before adding magnesium, bring the farm's irrigation water and liming history to the discussion.
Rates for corn
On corn, a soil test of 0–50 ppm Mg is rated low and calls for 50–100 lb/acre broadcast or 10–20 lb/acre banded; 51–150 ppm needs no broadcast Mg.
If dolomitic lime has been used in the crop rotation, soils usually have a relatively high Mg level and the Mg soil test is not necessary.
Organic farms
Synthetic magnesium sulfate is allowed on an organic farm with a documented soil deficiency.
Keep the deficiency documentation together with the product review and the certifier's approval.
Symptoms
Magnesium is the central core of the chlorophyll molecule. It is mobile in the plant, so deficiency symptoms occur first in the oldest leaves. In corn the area between the veins turns yellow and a definite striping runs the full length of the leaf, appearing first on the lower leaves.
In potatoes, diseases, herbicide damage and environmental factors also cause leaves to die prematurely, so plant analysis is used to confirm a magnesium deficiency. Plant analysis works best in combination with soil testing.
If the only sign is early leaf death in potatoes, rule out disease, herbicide injury and weather stress before blaming magnesium.
Calcium-to-magnesium ratio
The need for an ideal calcium-to-magnesium ratio has never been verified by research throughout the Corn Belt. In Wisconsin, ratios from two to eight had no significant effect on alfalfa and corn yield; recommendations emphasize adequate magnesium rather than a ratio.
If a sales proposal is built on an ideal calcium-to-magnesium ratio, ask what the soil test says about magnesium supply instead.
Zinc sulfate (zinc sulphate) in agriculture: crop nutrition and use checks
Zinc is the only micronutrient that may be needed in a Minnesota corn fertilizer program, and it is not required in all fields. The DTPA soil test for zinc is highly reliable and accurately predicts the need.
Before choosing a zinc product, look at your crop, the field and the interpreted test result.
Rates by soil test
For corn in Minnesota, a DTPA zinc test of 0.0–0.50 ppm calls for 2 lb/acre banded or 10 lb/acre broadcast, 0.51–0.75 ppm for 1 lb banded or 5 lb broadcast, and 0.76 ppm or more for none. Carryover to later years is better with broadcast applications.
A zinc number only means something with its method. Keep the laboratory method, the units and the regional recommendation together, and do not take a category from an unrelated table.
Colorado uses the AB-DTPA test. For sensitive crops (corn, sorghum, beans, potatoes), 0–0.9 ppm Zn is low, 1.0–1.5 marginal and above 1.5 adequate.
In Colorado, 5 to 10 pounds Zn per acre, which is 15 to 30 pounds of zinc sulfate (36 % Zn), should be sufficient for two or three years of production. Broadcast-plowdown is generally the most effective method; banding may be preferred in shallow or minimum tillage.
Comparing zinc sources
Except for large particles of zinc oxide, all common zinc sources are equally effective, so cost should be a major consideration. Chelated zinc is commonly used when liquid starter fertilizer is applied directly on the corn seed; it typically costs more per pound of zinc applied.
Compare sources for the same placement and application system.
Zinc fully chelated with EDTA has been shown to provide the greatest stability of zinc across a range in soil pH values. Chelated zinc does not increase the potential for a yield response on soils testing 0.75 ppm or more.
Organic production
Sulfates, carbonates, oxides or silicates of zinc are allowed. Deficiency must be documented by soil or tissue testing or another verifiable method approved by the certifying agent, and micronutrients may not be used as a defoliant, herbicide or desiccant.
For an organic field, choose an allowed form such as a sulfate and keep the test or other verification that documents the deficiency.
Where deficiency occurs
Zinc deficiency is frequently associated with areas where topsoil was removed by leveling for irrigation, erosion or terrace construction, and with soils that are low in organic matter, sandy or alkaline (pH above 7.0). It is much more severe in years with cold, wet springs. Visual symptoms are confirmed by soil test or plant analysis.
Foliar zinc as a rescue measure
In season, zinc deficiency may be corrected by spraying a 0.5 % zinc sulfate solution (1 % for potatoes) at 20 to 30 gallons per acre, with a surfactant; a 0.5 % solution is 4½ pounds of zinc sulfate (36 % Zn) in 100 gallons of water. Foliar applications are effective in greening foliage but not as effective in producing a yield response, so they are a salvage measure.
When a foliar treatment is proposed, ask for evidence of yield recovery, not just greener leaves.
Crop symptoms and sampling
Young corn and sorghum plants show a broad band of white to translucent tissue on both sides of the leaf midrib, starting near the base of the leaf; generally it does not extend to the tip, and the midrib and outer margin remain green. Pinto beans are stunted, with yellowing upper foliage, browning or bronzing of older leaves, crinkled leaves that curl downward, and poor pod set.
For the zinc test, take a composite soil sample from the area suspected of being low in zinc, and avoid anything galvanized or made of rubber.
Mark the sampled patch and keep its field history with the laboratory submission.
Calcium chloride agricultural use
Calcium chloride is used in two agricultural ways. On cherries, salt sprays (usually calcium chloride) reduce and slow the infiltration of water into the fruit against rain cracking. In spray water, sodium and calcium chlorides also affect some pesticides but are often overlooked.
Next step
Confirm the crop and the deficient nutrient by testing before you buy. Certified organic production needs certifier approval for every substance; see the input approval check.