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POTASSIUM, CALCIUM, AND MAGNESIUM
Potassium can be applied at approximately a pound of potassium for each pound of potassium deficiency.
Some difficulties have been experienced with single heavy applications of muriate potash (KCl), although potassium sulfate (K2SO4) applications of 1000 lbs. have been made without ill effects. To avoid zones of extreme salt concentration, not more than 400 pounds of potassium salt should generally be added at one time. Should heavy application be desirable, or necessary, it is well to split applications into two or three applications per year. If a single heavy application is to be made, it should be done well in advance of cropping and thoroughly incorporated into the soil.
Cation balance is involved along with exchange capacity. A balanced soil with 9600 lbs. of exchangeable Ca per acre (exchange capacity of 32 meq./100 grams) should contain about 800 lbs. Mg per acre and 650 lbs. K per acre. Or the milliequivalents of Ca should be 65-80% of exchangeable cations per acre, Mg 10- 15% and K 2-5%. Local soils, crops, conditions, and percent of saturation desired will influence final recommendations.
Some additional recommendation problems to consider are the reserve supplying power of the soil in question, the rate of exchange of the K in the soil reserve, and the test procedure used by the laboratory. There are differences between tests and between different soils in regards to the amount of K which will extract by the same test. These are questions which can best be answered by soil fertility specialists familiar with the area and not by a general purpose manual such as this. They are questions, however, which should be considered with regard to the best answers available.
The crop need for K should be considered, as well as yield goals and economics in view of these factors of reserve supply and applied amounts. In some instances it is not economic to maintain the soil at the ideal level of potassium. For these soils and crops a lesser saturation percentage must be decided upon as determined by the prevailing factors.
POTASSIUM REQUIREMENT RATING FOR CROPS |
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|---|---|---|
| HIGH | MEDIUM | LOW |
| Alfalfa | Clover | Evergreen Shrubs |
| Asparagus | Corn (grain) | Flowers |
| Beans | Corn (silage) | Grass |
| Carrots | Flowering Shrubs | Hay (grass) |
| Beets, Sugar | Flowers (garden) | Pasture (grass) |
| Corn (sweet) | Fruit (small) | Shrubs |
| Field Beans | Grain (small) | Trees (fruit) |
| Golf Greens-Fairways | Lentils | Trees (shade |
| Grapes | Milo | Trees (nut) |
| Greenhouse Crops | Mint | Trees (timber) |
| Home Garden-Lawns | Silage | |
| Hops | Sorghum | |
| Melons | Soybeans | |
| Onions | ||
| Peas | ||
| Potatoes | ||
| Small Fruits | ||
| Strawberries | ||
| Tomatoes | ||
| Vegetable Crops | ||
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