Soils: November 2003

Do you want to get all you can out of your fertilizer dollars? If your pH is too low, you may be shortchanging yourself. To get the most out of your nitrogen, phosphorus, potassium and other nutrients, pH must be at the proper levels.

As pH decreases below 6.5, phosphorus becomes less available. On a relative scale, only about 30 percent as much phosphorus is available when pH is below 6.0 versus when pH is above 6.5. Nitrogen and potassium start becoming less available below pH 6.0. Both are about 30 percent less available at pH 5.5 and 70 percent less available at pH 5.0. As pH continues to fall below 5.0, nitrogen, phosphorus and potassium become so unavailable that they are of little use to a growing plant.

It is not uncommon for soil specialists at the Noble Foundation to see pH soil test levels below 5. Commonly when the pH is in the 4s, other nutrient levels will be high. This is because the nutrients are not available to be taken up by the plants, so they build up in the soil.

The most effective way to raise pH is to apply a good-quality agricultural lime. The two factors that determine quality of lime are the calcium and/or magnesium carbonate content of the liming material and how finely the lime is ground. Often, local rock pits sell a product as ag lime that has good carbonate content but is not ground very fine. This makes the lime less effective. The more finely ground the lime, the faster it will raise the pH of the soil.

Incorporating lime into the soil makes it react faster than if it is surface applied. Therefore, applying lime before plowing to establish a new crop is a good idea. However, applying lime whenever it is possible is better than not applying lime at all. If lime is needed, the sooner it is applied the better, since lime can take several months to react and raise pH.

The only way to know if and how much lime is needed is with a soil test. In addition to pH, a buffer index will be reported. This tells a soil specialist how much lime to recommend based on your soil type.

Currently, the Unimin pit at Mill Creek, Okla., has 75 percent ECCE lime on sale for $5.10 per ton. This makes it $6.80 per ton on a 100 percent ECCE basis, which is a very good price. They have informed me that this price will be in effect until Jan. 1, 2004. With calf prices being high, now might be an excellent time to do some capital improvement by liming fields that need it. Unless, of course, you don’t mind not getting all you can out of your fertilizer dollars.