# Determining limestone application rates.

In my article, "The prophet of lime" (75/5:36),I recommended V.A. Tiedjens' book, More Food From Soil Science. For whatever reason, Tiedjens does not give his formula for determining limestone application rates in this book, but he does in his subsequent book, Olena Farms, U.S.A, as follows:

Amount of available calcium needed per acre foot in pounds: Sand--400-800; loamy sand -- 800-1,600; sandy loam -1,600-2,400; silt loam-2,400-3,600; clay -- 3,600-4,800; clay loam 4,800-6,000; and muck soil--6,000-10,000. These rates were worked out by Tiedjens as a result of numerous studies.

The rate of application needs to be adjusted based on the amount of organic matter. If very low, use the low end of the soil type range. If very high (e.g., that garden which has been receiving regular applications of leaves and compost), use the high end.

Limestone is not all calcium. High magnesium (dolomitic) limestone may only contain 20 percent calcium while high calcium limestone may contain 45 percent calcium. Thus, from the limestone analysis you can calculate how many pounds of calcium will be in each ton of limestone applied.

To determine application rate have a soil test done, which will provide the amount of available calcium present, and subtract it from what is needed by the type of soil (as adjusted by the level of organic matter). This provides the amount of calcium needed to be added to the top 12 inches of soil. Dividing this by the amount of calcium in each ton of limestone will give the number of tons of limestone which needs to be applied for 100 percent base saturation. However, since Tiedjens felt 85 percent base saturation was the desired level to obtain, multiply the last figure by .85.

Example: You have a silt loam with average organic matter levels and inexpensive soil tests done through the local County Agricultural Extension Agent indicate there are 1,000 pounds of available calcium present. Subtracting 1,000 from 3,000 (average of 2,400 and 3,600) resulting in 2,000 pounds of calcium which needs to be added. Dividing this by the pounds of calcium in a ton of limestone (say 700) and multiplying by .85 means 2.43 tons (or 4,857 pounds) of limestone would need to be applied per acre foot. Since many plant roots penetrate to three feet, Tiedjens recommended tripling the application rate and letting calcium leach to the subsoil levels. Thus, in this example, he would have recommended application of 7.3 tons of this quality limestone per acre.

High calcium limestone runs between \$10 and \$17 per ton, depending on location. In the example used, this would run between \$73 and \$124 per acre, although the incorporation technique (e.g., deep disking or rototilling) would add to this cost.

Due to the cost, first using test plots is recommended. For example, stake out ten foot by ten foot plots and apply the equivalent rate of limestone by multiplying the test application rate by .0023 (100/43560). With the above example, tests of four, six, eight and ten tons per acre would seem appropriate with the test running for several years. The length of test required would be partially determined by the fineness of the limestone (i.e., the smaller the particle size, the quicker test results will be evident). Avoid using hydrated lime as it acts so quickly it can damage plants.

As noted in the sidebar to the referenced article, the amount of magnesium in dolomitic limestone can interfere with the calcium exchange process. Unless your soil is deficient in magnesium, use of high calcium limestone would be more appropriate.

Weeds are expensive

Weeds are one of the biggest causes of crop losses in the United States. While many people think of pesticides in terms of bug-killers, of the \$4 billion a year spent on about a billion pounds of pesticides in this country, herbicides account for 69 percent. Another 12 percent are fungicides and nematicides, leaving about 19 percent for insecticides and miticides.

In spite of this barrage of chemicals losses from weeds cost American farmers \$15.2 billion every year.

The USDA's Agricultural Research Service is studying genetic engineering of crops and improved application equipment so fewer chemicals are needed, as well as biological controls and allelochemicals.

New! Improved! Acid rain... now with herbicides!

If you've been concerned about acid rain, don't read this or you're sure to lose some sleep.

The U.S. Geological Survey has confirmed that herbicides applied to land can vaporize into the atmosphere and come back to Earth in rainwater, often at a great distance from where they were applied.

The 18-month study found traces of herbicides in the rainfall of 23 states. While most were below the levels considered potentially harmful by scientific bureaucrats, the atrazine in an Iowa spring shower was three times the safe level established by the EPA.

Most of the herbicides show up in rain that falls within one-to-two months after spring planting.

You can't feel safe just because you and your next-door neighbors aren't using herbicides. You could be the unwitting--and unwilling--recipient of chemicals that were applied hundreds of miles away.