The Cost of Maintaining the Lime Supply

What does it cost to provide and maintain a proper supply of lime in the soil?

Obviously the cost varies with conditions. I give one computation. In the North Central States, where about two-thirds of the country's agricultural lime is used, lime delivered at the farm frequently costs about $3 a ton. If 3 tons an acre are needed to bring the soil to a pH of 6.5, a capital investment of $9 is required; at 4-percent interest that represents an annual carrying charge of 36 cents. If the annual net loss or depletion of lime is 200 pounds an acre, it will take 30 cents annually to cover this. Thus, under these conditions, the total annual cost per acre of providing and maintaining a satisfactory supply of lime in a soil that needs 3 tons of lime an acre to start with is only 66 cents. The annual returns, as revealed by numerous field tests, from this investment in terms of increased yields of crops of higher quality, and soil improvement and conservation may easily amount to 10 or 20 times the annual cost. In fact, in time, it may mean the difference between complete crop failure with soil ruination, and bumper crops with permanent soil fertility and conservation. In these considerations it is understood, of course, that the lime would be supplemented with fertilizers as needed.

Because liming is so important in the humid regions, it is fortunate indeed that an inexhaustible supply of lime exists in most of the areas that need it. Calculations based on analyses of the earth's crust show that enough limestone exists for an application of approximately a half million tons to every acre of the earth's land surface, or close to 10 million tons for every acre of arable land. Moreover, the lime that leaches out of the land forms new deposits, pound for pound. Thus, the use of lime need never be curtailed because of an inadequate or dwindling supply.

We need more information particularly on two points : The loss of lime by leaching and cropping, and the fineness of grinding of limestone. Recommendations on the second point vary greatly. Authorities in several States favor rather coarsely ground material; others prefer finer grinding and have had laws passed that set up standards of purity and fineness.

A product that allows at least 50 percent to pass through a 60-mesh sieve is of high grade and economical as regards fineness for large-scale general use. Very fine material, most or all of which passes a 100-mesh sieve, is on the -market; it costs more, but is well adapted for small-scale use, such as gardens, intensive cropping, and special cases where only a small amount of quick-acting material is permissible, as in potato culture.

Differences in recommendations as regards fineness of grinding have probably arisen in some cases because of marked differences in the character of the stone being used. It is well known that the dolomitic stone is much less soluble than the calcium stone, and so probably requires finer grinding if equal activity is desired. But, all in all, the solubility or availability of agricultural lime as influenced by composition and fineness, its subsequent movement, use by crops, and loss by leaching, all deserve much additional investigation.

And Finally

It should be understood that the acids that cause soil acidity are not in themselves undesirable substances to have in a soil. In fact, without them soils would be unreactive and unretentive of the elements of fertility. The acids act as a great reservoir where calcium, magnesium, potassium, and other bases may be stored in a readily available form for crop use and regulation of soil conditions. An acid condition is simply a positive signal that the supply of these bases needs to be replenished. This replenishment is done for the most part by the use of lime, and the more acid the condition the greater the need of the replenishment.

One of the most telling arguments for the liming of soils is an exposition of the relation of liming to the utilization of atmospheric nitrogen. In the atmosphere over every acre of land there are, in round numbers, 35,000 tons of nitrogen, which, if transformed to a fixed (nongaseous) form like ammonium nitrate, would have a commercial value as fertilizer of more than 5 million dollars. It is ironical, then, that many yields are greatly reduced because of a lack of nitrogen in usable form. How can the farmer draw upon this tremendous and inexhaustible supply of nitrogen? He can do so by growing legumes, which, when properly inoculated and grown on land well supplied with lime and mineral nutrients, have the power of fixing atmospheric nitrogen that they can then use for the synthesis of their own proteins, and pass on for use by other plants, as well as animals. Nonlegumes, regardless of how grown, cannot utilize atmospheric nitrogen. They depend for nitrogen on that fixed by the legumes, or supplied in manure and commercial fertilizers.

Now, it so happens that the legumes best in quality of forage and soil building, such as alfalfa and the clovers, like lime; that is, they grow satisfactorily and fix nitrogen efficiently only when the soil is well supplied with lime. A season's growth of alfalfa on an acre under favorable conditions may fix atmospheric nitrogen worth $10 or $20 more than enough to pay the cost of an ordinary application of lime, which usually produces benefits for a decade or more. Yes, the cost of liming land is only a small fraction of the total value of all of the benefits lime produces.

THE AUTHOR

Emil Truog is professor of soils and chairman of the Department of Soils at the University of Wisconsin. His principal contributions pertain to soil testing for lime and fertilizer needs, methods of fertilizer application, availability of plant nutrients, and the training of soil scientists.