Right Use of Lime in Soil Improvement

by Alva Agee

Comparing lump lime with finely pulverized limestone, the factors of expense and discomfort and final lack of perfect distribution of the former remain important. The stone is relatively easy to handle, being slightly granular and passing through a distributor without trouble. The fact that it is not caustic, like the hydrated, is in its favor. When everything is taken into account, one is justified in using limestone or air-slaked lime at a cost per ton three-fourths as great as that of lump lime. It is to be borne in mind that in these estimates the cost per ton is not that at the factory or at one's own railway station, but on the farm. The freight and cartage to the farm are based on weight of material, and more material per acre is required when the worthless portion has not been driven off by burning. If one must use one and three-quarters tons of limestone to have the equivalent of one ton of fresh burned lime, it is evident that the cost of freight and cartage of the worthless portion might make cost prohibitive if distances were very great. Farms lying a long distance from a railway station may easily find that fresh burned lime is the only form of lime they can afford. The basis for correct estimate is cost delivered in the field.

Storage. One advantage possessed by the limestone is ease of storage. There is no inconvenience or loss. The stone may be ordered at any time of the year when teams are least busy upon other work, and it can be held till wanted. In this way the cost of cartage to the farm may be kept relatively low, and the material is at hand when wanted, regardless of rush of work or delays of railroads. This advantage is partial counterbalance to the cost of freight on the worthless portion of unburned stone.

Valuing Limestone. The estimates, so far as labor and convenience are concerned, are merely suggestive, and rest upon the presumption that the stone is satisfactorily fine. It has been urged in another chapter that immediate effectiveness is determined by fineness, but as a working basis we assumed that when all the stone would pass through a screen having sixty wires to the inch it would give the desired results. The coarsest portion would not be available at once, but when an application is heavy enough to serve for a year or more, we have enough very fine material in such a grade of stone to meet immediate need. When estimating values of such a grade and coarser grades, the amount per acre to be used is a factor. The coarse is unsatisfactory if the price is not low enough to permit an application sufficient for a considerable term of years, so that it will contain all the fine material needed at once. In that case the coarser material may be expected to meet later need, and may be even more desirable for such purpose, as it would not be subject to leaching.

Coarse grinding costs much less than fine grinding, and it is the resulting low price that permits the heavy application. As stone varies in hardness and ability of the small particles to withstand disintegrating forces in the soil, an estimate of the difference in price between a 60-mesh limestone and a 10-mesh one could not serve as a safe guide. The buyer should know the percentages of a limestone passing through screens of various sizes before he makes a purchase, and should demand part of the saving in cost of production that attends coarse grinding.

Oyster Shell. Ground oyster shell should be given about the same valuation as limestone. It is a lime carbonate, and the percentage of worthless material in it varies somewhat It is coarsely ground, but the large pieces disintegrate in the soil much more rapidly than limestone would do. It contains a little nitrogen and phosphoric acid, partially available, as an offset to coarseness and some lack of purity, as compared with the highest grade of fine stone. It is profitable to buy oyster shell at limestone prices if used liberally enough to furnish a supply for a term of years. The oxide, or burned shell lime, would be nearly the equivalent of burned stone if it did not change to hydrate and air-slaked forms so rapidly that it rarely is on the market in the full strength of fresh burned lime.

Hardwood Ashes. As a source of lime, ashes have become far too expensive. The composition of ashes on the market is widely variable, dirt and moisture often accounting for much of the weight. The lime in fresh burned ashes is peculiarly effective, being finely divided and in oxide form, but the ashes on the market have much of the lime water-slaked and air-slaked. Unless analysis is made at time of purchase, a buyer should not estimate the content of lime in a ton at a value greater than assigned to one-half of a ton of limestone. The additional value of the ashes, due to the potash content, is wholly another consideration.

Marl. No more should be paid for a ton of good chalk marl than an equal weight of fine limestone would cost. Each is a good carbonate of lime, with the same capacity for destruction of acids.

Agricultural Lime. This variable product should not be bought unless actual composition is known, or the cost is as low as that of pulverized limestone, and even then it may be a bad purchase, the methods of the manufacturer being the determining factor. If such lime is chiefly a dumping place for low-grade stone and forkings, it has small agricultural value.

Land Plaster. The soil wants lime in carbonate form. The oxide and hydrate change to carbonate, and therefore are good. Land plaster is a sulphate, and its tendency is to make a soil sour. It should not be considered as a means of correcting soil acidity.

Basic Slag. The amount of effective lime in basic slag, as made by modern methods, is so small that its value is nearly negligible. Basic slag is a good source of phosphorus, and in addition has a tendency toward correction of soil acidity, but such tendency has little cash value for land that requires a considerable dressing of lime to furnish a base with which soil acids may combine.