Studies on calcium as an important nutrient for legumes have shown that the amount of this element required by these plants is large in comparison with the needs of non-legume plants. For 25 bushels of wheat and a ton of straw, only 5 pounds of calcium are needed. For 50 bushels of corn and a ton of fodder a like amount must be provided. To produce two tons of clover hay—about the crop that might be expected on 50 bushel corn land—the soil must supply 80 pounds, or 16 times as much calcium. A two-ton hay crop of soybeans, often considered able to grow on sour soil, requires 55 pounds of calcium. Legumes make large demands on the soil for calcium in comparison with other crops, and for this reason they represent the first group of crops to show disaster from a depleted supply of calcium in the soil.

In terms of the amount of limestone required to supply this required calcium, however, the figure is small. Pure limestone contains 40% calcium, or 40 pounds per hundred, hence a crop of 50 bushels of corn and stover would take calcium from the soil, equivalent of only 12 1/2 pounds of limestone. Red clover, a much heavier feeder on calcium, would take for a two-ton crop, the calcium that would be supplied by 200 pounds of pure limestone. Soybeans at the same acre yield would need about 150 pounds. Thus the actual calcium needs of the crop can be supplied in relatively small quantities of limestone if it can be delivered to the plants in such a way that they can use it fully. In respect to the crop needs of calcium, therefore, we may think of limestone in terms of pounds rather than tons, provided this is delivered to the plant in usable form.

As a rock, limestone is usually considered insoluble, yet this is not the whole truth when one recalls the numerous caves dissolved out of limestone by running water. When finely ground, of course, limestone becomes more soluble in the same way that powdered sugar dissolves more quickly than rock candy, yet both are the same chemical composition. When limestone is ground into a powder that is fine enough to pass a sieve with 100 holes per linear inch, or 10,000 holes to a square inch, its action in the soil is practically as rapid as that of the water soluble forms of lime, namely, quick lime and hydrated lime. The finer grinding of limestone with this resulting increase in solubility make it behave like a fertilizer in speedy effects.

If limestone is to be rapid in its action it must be finely ground. Much pulverized, or powdered, stone is now available as a consequence of improved methods of separating this fraction during grinding. Likewise channels that formerly consumed such output are now using less, so that it is available at prices more conducive to agricultural use. Some quarries are providing stone of such fineness that all of it passes the 100 mesh screen, while many have 40 mesh, or 30 mesh, stone. These latter contain no particles larger than those which will pass screens of such size and usually have about one-half, by weight, fine enough to pass the 100 mesh screen. These also lend themselves to drilling better than the 100 mesh material which does not flow through machinery easily.

The regular 10 mesh stone commonly broadcast at heavy rates might also be drilled according to this plan but it contains such a small portion of finely ground powdered stone that it is slower in its action. If larger amounts can be drilled so as to put into the soil as much powdered stone as is added by the finer material, similar results may be expected. Such large amounts cannot be handled so easily through the drill, nor with so little wear on the machinery. It seems doubtful economy to drill the coarser stone in place of the 40 mesh and finer material. For drilling purposes and effective results the finer stone should be considered.

If smaller amounts of finely ground limestone are to be successful in supplying plants with calcium and establishing the crop, the limestone should be drilled into the soil. Broadcasting such small amounts as 500 pounds per acre is not significant in its effects. Yet when this same amount is drilled, each drill row represents small soil areas where the limestone is concentrated and the soil along the row is more highly saturated with lime. Experimental studies show that the higher the degree of saturation of the soil by lime, the more readily does the plant secure the lime. Thus, the plants find in the drill row this favorable condition for supplying lime and will grow there. As is true for wheat and other drilled grains, so it is true for legumes—their establishment in the drill row only usually means plenty of plants per acre and a good stand.

Since fine limestone is considered much like a fertilizer, naturally the season for drilling it might be expected to be that time when the legumes are seeded. It has been found a good practice to drill the limestone in the spring when the clovers and other lime-loving legumes are sown. The fertilizer attachment of the grain drill will deliver the limestone, while the grass seed attachment delivers the seed. In this way one operation over the field completes the seeding. If the drill is not run into the soil deeply, the seed may be delivered down the spout and the seeds and limestone put into immediate contact. If the seeds are covered too deeply by soil or heavy droppings of the dry powdered stone, the germination and stand may be disturbed. The seed delivery spouts on the drill may be detached from the sprouts leading down to the drill shoe, and the clover seed scattered on the surface of the soil. The seed spouts may also be extended to scatter them behind the drill, where they will fall into the drill furrows immediately over the limestone and be covered well enough by the first rain.

When drilling the fine limestone in the spring season, it should be done as early as possible because of the well known need for seeding clover early. This is sometimes impossible because the soil is too wet to permit going over it with the drill, and the wait for suitable soil conditions delays the seeding until the nurse crop is so large that the clover will be smothered out, or fail because of moisture shortage. It is not necessary that the limestone and the seed go on together, provided the soil is not cultivated or disturbed between these two operations. Consequently, the fine limestone may be drilled during the winter when soil conditions permit. The broadcast clover seeding may follow at the proper date. This will serve practically as well as drilling the two together.

As for the time when fine limestone may be drilled most conveniently and effectively, the fall seeding season is a good one where wheat or barley is the nurse crop. If oats serves as such, the limestone may be drilled similarly with the oats in the spring and the clover broadcast later. When the legumes are seeded alone, then the limestone may well be drilled at their seeding season.

“How long will the fine limestone last?” is a common question when one contrasts this method with that of broadcasting a heavy application of coarse material that is effective to the legume crops in more than one round of the rotation. Legumes are the first among the crops to need lime, consequently, the fine stone is drilled with the legumes. The effect will last longer than this one crop if the soil is not disturbed. Sweet clover has reseeded itself after a start with fine lime, showing that the effect can carry over to the third year. When only the small soil areas represented by the drill rows are treated and the ground plowed afterward this small amount of limed soil is too thoroughly scattered through the great soil mass to lend much effect. When the next legume crop comes around in the rotation another limestone treatment should be used. Because broadcast heavy liming is an arduous task and represents a significant investment, one naturally hopes that its effects will last a longer time than for one single year of rotation. Drilling the fine lime is a simple, one-man operation of moderate cash outlay and it might be considered as a part of the treatment for every legume seeding.

The most effective method of drilling fine limestone is by means of the fertilizer attachment on the grain drill. This will handle limestone effectively though one cannot expect even this machine to operate without attention. One must always make sure that the stone is not failing to get down into the distributing machinery satisfactorily. It is also necessary to learn the rate of delivery. Some careful tests have shown that very fine limestone was delivered at only three-fourths of the rate as given for the particular set of gears and gate opening specified for that of fertilizer. If one is to drill 500 pounds of the finer stone it may be necessary to set the machinery at a higher figure than that for fertilizer delivery.

As the declining fertility of our soils becomes more widely recognized and the use of fertilizers to replace it becomes a more general practice, the fertilizer drill will be a more common machine for applying limestone as well. In respect to farm machinery, the fine limestone drilling methods will fit into the already common stock of farm equipment and call for no special machinery of limited use.

As the soils in the regions of great rainfall and heavier crop production have become low in lime—now being especially recognized by clover failures—so have they also become correspondingly low in other nutrients not so grossly removed by plants. The soil deficiency in these is just as disastrous since the crop is impossible unless each of the required nutrients is amply supplied. The use of fine lime drilled with wheat has sometimes improved the wheat crop, pointing out that the soil was low in calcium even for wheat, and doubtless for corn and other crops that require but small amounts of it. Liming ahead of corn has improved this crop, probably by indirect as well as by direct effects through the calcium supplied. Oats have sometimes been improved by liming and reports of improvement in soybeans from limestone drilled with them are not uncommon. Its benefit on oats and wheat nurse crops, suggest similar effects from it on barley serving the same purpose, especially since barley is the most sensitive of the small grains to the lack of lime. The low supply of lime that may be disastrous to the extent of complete crop failure for legumes, is therefore injurious to many other crops.

This declining fertility level is evident in spite of the fact that a liming treatment, especially a heavy application, helps much in making other plant foods more effective. It is now known that liming helps the plants to obtain more potassium. Also it is instrumental in making a phosphorus treatment more beneficial. On limed land phosphorus is usually more effective than on unlimed soil. Lime also helps the plant to get nitrogen. It aids the plant in making much better use of the limited supplies of these other nutrients. It does not add these to the soil, hence the already low supply will be more rapidly depleted by liming. If, however, clovers can be grown and larger crop yields result, the restoration of the fertility should be quickly undertaken when this soil need is fully appreciated. As we use more limestone, attention must likewise be given to other deficiencies of soil fertility which this practice will help bring to our notice, and for which limestone cannot be a substitute.

To date the drilling of the finer limestone has been tried with successful results by farmer cooperators in many parts of the state. The soil types represented include the following: Boone, Cherokee, Crawford, Decatur, Edina, Gerald, Grundy, Knox, Lebanon, Marshall, Memphis, Oswego, Putnam and Summit silt loams; the Shelby and Lindley loams; Clarksville and Baxter gravelly loams; Lintonia fine sandy loam; and Wabash clay loam. By no means have all soil types been included in this rather extensive list, but those of level topography, heavier subsoil and significant degree of acidity have been grown to acid sensitive crops by means of lighter applications of limestone drilled on them. They testify to the success of this practice on those soils most difficult to seed to clover. Not only red clover, but sweet clover, and in some cases, alfalfa has been started by this treatment. Unfortunately, liming cannot offset bad seed, summer drought or infertility, but it can care for the calcium deficiency, or lime need, on many of the prevailing soil types in the state.

In terms of the labor of distribution, the drilling method effects a real saving. To drill 500 pounds per acre on 20 acres is a one-man labor load, totaling five tons of material, while the corresponding labor load of 40 tons broadcast might require the help of the neighbors. It is this labor requirement that should be considered as the significant advantage of the finer limestone, and that makes this method lend itself to bringing limestone to soils where the other method might mean too great an initial cost. The smaller amount of limestone means less initial cash outlay; it permits the stone to be hauled to greater distance from railroads or delivery points, and makes possible liming within the farmer’s own labor. The one-man labor load and smaller amounts of stone required make delivery possible at any time with storage for later use. When its use becomes more widespread, the stone may be stocked more generally by local dealers and thus still greater economies effected. Under such conditions, its costs when used regularly in every rotation should not exceed the costs of heavier applications of coarser stone applied less often.

This method of handling the liming need of the soil reduces it from a complex problem of large cash outlay and extensive labor, to a regular farming practice that can be geared into the routine farm program without its disruption. On such a basis the drilling of fine limestone may be accepted as a regular part of the legume seeding whenever it comes around in the rotation just as fertilizing should be a part of wheat seeding. Under such conditions more legumes can be successfully grown, more fertility restored to the soils and higher profits returned by the land.