CHAPTER VI

WHY ARE LIME SOILS STRONG?

T has long been an adage that "a lime

IT

country is a rich country," but the full why this is so is yet a matter of many doubts. Pure science has much to reveal before conjectures can be wholly removed and before the how and why of lime in soil productivity can be one of the generally recognized beacon lights in practical agriculture which it is destined to become. And after pure science has done its work, applied science must needs construct the sailing chart for the guidance of the farmer before be can be fully able to develop, conserve and utilize lime with the economy and high efficiency needful for continued crop production. Many of the facts and some of the underlying principles needful for the direction of practice are known and may be stated.

The source of lime in soils. All lime in soils is derived primarily from the primitive

rocks by their reduction to fine fragments, or by their solution, chemical and physical; and, on the average, 3.5 pounds in every 100 pounds of primitive rock is calcium, one of the elements, as are iron, gold, carbon, sulphur, oxygen and nitrogen; and this calcium, united with oxygen, is the lime of commerce, obtained by burning limestone in kilns. But when such rocks are broken down into soil and this is acted upon, as such, by Nature's agencies, the lime dissolves out and is borne away in the drainage waters in immense volumes so large that, on the average, each cubic foot of river water carries to the sea more than 2.1 ounces of lime compounds, eight-ninths of which is lime carbonate, the basis of limestone, the chief ingredient which deposits on the inside of tea kettles, and the lime compound which plays so important a part in determining the productive capacity of soils.

How limestone and lime soils are formed. Much of the more than 300,000 tons of lime carbonate leached out of soils and the underlying rocks and carried into the sea per each

cubic mile of water is again laid down in the shallower waters off shore by coral and shell-forming animals, giving rise to broad stretches and thick beds of limestone material, having entangled with it silts, sands and organic matter in greater or less quantity. These limestone deposits when, by future upward movement of the earth's crust, they come to be portions of the dry land, are again subjected to the processes of weathering, which carry back to the sea the bulk of the lime carbonate, leaving a stratum of overlying soil rich in lime and usually other essential soil ingredients. By the continentwide glacier-grinding an immense amount of rock pulverizing and distribution took place in comparatively recent times. In this way limestone sections were overswept, and much of the lime rock was broken, ground and spread broadcast, deeply and intimately commingling the lime fragments with soil materials, thus producing soils rich in lime carbonate where otherwise such could not have been formed. This gigantic liming operation of Nature occurred too recently

for the application to have been dissolved away, and we thus have wide areas of soils rich in lime not directly underlaid by limestone. Indeed, most of the northern United States, reaching from the Atlantic to the Rocky Mountains, and lying to the north of the Ohio River, are covered with soils richer in lime on account of this glacial action. In the arid and semi-arid regions of the world, where there is comparatively little leaching, nearly all soils may be rich in lime carbonate because, as the soil and rock decay under the conditions of scanty rainfall, the lime carbonate produced tends to accumulate toward the surface under the influence of capillary rise and surface evaporation of the soil moisture, and so the soils of the western United States are nearly all rich in lime. On the Atlantic and Gulf coasts, where glaciers have not operated, but where heavy rainfall and consequent leaching have prevailed for long periods, the soil content of lime carbonate is necessarily low, and for this reason such soils are naturally less productive than they could otherwise be.

Effect of lime carbonate. In outlining some of the ways in which lime carbonate tends to produce and to maintain rich soils, it should be understood that when ordinary lime is applied to a field, whether it be ground or slaked, it is very soon converted into the lime carbonate by the union with it of carbonic acid from the soil or air, and the beneficial effects it is observed to exert are very largely those due to the lime carbonate thus formed. The only reason for applying burned or slaked lime to soils has been that until recently the burning of limestone and slaking it has been the cheapest method of getting the rock in a sufficiently fine powder so that a small amount may be spread over a large area, and so that a small quantity, by weight, of the lime carbonate has a sufficiently large surface upon which soil moisture may act and dissolve it rapidly, for it is only after it is in solution that its effects in the soil are felt.

One of the most important effects of an abundance of lime carbonate in soils is the influence it exerts in tending to bring about