Sour Soils

Loss of Lime. Nature made the value of land as a producer of food

utterly dependent upon the activity of lime, and at the same time gave

it some power to shirk its work. In a normal soil is a percentage of

lime that came from the disintegration of rock of the region or was

transported by action of water on a huge scale. Possibly rarely would it

be in insufficient amount to keep a soil in a condition friendly to

plant life, and to feed the plant, if it stayed where nature placed it

and kept in form available for the needs it was intended to meet. There

is land that always was notably deficient in this material, and there is

land that was known in the early history of the world's agriculture to

be "sour," but the troubles of our present day in the case of the

farming country in the humid region of the United States is less due to

any natural absolute shortage than to combination that destroys value

and to escape by action of water.



Prevalence of Acidity. The results of experiment station and farm

tests are conclusive that the soils of the greater part of all the humid

region of the United States show lime deficiency. Formerly, acidity was

associated in our minds with wet, low-lying land, but within the last

twenty years we have learned that it prevails in light seashore sands

along the Atlantic shore, in clays, loams and shales stretching to the

Appalachian system of mountains, on top of mountain ranges and across

foothills to our central states, and through them in stretches to the

semi-arid lands of the west. While not all this land has fallen into the

lime-deficient class, and the great part of some states remains

alkaline, the tendency toward acidity is continuous.



Crop production in great portions of the Mississippi valley is

restricted by lack of lime in the soil, and some states to the eastward

have one-half to nine-tenths of their acreage too low in lime for the

best results. Calcareous soils have been losing their distinctive

feature, and the immense areas of land naturally low in lime have

remained hampered in ability to make full returns for labor, fertilizer

and seed. It is this situation that brings the right use of lime on

land to the front as a matter of fundamental importance to the farmer.



Causes of Soil Acidity. If any discussion of the causes of soil

acidity would delay a decision to apply lime where needed, the time

given to such discussion would be worse than wasted. It is much more

important to be able to detect the presence of harmful acids and to

neutralize them than it is to know why the soil should be in such plight

that it could not supply the required lime and had become dependent upon

its owner for assistance. On the other hand, some of us find it

difficult to accept a fact without seeing a reason for it, and we may do

well to consider several causes that may be at work to put a soil out of

the alkaline class.



Leaching. One cause that appears obvious and easy of acceptance is

leaching. In the case of one Pennsylvania farm, lying in a limestone

valley, the lime had been washed out by action of water so freely that

caverns formed under the surface, and a test showed a marked deficiency

in the top soil. This land ceased to grow clover, and plantain and

sorrel abounded. This case, which is not an isolated one, showed an

unusually rapid loss, but we always expect to find the water from wells

and springs in a limestone country strongly impregnated with lime.

Drainage waters contain it. The draft by action of water is continuous,

and in some types could easily account for sufficient loss to change the

nature of the soil. We may place undue emphasis upon this factor, as

other causes are at work, but leaching is a leading source of loss.



Chemical Compounds. A serious cause of lime exhaustion that is being

studied by soil chemists is the presence of compounds in the soil that

combine with the lime and rob it of ability to serve the soil when new

acids form. The practical farmer accepts the statements of the chemists

on this point, and probably would not have his interests served by any

exact knowledge of the nature of these agents.



Decaying Vegetation. A cause of acid conditions that is widely known

and accepted, and that may therefore stand out in our thinking with

undue prominence, is connected with the decay of green vegetable matter

in the soil. Many of us have seen fields rendered temporarily

unproductive by the plowing down of a mass of immature plants in

midsummer. All organic matter, indeed, in its decay makes a draft upon

the lime content of the soil in which it may be buried.



Removal in Crops. Lime is taken out of land by plants, and the loss is

a considerable item, but our interest is in the form of lime that can

correct soil acidity, and we know that compounds of lime that are

worthless for this purpose may be the chief source of the lime in our

crops. A determination of the lime in the ash of a crop does not give

data of much practical value.