CHAPTER VIII

SUMMER FALLOWING

Origin of Fallowing. The practice of fallowing or "resting" the land is a very old one, being mentioned in the twenty-fifth chapter of Leviticus, where the people are commanded to rest the land every seventh year. "The seventh year shall be a sabbath of rest unto the land.” It is not known if this law was introduced into the Jewish code from a knowledge of the effect of fallowing on the soil, or if it had more to do with the mystical meaning that seems to be associated with the number seven in the Hebrew religion.

A study of the history of agriculture leads one to believe that when the nomadic tribes first settled down to anything like systematic cultivation of the soil, they grew one crop (probably of the wheat family) continuously on the same field, until the soil became so impoverished that it could no longer be tilled with profit. They then moved to other sections where virgin soil was to be found, and repeated the process. In the course of time it was discovered that these lands which had been abandoned would again produce good crops after a period of "rest" as it was called. This led to the practice of cropping the land one year, and allowing it to lie idle the next. It was later discovered that if the soil was frequently stirred during its resting period the growth the following year would

be much more luxuriant than if the ground was left undisturbed. From this beginning arose the practice of summer or bare fallowing as it is understood to-day. Later experimenters found that practically as good results could be obtained by the use of the so-called "fallow crops" in place of the year of rest. These are simply crops like Indian corn, turnips, potatoes, etc., which are intertilled and kept free from weeds during at least a part of their period of growth, and their introduction has practically done away with the use of the bare fallow in most localities.

It is now well understood that what was formerly called resting the land is in reality a method of bringing about ideal conditions for the transformation of potential food into forms available to the plant. This practice of fallowing the land has practically fallen into disuse, but is being so strongly advocated in some quarters at the present time that it seems proper briefly to discuss the subject here.

Fallowing adds nothing to the Soil.-The chief advantages claimed for summer fallowing are: (1) It makes plant food available, thus increasing the succeeding crop. (2) It enables one to rid the land of weeds. (3) It destroys large numbers of injurious insects. It is doubtful, however, if under good conditions of tillage and soil management, fallowing is ever necessary. It adds nothing to the soil, but merely presents conditions that are favorable to the conversion of potential plant food into available forms; and the increase in the crop following the fallow is seldom sufficient to recompense the farmer for the year of non-production. The crude methods of culti

vation in use in earlier times doubtless made fallows necessary, but the introduction of modern machinery,

Diagram showing the construction of the lysimeter used at the New York State Experiment Station to study the loss of nitrogen from the soil by leaching

and more rational methods of tillage, have for the most part removed this necessity.

There is no doubt of the efficiency of fallowing as a method of making plant food available, especially if the soil is frequently stirred. The conditions brought about by this treatment of the soil are just those

which hasten nitrification, for it has been shown that the nitrifying bacteria thrive best in a warm, well aerated soil. The result of fallowing is, that during the hot summer months the process of nitrification goes on very rapidly, and as there is no growth to remove them, the nitrates accumulate in the soil in large quantities.

Nitrogen May be Lost Through Fallowing.-Attention has been called to the fact that the nitrates are easily leached out of the ground if present in any considerable amount. One of the dangers of the practice of fallowing is that if the land is left bare during the heavy rains of fall and winter, a large part of the nitrates formed during the summer months may be lost in the drainage water, a state of affairs that is to be avoided if possible. Snyder in a Minnesota bulletin reports an experiment in which for every pound of nitrogen made available by fallow treatment, five pounds of total nitrogen was lost from the soil. At the New York Experiment Station at Geneva, tests were made to determine the loss of nitrogen in drainage water. Lysimeters were constructed to simulate natural conditions as nearly as possible and yet allow the collection of the drainage water. Grass was grown on one of these lysimeters, being frequently mowed, as is done on a lawn. The soil in another was kept bare, no plants at all being allowed to grow, and the surface was frequently stirred. The drainage water from the lysimeters was all collected, and the nitrogen determined. It was found that in the case. of the lysimeter on which the sod was growing, practically no nitrogen was lost in the drainage water,

while in the other the loss of nitrogen amounted to from 218 to 357 pounds of nitrogen per acre each year. There is no doubt that these figures are in excess of the loss that would actually occur under field conditions, as the drainage in the lysimeters was perfect, and the effect of capillarity was probably less

Sometimes the same forces which make soils destroy them as well. This granite knob was once covered with soil which has been washed away, probably as a result of the removal of the forest

than would have obtained in the field. They show, nevertheless, in a marked way the danger of great loss of nitrogen if the summer fallow is followed by heavy fall rains. In these experiments it was found that the loss was small in the summer months, nearly all of it occurring during the fall and winter. This loss of nitrogen amounts to from two to four times that