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

removed by a crop of corn, and it will be remembered that it is the nitrogen which is in the form most available to plants that is lost by leaching.

Growing Crops Prevent Loss of Nitrogen. These experiments are interesting also because they show how slight is the danger of loss of nitrogen if a crop is kept growing on the land. Numerous other experiments have confirmed this observation that if the field is covered with a growth of plants practically no nitrogen is lost in the drainage water, not because the nitrates are not formed but because the plants appropriate them as fast as they are produced. If then, the field which has been lying idle during the summer is planted to a crop before the fall rains begin, the loss of nitrogen will probably be prevented. The whole secret of preventing the waste of nitrogen from the soil is to have some crop on it during all the growing season. Nitrification takes place very slowly after the warm weather of summer has passed, so there is little danger of loss of nitrogen through leaving the ground bare in the late fall, provided a crop has been growing on it during the period that was favorable to nitrification. For this reason there need be no fear of loss of nitrogen as a result of fall plowing.

Another Point of View.-There are, however, two sides to the question of the desirability of summer fallows. King cites experiments of his own which show (by determinations made April 30) that the plots which had been fallow the previous year contained 245 pounds more nitrate nitrogen per acre than the corresponding plots on which crops had been produced. His experiments further showed that the

amount of nitrate nitrogen in the fallow plots at that date was actually more than it was on August 22 of the year before. "From this it is clear that the crops on fallow ground start out in the spring under conditions very superior to those on the fields which had not been fallow." (King.) Unfortunately these experiments throw no light on the losses through drainage, and it is impossible to decide whether this desirable condition in the spring has not been brought about by too great a drain on the total nitrogen supply of the soil.

Summer fallowing has a tendency to conserve the moisture of the soil, as one can readily imagine when he recalls the rapid rate at which plants remove water from the ground. The tillage incident to the fallow also prepares an earth mulch and prevents loss of water by evaporation. At the Wisconsin Experiment Station it was found that in the spring following a summer fallow, the land which had been fallowed contained 203 tons more water per acre than did that which had been cropped the previous season. The following quotation is the closing paragraph of King's work entitled "The Soil":

"In very wet climates or more especially in those which have heavy rainfalls outside the growing season, so that excessive percolation and loss of plant food through drainage is large, summer fallowing in broad fields can not be recommended. But in dry countries, where the loss of plant food through drainage channels is small, broad field summer fallowing may in some cases prove decidedly advantageous, because with the deficient rainfall, there may not be

moisture enough to mature a crop and at the same time to develop a sufficient store of plant food from the native fertility of the soil to meet the demands of the next season. At all events, the arguments urged against fallowing in countries like England do not apply to the semi-arid districts of the world with equal force."

Need of Further Investigation. This is one of the many problems in agriculture which calls for more thorough investigation and, fortunately, is receiving the attention of some of our experiment stations at the present time, so that more scientific data may be hoped for in the near future. The claim that fallowing is efficient in the destruction of weeds and injurious. insects is a valid one, but the same results may probably be obtained by a judicious rotation and by the use of cultivated crops, without allowing the ground to lie idle. After all, the practical question is whether the one crop after the fallow is equal to the two crops that would otherwise be produced, and the consensus of opinion among practical farmers seems to be that it is not.

Short Fallows Desirable.-While the long summer fallow is to be recommended only when the soil has been abused and has become so foul with weeds that no other method will remove them, frequent use should be made of the short fallow (i. e. between crops). It will be found advantageous in many instances to plow the land immediately after the removal of one crop and keep it well stirred until the planting of the next. By this means loss of moisture from the soil is prevented and the decomposition of the organic matter is