In some parts of the West there is a lack of decaying vegetable matter in the soil, because the few plants which naturally grow there have small roots, and leave little vegetable material behind when they decay. For this condition one of the best crops to employ in rotation is sugar-beets, because they strike many small roots deep into the earth. As these decay, each leaves behind a tiny load of vegetable mold deep in the earth, and also makes the soil more porous. As the principal elements of the soil needed by sugar-beets are carbon and oxygen, which are absorbed from the air and sunshine, and as the beets can be sold at a good profit, it is an excellent crop to employ in rotation. In the United States records in various states show that where sugar-beets are used in rotation, the wheat and corn yield is increased from two to four times, and in Germany they are largely used to restore the fertility of the land, even if the sugar-beets themselves are sold at a loss. It is most important that farmers should understand the principle of rotation of crops, because nothing is taken from the soil so quickly or in such large quantities as nitrogen, and nothing is so easily put back; while, if it is not so replaced, the land becomes worthless. A comparison of the results of single cropping and the rotation of crops has been clearly shown at the Experiment Station of the Agricultural College of the State of Minnesota, where for ten years they have planted corn on one plot of ground. For the first five years it averaged a little more than twenty bushels per acre, and for the last five years, eleven bushels. On another plot, where corn was planted in rotation, the average yield was more than forty-eight bushels, the difference in average in the two plots being thirty-two bushels, or twice the value of the entire average yield on the exhausted ground. The corn grown at the end of the ten years was only about three feet high, the ears were small, and the grains light in weight. But it cost just as much to cultivate the land that produced it as it did to cultivate the land that produced forty-eight bushels. Of the other two elements, potassium is found abundantly in most soils. It is also found in a readily soluble form in various parts of the United States and is sold at a very low price. But even if these deposits were exhausted we could still use the rocks which are very rich in potassium, and are very abundant, in a pulverized form, or potash could be manufactured from them.