Page:Farmers of forty centuries.djvu/233

Rh We have inserted in this table, for comparison, the crop of rice, and have increased the crop of potatoes from three hundred bushels to four hundred bushels per acre, because such a yield, like all of those named, is quite practicable under good management and favorable seasons, notwithstanding the fact that much smaller yields are generally attained through lack of sufficient plant food or water. From this table, assuming that a crop of matured grain contains 11 per cent of water and the straw 15 per cent, while potatoes contain 79 per cent and beets 87 per cent, the amounts of the three plant food elements removable annually by 1000 pounds of crop have been calculated and stated in the next table.

From the amounts of nitrogen, phosphorus and potassium applied annually to the cultivated fields of Japan and from the data in these two tables it may be readily seen that these people are now and probably long have been applying quite as much of these three plant food elements to their fields with each planting as are removed with the crop, and if this is true in Japan it must also be true in China. Moreover there is nothing in American agricultural practice which indicates that we shall not ultimately be compelled to do likewise.