A crop of wheat like the one stated, if no part of the plant food contained in the grain or straw were returned to the field, would deplete the soil to the extent of about 90 pounds of nitrogen, 15 pounds of phosphorus and 65 pounds of potassium; and the crop of soy beans, if it also were entirely removed, would reduce these three plant food elements in the soil to the extent of about 240 pounds of nitrogen, 33 pounds of phosphorus and 102 pounds of potassium, on the basis of 45 bushels of beans and 5400 pounds of stems and leaves per acre, assuming that the beans added no nitrogen to the soil, which is of course not true. This household of farmers, therefore, in order to have maintained this producing power in their soil, have been compelled to return to it annually, in one form or another, not less than 48 pounds of phosphorus and 167 pounds of potassium per acre. The 330 pounds of nitrogen they would have to return in the form of organic matter or accumulate it from the atmosphere, through the instrumentality of their soy bean crop or some other legume. It has already been stated that they do add more than 5000 to 7000 pounds of dry compost, which, repeated for a second crop, would make an annual application of five to seven tons of dry compost per acre annually. They do use, in addition to this compost, large amounts of bean and peanut cake, which carry all of the plant food elements derived from the soil which are contained in the beans and the peanuts. If the vines are fed, or if the stems of the beaus are burned for fuel, most of the plant food elements in these will be returned to the field, and they have doubtless learned how to completely restore the plant food elements removed by their crops, and persistently do so. The roads made by the Germans in the vicinity of Tsingtao enabled us to travel by ricksha into the adjoining country, and on one such trip we visited a village mill for grinding soy beans and peanuts in the manufacture of oil, and Fig. 136 shows the stone roller, four feet in diameter and two feet thick, which is revolved about a vertical axis on a circular stone plate, drawn by a donkey, crushing the kernels partly by its weight and partly by a twisting motion, for the arm upon which the roller revolves is very short. After the meal had been ground the oil was expressed in essentially the same way as that described for the cotton seed, but the bean and peanut cakes are made much larger than the cotton seed cakes, about eighteen inches in diameter and three to four inches thick. Two of these cakes are seen in Fig. 137, standing on edge outside the mill in an orderly clean court. It is in this form that bean cake is exported in large quantities to different parts of China, and to Japan in recent years, for use as fertilizer, and very recently it is being shipped to Europe for both stock food and fertilizer.