China, whether derived from the subsoil or from the silts and organic matter of canals and rivers, must have played an important part in the permanency of agriculture in the Far East, for all such additions have been positive accretions to the effective soil, increasing its depth and carrying to it all plant food elements. If not more than one-half of the weight of compost applied to the fields of Shantung is highly fertilized soil, the rates of application observed would, in a thousand years, add more than two million pounds per acre, and this represents about the volume of soil we turn with the plow in our ordinary tillage operations, and this amount of good soil may carry more than 6000 pounds of nitrogen, 2000 pounds of phosphorus and more than 60,000 pounds of potassium.
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Fig. 139.—Gardener thoroughly incorporating fertilizer with his soil preparatory to planting a second crop of the season, May 24th, Shantung, China.
