large, through the persistent repetitions which have prevailed for centuries. If the yearly application of such water to the rice fields is but sixteen inches, and this has the average composition quoted by Merrill for rivers of North America, taking into account neither suspended matter nor the absorption of potassium and phosphorus by it, each ten thousand square miles would receive, dissolved in the water, substances containing some 1,400 tons of phosphorus; 23,000 tons of potassium; 27,000 tons of nitrogen; and 48,000 tons of sulphur. In addition, there are brought to the fields some 216,000 tons of dissolved organic matter and a still larger weight of dissolved limestone, so necessary in neutralizing the acidity of soils, amounting to 1,221,000 tons; and such savings have been maintained in China, Korea and Japan on more than five, and possibly more than nine, times the ten thousand square miles, through centuries. The phosphorus thus turned upon ninety thousand square miles would aggregate nearly thirteen million tons in a thousand years, which is less than the time the practice has been maintained, and is more phosphorus than would be carried in the entire rock phosphate thus far mined in the United States, were it all seventy-five per cent pure.
The canalization of fifty thousand square miles of our Gulf and Atlantic coastal plain, and the utilization on the fields of the silts and organic matter, together with the water, would mean turning to account a vast tonnage of plant food which is now wasting into the sea, and a correspondingly great increase of crop yield. There ought, and it would seem there must some time be provided a way for sending to the sandy plains of Florida, and to the sandy lands between there and the Mississippi, large volumes of the rich silt and organic matter from this and other rivers, aside from that which should be applied systematically to building above flood plain the lands of the delta which are subject to overflow or are too low to permit adequate drainage.
