616 



SCIENCE 



[N. S. Vol. XXXIII. No. 851 



will hardly be urged that it is even chiefly due 

 to capillary and plant concentration such as 

 might prevail over large areas like the IJnited 

 States. At least the projection of such a 

 rate of concentration through any material 

 period forward or backward would point to 

 very unusual if not impossible conditions. 



If it be true that 1,200,000 tons of PO, are 

 lost annually from the soil of the whole United 

 States by drainage into the sea and that capil- 

 lary water is carrying toward the surface 

 18,000,000 to 40,000,000 tons, there would be a 

 total mean movement of 30,200,000 tons of 

 PO^ or 9,800,000 tons of phosphorus. A yearly 

 removal at this rate maintained for 10,000 

 years would require more phosphorus than is 

 carried in 10.5 feet of igneous rock, assuming 

 200 pounds as the weight of a cubic foot and 

 Clark's value cited above; and all of the phos- 

 phorus carried in 40 feet of soil weighing 

 4,000,000 pounds per acre-foot, containing 581 

 parts per million of phosphorus. A combined 

 chemical and mechanical erosion which would 

 remove 40 feet in 10,000 years, from the 

 United States, would have to exceed one inch 

 in 21 years. 



It appears to be overlooked, in making the 

 estimates, that capillary sweeping is very 

 often and strongly downward as well as up- 

 ward, and also that a large proportion, prob- 

 ably more than three-fourths of the rainfall, 

 not removed in the runoff, never penetrates 

 the soil beyond a depth of two feet and should 

 not, therefore, be used as a measure of surface- 

 ward movement of plant food below that 

 depth. We have measured the combined cap- 

 illary and internal-evaporation-movement out 

 of the 5- to 10-foot depth into the 0- to 5-foot 

 depth in four instances, two of which were a 

 clay loam and two a sandy loam soil. The 

 measurement was continuous through 314 

 days under a summer temperature. Under 

 the most favorable conditions for upward 

 movement water was carried from the 5- to 

 10-foot zone into the 0- to 5-foot zone at the 

 rate of three pounds per square foot during 

 the 314 days, where the surface was continu- 

 ously firm, while under a 2-inch earth mulch 

 the movement was 2.2 pounds. In the sandy 



loam the movement out of the 5- to 10-foot 

 zone into the 0- to 5-foot zone was less than 

 .8 pounds in 314 days. The annual combined 

 upward movement from the 5- to 10-foot zone 

 into the 0- to 5-foot zone, at the most rapid 

 rate, was .7 inch in the clay loam and .17 

 inch in the sandy loam. 



Assuming a soil solution containing 20 

 parts per million of PO^, the total phosphorus 

 which might thus be added to the surface five 

 feet from the five feet below, would be but 

 1 to .25 pound per acre annually and even 

 these values we regard materially too high for 

 average conditions, although they show a rate 

 less than one fifth that of the estimate cited 

 by Chamberlin. It is true that the capillary 

 and plant " cycles " are agencies which, at the 

 time, assist in the utilization of plant food 

 substances, but they primarily accelerate their 

 waste and should not therefore be reckoned as 

 " efficient factors " of secular maintenance of 

 soil productivity. 



We quite agree that the Mongolian races 

 have " demonstrated one mode of effective 

 secular maintenance of the soil productivity," 

 but we fail to see that it is " closely analogous 

 to the natural method of the geologic ages." 

 Our observations bring the conviction that 

 they return to their fields, year by year, a full 

 measure of all potassium and phosphorus re- 

 moved with their crops; that their cultural 

 methods very largely reduce losses by both 

 physical and chemical erosion; and that they 

 secure a very high efficiency for the plant food 

 used by the crops. All human and animal 

 excreta and all fuel ashes of country and city 

 are universally applied to the cultivated fields. 

 Enormous quantities of bean, rape seed, cotton 

 seed and peanut oil cake are used as fertilizers 

 annually and an enormous tonnage of canal, 

 reservoir and river mud is also applied, even 

 to the extent of 70 to 100 tons per acre in 

 some instances, as single dressings which must 

 carry to the fields not less than 100 to 150 

 pounds of phosphorus. Then their very ex- 

 tensive practise of irrigation adds, with the 

 silt and soluble plant food carried in the 

 water, quite as much fertility as is removed 

 by leaching, and all irrigated areas are placed 



