240 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 2 



phate are put at 26,000 million tons. A high estimate of world use 

 of all phosphatic fertilizers is 25 million tons a year. But, with world 

 population increasing rapidly and with the use of fertilizers still only 

 partly established in some of the large crop -producing regions, a high 

 estimate must be taken in making any long-term prediction. There 

 would seem to be enough rock phosphate in known and workable 

 deposits to last for another thousand years. 



The phosphorus in fertilizers is just as exposed to the processes of 

 soil fixation as is the soil's own supply of available phosphorus. Even 

 in favorable conditions not more than 25 percent of the added fertil- 

 izer phosphorus enters current or subsequent crops. Despite con- 

 siderable study by twentieth-century science, this problem remains 

 unsolved. The discovery of a phosphatic fertilizer producible from 

 mineral phosphate, which would (a) remain highly available to 

 plants and (b) resist soil-fixing influences, would greatly reduce the 

 world's annual consumption of mineral phosphate reserves. At pres- 

 ent, however, the best that can be done is to prevent a minor proportion 

 of the fixation loss by soil-management practices, e. g., liming to reduce 

 soil acidity, placing fertilizers in bands instead of broadcasting them 

 and thus reducing soil contact. There is some evidence that soils with 

 a high content of organic matter fix phosphate less severely. 



The continuous outflow of sewage from most centers of population 

 represents an enormous loss of phosphorus from the modern land 

 cycle. The human animal, except in countries such as China and Ja- 

 pan, no longer conserves his own organic wastes. With the widespread 

 introduction of water closets, these wastes are voluminously diluted 

 and eventually pass down rivers to the sea. Only a small fraction 

 of the phosphorus so involved is recovered. Liebig, in his denuncia- 

 tion of England's heavy use of bones, stressed this point. "England 

 annually removes . . . from other countries the manurial equivalent 

 of 3V2 million men, whom she takes from us the means of supporting, 

 and squanders down her sewers into the sea." It has been estimated 

 that the phosphorus in the sewage from 5,000,000 people is equivalent 

 to 17,000 tons of rock phosphate per year; Britain's current annual 

 wastage must be at least the equivalent of 160,000 tons of rock phos- 

 phate (while she imports some 1,200,000 tons of mineral phosphatic 

 fertilizer materials) . 



A more serious loss of phosphorus in the modern world is probably 

 that caused through soil erosion. When millions of acres of top- 

 soils are blown or washed away, several hundred pounds of phosphorus 

 (available plus fixed) are lost with each acre. The annual loss of 

 phosphorus by erosion in the United States was estimated in 1930 

 to be more than 2,000,000 tons. And we are still only on the verge 

 of reversing the widespread erosion of soils even in those countries 

 where the problem has been seriously and determinedly faced. 



