November 8, 1912] 



SCIENCE 



617 



agricultural practise of this doctrine on 

 much of the farm land of Germany, 

 France, Belgium, Holland, Denmark and 

 the British Isles, those countries have ap- 

 proximately doubled their average acre- 

 yields. The ten-year average yield of 

 wheat in the United States is 14 bushels 

 per acre, while that in Europe has gone 

 up to 29 bushels in Germany, to 33 bushels 

 in Great Britain, and to more than 40 

 bushels per acre in Denmark. The annual 

 application of phosphorus even to the soils 

 of Italy has already become greater than 

 the phosphorus content of all the crops 

 removed. The exportation of our highest 

 grade phosphate rock from the United 

 States to Europe now exceeds a million 

 tons a year, carrying away from our own 

 country twice as much phosphorus as is 

 required for the annual wheat crops of all 

 the states, and millions of acres of farm 

 land in our own eastern states have al- 

 ready been agriculturally abandoned, be- 

 cause of depleted fertility and reduced 

 productive power ; so that it is now impos- 

 sible for our congressmen to enter the 

 capital of the United States from any 

 direction without passing abandoned farms. 

 Ultimate analysis has shown that the 

 most common loam soil of soiithern Mary- 

 land,^ almost adjoining the District of 

 Columbia, contains only 160 pounds of 

 phosphorus, 1,000 pounds of calcium and 

 about 900 pounds of nitrogen in two mil- 

 lion pounds of surface soil, corresponding 

 approximately to an acre of land 6| inches 

 deep. The clover crops harvested from 

 the rich garden soil at Rothamsted in eight 

 consecutive years removed more phos- 

 phorus and calcium from the soil than the 

 total amounts contained in the plowed soil 

 ' See ' ' Leonardto'mi Loam, ' ' Bureau of Soils 

 Bulletin 54, and "Field Operations of the Bureau 

 of Soils" in Reports for 1900 and 1901; or see 

 pages 138 to 142 of "Soil Fertility and Perma- 

 nent Agriculture," Ginn & Company, Boston. 



of this worn-out Maryland land, whose total 

 nitrogen content is also less than would be 

 required for seven such crops of corn as 

 we harvest on good land in the central 

 west, which, however, contains ten times as 

 much of these plant foods as the depleted 

 Maryland soil. 



During the last ten years our population 

 increased 21 per cent., the same as during 

 the preceding decade, while the acreage of 

 farm lands increased only 5 per cent., and 

 the federal government reports all future 

 possible increase in farm land at only 9 

 per cent, of our present acreage. 



Average crop yields for four ten-year 

 periods are now reported by the United 

 States Department of Agriculture. A 

 comparison of two twenty-year averages 

 shows increased acre-yields of 1 bushel for 

 wheat and ^ bushel for rye, while the yield 

 of corn has decreased 1^ bushels and the 

 yield of potatoes has decreased 7 bushels 

 per acre, by twenty-year averages. These 

 crops represent our greatest sources of 

 human food, even our supply of meat be- 

 ing largely dependent upon the corn crop. 

 Less than twenty-year averages are not 

 trustworthy for a consideration of any 

 small increase or decrease in yield per acre. 

 It should be noted that during the last 

 forty years vast areas of virgin wheat land 

 have been put under cultivation, including 

 the Dakotas, which now produce more 

 wheat than all the states east of the Missis- 

 sippi, save only Indiana and Illinois. 



A comparison of the last five years with 

 the average of the five years ending with 

 1900 shows that our wheat exports de- 

 creased during the decade from 198 million 

 to 116 million bushels, and that our corn 

 exports decreased from 193 million to 57 

 million bushels. 



Thus we have fed our increasing pop- 

 ulation not by increasing our acre-yields, 

 but by a slight increase in the acreage of 



