620 



SCIENCE 



[N. S. Vol. XXXVI. No. 932 



mon prairie. We also find that, as an 

 average of triplicate tests each year, potas- 

 sium increased the yield of corn per acre 

 by 20.7 bushels in 1902, by 23.5 bushels in 

 1903, by 29.0 bushels in 1904 and by 36.8 

 bushels in 1905 ; while the addition of phos- 

 phorus produced a decrease of 0.1 bushel 

 in 1902 and an increase of 0.9 bushel in 

 1903, of 3.9 bushels* in 1904 and of 0.3 

 bushel in 1905. 



As an average of the results from twenty 

 plots of unfertilized land in the Penn- 

 sylvania rotation experiments with corn, 

 oats, wheat and hay (clover and timothy 

 mixed), the crop values in two consecutive 

 twelve-year periods decreased by 26 per 

 cent.; while, as an average of the twenty- 

 four years, the crop values were increased 

 62 per cent, by farm manure and 65 per 

 cent, with commercial plant food, as com- 

 pared with the results from unfertilized 

 land. 



The records from the Agdell rotation 

 field at Rothamsted show that as an aver- 

 age of the turnips, barley, clover (or 

 beans) and wheat the yield decreased on 

 unfertilized land by 42 per cent, measured 

 by the results from two consecutive thirty- 

 two-year periods; and, if we span a sixty- 

 year period, we find that the yield of tur- 

 nips on unfertilized land was 10 tons per 

 acre in 1848 and less than i ton in 1908 ; 

 that the barley yielded 46.5 bushels in 

 1849 and only 10 bushels per acre in 1909 ; 

 the clover produced 2.8 tons in 1850 and 

 less than 1 ton per acre in 1910 ; while the 

 wheat following clover produced 39.7 bush- 

 els in 1851 and 24.5 bushels in 1911. 



The application of plant food (for the 

 turnip crop only) in the same rotation 

 over a period of sixty-four years increased 

 the average yield of turnips from 1^ tons 

 to 17^ tons per acre, increased the yield 



'Irregular insect injury in 1904 (see Illinois 

 Bulletin 123, pp. 251, 252). 



of the barley following from 24.4 to 38.5 

 bushels, then increased the average yield 

 of legumes from 1,945 pounds to 4,413, 

 and increased the yield of wheat after 

 legumes from 25 to 34.8 bushels, as com- 

 pared with the unfertilized land. 



If, again, we span the sixty years, we 

 find that on the fertilized land the yield 

 of turnips was 12^ tons in 1848 and 17^ 

 tons in 1908; that barley produced 35.9 

 bushels in 1849 and 33.4 bushels in 1909 ; 

 that clover produced 3^ tons in 1850 and 

 4| tons in 1910 ; while wheat yielded 30.3 

 bushels in 1851 and 38 bushels per acre in 

 1911. 



Thus, the records show that during the 

 last four years, following a sixty-year 

 period, the plant food applied has in- 

 creased the yield of wheat by 55 per cent., 

 increased the barley by 234 per cent, and 

 the clover by 340 per cent. ; while the yield 

 of turnips on the fertilized land was 49 

 times as great as on the unfertilized land. 

 "With these facts in mind we may well 

 consider the following statements from 

 Whitney in Farmers' Bulletin 257: 



Apparently, these small amounts of fertilizers 

 we add to the soil have their effect upon these 

 toxie substances and render the soil sweet and 

 more healthful for growing plants. We believe it 

 is through this means that our fertilizers act 

 rather than through the supplying of food to the 

 plant. (Page 20.) 



There is another way in which the fertility of 

 the soil can be maintained, viz., by arranging a 

 system of rotation and growing each year a crop 

 that is not injured by the excreta of the preceding 

 crop; then when the time comes around for the 

 first crop to be planted again the soil has had 

 ample time to dispose of the sewerage resulting 

 from the growth of the plant two or three years 

 before. . . . Barley will follow potatoes in the 

 Rothamsted experiments after the potatoes have 

 grown so long that the soil will not produce pota- 

 toes. The barley grows unaffected by the excreta 

 of the potatoes, another crop follows the barley, 

 and the soil is then in condition to grow potatoes 

 again. 



