October, 1912.] 319 



BROADHALK WHEAT field.— Nitrogen in soil, lb. per acre. 



In soil 

 1865. 



In soil 

 1904. 



Gain or 

 loss in 

 39 years. 



Added in 

 manure. 



Added in 

 rain. 



Removed 

 in crop. 



Unaccount- 

 ed for. 



2,850 

 4,470 



2,290 

 4,970 



r toil 



-560 

 Plot 2- 



+ 500 



O. — U I] lilt 



Farmyar 

 7,800 



lulu OLl* 



150 

 d manure. 

 150 



600 

 1,990 



-110 



-5,460 



The soil has been getting richer for the last 20 or 30 years, and the 

 greater part of the nitrogen is wasted because bacterial action sets the 

 nitrogen free as gas. There is another principle illustrated here ; that in 

 very rich land the wasteful agencies are so speeded up as to prevent any 

 continued accumulation of fertility out of the unused residues of the 

 manures put on. Higher fertility means a higher level cf waste. 



How Nature Accumulates Plant Food. 



We will now take another plot on the same field to illustrate its 

 recuperative actions. 



This is a part of the field that has been allowed to run wild siuce 1881. 

 The difference between the two plots lies in the fact that on the land 

 running wild the vegetation is never removed but allowed to die natur- 

 ally. Hence not only is the nitrogen taken out by the crop returned to 

 the soil, but also a large stock of carbonaceous matter, and this carbon- 

 aceous matter furnishes a bacterium present in the soil, Azotobacter 

 chroococcum, which will enable it to fix atmospheric nitrogen :— 



Broadbalk Field, Rothamsted. 

 Land allowed to run wild. Nitrogen in Soil, lb. per acre. 



Broadbalk 



In soil to 27 in. 



Added by rain. 



Gain in soil 

 per annum. 



1881 



1904 



5,910 



8,110 



90 



92 



This plot gives us a cine to the source of the vast accumulations of 

 nitrogen in the old prairie soils. 



Heating the Soil. 



By putting the soil through various processes of partial sterilisation, 

 such as heating or treatment with antiseptics, we can eliminate certain 

 organisms which keep in check the useful bacteria in the soil. Heating 

 the soil to the temperature of boiling water for two hours will double its 

 productivity and such a process has been found to be commercially pro- 

 fitable in the case of green house soils. The partial sterilisation processes 

 restore and even enhauce its fertility by eliminating its injurious organ- 

 isms. At present the processes have not been extended to the open held 

 but progres is being made in that direction and gives some promise of a 

 method by which ultimately the unseen fauna and flora of the soil will be 

 domesticated, the useful races encouraged and the noxious repressed just 

 as the larger flora and fauna have been reduced to our service since the 

 days when primitive man first turned from hunting to agriculture, 



