318 



[October, 1912. 



THE FERTILITY OF THE SOIL. 



The following is taken from a discourse delivered by Mr. A. D. Hall, 

 p.r.s., before the Royal Institution on May 24th last :— 



Definition of Fertility. 



The fertility of the soil is best defined as that property for which a 

 man pays rent- Nitrogen is the main factor determining fertility because, 

 in the first place, it is one of the neceesary and most expensive elements 

 in the nutrition of the plant, and, secondly, because its amount in the soil 

 is subject to both gains and losses from causes which are more or less 

 under the control of the farmer. It can be taken as settled nowadays 

 that the plant itself can make no use of nitrogen gas but must draw 

 combined nitrogen in one of its simpler forms from the soil. 



Duration of Fertility. 



The question of the duration of the fertility of the land under con- 

 tinual cropping is exciting attention at present as the United States has 

 begun to take alarm at the reduced reproduction of some of its most 

 fertile lands. As a rule all virgin soils are not rich and the system of 

 cropping alternately has reduced great areas to such a poverty- stricken 

 condition that it has been allowed to go derelict. 



Experiments on wheat. Broadbalk Field, Rothamsted. 



Average Produce of Grain, first 8 years (1844-51) and the successive 

 10-year periods, 1851-1911. 







Averages over 



Plot. 



Manure. 



8 years, 

 1844-1851 



10 years, 

 1852-1801 



10 years, 

 1862-1871 



10 years, 

 1872-1881 



2 

 3 



Farmyard manure... 

 Unmanured 



Bush. 



28-0 

 172 



Bush. 

 34-2 

 15-9 



Bush. 

 37-5 

 145 



Bush. 



28-7 

 10-4 







10 years, 

 1882-1891 



10 years, 

 1892-1901 



10 years, 

 1902-1911 



00 years, 

 1S52-1911 



2 

 3 



Farmyard manure... 

 Unmanured 



Bush. 



38-2 

 12'6 



Bush. 

 39-2 

 12-3 



Bush. 

 35'1 

 10'9 



Bush. 

 35-5 

 12 8 



The results of this plot show two principles at work :— The tendency 

 of the land under an unchanging system of farming to reach a position of 

 equilibrium when the only variations in the crop are those brought about 

 by seasons ; and, secondly, that regeneration of the nitrogen stock in the 

 soil is possible by natural causes alone. 



Over manuring. 



We now turn to one of the other plots which receives an excess of 

 farmyard manure each year. The manure supplies about 200 lb. of 

 nitrogen per acre, the crop only taking away about 50 lb . so that natur- 

 ally the land is increased in its fertility. 



