November 6, 1908] 



SCIENCE 



621 



produced by the mineral constituents with- 

 out nitrogen; from this point the increase 

 of yield is roughly proportional to the sup- 

 ply of nitrogen, until it reaches an excessive 

 amount. The table also illustrates the gen- 

 eralization which is familiar to economists 

 under the name of ' ' the law of diminishing 

 returns"— that the first expenditure of 

 fertilizer or other factor of improvement 

 is the most effective, each succeeding appli- 

 cation producing smaller and smaller re- 

 turns, until a further addition causes no 

 increase in the yield. If the cost of the 

 fertilizer, added to a prime outlay of 80 

 shillings per acre for the cultivation, and 

 the value of the returns in cash, are ex- 

 pressed in the form of a diagram, the law 

 is clearly expressed by the series of curves 

 in the figure, where the cost of production 

 forms a straight line that is always inter- 

 sected by the curves expressing the value 

 of the returns, which begin by rising more 

 rapidly than the cost of production, but 



Mineral Manures +200 lb. +400 lb. +600 lb. *800]b.ATnm.SaH5- 



Eelation between cost of production and returns 

 with varying quantities of manure 



tend to become horizontal. The point of 

 intersection when profit ceases is nearer the 

 origin the lower the range of prices obtain- 

 able for the crop, as shown by the two 



curves representing the returns at low and 

 high prices, respectively; this demonstrates 

 that the expenditure on fertilizers or any- 

 thing else required by the crop must be 

 reduced when prices of produce are low, 

 or, as expressed by the late Sir John 

 Lawes, high farming is not remedy for low 

 prices. 



Liebig's law of the minimum must, how- 

 ever, be extended to all the factors affecting 

 the yield as well as to the supply of plant 

 food, e. g., to such matters as the supply 

 of water, the temperature, the texture of 

 the soil. Any one of these may be the 

 determining factor which limits the yield, 

 or two or more of them may act successively 

 at different periods of the plant's growth. 

 On poor soils the water supply is very often 

 the limiting factor, on very open soils be- 

 cause the water actually drains away, on 

 extra close soils because the root range is 

 so restricted that the plant has but little 

 water at hand and the movements of soil 

 water to renew the supply are very slow; 

 in either case for comparatively long 

 periods the plant will be sure to have as 

 much nutriment as is required for the small 

 growth permitted by the water present. 

 It is only when the water supply is sufS- 

 cient that the resources of the soil as re- 

 gards all or any of the constituents of a 

 fertilizer are tested, and may become in 

 their turn the limiting factors in the growth 

 of the crop. Hence it follows that fertil- 

 izers may often be wasted on poor land, 

 ■where growth is limited by the texture of 

 the soil, by the water supply or some other 

 factor hardly controllable by the farmer: 

 it is a truism that poor land can not be 

 converted into good by manuring and that 

 fertilizers give the best returns when ap- 

 plied to a good soil. 



One fundamental difficulty still remains 

 in considering the action of fertilizers : 

 it has already been pointed out that a soil 

 by no means notably fertile may contain 



