CH. i] Limiting Factors 3 



making better growth, and to speak of it as the "limit- 

 ing factor." Thus on a dry chalky soil the water supply 

 is often the limiting factor; if more water is got into the 

 soil a bigger crop will be obtained. In the cold summer 

 of 1916 the temperature was on many farms the limiting 



Pot No. 47 55 63 



Fig. 1. Tomatoes growing on a light sand with varying food supply. 



Pot 47, without manure. Pot 55, one dose of manure. 

 Pot 63, two doses of the same manure. 



factor; had the days and nights been hotter the plants 

 would have made more growth. On poor soils the food 

 supply is the limiting factor, and addition of more food 

 in the form of manure will increase the crop. The 

 problem of successful management of soil fertihty 

 resolves itself into finding out what is the limiting 

 factor and then correcting it as cheaply and completely 



12 



