xiv . INTRODUCTION 



the production of the desired crop. It is possible to increase the 

 retentive power of a soil for water, and to diminish the evap- 

 oration of the water it already contains. It is equally possible 

 to reduce the amount of water in a soil which is naturally 

 too wet. The surface temperature of the soil can also be 

 increased in spring and summer by lessening its contents 

 of water. Both the consolidation of the soil, and the loosening 

 of its particles till they become a fine powder, are to a con- 

 siderable extent under the farmer's control. By skilful 

 management the salts of alkali lands can be prevented from 

 rising to the surface and becoming a source of mischief. In 

 every case a knowledge of the physical properties of the soil, 

 and of the physical actions which go on within it, places 

 them more or less under our control. 



The overwhelming importance of the physical conditions 

 of plant growth is perhaps most strikingly seen in the case of 

 sandy soils extremely poor in plant food, which, nevertheless, 

 from their extremely favourable physical condition, and the 

 equally favourable climate of the locality, are soils of high 

 agricultural value. Such an example is furnished by the 

 narrow band of sandy soil in the State of Florida now 

 devoted to the cultivation of pine-apples. This sand is almost 

 entirely destitute of plant food, yet it responds so abundantly 

 to the capital invested in it that the planted land has become 

 worth from ^loo to ^500 per acre. 



It is clear then that we must not judge of the value of 

 a soil by the result of its chemical analysis ; we must take 

 its physical properties also largely into account. Indeed, in 

 a majority of cases, the physical properties and climate 

 will do more to determine its fertility than its chemical 

 composition. 



