INFLUENCE OF MOVEMENTS OF WATER 197 



were chloride 906, sulphate 9-4. Kainite when applied to 

 a moist soil must be quickly separated into its constituent 

 salts, the potassium, sodium, and magnesium compounds 

 having each very different rates of diffusion. A similar 

 separation of the constituents will occur when any saline 

 mixture is applied to the soil. 



Urea, according to Graham, is a substance of very con- 

 siderable diffusive power, nearly equal in this respect to 

 sodium chloride. As urea is also not retained by soil, it is 

 clear that the application of fresh urine to soil will result in 

 a distribution of nitrogenous matter within it, similar for a 

 time till the conversion of urea into ammonium carbonate 

 has taken place to that occurring after an application of 

 sodium nitrate. 



Illustrations of the results produced by the diffusion of 

 salts in the soil will be found further on. 



Influence of Movements of Water. It will be readily 

 understood that any movement of the water in a soil, whether 

 of the nature of a downward percolation, or of a rise brought 

 about by capillary action, must carry with it the salts which 

 the water holds in solution. The effects which will follow 

 the descent of pure rain water upon the surface of a soil are 

 not so obvious. In considering this, the most common action of 

 water on soil, we must distinguish between two cases, namely 

 whether the soil is dry or wet when the rainfall takes place. 



If a steady and continued rainfall takes place on the sur- 

 face of a homogeneous soil, free from fissures, and in a dry 

 condition, the water descends through the soil as a liquid 

 column ; the lower surface of this column continually dissolves 

 the salts it meets with, while the column is pushed further 

 and further into the soil by the continual additions of rain 



