318 ROAD-DRIFT. 



862. Water is of service in temperate climates 

 as a solvent of saline matters, as assisting the decay 

 of organic matters in consequence of the air which it 

 holds in solution, as bringing saline substances which 

 are useful to plants, and as affording a supply of 

 organic matter capable of affording ammonia, nitric 

 acid, &c., by its subsequent decomposition. 



863. In flooding land, the saline substances con- 

 tained throughout the soil, and formed by the decom- 

 posing agency of the atmosphere (651), are dissolved, 

 and consequently brought into a condition fit for 

 absorption by growing plants ; but quite independent 

 of this, almost all water contains a considerable 

 quantity of inorganic matter (76), which in many 

 cases is a valuable addition. 



864. In those cases where drainage-water is allowed 

 to mix with that employed for irrigation, of course 

 the organic matters and saline substances which the 

 former contains, produce their effect in addition to 

 that of the latter. The benefit is produced almost 

 entirely by the liquid, and the substances which it 

 holds in solution ; the fine mud which it leaves on the 

 surface of the ground is of comparatively but little 

 value. 



865. Road-drift and the scrapings of ditches are 

 often used as manures with very beneficial results : 

 their value of course depends in great part on their 

 composition, and the nature of the soil to which they 

 are applied ; the scrapings from roads made of stone, 



