264 



IMPROVEMENT OF THE SOIL. 



the water has run, before it reaches the place where it is 

 taken on to the land, the more remarkable its effects. This 

 is due to two causes ; 1. It obtains a larger quantity of gas- 

 seous bodies such as oxygen and ammonia ; and 2. it has been 

 shown, that water from streams contains crenic and apocrenic 

 acids often combined with silica, and also other salts, which 

 it has dissolved out of the soil or rocks, as it has passed over 

 them. 



(1) The first effect of water, when made to flow over the 

 soil by this process, is to soften it and render it more permea- 

 ble to the roots of plants, and to the air. 



(2) Water acts still further in dissolving out the food, and 

 producing those chemical changes which must take place in 

 the manures, before they are fitted for nourishment. 



Care should be taken, not to apply water so often as to 

 keep the soil in a state of paste, in which case, the plant may 

 increase in size, but the products will be loose and spongy in 

 texture, and vapid in taste. There is danger too, of favoring 

 the growth of rushes and other wild grasses, which will take 

 the place of the more valuable ones. 



Another caution should be given on this subject, particu- 

 larly applicable to garden plants ; upon which surface- water- 

 ing is sometimes practised during the dry season. The effect 

 of thus pouring water around plants, especially in the heat of 

 the day, is to render the soil compact and heavy ; thus pro- 

 ducing the very evil which it is intended to remedy. It ex- 

 cludes the air and the water which it contains from the roots. 

 If surface-irrigation is ever practised on garden vegetables, it 

 should be done at night. 



Meadows seem to be most benefited by irrigation in our 

 climate, although we know that in some countries as Egypt, 

 it is practised upon all kinds of soil, and for every species of f 

 crop. In the vicinity of Liegen (Germany), according to 

 Liebig, from three to five perfect crops of hay are annually 

 produced upon the same meadow, by covering the fields with 



