163 MANURES. 



usually only mineral matter. The direct effect of 

 the water of irrigation as a solvent and distributer 

 of the mineral ingredients of the soil, constitutes one 

 of its main benefits. 



To describe the many modes of irrigation would 

 be too long a task for our limited space. It may be 

 applied in any way in which it is possible to cover 

 the land with water, at stated times. Care is neces- 

 sary, however, that it does not wash more fertilizing 

 matter away from the soil than it deposits upon it, as 

 would often be the case, if a strong current of water 

 were run over it. Brooks may be dammed up, and 

 thus made to cover a large quantity of land. In 

 such a case the rapid current would be destroyed, 

 and the fertilizing matter would settle ; but, if the 

 course of the brook were turned, so that it would run 

 in a current over any part of the soil, it might carry 

 away more than it deposited, and thus prove injuri- 

 ous. Small streams turned on to land, from the 

 washing of roads, or from elevated springs, are good 

 means of irrigation, and produce increased fertility, 

 except where the soil is of such a character as to pre- 

 vent the water from passing away, in which case it 

 must first be under-drained. 



Irrigation was one of the oldest sources of fertility 

 used by man, and still continues in great favor wher- 

 ever its effects have been witnessed. In England 

 and Scotland, much attention is now being paid to 

 the question of liquid manure irrigation, and an at- 

 tempt is being made to employ the vast discharges 

 of the London sewers. For this purpose it is in con- 



