EXTENT OF SOIL IRRIGATED IN EUROPE. 445 



As near as can be ascertained, the amount of water applied to 

 irrigated lands is scarcely anywhere less than the total precipita- 



power to those grown by the aid of irrigation. Garden vegetables, particularly, 

 profusely watered, are so insipid as to be hardly eatable. 



Canle snbnrbano qui siccis crevit in agria 



Dulcior, irriguo nihil est elutius horto.— Horace, 5, 2, 4, 16. 



"Wherever irrigation is practiced there is an almost irresistible tendency, 

 especially among ignorant cultivators, to carry it to excess ; and in Piedmont 

 and Lombardy, if the supply of water is abundant, it is so liberally applied as 

 sometimes not only to injure the quality of the product, but to drown the 

 plants and diminish the actual weight of the crop. Grass-lands are perhaps 

 an exception to this remark, as it seems almost impossible to apply too much 

 water to them, provided it be kept in motion and not allowed to stagnate on 

 the surface. 



Professor Liebig, in his Modern Agriculture, says : " There is not to be 

 found in chemistry a more wonderful phenomenon, one which more con- 

 founds all human wisdom, than is presented by the soil of a garden or field. 

 By the simplest experiment, any one may satisfy himself that rain-water 

 filtered through field or garden soil does not dissolve out a trace of potash, 

 silicic acid, ammonia, or phosphoric acid. The soil does not give up to the 

 water one particle of the food of plants which it contains. The most con- 

 tinuous rains can not remove from the field, except mechanically, any of the 

 essential constituents of its fertility." 



" The soil not only retains firmly all the food of plants which is actually in 

 it, but its power to preserve all that may be useful to them extends much far- 

 ther. If rain or other water holding in solution ammonia, potash, and phos- 

 phoric and silicic acids, be brought in contact with soil, these substances dis- 

 appear almost immediately from the solution ; the soil withdraws them from 

 the water. Only such substances are completely withdrawn by the soil as are 

 indispensable articles of food for plants ; all others remain wholly or in part 

 in solution." 



These opinions were confirmed, soon after their promulgation, by the experi- 

 mental researches of other chemists, but are now questioned, and they are not 

 strictly in accordance with the alleged experience of agriculturists in those 

 parts of Italy where irrigation is most successfully applied. They believe 

 that the constituents of vegetable growth are washed out of the soil by exces- 

 sive and long-continued watering. They consider it also established as a fact 

 of observation, that water which has flowed through or over rich ground is 

 more valuable for irrigation than water from the same source, which has not 

 been impregnated with fertilizing substances by passing through soils contain- 

 ing them ; and, on the other hand, that water, rich in the elements of vege- 

 tation, parts with them in serving to irrigate a poor soil, and is therefore lesa 

 valuable as a fertilizer of lower grounds to which it may afterward be con- 

 ducted. See Baikd Smith, Italian Irrigation, i., p. 25 ; Scott Moncrieff, 



