232 THE MONTHLY BULLETIN. 



if that be the case then it is obvious that over-irrigation, by filling too 

 much of the open space in soils, must militate against the maintenance 

 of a good air supply in the soil. We can not therefore expect, by with- 

 holding the amount of air which is required for normal plant root 

 development, to obtain normal tops of plants and therefore normal 

 production. 



Over-irrigation, therefore, is a reprehensible practice if viewed only 

 from the point of view of the soil's air supply. But there are more 

 reasons than the one just given for declaiming most vigorously against 

 the practice of over-irrigation. Not only does the filling of more empty 

 space than necessary by water mean the shutting out of air, but with 

 it it means that that much more soil surface is withdrawn from use- 

 fulness for root development. Most roots can not penetrate and can 

 not live in a saturated soil for reasons above given. The result is that 

 they do not ramify into these water-logged layers of soil and therefore 

 there is that much less soil surface for them to grow on. But this 

 means not only a poorer supply of plant food, since each additional 

 particle of soil which the root covers means that much more plant food, 

 but it also means more water and thus, ludicrous as the statement 

 appears at first sight, plants may often suffer for want of water in 

 water-logged soils with many times more moisture than similar plants 

 on similar soil which is drained and contains many times less moisture. 



Excessive moisture supply, moreover, is detrimental to the main- 

 tenance of soil fertility because it makes better conditions for rapid 

 clay formation by the leaching out of the base, like potassium and soda, 

 from the feldspars in the soil, which are among the most common 

 minerals. Clay formation in its turn tends to poorer aeration and 

 therefore the production of uncongenial conditions for root develop- 

 ment. 



The soil bacteria also, upon which we depend for the solution of 

 many of the essential elements of plant food, or upon their preparation 

 for use b,y plants, and particularly the nitrogen compounds, must have 

 air for their development. The more soil surface we saturate the 

 more we limit habitable conditions for the bacteria within the soil, 

 and therefore militate against the proper supply of available plant 

 food. 



We therefore see that the water-logging of soil, through over-irriga- 

 tion, makes impossible the proper supply of air for the roots — makes 

 impossible large and healthy root sy.stems ; that it leaches out important 

 elements of plant foods, and hastens the formation of clay, which makes 

 soils less pervious to air; that of necessity it raises the water table 

 and, through improving the conditions for capillarity, helps to accumu- 

 late alkali at the surface ; that for all these reasons it reduces, in just 

 such proportion as it makes impossible a large root development, the 

 surface feeding or foraging area of the roots, thus necessitating more 

 frequent and larger uses of fertilizers ; that it inhiljits the development 

 and maximum activity of the beneficial soil bacteria which are essential 

 to the production and maintenance of available plant foods, particu- 

 larly of the nitrogen order. 



All of the arguments above given would seem to me to be strong 

 enough to do away in practice with the excessive use of water in the 

 irrigation of land. But the question may still be asked : Is there not a 



