154 



THE FIRST BOOK OF FARMING 



and continuously to supply the place of that taken 

 by plant roots or evaporation from the surface. 



TOO MUCH WATER 



Some farm lands contain too much water for the 

 growth of farm crops; for example, bottom lands 

 which are so low that water falling on the surface 

 cannot run off or soak down into the lower soil. 

 The result is that the spaces between the soil par- 

 ticles are most of the time filled with water, and 

 this checks ventilation, which is a necessary factor 

 in soil fertility. This state of affairs occurs also on 

 sloping uplands which are kept wet by spring water 

 or by seepage water from higher lands. Some soils 

 are so close and compact that water falling on the 

 surface finds great difficulty in percolating through 

 them, and therefore renders them too wet for profit- 

 able cropping during longer or shorter periods of 

 the year. Nearly all such lands can be improved 

 by removing the surplus water through drains. 

 (See Chapter XXV.) 



Percolation and ventilation of close compact soils 

 can be improved by mixing lime and organic mat- 

 ter with them. 



NOT ENOUGH WATER 



In some sections of the country, particularly the 

 arid and semi-arid sections of the West, the soil 



