100 ELEMENTS OF AGRICULTURE 



CHAPTER XIX.— How Soils Lose Water 



98. How Soils Become Poor.— The fact that culti- 

 vated soils lose their fertility, becoming poor and pro- 

 ducing small crops, is only too well known. But how 

 this loss of fertility occurs is not so well known, and 

 the answer is not easy to find. 



Growing plants are very particular about their food. 

 They require a number of different compounds, which 

 must be supplied them in certain combinations, else 

 the plant will have none of them. If the soil should 

 fail to supply the plant with only one of the many 

 foods it requires, the plant starves, or if the food be 

 supplied in a form not acceptable to the plant, it will 

 not take it. For • instance, a soil that contains no 

 nitrogen, even though it contains every other plant 

 food, cannot grow crops. A soil that contains only 

 nitrogen combined in organic matter and provided 

 with no means of forming nitrates will be as barren 

 as a desert. Fertile soils are soils that supply all kinds 

 of plant foods and supply them in the form most 

 acceptable to plants. When the supply of any one or 

 more of the foods becomes, from any cause, exhausted, 

 the soil is called poor or worn, which means that it 

 cannot feed growing plants. The supply of plant food 

 in most soils is rarely excessive, and is often small. 

 It is an easy matter to exhaust, by improper methods 



