320 THE PRINCIPLES OF SOIL MANAGEMENT 



of organic matter. (2) By favoring the action of useful 

 bacteria, which is one of the most beneficial results of 

 farm manure, and also of lime. (3) By counteracting 

 the effects of toxic substances, as, for instance, the con- 

 version of sodium carbonate into sulfate by gypsum, 

 or the neutralization of acidity, or possibly the removal 

 of toxic organic substances by certain salts. (4) By 

 adding to the soil the nutrient materials absorbed by 

 plants, which results in the case of almost all substances 

 used as manures. 



186. Early ideas of the function of manures. 

 Manures were at one time supposed to pulverize the soil, 

 and the French word manceuvrer, from which the word 

 manure comes, means to work with the hand. This idea 

 probably originated through the observation that farm 

 manure, which was the only manure in use at that time, 

 made the soil less cloddy. 



It has been argued, notably by Jethro Tull, that as 

 tillage pulverizes the soil it may be used as a substitute 

 for manures. There are, however, conditions aside from 

 tilth that are influenced by manures, and good tilth 

 alone will not suffice to maintain a permanently intensive 

 agriculture. It is true in the United States, as it is in 

 Europe, that a large consumption of manures goes hand- 

 in-hand with a highly developed and intensive system of 

 farming. 



187. Development of the idea of nutrient function of 

 manures. While the use of animal excrement on cul- 

 tivated soils was practiced as far back as systematic 

 agriculture can be definitely traced, the earliest record 

 of the use of mineral salts for increasing the yield of 



