SOIL EXHAUSTION AND ROTATION IN CROPS. 87 



monia in another. It was the stable manure and ammonia 

 salts in those quantities which improved the "condition" of 

 the land by the equivalent of 20 bushels of wheat. 



We understand, then, that there is a natural quality in the 

 soil which we cannot easily bring below a certain limit ; and 

 there is a " condition," an artificial, temporary or adventitious 

 fertility, which we can easily increase and easily exhaust. 



•There are many circumstances which necessitate or justify 

 a Rotation of Crops. I will not attempt to enumerate tliem 

 all. Differences of soil and climate, the quantity of fertilizers 

 accessible, the demand in the markets, ease of transportation, 

 politicians, when they make fluctuating tariffs, weeds which 

 come to infest the fields, insects even, may make it advisable 

 to alternate our crops. It m?y not be uninstructive to go 

 back in history and give a sketch of the gradual development 

 of the practice of Rotation. 



The earliest husbandry was simply pasturage. When the 

 people of temperate climates found they could not support 

 themselves by killing wild animals and gathering fruits, the 

 natural produce of the country, they began to tame animals 

 and keep herds of cattle, sheep, etc. ; and you know that on 

 the vast plains of Asia and South America, this sort of pasto- 

 ral husbandry is still the only one known. As population be- 

 came more dense and land more valuable, people crowded 

 each other, and there was not room enough to roam about at 

 will and settle upon pasture wherever it could be found, un- 

 less, for a change, the people fell to fighting, and partially 

 killed each other off, thus leaving land enough for the sur- 

 vivors. When civilization began, it became necessary to 

 cultivate forage crops, or, at least, to take some care of the 

 natural meadows. The next step was to assist these natural 

 resources by growing some grain, and people began to break 

 up a little land, and cultivate wheat and the various grain 

 crops ; afterwards, attention was given to root crops. It may 

 not be possible now to show how these steps of progress have 

 taken place in any given locality ; but this is a general history 

 of the development of husbandry all over the world, wherever 

 it has attained any perfection. Farmers have always carried 



