io6 SOILS AND FERTILIZERS 



the decay of the plants ; the plowing under is done in 

 the spring before the plants have attained sufficient 

 growth to exhaust the moisture of the soil. It is not 

 to be supposed that a farmer would sacrifice in this 

 way a crop that is worth harvesting, except in extreme 

 cases. If stock is kept on the farm, a good crop may 

 be utilized for fodder and the manure will serve to 

 furnish humus and elements of fertility. Farmers 

 who do not keep stock will find themselves forced to 

 use green manure or apply commercial fertilizers to 

 keep their land from getting sterile. 



Animal Manure. Animal manure contains not 

 alone the indigestible portions of the food eaten by the 

 stock, but also worn-out animal tissues. It contains 

 nitrogen, phosphorus, and potassium. Average barn- 

 yard manure has 10 pounds of nitrogen, 6 pounds of 

 phosphorus, and 12 pounds of potassium to a ton, these 

 three plant elements being the ones most likely to be 

 needed in soil that has been cropped often. The quality 

 of animal manure depends upon the food eaten by the 

 animals, and their age and condition. If fed on cotton- 

 seed meal, for instance, their manure will contain from 

 75 per cent to 90 per cent of the fertilizing value of 

 the meal originally fed, but considering all the foods 

 eaten by live stock about one half of the fertilizing 

 elements eaten are returned in the manure. 



Amount of Manure produced by Animals. From 

 the study of a table computed from the amount of 

 manure produced annually by the different farm ani- 

 mals and the relative richness of the same in nitrogen, 

 phosphorus, and potassium, we learn that on the basis 

 of looo pounds of live weight, the horse produces 

 about 12 tons of manure (including bedding), which 



