128 CROPS 



107. Summary. — The crop plants are raised for certain 

 characteristic constituents, usually of value as food for stock 

 or man. In scientific feeding it is necessary to know the 

 amounts of the various food constituents in each crop, but 

 it is a difficult and tedious process to determine each separate 

 compound. For practical purposes it is sufficient to know 

 the amount of each group of compounds which have food 

 values. Consequently there is used a method which de- 

 termines the following constituents in an approximate but 

 fairly satisfactory manner: 



Water. 



Crude Fat, which consists of fixed oils, volatile oils, resins, 

 waxes, and chlorophyl, if present. 



Crude Fiber, which is principally cellulose and lignin. 



Ash, which consists of the inorganic, or mineral elements, 

 in the plant, although not combined in the ash as they were 

 in the original plant material. 



Crude Protein, which comprises proteins, amides, nitrates, 

 and other nitrogenous material, unless the proteins and 

 amides are determined separately, in which case the latter 

 consist of all nitrogenous forms except proteins. 



Nitrogen-free Extract, which consists of. sugars, starch, 

 and any other substance not determined above. 



The composition and yields of the various crop plants can 

 be found by consulting Tables I to III. 



Hay consists of the leaves and stems of certain grasses 

 and legumes which are cut about flowering time and dried 

 or cured so that they may be preserved. The time of cutting 

 is so adjusted that there will be a maximum crop consistent 

 with optimum composition. The older a hay crop gets, the 

 more crude fiber and the less crude protein, ash, and fat are 

 present. 



Some changes take place during the curing process, includ- 

 ing the production of volatile oils or similar compounds 

 which give additional palatability to the hay. 



Silage is another form of preserved crop, and is made 

 usually out of corn. The corn plant does not deteriorate in 

 food value as it grows older, and fairly mature corn is cut for 

 silage. The finely cut corn is packed tightly in an air-tight 



