MANURING. 119 



the form of leather scrap. But chemical analysis has clone much for the 

 science of manuring and is a great aid to the development of special fer- 

 tilization of crops, hut especially by the study of the crops themselves, 

 rather than the soil. 



MANURIAL VALUE OF A CROP OF CORN. 



The manurial values of different crops varies greatly, but the constitu- 

 ents of plants of the same natural order are about the same. For an ex- 

 ample I will mention corn. A crop of 60 bushels of Indian corn would 

 proportionately have about 6,000 pounds of dry stalks, cobs and leaves. 

 The whole crop would remove from the land 76 pounds nitrogen, 38 

 pounds potash, 41 pounds phosphoric acid, besides a large quantity of 

 silica and magnesia, and smaller quantities of soda, sulphur and iron; 

 these must be present in the soil, while practically all the rest of the crop 

 comes from the atmosphere. 



It has been often claimed that if the material contained in the twenty 

 bushels of corn is known, then it is only necessary to apply just that 

 amount of material and get the twenty bushels increase. In some ex- 

 periments tried this has proven true, but in ordinary practical work it is 

 not of much value for several reasons: 



1st. The material must be supplied in a known quantity and in a 

 soluble form. This is quite impossible under ordinary circumstances, for 

 in the application of home made manure we can not calculate exactly. 



2d. There are limits to production due to drought, or to too much 

 water, which may hinder chemical action and the consequent forming 

 of plant food. 



3d. Some plants have a much greater power of obtaining their food 

 from soils than others, and by chemical analysis of the plant we can not 

 tell anything about this power, nor how much of the nitrogen present 

 comes from the soil, nor how much from the air. 



It may be of interest to note how much valuable manurial material is 

 contained in a load of average manure; calling a wagon load one ton it 

 would contain 1,323 lbs. water, 111 lbs. ash and 13 lbs. nitrogen. The ash 

 would contain 24 lbs. potash and 7 lbs. phosphoric acid, and in this con- 

 nection it should be understood that all of this material is not plant 

 food that is available to plants the first year, but much of it is insoluble 

 and only becomes plant food perhaps after several years. 



DEFINITIONS. 



Nitrogen. This is found in nature as a gas in the atmosphere we 

 breathe, where it is combined with oxygen in the proportion of seven 

 parts nitrogen to one oxygen. We meet it in nitric acid, in ammonia, 

 saltpeter, etc. It enters largely into such foods as eggs, lean meat, 

 cheese, etc., where it is largely the muscle-forming portion. 



Phosphoric acid is a combination of phosphorous, oxygen and hydrogen. 

 It forms in combination with lime almost all the bony framework of our 

 bodies. 



Potash is an alkali, and is met with under manv familiar forms. The 

 potash of commerce is a combination of it with oxygen. In its metallic 

 state it cannot be kept in the presence of oxygen. 



Agricultural plants can be divided into nitrogen increasers and nitro- 



