THE CHEMISTRY OF THE SOIL. 



101 



Calcium nitrate is the manurial product obtained by the electric process 

 for the manufacture of nitric acid from the atmosphere. It* contains about 

 13 per cent, of nitrogen, and appears to have the same manurial value as 

 nitrate of soda that contains the same amount of nitrogen. Like cyanamide 

 it is not on the local market at present. Like this, also, its future success 

 depends upon its production at a rate enabling it to compete with sulphate 

 of ammonia. 



Humus and Green Manuring. 



Amongst the most effective means of adding nitrogen to the soil is the 

 application of vegetable matter in the form of farmyard or compost manures, 

 and the ploughing under of a green crop or green manuring. 



We have seen in the case of many leguminous crops (page 87) that they 

 are not onty independent of the soil for their supply of nitrogen, but that 

 their growth actually enriches the soil in this ingredient. The land on 

 which such a crop has been grown contains a larger proportion of nitrogen 

 than before. This property is turned into account in rotating crops, and 

 also suggests a means of supplying nitrogen to the soil without the addition 

 of nitrogenous manures. If a leguminous crop is grown, and is ploughed into 

 the land just before it reaches maturity, a manure is thereby added to the 

 land containing 100 lb. or more of nitrogen to the acre — that is to say, the 

 land receives a manuring of nitrogen equivalent to that produced by the 

 addition of over 4 cwt. sulphate of ammonia or of 8 cwt. of dried blood per 

 acre. The crops suitable for green manuring are those that mature most 

 rapidly and occupy the ground for the shortest time. The value of green 

 manuring to the physical nature of the soil is mentioned on page 70. 



Amount of fertilising ingredients added to the soil by ploughing under certain green 



crops. 



