162 CROP GROWING AND CROP FEEDING 



5 per cent, of the total amount of nitrogen in the soil. By far the greater 

 part of the soil nitrogen exists in the form of humus or organic matter 

 containing nitrogenous matter. "This humic matter is a mixture of various 

 bodies, the precise nature of which has been very imperfectly ascertained, 

 owing to their general insolubility and the absence of well marked chemical 

 properties. We will probably all agree that the nitrogenous organic matter 

 of soils is a residue left by the incomplete oxidation and decay of the dead 

 tissues of previously existing plants and animals, and that it has its primary 

 origin in the capacity possessed by plants of assimilating various forms of 

 inorganic nitrogen and constructing therefrom nitrogenous organic bodies 

 containing nitrogen, carbon, hydrogen and oxygen, with the addition, in 

 many cases, of a small quantity of sulphur." (Rothamsted Lectures. 

 Warington.) It was found in the experiments at Rothamsted, in England, 

 that in a meadow in grass for thirty years there was an increase of nitrogen 

 in the surface soil at the rate of 50 pounds per acre per annum. 



A careful account was kept of the manure applied to this meadow during 

 the time; the meadow was mown annually and the hay weighed. It was 

 manured with city manure from the London stables each alternate year, and 

 had small annual dressings of superphosphate, sulphate of potash and 

 nitrate of soda. After making a liberal estimate for the nitrogen in the 

 manure, it was found that there had been a considerable gain in nitrogen 

 over and above the amount applied in the manures. The total gain was not 

 less than 32 pounds per annum, as the whole manure was charged to the field, 

 and no account taken of the nitrogen lost from the soil or taken by the crop. 



From the growing of the clover there was also found a still greater 

 increase of nitrogen in the soil. Unmanured barley following clover, made 

 58 bushels per acre, while the part without clover and following 

 barley made but little over 37 bushels per acre. In a four 

 year rotation in which clover was used once in the four years 

 for forty years, the average annual amount of nitrogen removed 

 in the crops in excess of that contained in the manure was over 

 30 pounds per acre, while the fertility of the land has not diminished. Mr. 

 Warington adds: "It must not be supposed that a leguminous crop neces- 

 sarily leaves a soil richer in nitrogen than it was before its growth. The 

 sensible increase in the soil takes place only when the soil at starting was 

 not too rich in nitrogenous organic matter, and when the leguminous 

 growth was abundant. * * * The rich kitchen garden ground at Rothamsted 

 shows a considerable loss of nitrogen during the continuous growth of red 

 clover. But in. these cases the fact of the gain of nitrogen can probably be 

 established if we regard the large amount of nitrogen removed in the crop, 



