t 532 ] 



there are crops on them or not, When a soil is in good 

 condition as much as 80 Ibs. of N are converted into nitrates 

 (Sodium, Potassium and Calcium nitrates chiefly) per acre, 

 to a depth of 27 inches, the largest quantity being formed 

 in the top 9 inches. The ratio has been found in England 

 between the first 9 inches, the next 9 inches and the 

 last 9 inches to be 100 t 60 : 30. Crop residues being 

 easily nitrifiable, those crops which leave behind a large 

 quantity of organic matter go to improve soils irrespective of 

 any consideration as regards root-nodules &c. Again, old 

 nitrogenous organic matter in the soil nitrifies much more 

 slowly than recent organic matters. Restoring the straw of 

 a newly grown crop is therefore very essential in forming 

 nitrates. 



852. NH 3 is absorbed by plants both by roots and by 

 leaves, HNO 3 only by roots. The darkness of colour of 

 leaves is intensified with NH 3 which also stimulates the 

 growth of leaves and stems at the expense of flowers and 

 fruits. 3 to 10 Ibs. of NHs is found deposited by rain water 

 per acre per annum. Nitric acid is also present in rain 

 water, dew, fog, snow and other meteoric water. Nitrous 

 oxide (NaOs) occurs as well as Nitric oxide (N 2 Os). But 

 ozone and H^Oa convert the N 2 O 3 into N 2 O 5 . From 3 to 7 Ibs. 

 of N 2 O 5 (including the convetred N 2 O 3 ) have been found 

 deposited per acre per annum. The total amount of combined 

 N useful for plant life, deposited per acre per annum as 

 NH 3 , N 3 O 5 , organic dust &c., has been found to be on the 

 average 4i Ibs. at the Rothamsted Experimental Farm in 

 England, Continual calculations give over 10 Ibs. 



853, The amount of N washed out from soil varies under 

 varied conditions, (i) according to the severity of rainfall, 

 (2) according to the texture of soil and the nature of cultiva- 

 tion, (3) according to the slope, (4) according to its absorptive 

 power and chemical composition and (5) according to the 

 nature of the crop growing on the soil, or whether there is 



