Jatindka Natii Sen 37 



Experiments in Lysimeters. 



Nitrates resultins; from nitrogenous organic materials dissolve in the 

 water present in the soil. The soil solution, however, does not remain 

 stationary but undergoes continual movements. It therefore follows that 

 the efficacy of a nitrogenous manure will not depend merely on the rate 

 of formation of nitrates but will be considerably modified by the various 

 factors which regulate the movements of the soil solution. For example, 

 in the case of two fields where the rates of the formation of nitrates are 

 the same, if the downward movement of the soil sohition (drainage) is 

 more rapid in one field than in the other, the nitrates will be more easily 

 leached out from the first field and will thus be less available for the 

 nutrition of plants. 



In the experiments with the jars mentioned above the soil was sub- 

 jected to abnormal conditions. For example, the ordinary movements 

 of the soil solution going on in the field could not occur in these jars, as 

 the soils in these were quite isolated and were not in contact with the 

 earth. In order to study the variation in the nitrate contents of soils 

 (containing potsherds) under ordinary field conditions, the following 

 experiments were simultaneously carried out. 



A series of nine pits, each 1/1000 of an acre in superficial area, were 

 dug out in a cultivated field. These had vertical soil walls. The bottom of 

 each pit was carefully sloped towards a point in one side where a bent 

 iron pipe was put in. On this side a brick wall was built up, suitably 

 strengthened by short lengths of flanking walls. For the purposes of 

 demarking the plots and holding irrigation water, each pit was bounded 

 on the surface by small brick walls. These walls were six inches higher 

 than the existing level of the soil and only six inches deep in the top soil. 



The pits were first filled with alternate layers of broken bricks and 

 rubbish, to a depth of eight inches. This layer was levelled in the same 

 way as the bottom of the pit. Over this was put a mixture of manured 

 soil and potsherds of the same composition as used in the jars, i.e. ten, 

 twenty and thirty per cent, potsherds. 



The soil mixture was put into the pits, layer by layer, about five 

 inches being put at a time and gently pressed with feet before the next 

 layer was put in. 



The depths of the soil mixtures in the pits were two feet, three feet 

 and four feet respectively. The mouths of the iron pipes where they 

 entered the pits were suitably protected by pieces of wire gauze and 



