38 The Inflnei^cc of Potshenls on Nitrijjcation 



layers of hajri. This arrangement served to prevent the pipe from being 

 blocked up with soil. Any drainage waters which collected at the mouth 

 of the pipe could therefore flow out easily. It is thus seen that the pits 

 are somewhat analogous to the gauges which are often built in connec- 

 tion with the study of drainage waters. 



After the soil mixture had been filled in, the gaixges were flooded till 

 percolates came out through the iron pipes at the bottom. This applica- 

 tion of water produced a settling down of the soil to about the same con- 

 dition as would happen in the fields. 



Samples of soil were taken once every fortnight with the help of 

 boring cyHnders and analysed for nitrates. 



The results of the analyses are recorded in a tabular statement below. 



The results of these analyses are entered graphically in the accompany- 

 ing charts (Nos. 1, 2 and 3). It will be noticed that, except in the case 

 of the 2 ft. gauges during the months of December and onwards, the 

 soils of all the gauges containing thirty per cent, potsherds contain the 

 highest amounts of nitrates as compared with other gauges of the same 

 depth. Even in the case of 2 ft. gauges, although the one containing 

 twenty per cent, potsherds takes the lead during later periods, the con- 

 centration of nitrates in the earlier stages was greatest in the gauge con- 



