Jatindra Nath Sen 39 



taining thirty per cent potsherds. Thus it is seen that although the soils 

 of the thirty per cent gauges were more open and thus liable to a quicker 

 drainage of the nitrates dissolved in the soil solution, they were still 

 generally richer in nitrates than the other soils. 



Taking individual gauges, it is seen that the amounts of nitrates were 

 practically the same during the first three months or so. It was only 

 after this period that they suffered an increase. This bears out the 

 utility of applying manures at least three months in advance. In actual 

 practice this has also been found to be the case. For example, in the case 

 of tobacco, the manure should be applied in June or July, as complete 

 nitrification takes time and various intermediate oxidations have first 

 to take place. 



The general increase in the content of nitrates has been maintained 

 from October, with occasional fluctuations, till the end of the period of 

 the experiments (February). This increase seems to be due to a com- 

 bination of favourable causes (see Chart No. 4). 



An examination of the rainfall data of this season shows that there 

 were heavy rainfalls in September and few rainless days till the middle 

 of October. From this time there was practically no rainfall except 

 light showers in the latter part of the month and then again towards 

 the end of January and the beginning of February. 



A fall of rain greatly modifies the nitrate contents of soils. Not only 

 does it leach out some of the nitrates but is liable to give rise to deni- 

 trification. But the advent of rain-water, charged with dissolved oxygen, 

 replenishes the supply of oxygen in the soil atmosphere^. Again, after 

 the rain there occurs a downward movement of the excess of water which 

 causes a flow of air in the soil. Hence, after the stoppage of rains, not 

 only do the chances of loss of nitrates by leakage and denitrification 

 diminish but there is set up a stimulus to increased formation of nitrates. 



A similar indraught of air takes place when the level of the subsoil 

 water falls lower. In the chart are plotted the levels of the river Gandak 

 on the difierent dates. The gauges are situated about 400 yards away 

 from the river. The movements of the underground water near the 

 gauges no doubt suffer a "lag" as compared with the rise and fall of the 

 river level, still the curve in the chart may be taken to give a general 

 indication of the nature of the movements of the soil water level. 



' E. J. Russell and A. Appleyard, " The Atmosphere of the Soil," Joiirn. Agric. Sci. 

 1915, 7, p. 1; E. H. Richards, "Dissolved Oxygen in Rain-water." ibiil. 1917, 8. 

 p. 331 ; also E. J. Russell and A. Appleyard, "The Influence of Soil Conditions on the 

 Decomposition of Organic Matter in the Soil," ibid. p. 385. 



