t Sio ]' 



8 1 6. In the case of phosphoric acid, on the other liand, 

 we should take into consideration silt deposit, where this 

 takes place and the settling of cosmic or meteoric dust. Per- 

 manent fertility cannot be exhausted in the case where there 

 is annual movement of silt from higher to lower ground by 

 the monsoon rainfall. For certain localities therefore Pro- 

 fessor Wallace's remark that the permanent fertility can never 

 be exhausted is correct. -But that such minimum of fertility 

 can be added to by manuring and more grain produced per 

 acre, admits of no doubt. The fuller utilisation of excreta, 

 human and animal, is of first consideration and then other 

 sources of manure can also be considered. 



817. European tea, indigo and coffee planters have begun 

 to complain of exhaustion of soil. The tea now produced 

 is weak, poor, thin and of inferior quality as compared to 

 what was obtained 10 or 20 years ago and quite a crisis has 

 arrived in the life of tea cultivation, Among the most useful 

 suggestions that have been made in the matter of manuring 

 tea gardens, is the growing of castor-oil plants close to these 

 gardens and utilizing the cake. 



8 1 8. It has been said that chemical analysis is not a 

 sufficient guide for judging the actual value of soils but only 

 its potential value ; in other words, that it does not give any 

 idea of the amounts of plant-food existing in an available 

 form, but only the total quantities of plant-food present. With 

 regard to potash and phosphoric acid, however, this remark does 

 not apply as an empirical method has been successfully applied 

 by Dr. Bernard Dyer of London of finding out the quantities 

 of PsO 5 and KsO existing in an available form for the immediate 

 use of plants. With regard to nitrogen, however, no satis- 

 factory method has yet been discovered of finding out the 

 proportion of available nitrates &c. present in the soil. 

 Indeed, it is difficult to find this out with reference to any soil, 

 as nitrates are so easily washed out. At one time there may 

 be as much as per cent, of available nitrates &c, in the soil, 



