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become poor in these constituents and may be benefited by 

 phosphatic and nitrogenous manures are well known facts. 

 At the same time, it should be remembered that there are 

 three natural methods of recuperation of Nitrogen which is 

 the most important factor in determining fertility: (i) by 

 rainfall, (2) by the return of the produce of the soil to the soil 

 in the form of excrements, bodies of dead animals, &c., and 

 (3) by the action of nitrifying bacteria especially in connec- 

 tion with the roots of leguminous crops. The total produce 

 of food-grains in India has been estimated at eighty million 

 tons and the total export of food-grains at 2,500,000 tons, 

 i.e., at about 3 per cent. So we may assume that 3 per cent, 

 of the plant-food derived from the soil is absolutely lost to the 

 country annually. There is also another loss due to burning 

 of some of the excrements as fuel, the Nitrogenous portion 

 of plant-food being entirely dispersed by burning. What 

 the proportion of such excrements that are burnt, is, cannot 

 be determined. Now one crop takes up per acre from the soil 

 an average of about 15 Ibs. of Nitrogen and yi Ibs. of PgOs- 

 The grain is only exported and not the straw. So it is 

 only 3 per cent, of an amount less than 15 Ibs. of N. and 7^ of 

 P 2 O 5 , that is lost by export and we can add the N. which is lost 

 by burning of cowdung to this. Most likely the total loss 

 of N. per acre by cropping is less than 3 or 4 Ibs. per annum 

 and 3 or 4 Ibs. of N. per annum comes down by rain alone in 

 the form of nitric acid and ammonia. Then there is the 

 accumulation by leguminous crops. So, Professor Wallace's 

 opinion is probably correct as far as N. is concerned. The 

 question of supply of P2Os by conservation of bones or 

 application of phosphatic manures is therefore of the utmost 

 value for maintaining what Professor Wallace calls the 

 permanent fertility of soils, as it" is perhaps possible to ex- 

 haust the permanent fertility so far as P2Os is concerned 

 where the proportion of this constituent in the soil is only -05 

 or less per cent. 



