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no offensive odour it should be readily used for manure. At 

 Poona it is used for sugar-cane and at Allahabad for grass 

 land with very satisfactory result. The sullage water of 

 town drains which is usually run into the nearest river is 

 also a valuable manure. Mr. Wyer, a Collector of Meerut, 

 utilised his small farm for the purpose of illustrating its value 

 to cultivators. Two irrigations with it doubled the outturn 

 of cotton, maize, juar, and oats over that obtained with 

 well water. There is indeed a large supply of manure in 

 cities and mofussil towns which is usually allowed to go to 

 waste. Conservancy arrangements may be made a source 

 of profit if municipalities are properly conducted. 



847. The value of river, canal and tank silt as manure is 

 still more difficult to ascertain than the value of dung, urine 

 or town refuse. Silt is a very important source of plant- 

 food and recuperation of land. In eastern Bengal, large 

 tracts of country depend on silt only for manure. The 

 results of analyses made by Dr. Leather with the Upper 

 Eastern Jumna Canal silt show that the silt deposit during 

 the monsoon period is more than sufficient for the rice crop 

 (32 Ibs. of N. and 41 Ibs. of P 2 5 per acre having been ac- 

 counted for from this source), while during the cold 

 weather when the canal water is clear, the amounts of N. 

 and P^Os supplied by silt deposit are very insignificant (only 

 \ a Ib. of N and i Ib. of P 2 5 per acre). All silts, however, 

 are not valuable. Sandy silt may be deposited on good soil 

 and cause damage to the soil. 



848. Humus or vegetable refuse in soil is of little direct 

 use to plant. Some experimenters have even opined that 

 humus is poisonous to plants ; but the balance of evidence 

 shows that indirectly it is a valuable source of plant-food and 

 to the lower forms of vegetable life it is a direct source of 

 food. Ammonia and nitrates, which are the principal forms 

 in which N is taken up by plants, are present only in very 

 minute proportions, the greater proportion of N remaining in 



