CH. viij Nitrate of Soda 129 



ordinary sea-water. The crude nitrate is excavated by 

 a process of trenching, it is then crushed, purified by 

 recrystallisation and put up in bags for the market. 



The commercia] product is not quite pure, but it is 

 guaranteed to contain 95 per cent, of nitrate of soda and 

 often contains even more. 



Nitrate of soda is very quick acting as a fertiliser and 

 can be taken up immediately by the plant. It finds 

 application in two cases: (1) in case of emergency, when 

 young plants are suffering through the attack of a pest, 

 or in cold wet weather; (2) in ordinary practice as a top 

 dressing for the crop. It causes increases of practically 

 aU crops in England and the dressing applied varies 

 from 1 cwt. per acre, suitable for wheat in spring or 

 grass laid in for hay, to 10 cwt. per acre used on the 

 valuable early cabbage and broccoli crops in Cornwall. 

 In other countries, however, good returns are not always 

 obtained: in parts of Australia and New Zealand phos- 

 phates are the limiting factor : in Western Canada water 

 appears to be; in none of these cases do nitrates give 

 the same high returns as in this country. 



Besides causing increased growth nitrate of soda pro- 

 duces certain qualitative effects on the crop. It imparts 

 darker green colour and greater size to the leaf : in the 

 case of straw crops it may so enlarge the leaf and the 

 head that the straw is unable to carry the weight in wet 

 weather, and the crop becomes laid. Applied in excess 

 it tends to thin the cell walls, making them more readily 

 penetrated by fungoid pests, and it also appears to affect 

 the composition of the sap in some way so that the fungi 

 develop more readily than usual. 



In addition to these effects on the plant another effect 

 is produced on the soil. The nitrate of soda is not taken 

 B. s. 9 



