32 ARTIFICIAL MANURES [CH. 



At the Harper Adams College 1 the results for the three seasons 

 1913-15 were: 



lOcwts salt 

 No salt 5 cwts salt after sowing, after sowing 



27i 35J 36 tons per acre 



All plots received farmyard manure, and in addition 2 cwts 

 of dissolved bones, J cwt superphosphate, and \ cwt sulphate of 

 ammonia per acre. 



In the Cockle Park trials 2 , 2 cwts of salt increased the yield of 

 mangolds by nearly 4 tons per acre on an average of 5 years. 

 Good results have also been obtained elsewhere. 



Cereals, especially wheat, used to receive salt in the old days, 

 and might well do so now on thin light or chalky soil. Only a 

 few experiments have been made on the subject: in Yorkshire 

 salt increased the yield of barley, both in the dry season of 1901 

 and the wet season of 1903, but the results of later experiments 

 were not conclusive 3 . 



There is considerable evidence that sulphate of soda liberates 

 potash from the soil. It has been used for many years at Rotham- 

 sted, often with good effect and never with bad. It must, how- 

 ever, be free from acid. Some samples contain a fair quantity 

 of potash : one recently analysed at Rothamsted had as much as 

 23 per cent., equivalent to 47*4 per cent, sulphate of potash. 



Lime. For leguminous crops it is probably safer to use lime 

 than salt; this is dealt with on p. 3. 



Potatoes. This crop is too valuable to allow of any risks, and 

 it should receive all the potash that can be got together by pur- 

 chase, ashes, seaweed, etc. No one, however, need reduce his 

 area of potatoes because he is short of potash. Most large growers 

 have used it liberally for a number of years, and could probably 

 leave it out for a time without harm. But this risk could not always 

 be taken. Much depends on the nature of the soil, and on some 

 land it is still worth spending a good deal on sulphate of potash. 



Farmyard manure as a saver of potash. Farmyard manure is 

 fairly rich in potash, a 10 ton dressing supplying no less than 



1 The experiment is described in Harper Adams Report for 1909, p. 14. 



2 Cockle Park Bull No. 16, 1911. 



3 See Leeds Bulls. Nos. 22 and 39 for the earlier experiments, and No. 75 for 

 the later ones. 



