III.] AVAILABILITY OF NITROGENOUS MANURES 93 



While these results might not be exactly borne out 

 on other soils, it will be within the limits of ordinary 

 error to conclude that, for equal amounts of nitrogen, 

 nitrate of soda possesses a slightly greater value than 

 sulphate of ammonia, but that the choice between the 

 two should be dictated by the relative price of the 

 nitrogen per unit, the nature of the crop, and the 

 amount of carbonate of lime in the soil. Since sulphate 

 of ammonia contains approximately 20 per cent, of 

 nitrogen against 15 per cent, in nitrate of soda, the 

 relative prices of the two manures ought to be in the 

 ratio of 3 to 4; if sulphate of ammonia is £\2 per 

 ton, nitrate of soda, to yield an equivalent value of 

 nitrogen, ought not to cost more than £(^ per ton ; if 

 nitrate of soda is £\o per ton, the equivalent value of 

 sulphate of ammonia would be ;;^I3, 6s. 8d. per ton. 

 For mangolds, nitrate of soda should certainly be 

 chosen, unless the advantage in price is largely on 

 the side of the sulphate of ammonia, because of the 

 great value of the soda base in rendering available 

 the dormant potash so much required by the mangold. 

 On soils short of lime, and especially if they have any 

 tendency to become acid, nitrate of soda will always be 

 preferable ; and again, when extra large quantities of 

 nitrogenous fertilisers are to be used, as is sometimes 

 the case in market-garden work. For barley, sulphate 

 of ammonia is preferable, because of the better quality 

 it produces ; on the light soils also it should have the 

 preference, provided they are properly supplied with 

 carbonate of lime. 



But undoubtedly the best plan is to use a mixture 

 of the two fertilisers ; there is then nitrate for the 

 immediate use of the crop, and yet no great excess of 

 salt remains, with the risk of its being washed down 

 below the range of the plant's roots in the soil water ; 



