64 THE CHEMISTRY OF THE FARM 



farmyard manure in the farrow before growing potatoes 

 or roots, as any hindrance to decomposition is then 

 injurious. It is better, for several reasons, to apply 

 any considerable dressing of alkali salts in the autumn ; 

 their prejudicial effects will thus be obviated. 



Wood Ashes may also be employed as a potash 

 manure ; they will contain between 5 and 10 per cent, 

 of potash with a good deal of lime. The ash of young 

 boughs is richer than that from fall-sized timber. 



Potash manures produce their greatest effect on 

 meadow and pasture ; leguminous crops, potatoes, and 

 root crops may also be considerably benefited by their 

 use. Some garden crops, as artichokes and celery, are 

 greatly assisted by potash manures. Kainite is best 

 for grass, but sulphate of potassium should be used 

 for potatoes. Many soils, especially clay soils, are 

 naturally well furnished with potash ; on such soils 

 potash manures are almost without effect. 



Common Salt. — Chloride of sodium supplies no 

 essential ingredient of plant food. Salt is commonly 

 used for mixing with nitrate of sodium, and as a 

 manure for mangels; it has also been used success- 

 fally for cabbage. The little value which it possesses 

 is probably due to its action in the soil, where it wdll 

 help to set free more important constituents, and 

 particularly potash. 



Relative Value of Manures. — This may be arrived at 

 either by regarding their relative effect on crops, or by 

 reference to the market price of their constituents; the 

 two methods do not necessarily give the same result, 

 though they naturally tend to agreement. Wagner, 

 as the result of numerous experiments with nitro- 



