210 CHEMICAL FERTILIZERS 



light soils, although its slower action necessitates its use at 

 an earlier date. On light soils it is often necessary to use 

 potash as well as basic slag. Rothamsted results show that 

 the use of magnesium and sodium sulphate has an important 

 action on crop returns. It seems highly probable that some 

 of the calcium sulphate in superphosphate may serve a 

 similar purpose. Potash manures are especially valuable 

 on light soils. It is rare to find a light soil so well supplied 

 with potash as not to need potash manuring, but ordinary 

 farmyard manure, if well preserved, is fairly rich in potash, 

 and many farms depend largely upon this source of potash. 

 Where a farm contains some fields that are heavy and some 

 that are light, the fertilizing ingredients which the hay removes 

 from the heavy lands find their way through the beasts to the 

 light arable portion of the farm. Where there is a sufficient 

 rainfall, light soils can produce large flushes of green manure, 

 provided they are liberally supplied with all fertilizing materials. 

 Manures and Heavy Lands. Heavy soils are, for the 

 most part, poor in lime and phosphates, although they are 

 relatively rich in potash and nitrogen. When used for 

 arable purposes, farmyard manure is necessary to break up 

 the soil into a more open condition, suitable for cultivation. 

 The great success of the application of basic slag to heavy 

 soils may be attributed to their extreme poverty in phos- 

 phorus. Many heavy soils have been grazed for centuries, 

 and considerable amounts of phosphates and lime have been 

 removed in the bones of the cattle that have fed there. 

 Relatively, much less other fertilizing material is removed, 

 since nitrogen accumulates in the soil by the growth of 

 clover, and the soils are relatively rich in potash, of which 

 99 % of that eaten is returned to the soil by the cattle. Ashes 

 and other coarse granular material do much to improve this 

 type of soil. Such lands are undoubtedly hard to plough, 

 but give good returns for the fertilizers that are expended 

 upon them. If they are excessively wet, they may be econo- 

 mically drained by the use of the mole drain plough. With- 

 out any draining much can be done to dry out these heavy 

 wet lands by encouraging vigorous vegetation. By the use 



