22 



only be applied to light soils, to potash-loving plants, such as the 

 potato and vine, as in most cases the action of nitrate of soda sets 

 free a sufficient quantity in the clayey soils. 



Wood ashes were once the only source of potash ; now the saime 

 deposits in Germany are the chief. . . 



Kainit is the chief potassic fertihzer used in this country, contammg 

 about 12 per cent, potash. It should be applied in wmter before 

 growth starts, for the impurities in it to be washed away by ram ; it 

 may be mixed with basic slag. These remarks apply to all potassic 

 fertiUzers, as well as the fact that some form of lime is necessary to 

 help the soil hold them, or they will be washed away ; most soils, 

 however, contain enough lime to effect this. Kainit is a crude product, 

 i.e. unpurified; sylvanit is another form, cheaper and about as 

 effective. The price of kainit is about {,6 a ton. Of the manu- 

 factured products sulphate of potash and munate of potash are the 

 chief. The latter is very injurious to active rootlets, and, as its price 

 is high, sulphate should be preferred for ordinary purposes, although 

 sometimes inferior in effect. The choice of crude or of manufactured 

 potash salts depends on the soil and the time of appUcation. If 

 winter is the time, when rains can cleanse them, kainit or crude salts 

 should be used. If, on the other hand, potash is needed on a heavy 

 soil, especially near the time of the seed-sowing, manufactured or 

 purified salts are preferable, producing, moreover, better quality crops, 

 the price being about £i6 a ton. As regards wood ashes, they can be 

 applied with advantage, unless the potash has been washed out by 

 rain. Coal ashes, on the other hand, should be avoided, except for 

 heavy clay soils, which they help to lighten. They contain practically 

 no plant-food. 



Farmyard and Stable Manure. — ^This is very variable in quality. 

 Horse and sheep manure are considered richer than cow and pig manure. 

 On an average, in a ton of well-rotted farmyard manure there are about 

 10 lb. of nitrogen, 4 lb. of phosphates, and 10 lb. of potash. Perhaps 

 its chief value is in improving the soil physically and in setting free 

 plant-food already present, but unavailable. Soils rich in humus, 

 which is provided by farmyard or stable manure, can better withstand 

 drought than hght soils, the former retaining water better than the 

 latter. It also helps to make a clay soil more porous and workable. 

 Many chemical changes take place, when once the heap is made up 

 and left, involving loss both, in weight and value. The nitrogenous 

 materials are attacked by a certain bacterium, and part escapes 

 into the air in the form of ammonia and carbonic acid gas. Other 

 bacteria cause denitrification, entailing loss of nitrogen gas. After a 

 time the strawy part of the manure is converted into humus, involving 

 the loss of about a quarter of the original dry matter. The first two 

 processes go on most rapidly in the earliest stages, gradually becoming 

 slower and slower as time goes on, and it is then that the straw begins 

 to change to humus. It will thus be seen that manure laid loosely 



* Or lime— F. J. C. 



