48 CHAPTER IV 



(3) Nitrate of Lime. — Containing about 13 per cent, nitro- 

 gen immediately available. It is similar to nitrate of soda in 

 most respects. 



(4) Blood Meal. — Containing about 12 per cent, nitrogen, 

 which becomes available fairly rapidly. 



(5) Government Guano. — Containing about 10 per cent, 

 nitrogen, 11 per cent, phosphoric oxide, and a little potash, 

 all fairly readily available. Its composition is liable to vary 

 somewhat. 



(6) Superphosphate. — Containing, if of good grade, 15 to 20 

 per cent, phosphoric oxide. Soluble in water, and therefore 

 immediately available to crops. 



(7) Bone Dust. — Containing about 3 to 4 per cent, nitro- 

 gen and 23 to 24 per cent, phosphoric oxide. Should be as 

 fine as possible, as fineness increases availability. For best 

 results should be apphed early. 



(8) Basic Slag. — Containing about 8 to 20 per cent, nitro- 

 gen and 20 per cent, free lime. It is slow in action and should, 

 therefore, be applied early. It is said to act best on heavy, 

 wet soils. 



(9) Sulphate of Potash. — Containing 45 to 50 per cent, 

 potash in readily available form. 



(10) Muriate of Potash. — Containing 50 to 55 per cent, 

 potash in readily available form. Muriate (i.e., chloride) of 

 potash seems to injure the quality of certain crops, like tobacco. 



Use of Lime. — It is commonly stated that all normal fer- 

 tile soils should contain a certain amount of free lime (in the 

 form of calcium carbonate). Total absence of free lime gives 

 rise to the condition known as " acidity " or ' sourness," 

 which is unfavourable to many plants and soil micro- 

 organisms. Lime exerts both chemical and physical effects 

 in the soil, which may be summarised as follows : — 



(1) It prevents the formation of " acidity," thereby stimu- 

 lating the activity of desirable micro-organisms in the soil. 

 Notable among these are micro-organisms engaged in the de- 

 composition of organic matter, nitrification of organic nitro- 

 gen, and fixation of atmospheric nitrogen. Stated otherwise — 

 the effect of lime is to stimulate the decomposition of organic 

 matter and the production of nitrogenous plant food. 



(2) By interaction with mineral compounds in the soil, it 

 stimulates to some extent the production of available potash 

 and phosphoric oxide from the soil's reserve supply of these 

 plant foods. In this respect it must be classed as a " stimu- 

 lant," not " fertiliser." 



