[62 Commercial Gardening 



Iron is also one of the essentials of plant life, but there are usually 

 large available supplies in the soil. Without a trace of iron it would 

 be impossible for the chlorophyll or green colouring matter of leaves to 

 develop, no matter how perfect other conditions might be. Recently 

 sulphate of iron at the rate of 8 oz. to a square rod has been used where 

 iron has been considered deficient owing to the yellowish colour of the 

 leaves. When sickly looking yellowish-leaved plants will not respond 

 to a complete fertilizer, or to a nitrogenous manure, the soil is then 

 probably deficient in available iron. Very often, however, the yellowish 

 appearance of leaves is due to sour and sodden soil, or to the absence 

 of lime. 



Salt, or Chloride Of Sodium, is sometimes used as a special manure 

 for Asparagus and Sea Kale and other plants. In weak doses it seems 

 to be beneficial, and is said to liberate potash. From 1 to 2 Ib. to the 

 square rod may be used. Kainit, however, may be a safer manure to 

 use in quantity. 



9. VALUATION OF MANURES 



Chemical or artificial manures are valued chiefly by horticulturists and 

 agriculturists for the amounts of nitrogen, potash, or phosphates they 

 contain. The horticultural value, however, does not always correspond 

 with the commercial or market value, as the latter may be affected by 

 such questions as supply and demand, combinations, strikes, &c. The 

 cultivator naturally wishes to obtain the best value for his money. 

 Consequently, if he thinks he is paying too much for his nitrates, phos- 

 phates, or potash in a certain manure, he may cease to purchase it, and 

 buy another that will supply his wants at a cheaper rate. 



Artificial manures are now valued at "unit" prices for nitrates, phos- 

 phates, and potash, but these unit prices are subject to fluctuations. 



Nitrogenous manures are valued at a unit price fixed for the percentage 

 of nitrogen they contain; and nitrate of soda and sulphate of ammonia 

 are taken as the standard nitrogenous manures. Thus, if a ton of nitrate 

 of soda contains 15'5 units of nitrogen, and the price is 10 per ton, the 



10 

 value of the nitrogen will be tr^, or about 12s. lOd per unit. If 1 ton of 



sulphate of ammonia has 20 units of nitrogen, and is sold at 11 per ton, 



11 



the unit price is -gTp or 11s. It would therefore be cheaper to the grower 



to buy sulphate of ammonia at 11 per ton than to buy nitrate of soda 

 at 10 per ton, as he would be obtaining better manurial value to the 

 extent of Is. lOd per unit. Of late years the price of nitrogen has varied 

 from 8s. 3d. to 12s. per unit. 



For phosphatic manures superphosphate, basic slag, and ground Algerian 

 phosphates are taken as standards. In a superphosphate containing 32 per 



