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constituents only the potash is in readily available form, it must be 

 regarded mainly as a potassic manure, and one to be used for potash 

 feeding crops. Hence its application to Irish potatoes has been 

 found io give an increased yield. In its indirect action it can 

 compare very favourably with stable manure. On account of its 

 ready decay, it increases the supply of humus in the soil, and has 

 been found to improve light sandy soils. It can also be used with 

 advantage as a mulch. The cultivator of land near the coast will find 

 it ell worth the cost of carting it on to his land, especially if he 

 supplement it with some available nitrogen and phosphorus, in 

 the form of fertilisers, to render it a more perfect general manure. 



Guanos. — These manures form a bridge, as it were, between the 

 general and the special manures. Guanos vary much in composition 

 and though most of them contain all the manurial constituents some of 

 them may be classed as special manures, because they contain one of the 

 constituents in greater prominence. Thus some are said to be nitro- 

 genous and others phosphatic, that is, guanos with high percentages 

 of nitrogen and phosphorus respectively. 



Special Manures. — Since special manures are those containing only 

 one or two of the constituents of plant food, it is most convenient to 

 classify them according to which of the constituents they supply ; we 

 therefore have three groups, (i) nitrogenous —i. e., supplying nitro- 

 gen; (ii) phosphatic — i. 6., supplying phosphorus; (in) potassic — i.e., 

 supplying potash. A few remarks on the nature and action of the 

 important and best known special manures may serve as a guide to 

 their use in restoring the fertility of the soil. 



(i.) Nitrogenous Manures. — As the general tendency of these man- 

 ures is to produce a large amount t f leafy growth, care must be taken 

 lest a too liberal application damage the yield of fruit Nitrate of 

 Soda is of all manures the quickest in action. There are two reasons 

 for this. It is a very soluble compound, and, further, it contains its 

 nitrogen in the right form for immediate absorption by the roots. 

 These very properties call for great care in the use of the nitrate, for 

 on account of its solubility, it is very liable to be washed out of the 

 land by rain. It should only be applied at a time when the crop is in 

 a state of active growth and there is no probability of heavy rain. 

 Sulphate of Ammonia, which is a waste product in the manufacture 

 of gas from coal, is the great rival of nitrate of soda as a nitrogen 

 supplier. It has the advantage of being more readily retained by the 

 soil, and there is consequently not the same risk of loss by washing. 

 It is not so quick in its action since it is not ready for immediate ab- 

 sorption. The ammonia has to undergo conversion into nitrate. Lime 

 being necessary for this process of nitrification, sulphate of ammonia 

 should never be applied to soils deficient in that constituent. 



(ii.) Phosphatic Manures. — These are the manures whose effect will 

 be most noticeable on fruit trees. TLeir tendency is to increase the 

 yield of fruit and to hasten ripening. It should be remembered that 

 phosphorus occurs in soils and fertilisers usually in the form of com- 

 pounds, known as phosphates. For the most part, these compounds 

 are very insoluble, and this causes the plant to experience considerable 



