CHAPTER XXIV. 



THE NATURE AND USES OF MANURES. 



By W. S. Gray, B.Sc, A.I.C, late Lecturer on Chemistry at Wye Agricultural College. 



The problem of how to increase the crop- 

 producing power of soils is one of vital 

 importance at the present time. An average 

 soil contains all the constituents a plant 

 requires for its growth, but a sufficient quan- 

 tity may not be present in an available con- 

 dition to enable one to obtain the high yields 

 now demanded. 



The system of manuring by means of stock 

 is the mainstay of farming ; fruit growers, 

 and especially market-gardeners, rely much on 

 farmyard manure. The reason is not far to 

 seek, for dung contains everything the land 

 wants to enable it to grow large crops, except, 

 perhaps, phosphates. This being so, it is 

 worth while taking care of it in storage, as it 

 has been proved that fully 50 per cent, of the 

 value of dung is lost by exposure to rain. 



Horse manure is of a dry nature. It fer- 

 ments rapidly and is liable to " fire-fang " 

 unless well stored. 



Stable manure, purchased from towns, may 

 be of poor quality owing to the inclusion of 

 street sweepings and the loss of the urine. 

 Cow manure, on the other hand, is cold and 

 watery. In each case, however, the value 

 depends largely on how the dung has been 

 stored, and it has been shown that a layer of 

 earth on the top of a heap is one of the best 

 safeguards against loss. 



Numerous experiments at Eothamsted and 

 elsewhere have proved that to obtain the 

 largest crop yield it is better to employ a 

 moderate dressing of dung, plus artificials, 

 than to put on a very heavy dressing of dung 

 alone. By this procedure the soil is im- 

 proved in texture by the organic matter of 

 the dung, and the artificials enable a crop 

 to be given what it particularly requires. 

 Turnips need phosphates ; potatoes and fruit 

 respond readily to potash. The war has 

 shown us that we can supply this constituent 

 to a large extent by saving wood ashes, which 

 contain about 10 per cent, of potash. 



Nitrogenous artificials are of two kinds, 

 " readily Etvailable " and " slowly available." 

 The former type includes nitrate of soda, 

 sulphate of ammonia, nitrolim, nitrate of 

 lime and nitrate of ammonia. The " slowly 

 available " comprise shoddy, dried blood, 

 horn, hair, woollen and leather waste. 



Nitrate of soda is in a form ready for the 

 plants' immediate use, but is easily washed 

 out of the soil. Sulphate of ammonia is 

 slower in action but is " held " by the soil. 



Nitrolim is also slower in action, and 

 should not be applied with seeds, as it arrests 

 germination for about ten days, after which 

 the effect disappears. 



Nitrate of ammonia, a comparatively new 

 fertiliser, contains 35 per cent, nitrogen, as 

 compared with 15^ per cent, in nitrate of 

 soda, hence the relative cost for carriage per 

 unit of nitrogen is much less ; and, further, it 

 has no detrimental effect if applied to stiff soils. 



Shoddy hupplies nitrogen more slowly thaa 

 the above manures, but gives a good return ; 

 and where a steady application of nitrogen is 

 required over a more extended period, as ia 

 the case of hops, it is especially valuable. 



Dried blood is excellent, but the unit value 

 on the market is much too high as a rule to 

 justify its use. 



Horn and hair wastes, although containing 

 a high percentage of nitrogen, are slow ia 

 action. 



The Phosphatic Manures form another 

 group of fertilisers, and the most important 

 are Superphosphate and Basic Slag. The 

 former is obtained by treating rock phos- 

 phate with sulphuric acid, and so producing a 

 readily soluble phosphate which is quick in 

 action. Basic Slag is a by-product in steel 

 manufacture, and, although slower in action 

 than super, costs less per unit, and is to be 

 preferred on stiff land. BDue meal, in addi- 

 tion to containing about 45 per cent, phos- 

 phate, supplies 3 or 4 per cent, nitrogen, but 



