FERTILIZERS. 65 



good effect of plaster was its indirect action, which is a convenient 

 term for covering oiir ignorance. Phister serves directl}' as plant 

 food. Water passing through soil mixed with plaster, brings out 

 more potash. Plaster fixes ammonia, and by preventing evapora- 

 tion, is lieneficial in drought. Even with our imperfect knowledge 

 there are man}^ ways in which we can conceive of the beneficial 

 action of plaster. 



Mr. Iladwen said that it is impossible for the farmer to extract 

 the sixt3'-two pounds of plant food from a ton of manure. It is 

 easier to haul the whole of it on to the land. 



Prof. Atwater said, supposing it contains but sixty-two pounds 

 of plant food, this is not all its value. To get the largest possible 

 crop on his land, Mr. Lawes, in England, wonld use chemicals. 

 But in England, wliere there is less drought than here, and on a 

 naturalh' strong soil, these might answer as well as the manure. 

 Here, however, the evaporation is immense ; the rains settle down 

 into the subsoil, and in dry weather come up again. If we could 

 prevent them from escaping we should have no drought. Manure 

 in the soil may retard this evaporation. The other 1,938 pounds in 

 the ton undergo chemical changes in the soil, improve its texture, 

 and turn into active forms the inert plant food the soil contains. 



Mr. Hadwen asked whether manure w^ould become plant food 

 sooner when on the surface or when ploughed in. 



Prof. Atwater replied that manure acts in a great many different 

 wa^'s, and might sometimes become plant food sooner when applied 

 to the surface, and sometimes when ploughed in. AV ell-cured 

 manure, applied when in the proper condition, always works well. 

 But when the fermentation goes too far, not onl}' is much valuable 

 material lost but what remains becomes changed more or less to 

 inert forms. If the manure is to be fermented, the process should 

 not be too rapid nor carried too far. Now if the manure is spread 

 on the ground when it is fresh or partly- cured, it will not ferment 

 much ; it will lose extremely little A^aluable material, and rains and 

 melting snows will soak the material into the soil as fast as it is 

 rendered available, and thus it will be saved. If allowed to stard 

 in small heaps it is apt to ferment so much as to waste a good deal. 

 You must have it where the roots feed, and this is mostl}^ in the 

 first six inches of the soil. If you can apply it a considerable time 

 in advance, spread it on the surface ; there will then be less loss 

 than when put in even small heaps ; but the rain and the snow will 

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