146 ACTION OF SOIL ON FOOD OF PLANTS IN MA:NaTKE. 



For soils of this kind composts are not so well suited ; 

 and, instead of the earth, some very loose body onght to 

 be substituted for mixing with the manure. Turf-dust 

 will be found to answer the purpose best.* 



If the crops obtained from many fields by manuring 

 ^vith farm-yard manure, bone-earth, guano, and in many 

 cases also with Avood-ashes and lime, are compared with 

 what the same helds will yield in the unmanured state, 

 the effect of these manures seems truly marvellous. 



The yield of an unmanured field must correspond witli 

 the available nutritive substances which it contains ; a 

 lower crop corresponds to a smaller store of these matters. 

 In any one of the cases stated, if we compare the amount 

 of nutritive substances in the unmanured portion of a 

 field with the crop which it produces, and then compare 

 the additional nutritive substances or the quantity of dung 

 with the increased crop, the increase appears to be beyond 

 ah proportion much greater than the additional supply. 

 Hence we are led to suppose that the phosphoric acid, 

 potash, and ammonia given in the manure must be much 

 more efficacious than the substances present in the soil, or 



* It is, perhaps, much more important than manuring with composts, 

 Avhich always involves much labour and more carriage, to take ^ad- 

 vantage of the absorbent properties of earth and turf, for fixing the 

 nutritive substances contained in liquid manure. By covering the 

 ground of a drmghill, on an area of 10 meti-es square ( = 10'o sq. feet) 

 with a layer of loose tiu-f, 1 metre (=3"3 feet) deep, a bed of 100 

 cubic metres (=3, .500 cubic feet) of tiurf is formed, into which the 

 liquid portion of the manure in the dunghill may safely be allowed to 

 soak Avithout the least risk of losing the smallest portion of its usefiil 

 iugi-edients. The turf may then be used, like dimg, for manuring, ana 

 of course must be renewed every year. On fields which are not tilled, 

 such as meadows, liquid manure will natm-ally act with greater rapidity. 

 The turf found in the neighbourhood of Miuiich, when reduced to pow- 

 der, absorbs 7'892 grammes (= 122 grains) of potash, and 4'169 grammes 

 ( = 64 grains) of oxide of ammonium, per 1000 cubic centimetres ( = 61 

 cubic inches) Aveighing 330 grammes (11^ ozs.). 



