XII.] PHYSICAL EFFECTS OF FARMYARD MANURE 241 



slowness with which dung can yield up its contents of 

 nitrogen is particularly noticeable in the early spring, 

 when the land is cold and bacterial actions in conse- 

 quence go on very slowly. However rich the soil may 

 be in farmyard manure and its residues, the gardener 

 who is in a hurry to push on early production, finds it 

 very necessary to use an immediately active nitrogenous 

 manure like nitrate of soda. 



The value of farmyard manure to the land is by no 

 means confined to its fertilising action ; its physical 

 effects upon the texture and water-holding powers of 

 the soil are equally important ; indeed, for some crops, 

 and particularly in droughty seasons, these factors count 

 for more than fertilisers towards ensuring a good yield. 

 The farmyard manure, as it rots down in the soil, goes 

 to restore the stock of humus, which otherwise is always 

 tending to oxidise and diminish, and the humus, 

 considered merely from the physical side, contributes 

 largely to the fertility of the soil. In the first place, it 

 improves the texture of all soils ; to sands it gives 

 cohesion and water-retaining power, while by loosely 

 binding together the finest particles of clay soils it 

 renders them more porous and friable. When a piece 

 of old grass land, even on the stiffest of soils, has been 

 ploughed up, it is easy to see the beneficial effect of the 

 humus that has been accumulated ; after the winter the 

 plough slice will crumble naturally so as to harrow down 

 at once to a mellow seed bed, whereas a neighbouring 

 piece of the same soil that has long been under arable 

 cultivation will only show a number of harsh, intractable 

 clods. The importance of a good seed bed to the future 

 well-being and ultimate yield of the crop can hardly be 

 exaggerated ; it is the basis of all good farming, so that 

 even when the fertilising properties of farmyard manure 

 have been replaced by artificial manures, some other 



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