172 



Farmyard Manure. 



[JUNE, 



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 a stiff soil 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 have crumbled 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 cultiva- 

 tion 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 if the fertilising 

 properties of farmyard manure can be replaced by artificial 

 manures some other means, such as the ploughing in of green 

 crops, must be resorted to in order to maintain the stock of 

 humus. Of course the value of humus, and in this respect 

 of farmyard manure, will vary on different soils and with 

 different crops ; cereals, for example, are comparatively un- 

 affected by its absence, as may be seen by the manner in which 

 Mr. Prout grows cereals almost continuously on his strong 

 soil with artificial fertilisers only, but root crops are very 

 dependent on a mellow seed bed. This may be seen on the 

 Rothamsted plots ; the wheat which has now been grown 

 on the same land for 63 years comes as well and yields as big 

 crops on the plots receiving only artificial manures as it does 

 on the plot receiving dung, but on the mangold plots the 

 result is different. Where artificial manures containing no 

 organic matter have been supplied the tilth is bad, and in 

 trying seasons, when^ drought succeeds heavy rain soon after 

 sowing, the plant obtained is so imperfect as to reduce the yield 

 considerably. If the conditions are favourable to germination 

 and the plant once becomes established, then, as we have 

 previously seen in Table XIV, the plot manured with minerals 

 and nitrate of soda will grow a bigger crop than that receiving 

 dung, but this superiority is masked in many seasons by the 

 defective plant. 



