468 NORFOLK SOCIETY. 



the soil is left in so friable a state that the slightest brush of a 

 harrow, or even a shower of rain, carries the earth into the in- 

 terstices of the furrows and stops the gi'owth of grass. 



As to the depth of furrows, no specific rule can be laid down, 

 and practice on this point must be governed by the nature of 

 the soil and subsoil, modified, in some instances, by the crop 

 to be cultivated, and the kind and quantity of manure to be 

 applied. As a general fact, it may be said that stiff soils re- 

 quire to be ploughed more deeply than light soils. The for- 

 mer often contain the elements which nourish crops to a great 

 depth, and from their nature (as before described) require 

 deeper and more thorough ioosening. It is doubtful whether 

 practice has yet established any particular depth as most pro- 

 per, even for stiff soils ; but perhaps there has been a nearer 

 approach to seven inches as a standard, than to any other 

 depth. There are peculiar situations where a greater depth is 

 desirable, — as for alluvial or sedimentary soils. There are 

 many other cases where a loosening of the earth is advisable 

 to a greater depth than seven inches ; but, except in the cases 

 just specified, the question is, — ^would it be better to effect this 

 loosening by ploughing in the ordinary way, or with the sub- 

 soil plough ? This point will be more particularly considered 

 under the heads of trench ploughing and subsoil ploughing. 



2. Light, or Sandy Soil. The properties and action of this 

 kind of soil, may be said to be opposite, in some important 

 respects, to those of stift" soil. Sands and gravels, being desti- 

 tute of clay, do not "hold" manures; their porosity causes 

 them to be strongly acted on by the air, and their organic mat- 

 ter is quickly decomposed and dissipated. Soils abounding in 

 clay are too little acted on by the air ; those which contain no 

 clay are acted upon too much. These facts at once teach that 

 different modes of tillage are required in these cases. In sandy 

 soils we must guard against this too strong atmospheric ac- 

 tion, because it dissolves out manures too rapidly, and' carries 

 them off by evaporation and filtration before they can be ab- 

 sorbed by plants. Hence, fallowing, or repeated ploughing, so 

 useful in developing the vegetable nutriment which lies latent 

 in clay, would be decidedly injurious in sandy and gravelly 

 soils. The remai-ks of Dr. Lyon Playfair, of London, who is 



