NORFOLK SOCIETY. 465 



one of the changes which it is desired to produce in such soils, 

 is a higher temperature. Every farmer knows that his crops 

 require a certain degree of warmth. Now it is a known fact 

 that the absorption of oxygen produces heat. Thus the decay 

 of vegetable and animal bodies has been properly called a slow 

 combustion. The heat is, of course, sensible in proportion to 

 the rapidity of the combustion, but the amount evolved in the 

 process is the same, whether the combustion is slow or quick. 

 It has been already remarked, that clayey soils contain more 

 or less carbonaceous or organic matter, and the union with 

 oxygen which is effected by exposure to the air, actually im- 

 parts warmth to the soil, and this of itself, in many instances, 

 may do much towards the perfection and yield of crops. 



Upon these principles rest the advantages of thorough fal- 

 lowing, for stiff soils. The frequent workings produce that 

 aeration, or absorption of oxygen which is so important in 

 effecting the necessary decompositions, and bringing the soil 

 to a state which enables plants to derive from it full support. 

 But on soils destitute of clay, as flinty or sandy soils, these 

 beneficial results do not ensue from the same operation, be- 

 cause they are deficient in the elements — alkalies and organic 

 matter — which are not created by the process, but only made 

 soluble, in the former case. It is true that the necessity for 

 naked or open fallows on clays, has been, in some respects, 

 done away, by the cultivation of crops which tend to keep the 

 soil open — as the various root crops, peas and clover — but the 

 effect in both cases is similar, viz. : the improved friability of 

 the soil. 



The particular condition, then, of the seed-bed which we 

 wish to produce on stiff or clayey soils, is one of comparative 

 lightness and friability. Hence that mode of ploughing such 

 soils which effects the most thorough breaking and exposure 

 to the air, other cncumstances being equal, would be most 

 advantageous. It is proper to remark, however, that the par- 

 ticular kind of plough, as to shape and action, depends on 

 whether or not the land has a coating of vegetation to be 

 turned under. If it has no vegetation on its surface, the most 

 complete crumbling and mixture of its particles would best 

 coincide with the main principles hereinbefore laid down, and 

 to effect this a plough which in its breast and mould-board 

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