CH. v] Trenching 93 



E-othamsted have shown that the second method (the 

 loosening of the subsoil without additional manure) has 

 very little effect either on the water content, the amount 

 of plant food or the growth of fruit trees. There is no 

 evidence that this operation is worth doing ; the gardener 

 who takes the trouble to trench should certainly not 

 miss the excellent opportunity it affords for putting the 

 very necessary manure into the lower spit. 



There are, however, cases where the third method (the 

 inversion of the surface soil and bringing up of the sub- 

 soil) has worked very well, particularly on sandy soils 

 where the difference between the surface and the sub- 

 soil is less than on the loams and clays. The subsoil is 

 not particularly unsuited for the growth of plants, and 

 when brought to the surface it only requires proper 

 manuring to enable plants to make a satisfactory start. 

 Then when the roots grow down to the second spit they 

 come to the old surface soil and develop well: thus in 

 the end they range over two spits whereas on untrenched 

 land they cover one spit only. 



We can now make a general summary of the effects of 

 cultivation; they are: 



1. To change the clay and therefore the soil from 

 the sticky state which is bad for plants to the useful 

 crumbly state. 



2. To keep the surface fine so as to reduce the tem- 

 perature and conserve the water supply on hot fine daj^s. 



3. To give the crop a clear field for growth and reduce 

 competition by weeds: this seems also to enable the 

 bacteria more rapidl}^ to accumulate nitrates in the soil . 



4. In horticultural and market garden practice to 

 change the subsoil and make it as nearly as possible 

 like the surface soil. 



