PREPARATION OF SOIL. 123 



(B) Mode of execution of trenching. Trenching may 

 be done either by hand or with ploughs. The former 

 method is evidently preferable on account of the per- 

 fection with which the soil can be loosened, and it is the 

 only possible one in certain rocky soils, but is far more costly 

 than the latter. These can only be applied with efficacy 

 in deep loose soils, unless steam traction is used, which 

 allows considerable obstacles to be overcome, and loosens 

 the soil much better than implements hauled by teams.* 



Whatever may be the system adopted, three cases are to 

 be considered 1st, the arable soil is of superior quality to 

 the subsoil, and the latter cannot be improved by the action 

 of the air ; 2nd, the subsoil may be usefully modified by 

 atmospheric influences ; 3rd, the subsoil may improve the 

 arable soil if mixed with it. 



If the work is done by hand one proceeds in the following 

 way : In the first case part of the men open a trench to the 

 required depth so as to expose the subsoil which other men 

 disturb, leaving it in its place. In the second case the 

 arable soil is thrown into the trench so as to superpose the 

 layers in an inverse order. In the third case narrow vertical 

 slices are cut and mixed together before being modified. 



If, on the contrary, draught teams are used, one may go 

 to a certain depth without bringing the subsoil to the sur- 

 face by ploughing the arable soil with an ordinary plough 

 and following with the subsoiler in the same furrow, disin- 

 tegrating the subsoil without shifting it. 



To completely turn over the soil the best way is to use 

 1st, a plough of medium strength ; 2nd, a Bonnet trenching 

 plough. The first turns over the top layer of arable soil and 

 draws it into the furrow made by the trenching plough ; the 

 second draws from the bottom of the furrow opened by the 

 ordinary plough a new slice of soil which it tips over it. In 

 loose light soils these different implements may be replaced 

 by Coetgreave's trenching plough, which carries them all 

 fixed on the same beam. 



(C) Time most suitable for trenching. The most suitable 

 time seems to be the end of autumn or the beginning of 

 winter, for the soils are not too wet and have not become too 

 hard. It is also a slack time in farm work, which enables 

 the use of all the unengaged draught ; further, the soil 



*For further information see Trenching and Subsoiling for American Vines, by the 

 present translators, Department of Agriculture, Melbourne, 1901. 



