THE DOUBLE MOULD-BOARD TRENCH-PLOW. 135 



"When a mixture of the subsoil with the surface tends 

 to render the whole richer, trench-plowing is best ; hut 

 when the subsoil is of a more sterile character, it should 

 be only loosened with the subsoil plow, and more cau- 

 tiously intermixed with the richer portion above. 



It often happens that the subsoil plow is very use- 

 ful in loosening the soil for the purpose of allowing the 

 trench-plow to run more freely through it. 



THE DOUBLE MOULD-BOARD TRENCH-PLOW. 



This plow, sometimes called the Michigan Double 

 Ploio, is represented in Fis:. 110. It has two mould- 



boards on one beam. The forward or small one pares 

 off the surface or sod, and throws it into the previous 

 furrow, usually to a depth of three to five inches. The 

 larger one follows closely, lifting the under-soil upon 

 the top, and in sward land completely burying the sod 

 with the mellow earth from below. This is the best 

 implement for trench-plowing yet introduced into prac- 

 tice, and with double the ordinary amount of team, 

 will cut to a depth of nine to twelve inches. 



