60 



THE PRINCIPLES OF AGRICULTURE 



74a. The plowing under of green -crops sometimes gives 

 unsatisfactory results. If a heavy growth is plowed under when 

 the soil does not contain sufficient moisture to cause ready 



decomposition, this layer of foreign 

 matter prevents the passage of 

 the water from the subsoil to the 

 surface soil (Fig. 12). The crop 

 which is then planted must nec- 

 essarily feed for some time in the 

 surface soil, and in case of pro- 

 longed drought a partial or com- 

 plete failure of the crop may re- 

 sult. Heavy growths of cover - 

 crops, as well as coarse, strawy 

 manures, should be plowed under 

 when there is sufficient moisture 

 in the soil to cause decomposition. 

 In case it is necessary to plow 

 them under when the soil is dry, 

 a heavy roller will so compact the 

 soil that capillarity will be in part restored and decomposition 

 hastened. 



75a. While surface drains are to be avoided, yet it frequently 

 becomes necessary to provide a conduit or open ditch into which 

 tile drains may open, or to remove flood water. It is a common 

 error to have the banks too vertical. Through the action of frost or 

 the tramping of stock, the banks are constantly requiring atten- 

 tion. The ditch should be wide, and the banks should have a 

 gradual slope, as illustrated in Fig. 13. Grass-seed should be 

 sown over the sides and bottom, so that the sod will prevent 

 washing. One can drive across such a ditch. When possible, 

 this ditch would be made the boundary of a field, or be placed 

 near a fence. 



76a. The depth at which tile drains should be placed must be 

 determined by the nature of the soil. In very compact and 

 impervious soils, as clay, the drains must be closer together and 

 nearer the surface than in porous soils. Land may become so 



Fig. 12. The layer (a b) of unde- 

 composed herbage. 



