624 SOILS: PROPERTIES AND MANAGEMENT 



526. When to use green manures. The indiscrimi- 

 nate use of green manures is of course never to be ad- 

 vised, as the soil may be injured thereby and the normal 

 rotation much interfered with. When soils are poor in 

 nitrogen and humus, they are very often in poor tilth. 

 This is true whether the texture of the soil be fine or 

 coarse. The turning-under of green crops must be judi- 

 cious, however, in order that the soil may not be clogged 

 with undecayed matter. Once or twice in a rotation is 

 usually often enough for such treatments. Proper drain- 

 age must always be provided. In regions where the rain- 

 fall is scanty, very great caution must be observed in the 

 handling of green manures. The available moisture that 

 should go to the succeeding crop may be used in the 

 process of decay, and the soil left light and open, due to an 

 excess of undecomposed plant tissue. 



527. When to turn under green crops. It is generally 

 best to turn under green crops when their succulence is 

 near the maximum. In this case a large quantity of water 

 is carried into the soil, and the draft on the original soil 

 moisture is less. Again, the succulence encourages a 

 rapid and more or less complete decay, with the maximum 

 production of humus and end products. The plowing 

 should be done, if possible, at a season when a plentiful 

 supply of rain occurs. The effectiveness of the manuring 

 is thereby much enhanced. 



528. How to turn under green material. In general, 

 in turning under green manures the furrow slice should 

 not be thrown over flat, since the green crop is then de- 

 posited as a continuous layer between the surface soil 

 and the subsoil. Capillary movement is thus impeded 

 until a more or less complete decay has occurred, and the 

 succeeding crop may suffer from lack of moisture. 



