74 THE SOIL OF THE FARM. 



whose roots penetrate deep, and ramify extensively 

 throughout the soil. 



Among the various plants grown for green-manuring 

 are white mustard, buckwheat, rye, rape, vetches, Tri- 

 foUum incarnatum, and common clover. In many coun- 

 tries spurry, borage, and white lupin, are also largely 

 grown for the same purpose. Many of these crops, when 

 plowed in green, are, weight for weight, almost as good 

 as farm-yard manure, containing large quantities of ni- 

 trogen, phosjohoric acid, and potash. The great weight 

 of decomposable vegetable matter contained in the root 

 as well as the Iteaf of a crop, grown for being plowed in 

 as manure, is to be considered in estimating its effect as a 

 fertilizer. There can be no doubt that to this especially 

 is due the fertilizing effect of a clover stubble when 

 plowed in as a preparation for the following wheat crop. 



Eight to twelve tons per acre may be grown of any of 

 the crops we have named with the aid of guano. White 

 mustard comes to maturity in six or eight weeks, and 

 tv/o or three crops of it might bo grown on the same land 

 in a single season, after an early summer crop of peas and 

 potatoes. Only a light plowing is needed, and less than 

 a peck of mustard-seed will seed an acre, at a trifling 

 cost. Some of the other crops are not much less rapid 

 growers, and are also inexpensive to cultivate. 



Green-manuring ])rod aces the greatest effect on light 

 sandy soils in dry climates ; but it is profitably practised 

 also on heavy soils. The green crop should, if possible, 

 be plowed in just before the time of flowering, or at all 

 events after it has arrived at considerable growth. The 

 season of the year for ])lowing in must depend upon the 

 nature of the crop ; but the operation is best performed 

 in the heat of summer, as the conditions for rapid decom- 

 position are then actively present, after the plants are 

 turned in. To cover them effectually, they reiiuireto be 

 first heavily rolled. A skim coulter should be used in 



