48 HORTICULTURE, FORESTRY, FLORICULTURE 



as a fertilizer in the soil. Humus can be supplied to the soil most 

 cheaply by means of cover crops, an important part of their value 

 consisting in the furnishing of this material. The value of humus is 

 well illustrated by experiments at the Minnesota Experiment Station, 

 where corn grown continuously for six years on the same field 

 yielded an average of 21.4 bushels per acre, while corn in a three- 

 year rotation, including wheat and clover, yielded 47.1 bushels per 

 acre. As the plat producing corn continuously has sufficient plant 

 food to mature a normal crop annually, the low yield can only be 

 accounted for by the poor physical condition of the soil produced 

 through the depletion of the humus by frequent cultivation. (U. S. 

 E. S. B. 178.) 



Thus does humus play a very important part: (1) In keeping 

 the soil from washing; (2) in keeping it from becoming too dry in 

 midsummer; (3) in keeping it cool in the heat of the summer; (4) 

 in draining it in a manner; (5) in assisting in unlocking mineral 

 plant food; (6) in holding in an available form and in preventing 

 loss by leaching of mineral constituents; (7) in adding nitrogen; 

 (8) in making the soil warmer in spring; (9) in making the soil 

 more friable and loamy, and therefore cheaper and easier to handle. 

 As to the best methods of getting this humus in orchard soil, cir- 

 cumstances must govern in all cases. (Mo. E. S. Cir. 22.) 



Qualities Desirable in a Green-Manure Crop. No one plant pos- 

 sesses all the desirable qualities of an ideal green-manure crop. How- 

 ever, in the various crops used for such purposes, practically all the 

 desirable qualities are represented, though varying in degree. The 

 conditions under which a green manure is to be grown determine to 

 some extent whether a certain quality is desirable or objectionable 

 and must be taken into consideration in selecting the best crop to 

 grow. 



A green-manure crop should be a legume wherever possible, in 

 order to obtain the addition of nitrogen to the soil. It is also neces- 

 sary that a good growth be made, in order to have a large quantity of 

 organic matter to turn under and incorporate with the soil. Along 

 with good growth should be a heavy development of nodules on the 

 roots, as this is believed to indicate great ability to fix atmospheric 

 nitrogen. 



The quality of being able to stand trampling with a minimum 

 of injury is very important where the crop will be subject to such in- 

 jury, as is the case in citrus orchards where the picking of fruit takes 

 place while the green-manure crop is yet growing. Uprightness and 

 nontwining stems are also desirable where an ordinary moldboard 

 plow is depended upon for turning under the crop. However, if a 

 disk plow is used or the crop is worked in with an ordinary disk har- 

 row, this does not make so much difference, and where the growth 

 is not allowed to become too rank little difficulty is experienced in 

 plowing it under. 



The texture of the stem should be such as to decompose readily. 

 Practically all crops, however, if turned under at the right stage of 

 growth decay readily. Thus, the question of decomposition is one of 



