WINTER GEEEN-MANUEE CEOPS. 15 



labor is necessary. The inoculation of this crop may also be attained 

 by spreading inoculated soil over the field at the time of seeding and 

 working it in Avith the seed, or the seed may be inoculated with pure 

 cultures of the bacteria which form nodules on the roots of this plant. 

 Such cultures have been distributed by this Department for several 

 years, and the results obtained from their use have been favorable in 

 many cases. 



COMMERCIAL FERTILIZERS. 



In the citrus orchards of California commercial fertilizers are quite 

 generally applied, while in few deciduous orchards are fertilizers used 

 in any form. "\A'liere fertilizers are used they are usually applied in 

 connection with a green-manure crop. 



The value of a green-manure crop is largely due to the part it plays 

 in liberating plant food in the soil. In the deca}^ of organic matter 

 and the giving off of carbonic-acid gas, the action on phosphorus and 

 potassium compounds is such as to make them more available as 

 plant food. Vegetable acids, which are always more or less present 

 with a green-manure crop, also aid in liberating plant food. Thus, 

 elements present in a soil but not available as plant food may be 

 made so by the use of a green manure.'* 



From the facts just stated it will be readily seen that a green- 

 manure crop may serve a useful purpose when used in connection 

 with commercial fertilizers, especially where the various plant-food 

 elements are only partially available in the soil. 



WINTER GREEN-MANURE CROPS NOW USED IN CALIFORNIA 



ORCHARDS. 



The green-manure crops now used in California, in the order of 

 their importance, are as follows: Common vetch, Canada field peas, 

 bur clover, fenugreek, hairy vetch, and Indian melilot. 



Common vetch and field peas are by far the most extensively 

 planted, while hairy vetch and melilot are very little used. Bur 

 clover and fenugreek are used to but a limited extent, although they 

 are of considerable importance. 



COMMON VETCH. 



The common or spring vetch (Vicia sativa) is the most exten- 

 sively grown green-manure crop in California. It is being grown 

 throughout the orchard sections wherever green-manure crops are 

 being used at all (see fig. 3). It is adapted to quite varied con- 

 ditions and succeeds in all sections of the State. In the coast sec- 

 tions, as well as inland, it makes a good growth and does well on both 

 the light and the heavy soils. 



"See E. W. Hilo:ard. Soils, pp. 19-21, 63, 12fi, and 394-396. 

 190 



