PEAR GROWING IN CALIFORNIA. 



323 



being scarce in soils of all arid sections the cover crop is needed 

 especially to supply this very desirable part of a fertile soil. While a 

 heavy growth of wheat, rye. or barley will, when plowed under, result 

 in the formation of humus, there is nothing more satisfactory than 

 leguminous cover crops. 



Failure to grow a satisfactory cover crop is often due to the fact that 

 the seed of Mdilftlux imlim, or whatever other crop is used, is sown in 

 the fall in ground that is dry, and a lack of moisture may exist for 

 weeks or months after sowing. It is very important, to prevent a. poor 

 crop or an entire loss from drought conditions, to irrigate the land 

 before the cover crop is sown. Whenever irrigation water can be 

 secured its use will abundantly repay the effort and expense of appli- 

 cation. 



LEGUMES. 



Since the discovery that plants belonging to the family LeguminosaB 

 have the power, through the agency of bacteria occurring in nodules 

 on the roots, of drawing upon the nitrogen of the air and adding it 

 to the soil, all plants belonging to this family have become recognized 

 as being of extreme value as cover crops. This is because of the 

 scarcity of nitrogen in our orchard soils in general. Burr clover, 

 which grows so commonly throughout the northern part of Cali- 

 fornia, is a very satisfactory legume for orchard cover crop purposes. 

 In many places it grows wild and makes a dense crop. Sweet 

 clover (Mel Hot us indica) is used commonly in orchards of southern 

 California and is gradually becoming recognized as one of the best 

 legumes for the north. Another satisfactory legume for the northern 





FIG. 129. A good cover crop of hairy vetch, Vicia villosa, growing in a Santa 

 Clara Valley orchard. 



