WINTER GREEN-MANURE CROPS. 19 



sections. At least 80 pounds of seed per acre should be used, and 

 unless seeding conditions are very favorable more rather than less 

 is recommended. 



During the past few winters the general crops of field peas and 

 vetch throughout the orchard sections of California have shown 

 that peas make a stronger individual plant growth than vetch, but 

 do not make as heavy a yield of green manure. When sown during 

 the latter part of September the peas have made a growth of from 

 24 to 36 inches, while common vetch made from 15 to 18 inches. 

 This is representative of the usual comparative stem growth of the 

 two crops. In the citrus orchards of southern California peas should 

 be turned under earl}^ in February, and in the northern part of the 

 State during the latter part of February or the first of March. 



BUR CLOVER. 



There are a number of kinds of bur clover, of which only two 

 are yet much grown in California, namely, the common or toothed 

 bur clover {Medicago hispida denticulata) and the spotted bur clover 

 (Medicago arahica). The toothed bur clover is the one most com- 

 monly seen, being thoroughly naturalized, but the spotted bur 

 clover, though less abundant, grows equally well. It differs from 

 common bur clover in having a brown spot on each leaflet and 

 longer and softer spines on the burs. 



Bur clover makes a decumbent growth, the stems being rather 

 small and ciuite succulent when young, but it withstands considerable 

 trampling. The roots are shallow but numerous and usually have 

 many nodules. The crop has been grown to quite an extent for green 

 manure, but on account of its not making a good early-winter growth 

 its use will always be limited. In orchards where bur clover has 

 been once planted it will spring up for several years. This is due 

 to the hard seeds that do not germinate the first year. In the citrus 

 orchards of southern California bur clover is sown at the same time 

 as vetch, which is during September and early October. To obtain 

 the best results, seeding as early as possible in September is advised. 

 Twent\^ pounds of seed (hulled) per acre should be used, care being 

 taken to plant shallow, as deeply covered seed will not germinate 

 but will hold over in the soil. The sowing of seed in the bur is not 

 recommended, because the bur delays germination and occasions 

 very uneven stands, to say nothing of the greater difficulty in sowing. 

 However, there is no longer need of using seed in the bur, as clean 

 .seed can be secured in quantity from western seedsmen. 



For use in deciduous orchards bur clover is of considerable import- 

 ance and if properly handled will serve a very useful purpose. At the 

 present time it is utilized only where it volunteers as a weed and 

 can be turned under at the regular spring plowing of the orchard. 



190 



