26 ORCHARD GREEN-MANURE CROPS IN CALIFORNIA. 
In Table II the weight of the green material produced per acre is 
presented, together with the weight of the same when dry. The 
green material was weighed at the time of cutting, and for estimates 
of the yield of dry matter was weighed again in thirty days. During 
this period the various crops had become nearly dry, but undoubt- 
edly the moisture content, even at this time, would vary to some 
extent, although not nearly so much as in the green state. ; 
That the yield of green material as shown by its weight may be 
misleading without proper correction for the moisture it contains is 
shown in Table IT in the case of the two lots of black-purple vetch. The 
first lot was quite succulent at the time of cutting, and consequently 
was very heavy in the green state, while the other was a little older and 
less succulent, and so was much lighter. The latter did not show the 
heavy loss in drying that the former did, however, and thus the dif- 
ference in the amount of organic matter of the two is not nearly so 
ereat as the difference in the weights of the green matter would indi- 
cate. In this connection it should also be noted that varying yields 
are often due to a difference in the stands rather than to differences 
in the growth of the crop. In the comparative data presented in 
the tables this has been reduced to a minimum by selecting for this 
purpose crops with as nearly uniform stands as possible. 
From all data available it seems clear that of the commonly grown 
ereen-manure crops, vetch, peas, bur clover, and fenugreek, the 
vetch returns the most organic matter to the soil and the peas the 
least. The light yield of peas is not due to a lack of stem growth, 
which on the contrary is always good, but to the generally poorer 
stand and more open habit of growth. Bur clover, while weighing 
heavy green, is very succulent when young, and when compared with 
an equal weight of green vetch represents much less organic matter. 
Fenugreek yields well, but not so much as vetch. 
In securing the yield of green manure per acre, as presented in 
Table I, the plants growing on a plat 6 by 20 feet were cut and 
weighed green and the yield per acre computed from these weights. 
In Table II a plat 10 by 10 feet square of each crop was cut and 
weighed green and the yield per acre thus calculated. The same 
was weighed again in thirty days, as shown in the table, giving the 
yields of the dry matter. In Table III the weights shown were 
taken from crops being grown by orchardists during the winter of 
1908-9 at the places mentioned in the table and are representative _ 
of these crops as grown under actual orchard conditions. To obtain 
the results the plants growing on a space between four trees were cut 
and the yield per acre calculated from such weights. 
190 
cm la a icc Ls 
