Green Manuring. 165 
humus to the soil. All plants by their decay in the soil add or- 
ganic matter to it, and this matter is of nitrogenous character, 
but leguminous plants do this and a great deal more, for by their 
exclusive ability to use atmospheric nitrogen, There is also 
special value in deep-rooting legume in soil amelioration. There 
is now reason to believe, as has already been stated, that where 
moisture is ample for both alfalfa and trees we shall come to 
using this plant for a permanent cover of orchard ground as a 
substitute for a part of the clean culture which is now observed. 
This is, in fact, already being done to some extent. It is also 
probable that alfalfa can be used for a certain time even where 
its permanent stand is not desirable, for it is not difficult to de- 
stroy alfalfa with a well-sharpened plow although the roots may 
have attained considerable thickness. Of course this, as already 
stated, depends upon moisture supply; where that is not abund- 
ant clean culture for moisture conservation is unavoidable. But 
where moisture in excess of the needs of the trees is available 
it will be used in future indirectly for their benefit in ways we are 
only just beginning to discern, and one of these is likely to be 
the summer growth of legumes in the orchard. 
This is, however, largely a matter for future determination, 
and under ordinary conditions may never be practicable. The 
wider problem is to secure a leguminous plant which will make 
a heavy growth during the winter months, so that it can be 
plowed in early in the spring, and the ground put in shape for 
the thorough surface pulverization to prevent evaporation of 
moisture during our long, dry summer. For this reason we can- 
not use many plants which are used for green-manuring in humid 
climates. Crimson clover, cow peas, etc., do not make good 
winter growth. They make exuberant growth for a time in the 
spring when heat is adequate and moisture abundant, but at 
that time it is too late to grow crops for plowing under because 
the soil is too dry for their decay and their presence tends other- 
wise to the loss of moisture and makes it very difficult to secure 
a good surface tilth. The greatest care must be had not to allow 
a growth of weeds to stand too long or its covering will do more 
harm than good. These tender legumes may have some local 
value on moist lands in the summer time, but hardy legumes are 
the desideratum both for winter forage and green-manuring. 
The common “bur clover” (Medicago denticulata) is proving very 
satisfactory in some parts of the State, and the “Canadian field 
pea” is coming into quite wide use in some of the southern citrus 
orchards. Experiments are also in progress with the lupines 
which may yield valuable results. 
