LUTHER BURBANK 
chard sap the ground and take the nourishment 
that the tree imperatively needs. But if the sur- 
face soil is turned under this vegetable matter will 
in itself. constitute a fertilizer. Unless the soil is 
unusually rich this should be supplemented with 
artificial fertilizers, of which nitrates, phosphates 
and complete mineral fertilizers often appear to 
have the best effect in rejuvenating an old orchard. 
In case the soil is a sandy loam, subject to rapid 
leaching, it may be desirable to sow a so-called 
“cover crop” to prevent the too rapid washing 
away of the plant foods in the rainy season. If a 
leguminous crop is grown, such as clover, crimson 
clover, cow peas, or vetch, these crops will in them- 
selves add to the nitrogen of the soil, as their roots 
have the power of taking this from the air. But 
it is urged by some eastern orchardists that care 
should be taken to avoid too much nitrogen. The 
roots of the tree reach down to rich subterranean 
sources that are likely to be well supplied with 
nitrogen, because the nitrates are very soluble and 
are pretty rapidly leached or filtered into the sub- 
soil. 
After preliminary treatment it has been found 
in many states best to sow a crop of clover, often 
with other perennial grasses, as a permanent crop, 
which should be cut and all material left on the 
ground for the protection and support of the or- 
[48] 
