tities for the growth, health and
bearing quality of nut trees. It is well to make sure of these elements
in the soils devoted to nut tree planting, but it cannot be emphasized
too often that all essential elements and factors should be taken care
of; anyone of them may be the limiting factor in crop failure; the one
that is absent is always the most important.

In regard to inorganic nutrients, more attention has probably been
devoted to citrus trees than to any other tree species, largely because
the soils of Florida and California require additions thereof. It would
be unfair to say that such main fruit crops as apples, cherries,
peaches, plums have been neglected; we merely possess more information
on the nutrients of citrus trees than on other tree crops, as far as the
micro essential nutrients are concerned. Most orchards and groves are
fertilized only with nitrogen, phosphorus and potash, and limed when
necessary. Nitrogen can stimulate size of fruit at the expense of
quality.

A paper by P. W. Rohrbaugh[16], Plant Physiologist of the California
Fruit Growers Exchange, Ontario, California, deals with eleven mineral
nutrient deficiencies and their causes, viz: calcium, magnesium, potash,
phosphorus, sulphur, nitrogen, iron, boron, zinc, manganese, copper, and
this might well be used as a guide for nut trees.

6) Miscellaneous

A few oddities may also be mentioned for anyone inclined to experiment:

From Holland it is reported that an avenue of large handsome shade trees
close to a century old, all died in one year, except where a junk dealer
had stacked a pile of old metals. The trees had exhausted the inorganic
nutrients within reach of their roots in the soil, but the junkpile had
replenished them sufficiently, so that those within reach of it kept
alive to this day, twenty years later.

A rock mulch is reported to have improved the growth of lime and lemon
trees considerably[17], and it would seem that similar experiments
should be made on young nut trees, just before bearing age in a
comparative test with a check planting. Stones can be selected for the
nutrients they contain, and a geologist can easily point out those
containing the greatest number of elements. No one could go wrong in
placing a few rocks of limestone or dolomite near the base of a tree,
and let rain and sunshine, heat and frost attend to the fertilizing in a
slow but perpetual manner.

Maple sugar contains manganese[18], showing th