he soil is a Riverdale
(tentative series) sandy loam that had been in orchard grass sod for 10
years before the experiment was begun. Much of the land on the Plant
Industry Station farm is now known to be low in available magnesium and
potassium. Tree crops, including peaches, pears, and apples, have shown
deficiencies of one or both of these elements. The trees were planted 20
feet apart on the contour in pairs, one of each variety in a plot, with
six plots in a row. The 36 two-tree plots were in six rows. Thus, the
experiment was arranged in a 6 by 6 Latin square and six fertilizer
treatments were used. After planting, the trees received frequent
cultivation and a uniform application of one pound of 10-6-4 fertilizer.
The following spring differential fertilizer treatments were applied:
Nitrogen, phosphorus, potassium, complete, nitrogen and potassium, and
check. The amounts applied per tree in fractions of a pound were
elemental nitrogen 0.2, phosphoric acid, 0.4, and potash 0.2. In the
spring of 1950, the amounts applied per tree were doubled; and these
same amounts were applied in the spring of 1951. Nitrogen was applied in
the form of nitrate of soda, phosphorus as 20 percent superphosphate,
and potassium as 50 percent muriate of potash. Strips about six to eight
feet wide on each side of the tree rows have been cultivated frequently,
but strips of orchard grass sod have been left in the tree row middles
to prevent soil erosion. The trees have been sprayed with DDT or
parathion or both to control Japanese beetles and mites.

Growth Responses

To determine the growth responses made by the two varieties to the
differential fertilizer treatments, diameters of the tree trunks one
foot above the soil were measured each spring before growth started.
These data are not given here because in 1949 and 1950 there were no
significant differences in the growth of the trees as a result of the
differential fertilizer treatments. However, trees of the Potomac
variety made more growth than those of the Reed variety. At the end of
the 1949 and 1950 growing seasons, the average diameters of the tree
trunks of the Potomac variety were 16.3 and 25.7 millimeters,
respectively; those of the Reed variety were 13.6 and 22.4 millimeters,
respectively. The differences 2.7 and 3.3 millimeters, are highly
significant. Under the conditions of this experiment, the trees of the
Potomac variety are much more vigorous than those of the Reed. T