Preliminary Report on Growth, Flowering, and Magnesium Deficiency of Reed and Potomac Filbert Varieties
H. L. Crane and J. W. McKay[10]
During the course of filbert breeding investigations at the Plant Industry Station, Beltsville, Md., covering a period of approximately 18 years, the leaves of certain seedlings scorched badly in mid or late summer. Certain other trees showed little or no evidence of this disorder. It was thought that, because filberts thrive best under maritime climatic conditions of cool summers and mild winters, this scorch was probably due to high temperatures accompanied by deficient soil moisture.
This breeding work resulted in the introduction in 1951 of the Reed and Potomac varieties, which were produced as a result of crosses between the American filbert, Corylus americana, and the European filbert, C. avellana. The original trees of these varieties had been under observation for more than 10 years, and their performance had been such as to indicate their suitability for home plantings under eastern conditions. Furthermore, these varieties had shown little or no evidence of scorch and had held their leaves well.
In early spring of 1948, an experimental orchard, consisting of 36 layered trees each of Reed and Potomac, was planted at Beltsville, for the purpose of testing them more fully than had been possible before as to their suitability for eastern conditions. The orchard was designed also for study of their response in tree growth and fruiting to differential fertilizer treatments. Although this experiment has been underway now for only three years, certain of the findings are thought to be of such importance that a preliminary report should be made at this time.
Experimental Plan
The site selected for the orchard is a gentle slope varying from five to 15 percent and providing good air drainage. The 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. The greater vigor of the Potomac trees may account for the fact that they produce suckers much more freely than do trees of the Reed variety. The habit of producing abundant suckers is an advantage in propagating by layering, but it is a disadvantage in orchard trees because the suckers must be removed for optimum nut production. Whether the differences in vigor and suckering habit of the two varieties shown thus far will affect their performance as orchard trees will have to be determined by future observations.