Impact of Tree Stand on Pecan Yields¹
Department of Horticulture
University of Georgia
Athens, GA 30602
Missing trees result in an incomplete tree stand and is a widespread problem in many pecan orchards and especially in orchards planted during the early 1900's. The magnitude of the problem becomes particularly noticeable from an aerial view of almost any old orchard. Growers who count vacant tree sites in such orchards are almost always surprised to find that the percentage of missing trees is much larger than they originally thought. The purpose of this paper is to emphasis the obvious; that is, missing trees reduce per acre nut yields.
The data were obtained
during 1987 from 10 blocks of pecan trees (461 acres) in Southwest Georgia.
The blocks were either adjacent to or within about 2 miles of each other.
Management was similar in all blocks except that 5 of the blocks were irrigated
by solid-set sprinklers whereas the other 5 were irrigated by drip. The drip
system was installed during the winter preceding the study. The solid set
sprinklers had been in place for several years but had not been operated very
effectively until the year of the study. Thus, the primary irrigation effect
was
on nut size
and not on increased fruit set. Cultivars were predominately Stuart' and Schley'.
Block composition varied from mixed to almost either solid Stuart or Schley.
The trees were planted in the 1920's at about 20 trees per acre. Within recent
years, some of the missing trees had been replanted but at the time of the
study, these trees were not large enough to substantially contribute to yield.
Occasionally, in some blocks, there were small areas in which the tree canopies
were too close together with the result that the lower canopy was in the process
of shading out. However, any negative effects of these crowded spots on yield
were considered to be insignificant with respect to this study.
The results are as expected; that is, per-acre nut yield increased in direct proportion to tree stand (Fig. 1). Each 10% increase in tree stand increased nut yield on the average by 160 pounds per acre. The relationship is not perfect which may reflect differences in irrigation systems, tree size, cultivar composition, or combination of these factors. Nevertheless, the relationship clearly demonstrates the importance of tree stand on per-acre nut yield. Extrapolation of the data to 100% tree stand indicates that the expected nut yield would be 1600 pounds per acre. This is not an unreasonable yield expectation for a well managed orchard consisting of a full stand of `Stuart' and `Schley' trees irrigated adequately with solid-set sprinklers. Obviously, replanting missing trees would, with time, increase yields. This would be especially true in Georgia where missing trees are common to many orchards.
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¹Originally published in
Pecan South 23(4)18-19.
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