Volume 49 Number 3 Article 32
Year 1995 Month 7
Title: Prediction of Site Index and Apple Rootstock Performance from Environmental Variables
Authors: W.C. Olien, D.C. Ferree, B.L. Bishop and W.C. Bridges, Jr.
Abstract:
Previously, we developed stability analysis
models for nine rootstocks tested over 19 apple
producing states and demonstrated significant
rootstock-site interactions for cumulative yield
(CY) and trunk cross-sectional-area (TCSA). A
key input in these models is site index (SI),
estimated from the mean over rootstocks within
site.
Our goal was to extend the usefulness of
these models by developing further models to
estimate SI for untested sites from climate
variables.
Prediction of SI from mean daily
maximum temperature (T) and total moisture
(M) (sum of precipitation and irrigation) was
evaluated over five periods based on previous
work and on approximate phenological phases
of the apple tree over the geographic area
included in this study: A = December-January
(dormant), B = February-April (prebloom), C =
May-June (set), D = July-September (growth to
harvest), and E = October-November (postharvest
to leaf senescence), resulting in ten
climate-time variables for model development.
Complete records of T and M were available
from 11 and 9 states, respectively.
SITCSA was
not significantly correlated with any T or M
variable and therefore may have been influenced more by soil factors or deviations in
orchard management practices than by climate.
SICY was well correlated with TC, TD and MC,
but TC and MC were strongly collinear.
Further
model development concentrated on prediction
of SICY from T variables over data from ten
states (with California removed as an outlier).
All one-, two-, and three-variable multiple regression models were evaluated.
We concluded
that SICY was best predicted from a linear
relationship with TC.
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