Abstract:
A portion of this study was initiated to provide the
basis for implementing a chill unit accumulation procedure
in Yemen. Most continuous or daily minimum, maximum
temperature models severely underestimated chilling units,
and slight modifications offered little improvement for the
complex models. Only the Crossa Raynaud formula approximated
generally accepted chilling requirements for the
peach and apple varieties tested. Of the average
temperature models, the Weinberger Sharp model is best
adapted to areas in Yemen where detailed meteorological
data are unavailable.
Another major goal of this study was to investigate
the feasibility of using modern analytical equipment to
make soil tests for arid regions cheaper, faster, and more
efficient. Soil test experiments clearly indicate that a
simple water DTPA extractant and Inductively Coupled Plasma
(ICP) spectroscopy can provide efficient measurements of B,
K, Ca, Mg, Na, S, Cu, Fe, Zn, Mn, P, Cl, SAR, PAR, and
carbonates in a one-step procedure. The sorption isotherms
of K, Ca, Mg, Na, P, S, Fe, Mn, Cu, Zn and B were
determined. Data from all elements except Mn and Fe
generally suggest that a plot of added vs. equilibrium
solution concentrations is linear when agriculturally
realistic rates are utilized. The linear regression
constants for P and K sorption isotherms corresponded very
well to the percent recovery in a multiple spiked solution.
This suggests it is possible to evaluate soil buffering for
P and K in a single two-step procedure.
The final experiments were initiated to investigate
the feasibility of utilizing tissue analysis to assist in
prioritizing fertilizer needs for specific locations. The
ratio based Diagnosis and Recommendation Integrated System
(DRIS) diagnosis generally agreed with the sufficiency
range method. DRIS was excellent in predicting relative
nutrient responses.
