Page 458 - Biosystems Engineering

432 Cha pte r F i f tee n

and date of application, caused a reduction of Ca content, especially
when used at low concentrations. Urea also caused a decrease of K
content, with the exception of the lowest concentration (0.75 percent),
which caused the reverse effect, an increase in the K level. Urea treat-
ment caused, regardless of its concentration, an increase of Mg
content and an increase in P levels at higher concentrations (3 to
6 percent). A higher ratio of K and Mg content to Ca content indicates
a lower storage ability of apples thinned with urea. Only urea applied
at 3 percent (recommended in practice), applied after termination of
blooming, did not change the proportion of K and Mg to Ca in com-
parison with the unthinned trees (control).
Treatment with urea usually did not change the firmness and
soluble solids of apples in relation to apples from unthinned trees.
Only treatment with urea at 6 percent resulted in apples that were
firmer and contained more sugars.
Treatment with urea at 1.5 to 3 percent after the end of blooming
had no visible effect on rotting and shriveling of apples and on the
incidence of physiological disorders during storage.
NAA alone at 40 mg/L, applied just after blooming, caused a
marked reduction of crop load and a marked increase in apple size
without influencing Ca content. Nevertheless, this treatment caused
K, Mg, and P content to increase. NAA at 40 mg/L did not influence
firmness of the apples but raised the soluble solids of the sap and
limited fruit shriveling during storage. Nevertheless, twice as many
apples showed internal breakdown. This indicated that these apples
ripened earlier than the controls.
Lower concentrations of NAA (25 mg/L) caused a reduction in
Ca levels and lowered fruit firmness at harvest. This was probably
connected with higher crop load.
CPPU at 20 mg/L caused a significant increase in fruit size as well
as a reduction of Ca level in the fruit, regardless of the date of applica-
tion. The influence of CPPU on the content of other elements depended
on the date of treatment. Consequently, a less desirable ratio of K and
Mg to Ca and related lowering of the storage ability was observed only
when CPPU was applied 2 weeks after bloom. Despite the fact that
these apples showed higher firmness than those from unthinned trees,
the apples showed more internal breakdown (although the differences
were statistically not significant). Bitter pit was found in some fruits.
Hand thinning done about 4 to 6 weeks after blooming did not
change Ca content in fruit but did cause an increase in K and Mg levels
and an increase of the ratio of K and Mg to Ca, which indicates a lower-
ing of storage ability of the apples. Nevertheless, apples from hand-
thinned trees showed the highest firmness ratings during storage.
In the second experiment on the Lobo cultivar, no single urea treat-
ment caused a significant crop reduction, but urea applied at 4 percent
(highest rate) at the beginning of petal fall caused a significant increase
in size (similar to that found in hand-thinned apples) (Table 15.5).