Agriculture Reference
In-Depth Information
the other hand, it appears that in certain cases nutrients may function partly or even
entirely in place of certain growth regulator substances. Moreover, there are several
examples of some additive and even synergetic effects of nutrients and plant growth
regulators (PGRs) on fruit quality. This is the case of gibberellic acid and nitrogen
compounds in reducing
creasing
, controlling
puffing
and delaying peel senescence,
as mentioned, and of synthetic auxins and potassium nitrate in increasing fruit size.
In fact, it has been suggested that growth regulators may act by directing the flow
of nutrients in plants to sites where they are required for protein synthesis, and even
that foliar application of K
+
and NH
4
+
ions may have a promoting effect on gibberel-
lin synthesis in tissues.
Organic Matter
There is little information about the effect of organic matter on fruit quality in cit-
rus, apart from changes it produces on soil structure. The most important beneficial
effect found is a higher resistance to freeze of fruits from orchards whose soils are
rich in organic matter. Improvement of soil structure, with some improvement in
aeration and its consequence on fruit quality, can be made through the use of or-
ganic matter. On the other hand, it is known that owing to the ameliorating effects
of organic matter on soil structure, potassium penetrates into dense citrus root areas
more rapidly. Organic matter seems to aid in the rate of phosphorus movement, as
heavily manured soils show deeper penetration than those not receiving organic
matter. Winter cover crops turned under in the spring and organic manures usually
decrease the severity of Zn deficiency.
Fertilization Guide
The aim of fertilization is to complement the supply of mineral elements in the
soil to obtain commercially acceptable growth and yields. There are several ways
to determine fertilizer needs, however leaf analysis provides a common method
for making comparisons from soil, field cultures, localities, years and climates.
Leaf analysis is useful primarily in determining the tree's current nutritional status.
Ranges for levels of nutrients in leaves for maximum production and fruit quality
are established as
deficient
,
low
,
optimum
,
high
and
excess
. These ranges, how-
ever, may be different from those for producing the maximum amount of vegetative
growth or largest fruit size.
Legaz et al. (
1995
) lists a range of elements in six-months old spring-flush leaves
from nonfruiting twigs for Spanish conditions (Tables
6.3
and
6.4
).
The type of nutrients required and the amounts depend on the soil type, grow-
ing region, cultivar, tree age, and crop load. Thus, soils with a low cation exchange
capacity (CEC) need supplementary amounts of all the major macro and micronu-
trients; that suit regions that differ on rainfall and temperature, and to replace those
