Agriculture Reference
In-Depth Information
or stable isotopes and the long distance transport is followed (eg. tip of a leaf blade).
The phloem mobility is high for most macro nutrients except Ca, while the interme-
diate mobility is present for the micro elements except Mn (Marschner
2012
). The
mobility determines the effectiveness of foliar applied fertiliser, with the movement
of a particular nutrient into the required tissues of the grapevine.
The vine demand for nutrient depends on the developmental stage and the level
of productivity and is generally met by nutrient acquisition and/or remobilisation
in stored parts of the vine. Because of limited mobility of some nutrients in the
phloem, uptake of some nutrients by roots becomes critical and can impact on the
development of the roots (Mengel and Kirkby
2001
). Nutrient uptake varies during
the growing season concurrent with changes in root growth activity. Generally, this
is high when the growth demands from other parts of the vine, such as shoots and
grapes, are low. Before flowering, shoot growth is strongly dependant on N mobil-
ised and transported from reserves stored during the previous season (Zapata et al.
2004
). The leaves, shoots and bunches are strong sinks for N assimilated during the
period from flowering to veraison. Between veraison and harvest, when N uptake
might slow or stop, redistribution from roots, shoots and leaves to bunches takes
place,. The redistribution of N is, however, dependent on N availability during the
berry ripening period. Therefore, the two most efficacious periods of N uptake by
grapevine roots are during periods of excess carbon supply available to the roots.
The first being after rapid shoot elongation ceases and the second after harvest,
this leads to further uptake of N and other nutrients during the post-harvest period
(Wermelinger
1991
). The stored N is important because early demand in spring can-
not be guaranteed by root uptake. Nutrient reserves in the permanent structure are
highest in winter but can be influenced by cropping levels, vineyard management
and environmental conditions.
Adequate nutrient supply to grapevines ensures sustained yield levels and is im-
portant for grape composition. A deficiency of any nutrient reduces yields, although
the reserves in the perennial structure of some nutrients in grapevines are important
during times of insufficient uptake. These occur in early spring, when root activity
is relatively low and demand by the developing canopy is high, also the uptake and
demand might not be matched during the berry ripening period. In both times the
demand for carbohydrates is high in relation to production, restricting the supply of
assimilates to the roots and therefore the energy for uptake. The supply of nutrients
can alter the grape composition directly, by moving them into the berry, or indirect-
ly by influencing vine development and yield level. N is the most dominant nutrient
affecting must composition, with impact on the wine making process and the wine.
The relationship between nutrient content in grapevine tissue and vine perfor-
mance (growth and yield) is important to develop nutrient standards. The adequate
(or optimal) range for a particular nutrient is greater than the deficient values and less
than the luxury upper values which can lead to undesired growth. Excess of nutrients
causes toxicity and nutrient imbalance results in the decline of growth and productiv-
ity (Smith and Loneragan
1997
). The increase of a nutrient in a deficient range will
lead to improved growth and to a dilution effect and lead to a greater deficiency of
another nutrient which was also lacking. The critical deficiency range also leads to
