To grow grape vines efficiently and effectively they need approximately 19 mineral nutrients. These nutrients (macro and micronutrients) along with water and carbon dioxide ensure the grape vine metabolises growth rates to maximise its crop.
In today’s viticultural management balanced vine nutrition is a major objective. Nutritional management of grape vines has an impact on grape/wine quality, sustainable yields and financial returns. To determine a balanced approach there are a number of areas one must study to formulate nutritional programs/measures before any visual or tangible results are achieved. This paper attempts to highlight some of the steps necessary within a day to day management program of a vineyard toward achieving a balanced approach, along with raising some practical points that can be considered efficiently to understand your vineyard’s needs as to whether nutritional adjustments are necessary.
Metabolic and functions of 9 key macro nutrients and the basic role they play
are featured below:
Nitrogen is necessary to ensure the overall structure and metabolism of
the grape vine is achieved.
Phosphorus determines carbon dioxide fixation, cell membrane development and
movement of essential structures. Its role also has a bearing on energy storage
and transfer.
Potassium ensures storage of metabolic byproducts, as well as synthesising
proteins.
Calcium determines cell membrane and cell wall structure. It also
establishes enzyme activity for vine growth and development and is a major
catalyst for metabolism.
Sulphur is responsible for amino acids and chlorophyll formation.
Copper is necessary for chlorophyll synthesis and lignin formation.
Zinc is necessary during the flowering/fruit set process and also
synthesises hormone throughout.
Boron ensures movement of sugars and
general metabolic activity including pollen tube growth.
Molybdenum has a role in conversion of nitrates and is important
in nitrogen-fixing bacteria in the soil, which effects an important part of the
cycle that makes atmospheric nitrogen available to the vine.
Soil characteristics have an important impact on
grape vine nutrition. They can influence a nutritional management program by the
amount of available stored nutrients within the profile.
This is why it is important to understand through appropriate soil testing.
Nutrient movement and behaviour in soils is dependent upon soil ph/ soil
composition, soil water content, amounts of nutrients in the soil and root
environment. Regular soil testing can determine shifts in composition and any
toxicity, which may impede nutritional balance.
Soil structure which includes slaking and dispersion
effects root penetration, aeration, nutrient holding capacity and water
infiltration in the profile. It is this area that determines the basis of a
balanced nutritional program and the ability to study data so that adjustments
can be made to maximise available nutrients to the grape vine.
Determining whether a soil profile has some salinity or acidification is
essential and is fundamental toward balanced results.
Nutrient uptake through phloem and xylem tissue is essential for continued and consistent growth rates. It is important to understand the growth cycle of the grape vine to determine nutrient requirements. Amounts of fertiliser at correct timings can ensure sustainable activity and growth rates, for instance poor vine nutrition throughout flowering can reduce bud fruitfulness. Equally, good vine nutrition at flowering and setting can improve fruitfulness. It is all a balance to achieve the desired end result and continual assessment of growth rates will determine progress.
Sampling for nutritional status should be completed every year and generally petiole testing is advantageous to assess deficiencies in the program. Representative samples throughout the vineyard at the same time each year will point out a trend in your program which gives you valuable information to make correct decisions. There are many services available today that will analyse samples and recommend nutritional change whilst there are many technical services that will advise on sampling techniques.
Water quality has a direct bearing on the
application of nutrients either by foliar or via drip. Poor water quality will
ultimately reduce effectiveness of fertilisers and may cause either bound
elements or blockages throughout the irrigation equipment. Equally water sources
with high amounts of nutrients within them can cause excessive vigour and/or
poor quality wine grapes. However, much must be learned from the assessment of
water and generally, the ph of water if between 6.0 and 8.0, is suitable for
irrigation on vines.
As a rule high alkaline water has a bearing on carbonate concentration which
will effect uptake of calcium and magnesium. High amounts of iron will also
cause blockage to irrigation equipment and cause discolour on leaves impeding
photosynthesis. Salts in water can also affect grape vine performance by
dissolved salts in the root zone and toxic ions impeding growth rates.
Grape vines are very sensitive to high amounts of boron. This toxicity can cause
leaf cupping and dark black spots around the leaf margins, which will ultimately
lead to leaf defoliation.
Armed with the information above decisions
regarding the correct fertiliser at the correct
time can then be made. A sound knowledge of
your soil, vine phenology, vine needs and requirements along with a
understanding of the chemical behaviour/nature of nutrients needed is then
required so that plans can be made to either adjust or maintain the nutritional
requirements of your vineyard.
Look at compatibility of fertiliser compounds when adopting foliar sprays
with chemicals and equally when mixed with one another. They may neutralise one
another rendering elements in unavailable forms or cause damage to irrigation by
binding together which ultimately is a financial failure. On poorly buffered
soils (sandy) the acidifying effect of some fertilisers (particularly nitrogen
fertilisers) can lead to problems with water infiltration and continue the acid
effect within the soil profile.
Mobile nutrients (nitrates) should be applied during active periods of root
growth and less mobile nutrients (phosphorus and potassium) should be applied at
other times within the season.
Foliar application of micro nutrients applied through the leaf stomata is
recommended when mixed with water and a wetting agent to ensure penetration.
Nutrients in wine quality must be studied for a
balanced approach to the program otherwise wine quality issues become apparent,
for instance, a minimum nitrogen content is required to ensure normal
fermentation. Excess nitrogen on the other hand will produce amino acids such as
histamine, and putrescine, which are human allergens.
High amounts of potassium result in lost malic acids inside the berries and
whilst acids can be added to musts the natural formed acids result in higher
quality wines. Magnesium deficiency as a result of excess potassium cause low
baume results and together with low calcium and high nitrogen rates bunch stem
necrosis can prevail.
To improve or maintain nutrient balance within the vineyard, analysis of
existing and regular soil reports is necessary, petiole sampling each season,
regular water testing to determine content and ph whilst continual study of
application/ chemical composition of all fertilisers applied will bring a
balanced approach.
An understanding of vine phenology and correct fertilisers at correct
times will ensure nutrients in wine quality are at optimum levels.
Other areas of the balanced approach is the application of mulches to influence
nitrogen supply including the adoption of mid row swords to use up considerable
amounts of nutrients if vigour is a problem.
Whilst there are many fertilisers on the market many of them will not suit your
operation so I urge consultation from the many professionals such as agronomists
and experienced managers whom see the results every day from a viticultural
perspective.
I cannot emphasis enough the need to plan, implement and assess performance with
nutritional programs as a means to a sustainable end.
A final word of recommendation is the consultation with your winery to obtain
must, fermentation, ph and acid values and other wine quality analysis that may
indicate excessive or low levels of nutrients that have been the result of your
program.
