• DamienCadle

Pruning with precision- The quest to control quality and quantity

Updated: May 5, 2020

Quality or quantity? I find myself asking that question a lot, especially when I’m standing in the wine isle of my favorite liquor store.

In Viticulture it has been a “white” or “black” situation for a very long time.

The unwritten rule of viticulture states that either you have a vineyard block that delivers quality grapes, or you have a cash-cow which sole purpose is to deliver tons of grapes, but you can’t have both. In this segment we are going to discuss the “grey” area and how soil- and vigour variation can be used to prune vineyards with precision.

Quality and Quantity

Quality is a pragmatic interpretation as the non-inferiority or superiority of something; it's also defined as being suitable for its intended purpose while satisfying customer expectations. Quality isn’t something that just happens accidentally overnight, it takes the extra mile which comes with blood, sweat and tears.

I feel quantity and quality with respect to vines could be compared to human’s needs and desires respectively. We humans need to eat, drink water and sleep in order to survive, but we thrive to eat gourmet dishes, drink Woolies bottled water and sleep on a Sealy Posturepedic mattress.

Vines need soil, sunlight, winter dormancy and pruning in order to survive and bear fruit. The actions that attend to the micro-climate of the grapes like leaf foliage, tipping, topping and other canopy manipulations give the vines a status that thrives for quality grape production.

Quality grape production is the product of thorough planning, preparation and full utilisation of resources.

Key factors that plays a role in Quantity and Quality vineyard production

Quantity / Quality

Soil potential : Quality and Quantity

Cultivar choice: Quantity

(Rootstock and cultivar combination)

Canopy Manipulations: Quality

Pruning for tons: Quantity

Pruning for flavours: Quality

Irrigating for tons: Quantity

Irrigating for stress-relief: Quality

Fertilizing for tons: Quantity

Fertilizing for health: Quality

Method of harvesting: Quality

Before we get down to the scientific stuff, I want to discuss the grey area in grape production with an example.

A class of 30 students wrote a performance test and the whole class achieved an average of 70%. The class is made up of overperformers and underperformers. On the one side we have the class-bankers, smokers and the ones who simply hate doing homework. On the other side we have the "wit-broodjies", head girl and head boy. I will leave each group’s performance to own judgement.

Is it fair to claim that every single student in the class has a performance score of 70%?

The Grey area

The yield of a vineyard block is calculated in tons per hectare and takes the average of all the grapes harvested from a production block. In viticulture the yield (in tons/ha) of a production block is used as a benchmark to measure its quality. A vineyard block yielding 6 tons/ha in Stellenbosch is regarded as a quality block, a block yielding 20 tons/ha in Stellenbosch would be regarded as a cash-cow whose sole purpose is to deliver as much tons as possible.

If the vineyard block has 100% consistency in soil, growth and manipulative actions throughout the whole production block, which is highly unlikely, it would be safe to use averages. But making conclusions without having any tangible information about the soil or the vine’s response to the soil. Is like shooting a shotgun from the hip with one eye closed.

My point is; taking production variation into account, what percentage of the production block contributes towards the average?

Pruning- Cutting back for the future

Pruning is the most important interaction humans have with a vineyard, besides the planting of the vine. Pruning is the process where shoots are cut back to the vines cordon in order to maintain fertility, vine form and control yield. Pruning occurs in the winter when the vines are dormant, most of the leaves are discoloured or have fallen to the floor. Great attention and thought should go into the pruning process as to how and when vines will be pruned, because it directly affects the quantity and quality of the coming harvest.

Pruning or harvest control, if you will, is the allocation of buds which in time would burst into a fruit bearing shoot directly affecting the harvest.

Why prune?

Vines are a creeper plant and will continue to grow and grow if not pruned. One would think, great bigger vines, more grapes, but no. Vines are basipetal, meaning they are most fertile at the base of the shoot. Therefore the growth has to be brought back to the cordon in order to be fertile. Pruning is done to control the balance between vegetative vigour and reproductive fruit production. Pruning is the first step of preparation for the coming harvest. The timing and method of pruning will greatly influence the vineyard’s status be it for quantity or quality.

Timing of pruning

The leaves have an important role to play besides supplying the bunches with nutrition and energy to ripen. After harvest the leaves will continue to photosynthesise until they get discoloured and fall to the floor. In this time the leaves will build-up much needed reserves like minerals and carbohydrates that is transported to the permanent woody structure of the vine until budburst occur in Spring. The reserves are responsible for budburst as well as sustaining the vine until new leaves are formed. Pruning before leaf fall can disrupt the accumulation of reserves leading to mineral deficiencies and poor bud maturation which directly affects your quality and quantity.

The best time to prune is when the xylem fluids are actively moving through the vine. In this occurrence water would freely flow out where the shoot is pruned.

The rule of thumb for pruning states that the earlier the vine gets pruned, the sooner budburst would occur in Spring. White cultivars are pruned before red cultivars and this allows white cultivars to bud earlier and ripen before the temperatures get too high, at this stage the red cultivars are in their peak and loving every moment of it.

The pruning time can be manipulated to great benefits for example a delayed pruning would lead to delayed budburst which could be very desirable in a frost prone area such as Rawsonville.

Methods of pruning

There is various styles and methods of pruning and each has its positives and negatives. In South Africa we have a range of methods, but today we will look at the “bokkop”, “kasenaav” and the classic spur-pruning.

Bokkop method roughly translates to a horned animal, keep in mind the V-shape of the horns refers to the two shoots which is left on one spur for dormancy. Each shoot will have 2-3 buds which would burst in Spring, basically double the bud load of the classic spur pruning method. This method is widely used to pump up the quantity of a block. This pruning method are suitable for very vigorous vines, because there is more growth, more grapes could be ripened.

The kasenaav method is specifically designed to accommodate extremely vigorous shoots of vines, but is not considered as a pruning method, rather a pruning tool to allocate more buds (4-6 buds) to a vigorous shoot.

The Classic spur-pruning method is the universal pruning method in most viticultural countries. The method is relatively simple and I’ll try to describe it as simple as possible; cut off the old shoots and leave 2 buds on the shoot closest to the cordon. I said relatively simple, because we are working with Mother nature and she isn’t very consistent. There are various factors to consider when pruning, which complicates the basic implementation of the spur-pruning method, like shoot direction, - position and – thickness.

Make a false move and your coming harvest is immediately affected. This is where experienced and educated workers must take over and make the right decision for each specific vine.

This pruning method is highly adaptive to different vigour areas, because more buds can be left on thicker shoots in order to balance the vigour out with more fertile buds. Once again, this judgement is left to the hard-working people in the vineyard.

Pruning and canopy management – Mankind’s contribution to Terroir

In my previous blog entry, Steak, wine and NDVI, we discussed the manipulation of canopies with the help of NDVI maps in order to promote certain flavours in vineyard. Please follow the link if you are interested

Pruning and canopy management is mother nature’s invitation to viticulturists to play a part in the terroir. It’s amazing to imagine that a viticulturist can use available resources, planning and preparation to make informed decisions, which would lead to the flavours and aromas we taste in wine.

It blows my mind and I hope in a year or two’s time every boutique wine farm would be using these methods in order to farm for flavour and quality. If viticulturists can obtain knowledge of their soil-(EMI) and growth (NDVI) variation combined with environmental factors such as solar radiation, the manipulation possibilities could be endless…

I am going to use the Afrikaans saying once again; “om te meet is om te weet”. If you have knowledge of every factor contributing towards a vine’s current growth, then you would have knowledge of how to manipulate the vine for the future.

See pruning as a brand-new haircut and canopy management actions as the wax, gel or hairspray. The pruning would control the frame of the vine and canopy management is the actions done to ensure it looks good and tastes good.

Precision Pruning

Precision is defined as the quality, condition, or fact of being exact and accurate. A target is essential, be it in production or in our lives, for the existence of accuracy. Without a target we would never know where to aim.

At Revolute Systems we strive to provide farmers with a network of information (soil, growth and environmental factors) of their production blocks in order to make informed decisions, solve problems and strive for precision agriculture.

EMI Soil analyses

We offer a physical approach to soil analyses, looking into soil at various depths of 25cm, 50cm and 90cm. The EMI Scanner (Electro Magnetic Induction) uses electric conductivity measured in EC at ms.s-1 . The instrument’s “superpower” is to identify variation in physical soil properties based on the EC of the soil. The variation is based on texture and provides us with an indication of the water holding capacity of what each texture can endure, while also giving us a very strong indication if the soil tends to have more clay or more sand.

I would like to add that the instrument does not measure any chemical properties in the soil.

Chemical variation in soil would also affect the physical properties of the soil, therefor if the physical maps are used to allocate profile points for chemical soil samples in representative areas instead of doing a 50m x 50m soil sample grid.

Illustration 1: (Left) NDVI map indicating growth variation. Dark green indicates very healthy and vigorous vines. Light green indicates weaker vigour. (Right) EMI Soil map indicating soil variation. The dark brown is an indication of heavier soils with more water holding capacity, more clay dominant soils, if you will. The lighter brown indicates lighter soils with less water holding capacity, usually dominant sandy soil.

NDVI – Vigour variation maps

For an in depth explanation of NDVI refer to my colleague, Berno Greyling’s blog entry; NDVI- Over promising and easily under delivering at .

Just to sum up, NDVI (Normalized Differentiated Vegetation Index) is an index of how healthy a plant is growing. It is a very useful tool to make informed decisions, especially in pruning time. NDVI can be used as a guide to prune with precision and accuracy. If elevated it’s possible to see vigour variation in vineyards with the human eye, but standing in the vineyard, everything looks the same. This tool helps us to identify strong growing areas and weak growing areas which allows us to give the needed attention to these areas in order to maintain quantity without losing quality.

Illustration 2: (left) NDVI Vigour variation map. (right) Environmental factor map of elevation. The blue is more elevated than the red. See the big influence environmental factors could have on natural vigour.

Pruning for quality or quantity

Knowledge of al these contributing factors could be used to prune for quality or quantity. Working with natural vigour to adapt the pruning time as well as the method. This allows a great balance between vigour and grape production which promotes quality without the risk of losing quantity.

Pruning could be used to manipulate flavours in wine; therefore, the winemaker should be next to the viticulturist when deciding on pruning methods and times.

Pruning depends on what the winemakers want to achieve with their wine styles the following year. If the vigour allows it, more buds can be allocated to the vines leading to much denser canopies which would most probably deliver wines with a high natural acidity and green, vegetative aromas. The other route is to allocate less buds which would lead to very fertile basal shoot. When combined with proper canopy management actions, like leaf foliage will ensure a well-aerated canopy with bunches exposed to the sun, this delivers more tropical and fruity flavours in wine.

Last thought

Instead of classifying a vineyard as being a quality or quantity production block. Gather knowledge of your soil and natural vigour, then zone off the production area into a quality section and a quantity section.

If quantity is the main aim of production, make sure that enough resources are used with just enough attention.

If quality is the main aim of production, make sure to use resources with precision and manipulate them precise.

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