Plumpton Notes: Part 3

June 23, 2023

Index _{10. Vine Nutrition} _{11. Vineyard Floor Management} _{12. Pest Management in Vineyards}

10. Vine Nutrition

10.1 Soil Fertility

Soil is the primary raw material from which all food is produced, and so is the basis of all agriculture.

Agriculture is blessed with a raw material that, with careful husbandry and supplementation of some ingredients, will regenerate itself to be used year after year.

The soil is not a simple inert medium. For plants to grow in it, it must have a characteristic called fertility.

Essential that a good farmer understands the basics of soil science so that he/she can assess & maintain the soil's fertility.

Fertility is a complex feature influenced by the following factors:

Texture
Structure
Organic matter content
Mineral content
Availability of air and water
Acidity

10.1.1 Soil Texture

The size of particles that make up soil and their proportions relative to each other.

The particles in soil are graded according to their diameters in the following way: 0 – clay – 0.002 – silt – 0.02 – fine sand – 0.2 – sand – 2 – gravel – 2+ (mm)
Heavy soils: high clay Light soils: high sand

Clay soils retain more moisture than others, as they comprise very small particles: a kilogram of clay will contain a much larger surface area for water adsorption than a kilogram of sand.

Clay soils will also hold more minerals, as the particles are negatively charged.

But clay soils have several disadvantages:

Take longer to heat up in spring and tend to be colder all year round.
Swell when they absorb water and shrink when they dry. This can cause severe cracking.
As clay becomes wet, it becomes very sticky
If clay soils are worked when wet, their structure can deteriorate severely.

The ideal soil texture is loam, which combines the nutrient-holding features of clay with the good drainage of sand.

Soil textures can be assessed by feel.

10.1.2 Soil Structure

Describes how the soil forms lumps or crumbs

Controls water and air availability to plants and fine-feeding roots' ability to divide within the soil and hence exploit the essential plant nutrient supply.

Influenced by agents such as:

Organic matter
Earthworms and other soil organisms
Wetting and drying
Freezing and thawing
Presence of plant roots
Cultivation
Texture
Drainage
Compaction

Good soil structure is where the particles form firmly bonded, stable, crumb or granular rounded aggregates 1 – 5 mm in diameter. For this to occur, there must be high to moderate organic matter content (3 – 10%).

Poor soil structure leads to capping, puddling and sieving.

10.1.3 Soil Organic Matter

The raw material consists of plant and animal remains and animal excreta. Broken down in the soil by soil organisms: beetles, mites, earthworms, fungi and bacteria.

These are present in vast numbers in fertile soil; worms can number 2 million per hectare, and microorganisms can weigh 2.5 t/ha.

Organic matter is composed of:

Sugars, starches, cellulose, nitrogenous compounds
Lignins and mineral matter

The soil organisms rapidly break down the sugars, starches, nitrogenous compounds and some cellulose. This process is called mineralisation.

The remaining matter is decomposed much more slowly and forms a black or brown mixture called humus.

This humus has several beneficial effects on the soil:

Maintenance of soil structure
Retention of available nutrients
High water-holding capacity
Low plasticity and cohesion
Gradual release of available nutrients
Darkening of colour

Losses of organic matter from arable soils will be increased by any activity that increases microbial activity, such as cultivations and nitrogen fertiliser applications. Permanent pasture and minimally cultivated soils maintain their organic matter content better than cultivated soils.

10.1.4 Soil Depth

Very important, as it can compensate for low nutrient status and low water-holding capacity. When digging soil profile, look for:

Drainage barrier
Root barrier
Pale & mottled colours (poor aeration)

10.1.5 Water and Air in the Soil

Water is essential in the soil as:

It allows organisms to live in the soil and break down organic matter to release nutrients for the plant.
Maintains structure (e.g. prevents erosion)
The plant absorbs most of its nutrients from the soil in water and relies on this water for the transport of nutrients and sugars within its body
It keeps plant cells turgid ('bloated') to provide support.

Vines need at least 500 mm of available water during the growing season.

Aeration is essential in the soil as:

Provides oxygen to aerobic organisms and suppresses the growth of harmful anaerobic organisms.
Removes carbon dioxide and other waste gasses formed by the breakdown of organic matter and by plant roots
Provides the roots with essential oxygen, thus sustaining their respiration & growth.
Prevent the reduction of iron and manganese to their reduced forms, particularly in acid conditions, which are toxic to plants.
This air movement can be severely restricted in poorly structured clay soils and heavily compacted soils.

10.1.6 Soil Nutrients

Soil nutrients are divided into major or minor elements according to the relative quantities plants use.

Major elements:

Element	—	Description
Nitrogen	N	Major constituent of plant cell proteins, nucleic acids, chlorophyll, & hormones. Second only to water in controlling plant growth.
Phosphorus	P	Key element in energy fixation. Encourages root growth and the ripening process.
Potassium	K	Regulates flow of water and sugar in the plant, regulates internal acidity, enzyme activator. Encourages ripening.
Calcium	Ca	Regulates cell acidity, a component of cell walls.
Sulphur	S	Essential constituent of some amino acids and enzymes.
Magnesium	Mg	Essential component of chlorophyll, regulates internal acidity and sugar metabolism. Encourages ripening

Minor or trace elements include Boron, Manganese, Copper, Iron, Molybdenum, Zinc, Cobalt, Chlorine & Silicon.

A deficiency of any of these elements will lead to serious crop reduction and in some cases will lead to leaf or shoot symptoms.

Carbon ©, Hydrogen (H), and Oxygen (O) are also essential for plant growth, but these are taken from the air or as water, and so are not considered as soil nutrients.

10.1.7 Soil Acidity

Soil acidity is measured by the pH scale. This measures the concentration of hydrogen ions in the soil solution. A pH value of 4 ~ 7 is acid, pH 7 is neutral, and 7 ~ 8.5 is alkaline.

Acidity has a considerable influence on nutrient availability and soil organisms. Different crops have different pH tolerances.

Soils tend to become more acidic with cultivation due to the release of organic acids on the breakdown of organic material.

10.2 Vine Nutrition

Vineyard nutrition is not an exact science as:

Soil fertility is a complex concept
Low nutrient crop, as:
- Little is exported from the field
- Perennial plants explore a large area of soil
Influence of rootstock
Problem of quality vs. quantity

Grapevines can grow and crop satisfactorily in a wide range of soils, but many ignore vine nutrition at their peril!

Need to answer these questions: 1. What are the essential elements for the growth and performance of vines? (See above) 2. How can you measure the need for these? 3. What fertilisers can you use to fulfil this need? 4. How much and when should these be applied?

10.2.1 Determining the Vine’s Nutritional Requirements

Calculating the loss of nutrients from the field Could be simple, but in fact, complicated:

Losses	Gains
Uptake by vine Removal of crop Leaching Erosion	Return of leaves and prunings Fixation of Nitrogen from air Rain

Soil analysis Essential before planting and every 2 – 3 years The most crucial part is getting a representative sample:

Divide the vineyard into blocks according to different types of soil
Don’t sample areas that have had recent fertiliser applications or very wet soils
At least 25 samples/block. Use a zigzag shape
Depth 20 – 60 cm, but useful to take surface ones as well.
The larger the sample, the better
Mix samples in a bucket, then send about 500 g

Nitrogen is not usually measured in soil analysis, as its levels are particularly dependent on seasonal factors such as soil moisture, aeration, temperature and the activity of soil organisms.

Interpretation is not easy, but can use ADAS figures as a rough guide.

Leaf and petiole analysis Remove 100 leaves from the nodes opposite the lower bunches at veraison or full bloom (or both). In dry areas, samples should be taken early in the day (before stress) but not directly after overhead irrigation.

Wash leaves to remove pesticides, dry, and then send off leaves or petioles for analysis.

Useful for:

Confirming visual symptoms
Comparing good vine areas with bad
Assessing the effectiveness of fertiliser applications or changes in practices such as irrigation and weed control

Unfortunately does not tell you how much to add.

Observing deficiency symptoms Must learn to recognise them, but:

If symptoms are sporadic, they are probably due to something else, such as root or bark damage, girdling with ties, viral diseases
Deficiencies might affect vine performance without showing symptoms (‘hidden hunger’) e.g. Magnesium & zinc
Multiple deficiencies are difficult to diagnose

10.2.2 Fertilisers

Straights: containing only 1 plant nutrient Compound: two or more nutrients (more expensive, but more commonly used as easier) Organics: derived directly from fresh or composted plant or animal material.

Nitrogen

Ammonium nitrate: (34% N): most popular, used in spring or early summer
Ammonium nitrate lime: (21 – 26% N) same as before, but better on acid soils, as it does not raise acidity. Difficult to store, as it soaks up moisture & goes pasty
Urea (46% N): the cheapest & most concentrated but needs to be washed or worked into the soil, or losses are high, particularly in alkaline soils.

Phosphorus (P) Can be: Water-soluble: readily available to plants Citrate soluble: slowly available to plants Acid soluble: unavailable, except in acid soils

Triple superphosphate (47% water-soluble): treated with phosphoric acid
Superphosphate (18 – 25 water-soluble): ground rock phosphate treated with sulphuric acid. Most commonly used, usually mixed with sulphate of ammonia and a potassium carrier.
Ground rock phosphate or Hyperphosphate (29% P): acid-soluble P only, so use only in acid soils. Permitted by the Soil Association.

Potassium (potash)

Muriate of potash (potassium chloride): Commonest form (cheapest) but does not store well or spread easily. High chlorine levels can be toxic to the vine.
Sulphate of potash: more expensive. Restricted use is allowed by the Soil Association. Potassium nitrate – too expensive, but can be used in foliar sprays & fertigation.

Magnesium

Epsom salts (10% MgO): magnesium sulphate. Soluble, quick acting, often used as a foliar spray. Restricted use allowed by the Soil Association
Kieserite (16-17% MgO): slower acting, minimum 1 month, restricted use by SA
Calcinated magnesite (48% MgO): the most concentrated form, but the slowest acting (3 months)
Dolomitic limestone (9% MgO): can be used instead of lime in acid soils.

Calcium Used to correct soil acidity. Measure in CaO units.

Graded according to neutralising values (NV), which is the same as % CaO content. Limestone or chalk (NV50 –55) or dolomite (magnesian limestone NV50 – 55) is used. The finer the lime, the more rapid its reaction. Particles greater than 2 mm are ineffective.

The amount needed will depend on the following: * Actual soil pH & optimum required (6 ~ 7.5 depending on rootstock) * Soil texture (clay soils need more) * Soil organic matter (organic soils need more due to high buffering capacity)

Autumn is the best time to apply. Do not apply rates above 10 tons/ha in a single application

Organics Derived from plant and animal materials

Advantages:

Cheap or even free
High in humus, therefore good for soil structure & water retention
Encourage soil organisms
Improved soil aeration
Slow-release
Often approved by Soil Association

Disadvantages:

Slow release, often nutrients are in insoluble forms that need to be broken down by micro-organisms, thus requiring incorporation into the soil
Bulky and so expensive to transport and spread

Farmyard manure (FYM)

Animal dung & urine, and litter are used as slurry
Animals only use about half the nitrogen, most of the phosphates and nearly 40% of potassium found in their feed. The rest remains in the faeces.
Varies in composition, according to the animal that produces it, whether it is breeding or fattening stock (better), the way the animals are kept and the amount of straw used, the time and manner of storage

Slurry

Cheaper than using straw, easier to handle & store
Again, very variable composition.
Higher risks of polluting watercourses, particularly if applied in cold weather when microbial activity is insufficient to bind the nutrients.

Cereal straws

One ton of straw supplies about 4 kg N, 1 kg phosphate & 9 kg potash but needs the addition of about 6 kg extra nitrogen.

Green manuring

Growing and ploughing in green crops to increase the organic matter content of the soil.
Planting is usually in the early autumn, ploughing-in in early summer.
Most common is white mustard, sown at 9 ~ 17 kg/ha, which can produce a crop ready for ploughing within 6 ~ 8 weeks.
Fodder radish also grown
Leguminous crops such as vetch will increase soil nitrogen content due to their associations with Rhizobium bacteria in their root nodules.
Cereal roots can also be beneficial, as their roots break up the soil.

A good crop can produce 20 t/ha, which will produce 300 – 600 kg of humus Improvement of OM of soil is short-lived as the crop consists mostly of cellulose, which is rapidly broken down.

Cover crops have other advantages, such as reducing water run-off, facilitating weed control, binding nutrients otherwise lost by leaching, and reducing dust problems.

Can be too much competition with the vine in dry summers.

Foliar fertilisers

Advantages:

Less waste
Useful for nutrients that may otherwise become immobilised in the soil
Some can be applied at the same time as pesticides (not chelates with copper)
Very rapid action

Disadvantages:

Some nutrients, such as phosphate, are not easily taken up by the leaves
Risk of leaf burn if the concentration is too high

Best to apply under conditions in which the droplets remain unevaporated on the leaf surface to allow for penetration.

Best to use high volume applications (over 1000 l/ha) Usually only used for temporary deficiencies as high doses and concentrations will cause scorching

10.2.3 Fertiliser Application

Pre-planting

To correct soil deficiencies or high acidity (raise pH above 6)
To give young plants a good start in life

Especially used for slow-migrating minerals like P, K, Ca & Mg, not usual for nitrogen due to the high level of mineralisation of organic matter & high mobility.

Common to add organic manure to improve soil structure and stimulate soil life.

Fertilising established vines Based on the assessments above Importance of balanced nutrition, in particular: Mg/K, N/K, Mn/Fe

Timing:

N in spring. The greatest period when the vine’s demand outstrips the soil’s supply is at flowering
P & K in autumn (or spring in light soils)

11. Vineyard Floor Management

11.1. Introduction

The aim of vineyard floor management (VFM) is not just to control the weeds in the vineyard but to provide an ideal environment for root development and the vineyard's management.

Ideal Soil Condition	Soil Management Technique
Loam texture	-
Stable crumb structure	Adding OM, lack of disturbance, VFM
Sufficient water	Irrigation, improve structure, VFM
Good drainage and aeration	Drainage, good structure, control soil compaction, VFM
High level of microbial and microbial activity	Correct pH, add OM, reduce chemical ferts & herbicides, VFM
pH 6.5 – 7.5	Lime applications
Sufficient nutrients	Fertiliser/FYM applications, VFM
Sufficient depth & volume	VFM, drainage

11.2 The need for weed control

A weed is any unwanted plant in a cultivated area.

Calling a plant a weed is very subjective, e.g. blackberry is generally regarded as a weed, but in the USA, they can be encouraged, as they are the overwintering host of the Anagrus wasp that parasitises the grape leafhopper.

Disadvantages of weeds:

Compete with vines for soil water, space & nutrients. The dock can even block drainage pipes.
- Note that wild plants are usually better adapted to the soil conditions than crop
Smothering of aerial parts of the vine, especially young ones
Hamper the passage of:
- Machinery, e.g. harvesters & black nightshade
- Manual labour – e.g. thistles, nettles, brambles
Increase frost risk by forming an insulating layer on the soil surface
An act as hosts for pests and diseases, e.g., broad-leaved species of ground cover will host eggs of light brown apple moth in Australia
Look unattractive

Advantages of ‘weeds’:

Prevent soil erosion
Prevent nitrate leaching
Encourage biodiversity
Reduce excess vine vigour
Improve soil structure
Indicator weeds
Can look attractive
Possible crop

Important to understand wild plants:

Identify, particularly when young
Know whether ephemeral, annual, biennial, perennial, monocotyledon, dicotyledon
How they reproduce, spread and perennate

The main weed control methods in vineyards are cultivation, ground cover, herbicides & mulching.

Need to know how to do it and the advantages and disadvantages.

11.3 Cultivation

Traditional method: ‘quatre façons’:

Autumn (after harvest): the soil is ridged up under row with vineyard plough max 20 cm in depth, creating a middle furrow.
Spring (when soil is dry enough): de-ridging with shares pointing inwards & inter-row shares (finished off manually)
Can be repeated twice during summer or replaced by other tools such as harrows (spring tines, discs, duck’s feet) or powered implements (rotary cultivators, power harrows), inter-row weeders

To preserve its structure, the soil must be cultivated as little as possible and never when wet. It is best to cultivate when vine roots are active (6 leaves apparent) to take up released nitrates.

Advantages:

Very effective weed control
More efficient use of fertilisers
Decreases disease risk due to burying of trash and reducing puddling
Decreases soil compaction
Increases rain penetration, thus reducing runoff and erosion
Increases soil evaporation in damp climates, decreases it when dry
Brings stones to the surface
Encourages root vigour and deep root development
Protection of trunks against the winter cold
Aesthetic
Ecologically sound

11.5 Natural Vegetation

Well-suited to conditions, cheap and leads to greater biodiversity, but it can be difficult to manage and harbour pests.

Important to manage cover crop properly:

Mow very closely before budburst (frost)
Mow again a couple of weeks before flowering to boost vigour
Allow to grow at veraison
Alternate row mowing will allow better biodiversity

Note that some cover crops will not survive close mowing.

As crops get more mature, their biomass increases, and they become woodier, thus taking longer to break down when mown or incorporated into the soil.

Advantages:

Increased bearing capacity (trafficability) of the soil, particularly in wet weather
Good soil structure: high organic matter levels and roots break up soil, reducing compaction.
Leguminous plants (clovers, medics and vetches) can reduce fertiliser requirements.  Control of vine vigour due to competition with water
Encourage deep rooting in vines
Reduced erosion risk & increased water infiltration
Suppression of undesirable weeds by competing for light
No dust or mud problems
Surface mulch is formed, which can trap moisture in the soil
Reduced nitrate leaching.
Possibility of secondary crop
Aesthetic
Environmentally acceptable, can increase biodiversity.
Promotes soil life

Disadvantages:

Reduction in vine vigour can be excessive, particularly with young vines, poor and shallow soils or dry climates (<650 mm annual rainfall)
Humidification of microclimate, encouraging fungal diseases
Cooling of microclimate, discouraging ripening
Inefficient use of fertilisers
Increased spring frost risk
High maintenance costs compared with herbicide control, particularly as the under-row area usually has to be controlled separately
Can be too slippery on slopes

Generally regarded as a quality method, and gaining in popularity for low density highly mechanised vineyards.

Good compromise could be to alternate rows of cover crop/cultivation, changing around every few years.

11.5 Chemical Weed Control

Also called minimal cultivation or no-till cultivation

Vines are one of the last crops to be grown with the aid of herbicides, as vines are very sensitive to weedkillers, and selective weedkillers are rare (often selectivity is only due to dose levels).

Herbicides are grouped according to their mode of action: – Pre-emergence (residual) – Contact – Systemic

11.5.1 Pre-emergence Herbicides

Poorly-soluble compounds become trapped in the upper layers of the soil. They are absorbed through the roots and inhibit photosynthesis in young seedlings. They are best applied before budburst on weed-free soils (weed-shadow effect). The higher the clay content of the soil, the less they are leached, and so the less risk there is to the vine.

They are slowly broken down by micro-organisms, but their effect can last several months. Prolonged use can cause problems in re-plantations.

Residuals approved in the UK include Isoxaben (FLEXIDOR) and propyzamide (KERB). Simazine used to be used, but there is now too much resistance to it, so its approval has been withdrawn.

11.5.2 Contact Herbicides

Also called ‘wilters’ or knockdown’. Absorbed through the green organs on which they land, stay localised, and destroy those parts.

The effect is only temporary in plants with well-established root systems, such as perennials. They are broken down in the soil almost immediately in some cases.

Contacts approved in the UK include:

Diquat (REGLONE)
Carfentrazone-ethyl (SHARK)

11.5.3 Systemic Herbicides

Absorbed by the leaves (sometimes roots) and translocates in the sap (upward and downward systemy). Destroy the whole plant, usually by destroying the chlorophyll, preventing root growth and distorting growth.

Generally very slow acting.

Approved in the UK:

Glyphosate (ROUNDUP) – Dangerous to vines
Fluazifop-P-butyl (FUSILADE MAX)

Do not use common hormonal herbicides such as MCPA & 2,4-D!

11.5.4 Herbicide Selection

Selecting the correct herbicide depends on: * The weeds you wish to control * The type of soil * The age of vines * Time of year

115.5 Herbicide Application

Usual programme: Get weeds well under control in the first few years by many applications, and then reduce numbers

Systemic after leaf-fall if perennial weeds present
Pre-emergence before budbreak
Spot applications of contacts (or systemics) after budburst

Minimal cultivation is usually used over the whole vineyard surface in high-density plantations, but it is reserved for the under-row region in lower densities.

Advantages of using herbicides:

Least expensive in terms of manpower and equipment
Highly effective
Hand-held applicators are particularly good for plots that are inaccessible to machinery
Suited to stony soils
Maintains good levels of organic matter  good soil structure  Reduced spring frost risk

Disadvantages:

Herbicides can be expensive to buy
Can be toxic to young vines (must be protected) and vines in light soils  Promote high vigour
Some risk to the operator (esp. Paraquat)
Some risk to the environment, especially waterways
Decreased activity of some soil microorganisms and invertebrates
Can get trapped in soil (Paraquat)
Soil surface can become rutted & soil compacted
Increased erosion
Increased disease risk
Manures and fertilisers are more difficult to incorporate into the soil
High level of nitrate leaching in winter
Weed resistance (e.g. Glyphosate & willowherb)
Unaesthetic
Unsustainable
Lack of wild plants can increase pest problems, e.g. omnivorous leaf-roller

In conclusion:

Still very popular due to low labour costs
Less popular than it used to be due to environmental concerns.

11.6 Mulching

The spreading of matter onto the soil surface to suppress weeds (and ultimately provide a food source for the plant) by preventing light from reaching the young weeds.

Types of mulches: black polythene, straw, grass clippings, paper, tree bark, wood (not coniferous) chips, marc, timber milling, sugar refining & household waste.

‘Strategic’ mulching can be used to:

Reduce variability in the establishment of young vines by applying mulches with a high C:N ratio (straw, paper, woodchip) on more vigorous plants
Materials with higher nutrient components (manures, mushroom compost) can benefit sections of poor growth
Deeper mulches reduce soil moisture in wetter months
Organic materials that encourage earthworms can assist drainage in waterlogged areas (don’t use fresh manures).

Optimal depth depends on the properties of mulch material and site characteristics: most compost mulches are used between 50 & 100 mm. Organic mulches need to be topped up each year.

Can be used in the alley or under the row.

Advantages:

Effective if spread thickly enough
Conserves water- reduces soil water evaporation and increases water infiltration (good for dry climates)
Increased earthworm activity and surface soil microbial activity  Improves soil structure
Reduces erosion (except plastic)
Reduces soil temperature variation: limits heat loss from soil at night & reduces maximum soil temperature
Protects roots from cold
Increased vigour & yield with little change in quality

Disadvantages:

Expensive to spread
Encourages superficial rooting
Can promote high vigour
Increases frost risk
Risk of nitrogen deficit
Possible increase in fire risk
Possible pest infestation

11.7. Other Methods

11.7.1 Animals

Sheep, poultry, rabbits Trunks must be long enough & young plants protected Beware of pesticide poisoning

11.7.2 Flame Weeding

Either with a ‘flame-thrower’ (Atarus Ranger 3000) or a tractor-mounted heated stainless steel mesh with a blower unit.