Fruit – Lesson 1: Application of foliar nutrition

This course is divided into three sections.

Foliar Nutrition 
We will look into the basic principles behind how elemental foliar nutrition can be used in fruit crop production, the relationship between elements and how available to the plant these nutrients are.

Biopesticides
We hope to give you an understanding of the alternatives to chemical-based plant protection products, what they are made of, how they work and some guidance on practical use of them as a sprayer operator. 

Current Issues & Emergency Procedures
This section will cover the key changes in pesticide approvals and revocations. It also covers details on how to protect water, operator qualifications and NSTS testing. There is also good advice on what to do in an emergency and how to safely use rodenticides. 

Lesson 1 – Foliar Nutrition:

In this lesson you will learn more about what plants need for growth and quality fruit production. Elements will look in detail at:

  • Plant growth and essential nutrients
  • Nutrients and interactions
  • Foliar applied nutrients
  • Foliar nutrient uptake
  • Function of nutrients
  • Nutrient deficiency or excess

Plant growth and essential nutrients

In this section you will learn more about the requirements for plant growth, macro- and micro-nutrients as well as different application methods.

Plants produce energy via the process of photosynthesis – which converts energy from sunlight into chemical energy to fuel growth. 

Photosynthesis uses:
Water 
Sunlight
Carbon dioxide from the air

Plants also require 12 mineral nutrients, which usually come from the soil and enter through the roots. These are divided into ‘macro-nutrients’ and ‘micro-nutrients’.

Macro-nutrients are required in large quantities and micro-nutrients are needed in relatively small quantities. But both are equally important for plant growth. 

Macro-nutrients

  • The primary macro-nutrients are: nitrogen (N), phosphorus (P), potassium (K). These are needed in relatively large amounts by plants.
  • Intermediate amounts of secondary macro-nutrients needed by plants are: magnesium (Mg), calcium (Ca) and sulphur (S). 
  • Macro-nutrients and are often applied to the root zone as granular fertiliser or via fertigation. They are used as supplementary foliar feeds to correct deficiencies or deliver extra nutrition at certain growth stages.
Picture: © R. Killian

Micro-nutrients

  • Trace or micro-nutrients are: zinc (Zn), boron (B), copper (Cu), iron (Fe), manganese (Mn) and molybdenum (Mo). These are needed only in small ‘trace’ amounts. Micro-nutrients tend to be applied as foliar nutrition or via fertigation in substrate/coir crop systems.

Quick Quiz: Nutrient sorting

Use the information you have just read, to sort the following pairs into macro-nutrients or micro-nutrients (drag and drop). Check each answer, then move on to the next question until you finish the quiz to find out your overall score.

CONTINUE LESSON

Nutrients and interactions

In this section we look at:

  • Soil or water pH
  • pH and nutrient availability
  • Nutrient ratios

Check the pH

Nutrients from soil-applied fertilisers are partially lost due to:
Less direct or inefficient application of the fertiliser
Nutrient leaching
Nutrient lockup, secondary reactions in the soil or between nutrients.

The acidity (pH) of the soil or water for fertigation also influences nutrient availability and the uptake of macro- and micro-nutrients. The optimum pH range for most plants is between pH 6 to 7, although this may vary depending on the crop, for example blueberries prefer pH 4.3 to 5.5. 

If the soil pH falls outside the optimal range, uptake of certain nutrients becomes reduced – potentially leading to deficiencies. 

This doesn’t mean the nutrient is not in the soil, but the chemical environment is not suitable for uptake of that nutrient. This usually takes place in highly alkaline (greater than pH 7.5) or highly acidic (less than pH 5.5) situations. 

If the soil is outside the desired pH range:
It can be lowered by applying sulphur 
It can be raised by applying lime

This nutrient availability table shows the pH at which various nutrients are most available. For example – nitrogen is most available at a pH from pH 6 to 8 and declines outside this range.

Quick Quiz: Best availability

Refer to the chart above to answer the following questions about nutrient availability. Check each answer, then move on to the next question until you finish the quiz to find out your overall score.

CONTINUE LESSON

Nutrient ratios

The ratio between certain nutrients can also cause interactions.

  • These can be positive – synergistic 
  • Or negative – antagonistic

Synergistic relationship
This occurs when the high level of a particular nutrient increases the demand by the plant for another nutrient.

For example: increased nitrogen levels create a higher demand for magnesium – to facilitate the creation of more chlorophyll.

Antagonistic relationships
High levels of a particular nutrient in the soil can interfere with the availability and uptake of other nutrients.

For example: applying too much calcium and magnesium can cause a potassium deficiency (K/Ca and K/Mg ratio).

Fine balance

Applications of high levels of the most common nutrients – nitrogen, phosphorus and potassium have the potential to cause plant deficiencies of other essential elements.

  • High nitrogen levels can reduce the availability of boron, potassium and copper
  • High phosphate levels can influence the uptake of iron, calcium, potassium, copper and zinc
  • High potassium levels can reduce the availability of magnesium.

Nutrients can act as antagonists in a couple ways. If calcium levels are in excess it can simply out-compete other elements, such as potassium and magnesium, for uptake sites on the roots. Or it can change soil chemistry by raising pH to the point iron and boron become unavailable.

This is illustrated in Mulder’s Chart, which shows some of the interactions between plant nutrients. It also illustrates the relationships between nutrients.

  • Antagonism results in decreased availability of a nutrient to the plant due to the action of another nutrient.
  • Stimulation is a high level of a nutrient that increases demand by the plant for another nutrient.

Quick Quiz: Mulder’s Chart

Use the Mulder’s Chart above to find the relationship between nutrients. Check each answer, then move on to the next question until you finish the quiz to find out your overall score.

CONTINUE LESSON

Foliar applied nutrients

Foliar-applied nutrition (foliar feeding) delivers a number of benefits, but it does have some drawbacks. Used to supplement soil applied fertilisers, it directly delivers nutrients onto the plants’ leaves and fruit where they are absorbed and used. 

Foliar feeding is considered an almost immediate way to feed plants and is usually used to correct micro-nutrient deficiencies, such as manganese, iron, boron and zinc. It also delivers extra levels of macro-nutrients at certain growth stages or when deficiencies are detected.

Advantages of foliar nutrients

  • Foliar nutrients have an almost immediate effect on the plants 
  • Liquid fertiliser is formulated to quickly provide nutrients in a usable form for the plant
  • Delivers nutrition in situations when root-uptake is low
  • Effective in cold or waterlogged soils, drought conditions and in soil nutrient lockup
  • Directly delivers nutrition to the sites of use, such as leaves and fruit 
  • Useful for nutrients which are relatively immobile
  • Avoids nutrient leaching which can occur from soil-applied fertiliser, potentially causing environmental pollution and breaching legislation such as the Ground Water Regulations 2009 (GWR) and Water Framework Directive 2009 (WFD)
  • Avoids soils nutrient antagonisms or nutrient lock-up due to soil pH or imbalances between nutrient ratios. 

Disadvantages of foliar nutrients

  • It is not a slow release/sustained form of nutrition 
  • Frequent applications required compared with ground-applied fertiliser
  • Cannot deliver the plants’ total/annual nutrient requirement 
  • If applied in high concentrations or high temperatures plant damage can occur (leaf scorch, phytotoxicity or defoliation).

Quick Quiz: Foliar nutrients

Use the information above to help you to select the correct missing words.

Foliar nutrient uptake

This section helps you to learn more about:
Leaf anatomy and nutrient uptake
Different nutrients’ absorption rates
Top tips for good uptake

Understanding some of the mechanisms behind foliar feeding is useful to help increase the uptake of foliar nutrition. The main way nutrients get into the leaves is through the leaf cuticle or stomata.

Stomata 

The main function of stomata, which are small pore-like structures found on leaves, is to open and close to allow carbon dioxide, oxygen and water exchange with the atmosphere. 

When open, stomata can also allow nutrients to enter. If the stomata stay closed, for example in high temperatures or in drought conditions, this will reduce or prevent nutrient solution uptake.

The cuticle

The cuticle is the main entry point for nutrients, but it can also present a barrier. This is because it is a waxy layer of cells on the leaf surface, which protect the plant against water evaporation.

A nutrient solution applied to the leaves moistens the surface, allowing the cuticle cells to slightly spread. This enables the nutrient solution to reach the inner cells of a leaf.

This means foliar nutrition is best applied in an adequate water volume to achieve good coverage and surface wetting of the leaf.

Adjuvants assist

Using wetter or sticker adjuvants can also improve coverage and retention, increasing leaf penetration and nutrient uptake. Once absorbed into the leaf by either the cuticle or stomata, nutrients can be transported through the vascular system to leaves, flowers and fruits for storage or use.

Quick Quiz: Foliar uptake

Look at the leaf cross-section diagram and use the lesson content above to answer the following questions.

CONTINUE LESSON

Top tips for good nutrient uptake

  • Young leaves have the best uptake because they have a thinner cuticle
  • Avoid high concentrations that are more than 4 – 5% by volume in water
  • Good leaf coverage increases nutrient uptake 
  • Most effective in slow drying conditions
  • Wetter/sticker adjuvants can increase uptake
  • A slightly acidic spray solution generally improves leaf uptake
  • Where required, use water conditioners such as H2Opti/X-change.

Nutrient functions

Essential nutrients play different roles in plant growth and development. The information below shows examples of where each nutrient might be used.

Nitrogen

Promotes vegetative growth – increasing vigour and new shoot growth.

Phosphorous

Stimulates root development, promotes fruit ripening/quality and counteracts the effects of excessive nitrogen.

Potassium

Promotes fruit quality and tolerance to stress/disease.

Calcium

Required for cell wall formation and root development. Improved fruit quality and shelf-life. Increased tolerance to stress/disease.

Zinc and Boron

Zinc is involved in flowering and pollination. Improves bud development, flowering and fruit-set. 

Boron promotes pollen tube growth, flowering and fruit-set. Increases calcium uptake.


Quick Quiz: Nutrient influence

How do nutrients influence plant growth and development? Use the table above to help answer the following questions.

Well done, you have reached the end of Lesson 1 – Application of foliar nutrition and you now need to complete the end of lesson test below. You should not move on to the next lesson, until you take this test. You will need 80% to pass. You can re-sit the test as many times as it takes to pass. Once you have passed this test, you can move on to Lesson 2.

To start the test, click on Fruit Course: End of Lesson 1 Test (Compulsory) below: