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Horticulture 1000
HT1102 - Plant management 2 - Fertiliser
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Fertiliser

Plant management or husbandry is the care and protection of plants so they grow successfully.

Plant growth is affected by the following things:

Plant growth is affected by the following things

Various management practices can be used to change the growing conditions, and include:

Nutrients

Minerals or nutrients, along with water, are taken up from the soil through the roots of the plant for their growth and development. Plants obtain nutrients by absorbing them in a soluble form from the soil water, when it is in contact with the root hairs.

If you are studying the soils achievement standard 90919 you will cover this topic in more detail.

The major nutrients or macronutrients are needed in large amounts.

They include:

Leafy plants like silverbeet require nitrogen to grow wellLeafy plants like silverbeet require nitrogen to grow well.

Nitrogen is used for leaf growth and the formation of proteins. Plants get nitrogen from nitrate ions dissolved in soil water. Legumes such as peas, beans and lupins can add nitrogen to the soil.

Bacteria live on the roots of legume plants in structures called nodules. They turn atmospheric nitrogen into a form that plants can use.

 
Root crops such as carrots require phosphorus to grow wellRoot crops such as carrots require phosphorus to grow well.

Phosphorus is needed for root growth and it helps seeds reach maturity. New Zealand soils are low in this nutrient so it is often applied as a fertiliser called superphosphate.

 
Tamarillo plants need potassium for flowering and fruit productionTamarillo plants need potassium for flowering and fruit production.

Potassium is used by leafy plants for photosynthesis, flowering, fruit ripening and improved disease resistance.

 

Sulfur is needed for the formation of proteins. In the past it has been lacking in New Zealand soils but it is rarely deficient now as it is added to the soil in the fertiliser superphosphate.

Calcium is essential for plants to reach maturity. It is found in lime and gypsum. Both of these substances are added to the soil to raise the pH of the soil.

The pH has some control over chemical reactions that take place in the soil.

A soil with a pH 6–6.5 suits most plants. A low pH soil makes some nutrients more soluble and can slow bacterial action, which means organic matter is not broken down. A high pH stops some nutrients from being released.

Adding lime to soil raises pHAdding lime to soil raises pH.
Lime can be spread or broadcast over the soilLime can be spread or broadcast over the soil.
 

Magnesium is needed for plants to carry out photosynthesis. It is added to the soil in dolomite lime.

Fertiliser programmes

Nutrients are especially important because:

When a nutrient is not available or is in short supply a deficiency can occur.

Types of fertiliser

There are many different types of fertilisers available to supply nutrients to the soil, including:

NPK ratio

The ratio is a series of three or more numbers found on the packaging of fertiliser. This shows the proportion of the major nutrients in the fertiliser.

The numbers found in the ratio are the percentages of nitrogen (N) phosphorus (P), potassium (K), and sometimes sulfur (S) and magnesium (Mg).

The numbers are always in the same order, N, P, K and S.

This information is useful as it tells you what the fertiliser will supply.

The grower can then match the soil and crop needs to a suitable fertiliser that can supply the nutrients.

The ratio for this fertiliser is 5–4–8The ratio for this fertiliser is 5–4–8.

The fertiliser contains:

  • 5% nitrogen
  • 4% phosphorus
  • 8% potassium.

Rose plants will benefit from this general fertiliser and especially the higher levels of potassium.

A simple fertiliser contains only one nutrient. Urea is an example of a simple fertiliser that provides nitrogen.

When the fertiliser contains more than one nutrient it is called a compound fertiliser.

How to apply nutrients

Fertilisers can be applied in different ways:

Fertiliser applies as a side dressingFertiliser applies as a side dressing.

In an established kiwifruit crop the fertiliser can be applied alongside the plant as a side dressing or as a foliar feed on the leaves.

 

Commercial growers take particular care about applying the correct amounts of fertiliser to produce the best yield. This is because fertilisers are costly and a waste of money if the grower applies more than what is needed to increase the yield.

Activity 1 The photos below show two stages of tomato development.

Vegetative leaf growth
Vegetative leaf growth
Flowering and fruiting
Flowering and fruiting

Some fertilisers and their NPKS rating

                                                                                                                                                                                                                                                           

Name of fertiliserOrganicInorganicNitrogen
      N%
Phosphorous
      P%
Potassium (potash) K%Sulfur
      S%
Urea   46 0 0 0
Hoof and horn   9 0 0 0
Sulphate of potash or potassium sulphate   0 0 40 18
Rock potash   0 0 60 very slow to release K 0
Sulphate of ammonia   √ and acidic 21 0 0 24
Superphosphate   0 9 0 10
Blood and bone   4-8 6-8 0 0
Ammonium nitrate   34 0 0 0

Activity 1A Activity 1A - Answer the following

  

Activity 1B Activity 1B - Answer the following

  

Activity 1B Activity 1C - Answer the following

  

Key points   Key points

The  major or macronutrients are needed in large amounts and include:

  • carbon, hydrogen, oxygen; these are supplied by air or water
  • nitrogen, phosphorus, potassium, sulfur, calcium and  magnesium, which are supplied by soil.

These nutrients are all required for specific functions and processes in the plant.

Nutrients are especially important because:

  • high-producing plants need high nutrient levels
  • they can be lost when the plants and fruit are harvested  or removed from the soil
  • leaching, irrigation and drainage can also remove them  from the soil.

When a nutrient is not available or in short supply a deficiency can occur.

There are many different types of fertilisers available.

On the packaging of fertilisers you find a series of three or more numbers that show the proportion of the major nutrients in the fertiliser. This is referred to as the NPK ratio.

 

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