Basic 7 · Science · Crop Production
Plant Nutrient Sources and Their Application
In this topic you will identify the nutrients plants need, list and categorise plant nutrient sources in your community into organic and inorganic, and describe the physical characteristics of fertilisers and how they are applied in the field.
By the end of these notes you should be able to:
- State the major and minor nutrients needed by plants
- Categorise plant nutrient sources into organic and inorganic
- Describe the physical characteristics and methods of application of plant nutrients
What you already know
- Plant cells and photosynthesis
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Cycles
- Sub-strand
- Crop Production
- Indicator
- B7.2.3.1.1 – Observe and list all plant nutrient sources available in a community and categorize them into organic and inorganic nutrient sources
Introduction
Just as we need a balanced diet, plants need nutrients from the soil to grow strong, green and productive. When a nutrient is missing, plants show signs of poor health.
1. What Plants Need
Plants make their own food by photosynthesis, using carbon dioxide, water and light. However, they also need mineral nutrients from the soil. These are grouped into macronutrients, needed in large amounts, and micronutrients, needed in small amounts.
2. Major Nutrients
| Nutrient | Function | Sign of deficiency |
|---|---|---|
| nitrogen (N) | leaf growth and green colour | pale yellow leaves; stunted growth |
| phosphorus (P) | root growth, flowering and seed formation | poor roots; purplish leaves |
| potassium (K) | strong stems, disease resistance, fruit quality | weak stems; brown leaf edges |
| calcium (Ca) | cell walls | poor growth of shoot tips |
| magnesium (Mg) | part of chlorophyll | yellowing between leaf veins |
| sulphur (S) | proteins | pale young leaves |
3. Micronutrients
Micronutrients include iron, zinc, manganese, copper, boron and molybdenum. Although needed in very small amounts, they are still essential. For example, iron is needed to make chlorophyll, and boron helps flowers and fruits develop.
4. How Plants Take In Nutrients
Plants absorb nutrients dissolved in soil water through their root hairs. If the soil is too dry, nutrients cannot reach the roots. Continuous farming on the same land removes nutrients, which must be replaced by adding manure or fertiliser.
5. Soil Testing
Farmers can find out which nutrients their soil lacks by soil testing. A sample of soil is taken to a laboratory, such as those of the Soil Research Institute in Kumasi, where it is analysed. The results show which fertiliser and how much to apply. This saves money and prevents the overuse of fertilisers.
New words
- nutrient
- A substance needed for growth and health.
- macronutrient
- A nutrient needed in large amounts.
- micronutrient
- A nutrient needed in small amounts.
- deficiency
- A lack of something needed.
Summary
- Plants need macronutrients (N, P, K, Ca, Mg, S) and micronutrients from the soil.
- Each nutrient has a function, and lack of it shows signs such as yellow leaves.
- Nutrients are absorbed in solution through root hairs and must be replaced after farming.
Class activity: Deficiency Detectives
- Study pictures of healthy and unhealthy plants.
- Identify possible nutrient deficiencies.
- Suggest how the farmer could correct each one.
You need: Compost sample, NPK fertiliser packet, Sealed cow-dung sample
Exercises
Answer in your exercise book first, then check your answers.
1. Which nutrient gives leaves their green colour and growth?
- A. nitrogen
- B. phosphorus
- C. potassium
- D. boron
Show answer
Answer: nitrogenLeaf growth.2. Phosphorus mainly helps…
- A. root growth and flowering
- B. leaf colour only
- C. stem weakness
- D. cell walls only
Show answer
Answer: root growth and floweringRoots and seeds.3. Micronutrients are needed in small amounts.
- A. True
- B. False
Show answer
Answer: TrueStill essential.4. A lack of a needed nutrient is a ______.
Show answer
Answer: deficiencyShortage.5. Name the three major nutrients in NPK and their functions.
Show answer
Answer: Nitrogen: leaf growth; phosphorus: roots and flowering; potassium: strong stems and disease resistance.NPK.6. Why must farmers replace nutrients in the soil?
Show answer
Answer: Crops remove nutrients as they grow and are harvested, so the soil becomes poor if nothing is added.Nutrient removal.
Lesson 2
- Strand
- Cycles
- Sub-strand
- Crop Production
- Indicator
- B7.2.3.1.1 – Observe and list all plant nutrient sources available in a community and categorize them into organic and inorganic nutrient sources
Introduction
Farmers in your community feed their crops in different ways: some use animal dung or compost, others buy bags of fertiliser from agro-input shops.
1. Organic Nutrient Sources
Organic manure: Plant nutrients from decayed plant and animal materials.
| Source | Description |
|---|---|
| farmyard manure | dung and urine of animals mixed with bedding |
| poultry manure | droppings of chickens; rich in nitrogen |
| compost | decayed plant and kitchen waste |
| green manure | green plants, such as legumes, ploughed into the soil |
| crop residues | stalks and leaves left after harvest |
| household waste | peels and food scraps (composted) |
2. Inorganic Nutrient Sources
Inorganic fertiliser: A manufactured chemical that supplies plant nutrients.
| Fertiliser | Main nutrient |
|---|---|
| NPK (e.g. 15-15-15) | nitrogen, phosphorus and potassium |
| urea | nitrogen (about 46%) |
| sulphate of ammonia | nitrogen and sulphur |
| triple superphosphate (TSP) | phosphorus |
| muriate of potash | potassium |
3. Comparing Organic and Inorganic Sources
| Feature | Organic | Inorganic |
|---|---|---|
| speed | releases nutrients slowly | acts quickly |
| soil structure | improves soil and water holding | does not improve soil structure |
| cost | cheap or free | expensive |
| bulk | bulky and heavy to carry | concentrated, easy to transport |
| environment | safe if well composted | overuse can pollute water and acidify soil |
4. Nutrient Sources in the Community
Learners can survey their community: poultry farms supply droppings, markets produce plant waste for compost, and agro-input shops sell NPK and urea. Many farmers combine both kinds, using manure to build soil and small amounts of fertiliser for a quick boost.
New words
- organic manure
- Nutrients from decayed living materials.
- compost
- Decayed plant and kitchen waste used as manure.
- inorganic fertiliser
- A manufactured chemical nutrient source.
- green manure
- Green plants ploughed into the soil.
Summary
- Organic sources include farmyard and poultry manure, compost, green manure and crop residues.
- Inorganic sources include NPK, urea, sulphate of ammonia, TSP and muriate of potash.
- Organic sources improve soil but act slowly; inorganic fertilisers act fast but are costly and can pollute.
Class activity: Nutrient Source Survey
- List all plant nutrient sources found in your community.
- Classify them as organic or inorganic.
- Present your findings in a table.
You need: Compost sample, NPK fertiliser packet, Sealed cow-dung sample
Exercises
Answer in your exercise book first, then check your answers.
1. Which is an organic nutrient source?
- A. compost
- B. urea
- C. NPK
- D. TSP
Show answer
Answer: compostDecayed material.2. Urea mainly supplies…
- A. nitrogen
- B. phosphorus
- C. potassium
- D. calcium
Show answer
Answer: nitrogenAbout 46%.3. Organic manure improves soil structure.
- A. True
- B. False
Show answer
Answer: TrueAdds humus.4. Green plants ploughed into the soil are called ______ manure.
Show answer
Answer: greene.g. legumes.5. State two advantages of organic manure over inorganic fertiliser.
Show answer
Answer: It is cheap and improves soil structure (or safe for the environment).Any two.6. Why do many farmers combine organic and inorganic sources?
Show answer
Answer: Manure builds the soil over time, while fertiliser gives a quick supply of nutrients.Combination.
Lesson 3
- Strand
- Cycles
- Sub-strand
- Crop Production
- Indicator
- B7.2.3.1.2 – Describe the physical characteristics of different plant nutrients (organic and inorganic) and how each is applied to plants in the field
Introduction
A farmer who applies fertiliser wrongly can waste money or even burn the crops. Knowing what each nutrient source looks like and how to apply it is important.
1. Physical Characteristics
| Source | Appearance | Other features |
|---|---|---|
| farmyard manure | dark brown, bulky, moist | smells when fresh |
| poultry manure | grey-white droppings | strong smell; can burn plants if fresh |
| compost | dark, crumbly, earthy smell | well rotted, no smell of decay |
| NPK | small coloured granules (often grey or multicoloured) | dissolves in soil water |
| urea | white, round granules | dissolves quickly; can evaporate if left on the surface |
| sulphate of ammonia | white or grey crystals | slightly acidic |
2. Methods of Application
| Method | How it is done | Suitable for |
|---|---|---|
| broadcasting | scattering evenly over the field | rice, pastures, closely spaced crops |
| side placement (banding) | placing a band a few centimetres from plant rows | maize, cassava |
| ring application | spreading in a circle around the plant | cocoa, oil palm, citrus trees |
| spot (hole) placement | placing in a small hole near each plant | maize, yam, vegetables |
| foliar application | spraying dissolved fertiliser on leaves | vegetables, quick correction |
| incorporation | mixing manure into the soil before planting | most crops |
3. Rules for Applying Fertilisers
- Apply the correct amount recommended by extension officers.
- Do not let fertiliser touch leaves or stems, which can burn them.
- Apply when the soil is moist, not during heavy rain.
- Cover urea with soil to prevent loss.
- Wear gloves and wash hands after handling.
- Store fertilisers in a dry, safe place away from food.
4. Applying Organic Manure
Organic manure should be well decomposed before use. Fresh poultry manure is too strong and can burn roots. Manure is usually spread and mixed into the soil before planting, or placed around growing plants as a top dressing. Composting kills harmful germs and weed seeds.
New words
- broadcasting
- Scattering fertiliser evenly over a field.
- side placement
- Placing fertiliser beside crop rows.
- foliar application
- Spraying nutrients on leaves.
- extension officer
- An agricultural adviser who helps farmers.
Summary
- Nutrient sources differ in appearance, smell and how quickly they act.
- Methods of application include broadcasting, side placement, ring and spot placement, foliar spraying and incorporation.
- Apply correct amounts safely, avoid touching plants and use well-rotted manure.
Class activity: Fertiliser Application Demonstration
- Examine samples of compost and fertiliser granules.
- Demonstrate ring and side-placement methods on a school garden or model.
- Explain the safety rules.
You need: Compost sample, NPK fertiliser packet, Sealed cow-dung sample
Exercises
Answer in your exercise book first, then check your answers.
1. Spraying nutrients on leaves is…
- A. foliar application
- B. broadcasting
- C. ring application
- D. incorporation
Show answer
Answer: foliar applicationLeaves.2. Fertiliser for cocoa trees is usually applied by…
- A. ring application
- B. broadcasting
- C. foliar spraying only
- D. incorporation only
Show answer
Answer: ring applicationAround trees.3. Fresh poultry manure can burn plant roots.
- A. True
- B. False
Show answer
Answer: TrueToo strong.4. An agricultural adviser is an ______ officer.
Show answer
Answer: extensionHelps farmers.5. State three safety rules for applying fertiliser.
Show answer
Answer: Use the correct amount, keep it off leaves, wear gloves (or store safely, wash hands).Any three.6. Why should urea be covered with soil after application?
Show answer
Answer: It can change into gas and escape into the air if left on the surface, wasting nitrogen.Loss of nitrogen.
Homework
- Visit a farm or agro-input shop and list the nutrient sources seen and how they are applied.