.jpeg "Calculating Fertilizer Quantities for a Hectare for crops")
A Step by Step Method for Fertilizing Tomatoes, Potatoes, and Garlic
![Image: A wide agricultural field with various crops and a farmer checking the soil]
One day, an old farmer came to me with a simple question. "Doctor Samir, I apply fertilizer every season, but I never know if I am applying too little or too much. I need a clear method to calculate what my land actually needs."
That simple question is your passport to understanding one of the most important secrets of successful farming. Many farmers apply fertilizers randomly. They buy whatever is available in the market and apply it hoping it will be enough. The result is always the same. Either a deficiency that weakens the crop, or an excess that wastes money and pollutes the soil.
In this guide, I will teach you the correct method for calculating fertilizer quantities per hectare, with practical examples for three important crops: tomatoes, potatoes, and garlic. My promise to you is that after reading this article, you will be able to calculate the needs of any crop by yourself.
![Image: A wide agricultural field with various crops and a farmer checking the soil]
One day, an old farmer came to me with a simple question. "Doctor Samir, I apply fertilizer every season, but I never know if I am applying too little or too much. I need a clear method to calculate what my land actually needs."
That simple question is your passport to understanding one of the most important secrets of successful farming. Many farmers apply fertilizers randomly. They buy whatever is available in the market and apply it hoping it will be enough. The result is always the same. Either a deficiency that weakens the crop, or an excess that wastes money and pollutes the soil.
In this guide, I will teach you the correct method for calculating fertilizer quantities per hectare, with practical examples for three important crops: tomatoes, potatoes, and garlic. My promise to you is that after reading this article, you will be able to calculate the needs of any crop by yourself.
Before We Start
Why Do Fertilizer Calculations Fail?
Most of the problems I see in the fields are not caused by lack of experience. They are caused by three common mistakes:
Relying on ready made recipes without considering that every piece of land is different
Ignoring soil testing and treating the land like a black box
Not understanding fertilizer composition and confusing different products
Let us start from the beginning and build correct knowledge.
Most of the problems I see in the fields are not caused by lack of experience. They are caused by three common mistakes:
Relying on ready made recipes without considering that every piece of land is different
Ignoring soil testing and treating the land like a black box
Not understanding fertilizer composition and confusing different products
Let us start from the beginning and build correct knowledge.
Part One
Understanding the Language of Fertilizers
![Image: Different fertilizer bags with NPK and different percentages written on them]
Before you calculate anything, you must understand what the numbers written on a fertilizer bag actually mean.
![Image: Different fertilizer bags with NPK and different percentages written on them]
Before you calculate anything, you must understand what the numbers written on a fertilizer bag actually mean.
The Secret of Three Letters: NPK
Every fertilizer bag you find in the market has three numbers written on it, for example 10-10-10 or 20-20-20. These numbers are not for decoration. They are the language that fertilizers speak.
The first number (N): The percentage of nitrogen, responsible for leaf and stem growth
The second number (P): The percentage of phosphorus, responsible for root and flower growth
The third number (K): The percentage of potassium, responsible for fruit quality and disease resistance
A Clear Example:
A bag marked 15-15-15 means that every 100 kilograms of this fertilizer contains:
15 kg of nitrogen
15 kg of phosphorus (expressed as phosphorus pentoxide P2O5)
15 kg of potassium (expressed as potassium oxide K2O)
The remaining 55 kg are filler materials or carriers
Every fertilizer bag you find in the market has three numbers written on it, for example 10-10-10 or 20-20-20. These numbers are not for decoration. They are the language that fertilizers speak.
The first number (N): The percentage of nitrogen, responsible for leaf and stem growth
The second number (P): The percentage of phosphorus, responsible for root and flower growth
The third number (K): The percentage of potassium, responsible for fruit quality and disease resistance
A Clear Example:
A bag marked 15-15-15 means that every 100 kilograms of this fertilizer contains:
15 kg of nitrogen
15 kg of phosphorus (expressed as phosphorus pentoxide P2O5)
15 kg of potassium (expressed as potassium oxide K2O)
The remaining 55 kg are filler materials or carriers
Types of Fertilizers by Speed
Fertilizers are divided into two main types, and choosing the right type makes a big difference:
Type Characteristics When to Use Compound fertilizer (granules) Dissolves slowly, effect lasts for months Added to soil before planting Liquid fertilizer Absorbed quickly, immediate effect Used during growth as supplemental doses Organic fertilizer Improves soil properties, slow effect Added before planting to improve soil
Fertilizers are divided into two main types, and choosing the right type makes a big difference:
| Type | Characteristics | When to Use |
|---|---|---|
| Compound fertilizer (granules) | Dissolves slowly, effect lasts for months | Added to soil before planting |
| Liquid fertilizer | Absorbed quickly, immediate effect | Used during growth as supplemental doses |
| Organic fertilizer | Improves soil properties, slow effect | Added before planting to improve soil |
Part Two
The Golden Rule: Start with a Soil Test
![Image: A farmer taking a soil sample in a plastic bag]
This point is the most important in the entire article. Without a soil test, you are groping in the dark.
What Does a Soil Test Tell You?
The percentage of basic elements already present in the soil
The pH level which affects nutrient absorption
The soil type and how well it retains water and fertilizers
How to Take a Correct Sample?
Walk through the field in a zigzag pattern
Take samples from 10 to 15 different locations
Dig to a depth of 20 to 30 centimeters
Mix all the samples together in a clean bag
Take one kilogram of this mixture and send it to the laboratory
My Advice: Do this at least once every year. The cost of testing is very small compared to what you save on fertilizers and what you gain from better production.
![Image: A farmer taking a soil sample in a plastic bag]
This point is the most important in the entire article. Without a soil test, you are groping in the dark.
What Does a Soil Test Tell You?
The percentage of basic elements already present in the soil
The pH level which affects nutrient absorption
The soil type and how well it retains water and fertilizers
How to Take a Correct Sample?
Walk through the field in a zigzag pattern
Take samples from 10 to 15 different locations
Dig to a depth of 20 to 30 centimeters
Mix all the samples together in a clean bag
Take one kilogram of this mixture and send it to the laboratory
My Advice: Do this at least once every year. The cost of testing is very small compared to what you save on fertilizers and what you gain from better production.
Part Three
Tomato Fertilizer Requirements
![Image: A tomato field with red ripe fruits]
Tomatoes are among the crops that respond wonderfully to good fertilization. They are like a professional athlete, they need complete nutrition at the right time.
![Image: A tomato field with red ripe fruits]
Tomatoes are among the crops that respond wonderfully to good fertilization. They are like a professional athlete, they need complete nutrition at the right time.
Basic Tomato Requirements
For one hectare, tomatoes need:
Element Quantity Required Per Hectare Nitrogen (N) 150 kilograms Phosphorus (P2O5) 75 kilograms Potassium (K2O) 150 kilograms
For one hectare, tomatoes need:
| Element | Quantity Required Per Hectare |
|---|---|
| Nitrogen (N) | 150 kilograms |
| Phosphorus (P2O5) | 75 kilograms |
| Potassium (K2O) | 150 kilograms |
How to Convert These Numbers into Actual Fertilizer?
Suppose you bought a compound fertilizer 15-15-15. How do you calculate the quantity you need?
First: To calculate the amount of compound fertilizer needed to provide nitrogen
Every 100 kg of 15-15-15 fertilizer gives you 15 kg of nitrogen.
To get 150 kg of nitrogen, you need:
(150 × 100) ÷ 15 = 1000 kg of compound fertilizer
Second: What about phosphorus and potassium?
The same 1000 kg quantity will also give you:
150 kg of phosphorus (more than the 75 kg requirement)
150 kg of potassium (exactly matching the requirement)
This means that 15-15-15 compound fertilizer will give you more phosphorus than needed. This is not a big mistake, but it is a waste of money. The ideal solution is to use a compound fertilizer with different ratios, such as 20-10-20.
Suppose you bought a compound fertilizer 15-15-15. How do you calculate the quantity you need?
First: To calculate the amount of compound fertilizer needed to provide nitrogen
Every 100 kg of 15-15-15 fertilizer gives you 15 kg of nitrogen.
To get 150 kg of nitrogen, you need:
(150 × 100) ÷ 15 = 1000 kg of compound fertilizer
Second: What about phosphorus and potassium?
The same 1000 kg quantity will also give you:
150 kg of phosphorus (more than the 75 kg requirement)
150 kg of potassium (exactly matching the requirement)
This means that 15-15-15 compound fertilizer will give you more phosphorus than needed. This is not a big mistake, but it is a waste of money. The ideal solution is to use a compound fertilizer with different ratios, such as 20-10-20.
Fertilizer Application Timing (The Most Important Part)
Tomatoes do not eat all their needs at once. The correct split is:
Stage Percentage of Total Fertilizer At planting time 30% After the first fruit set 40% When fruits reach half their size 30%
Practical Application:
If the total quantity is 1000 kg of fertilizer:
First time: 300 kg with planting
Second time: 400 kg after fruit set
Third time: 300 kg when fruits reach half size
Tomatoes do not eat all their needs at once. The correct split is:
| Stage | Percentage of Total Fertilizer |
|---|---|
| At planting time | 30% |
| After the first fruit set | 40% |
| When fruits reach half their size | 30% |
Practical Application:
If the total quantity is 1000 kg of fertilizer:
First time: 300 kg with planting
Second time: 400 kg after fruit set
Third time: 300 kg when fruits reach half size
Part Four
Potato Fertilizer Requirements
![Image: A potato field with large tubers]
Potatoes are completely different. They grow underground, so they need special focus on phosphorus to strengthen roots and tubers.
![Image: A potato field with large tubers]
Potatoes are completely different. They grow underground, so they need special focus on phosphorus to strengthen roots and tubers.
Basic Potato Requirements
For one hectare, potatoes need:
Element Quantity Required Per Hectare Nitrogen (N) 150 to 200 kilograms Phosphorus (P2O5) 80 to 120 kilograms Potassium (K2O) 200 to 250 kilograms
Notice that potassium is required in larger quantities than for tomatoes, because potatoes need potassium to form large tubers and achieve high storage quality.
For one hectare, potatoes need:
| Element | Quantity Required Per Hectare |
|---|---|
| Nitrogen (N) | 150 to 200 kilograms |
| Phosphorus (P2O5) | 80 to 120 kilograms |
| Potassium (K2O) | 200 to 250 kilograms |
Notice that potassium is required in larger quantities than for tomatoes, because potatoes need potassium to form large tubers and achieve high storage quality.
Choosing the Right Fertilizer
The most suitable compound fertilizer for potatoes is 10-10-20 or 12-12-24. Notice the high potassium percentage in the third number.
Calculation Example Using 10-10-20 Fertilizer:
To get 150 kg of nitrogen from this fertilizer:
(150 × 100) ÷ 10 = 1500 kg of compound fertilizer
This quantity will also give you:
150 kg of phosphorus (suitable)
300 kg of potassium (slightly above requirement)
The most suitable compound fertilizer for potatoes is 10-10-20 or 12-12-24. Notice the high potassium percentage in the third number.
Calculation Example Using 10-10-20 Fertilizer:
To get 150 kg of nitrogen from this fertilizer:
(150 × 100) ÷ 10 = 1500 kg of compound fertilizer
This quantity will also give you:
150 kg of phosphorus (suitable)
300 kg of potassium (slightly above requirement)
Potato Fertilizer Timing
Stage Percentage of Total Fertilizer Before planting (in the soil) 50% 30 days after planting 25% 60 days after planting 25%
Important Warning: Potatoes are very sensitive to salinity. Do not place fertilizer too close to the tubers to avoid root burn.
| Stage | Percentage of Total Fertilizer |
|---|---|
| Before planting (in the soil) | 50% |
| 30 days after planting | 25% |
| 60 days after planting | 25% |
Important Warning: Potatoes are very sensitive to salinity. Do not place fertilizer too close to the tubers to avoid root burn.
Part Five
Garlic Fertilizer Requirements
![Image: A garlic crop with large bulbs and green plants]
Garlic is a unique crop. Its season is long, and it needs special care in fertilization. Mistakes in garlic fertilization lead to small bulbs that are not worth the cost of seeds.
![Image: A garlic crop with large bulbs and green plants]
Garlic is a unique crop. Its season is long, and it needs special care in fertilization. Mistakes in garlic fertilization lead to small bulbs that are not worth the cost of seeds.
Basic Garlic Requirements
For one hectare, garlic needs:
Element Quantity Required Per Hectare Nitrogen (N) 120 to 150 kilograms Phosphorus (P2O5) 60 to 80 kilograms Potassium (K2O) 150 to 200 kilograms
The ideal ratio between elements is 1 : 2 : 2.5 (nitrogen : phosphorus : potassium).
For one hectare, garlic needs:
| Element | Quantity Required Per Hectare |
|---|---|
| Nitrogen (N) | 120 to 150 kilograms |
| Phosphorus (P2O5) | 60 to 80 kilograms |
| Potassium (K2O) | 150 to 200 kilograms |
The ideal ratio between elements is 1 : 2 : 2.5 (nitrogen : phosphorus : potassium).
Garlic Fertilizer Timing
This point specifically makes the difference between a successful farmer and a failed one. Garlic needs fertilization at precisely defined times:
Stage Percentage of Total Fertilizer Before planting (in the soil) 30% 30 days after planting 20% 60 days after planting 20% 90 days after planting 15% 120 days after planting 15%
Why This Split?
Garlic has a long season (about 6 months). If you apply all the fertilizer at the beginning, you will lose a lot of it before the plants need it during the bulb formation stage.
This point specifically makes the difference between a successful farmer and a failed one. Garlic needs fertilization at precisely defined times:
| Stage | Percentage of Total Fertilizer |
|---|---|
| Before planting (in the soil) | 30% |
| 30 days after planting | 20% |
| 60 days after planting | 20% |
| 90 days after planting | 15% |
| 120 days after planting | 15% |
Why This Split?
Garlic has a long season (about 6 months). If you apply all the fertilizer at the beginning, you will lose a lot of it before the plants need it during the bulb formation stage.
Important Warning for Garlic
Excess nitrogen in the second half of the season causes a big problem. You will get dense green leaves but small bulbs. The plant puts all its energy into the leaves and forgets the bulbs underground.
Excess nitrogen in the second half of the season causes a big problem. You will get dense green leaves but small bulbs. The plant puts all its energy into the leaves and forgets the bulbs underground.
Part Six
Quick Reference Tables for Daily Calculations
To make things easier for you in the field, here are quick tables you can refer to.
To make things easier for you in the field, here are quick tables you can refer to.
Table 1: Amount of Compound Fertilizer Required Per Hectare (Using 15-15-15 Fertilizer)
Crop Total Fertilizer Quantity Notes Tomatoes 1000 kg Distributed over 3 doses Potatoes 1500 kg Distributed over 3 doses Garlic 1000 kg Distributed over 5 doses
| Crop | Total Fertilizer Quantity | Notes |
|---|---|---|
| Tomatoes | 1000 kg | Distributed over 3 doses |
| Potatoes | 1500 kg | Distributed over 3 doses |
| Garlic | 1000 kg | Distributed over 5 doses |
Table 2: Fertilizer Quantity Per Feddan (For Egyptian and Arab Farmers)
Because many farmers deal with feddans rather than hectares, here are the quantities per feddan (one feddan equals approximately 0.42 hectares).
Crop Fertilizer Quantity Per Feddan Tomatoes 400 to 450 kg Potatoes 600 to 650 kg Garlic 400 to 450 kg
Because many farmers deal with feddans rather than hectares, here are the quantities per feddan (one feddan equals approximately 0.42 hectares).
| Crop | Fertilizer Quantity Per Feddan |
|---|---|
| Tomatoes | 400 to 450 kg |
| Potatoes | 600 to 650 kg |
| Garlic | 400 to 450 kg |
Table 3: Nutrient Deficiency Indicators
Element Deficiency Signs Nitrogen Pale yellow leaves, starting from lower leaves Phosphorus Purple or violet leaves, weak roots Potassium Leaf tips yellow then brown and burnt Iron Upper leaves yellow with green veins
| Element | Deficiency Signs |
|---|---|
| Nitrogen | Pale yellow leaves, starting from lower leaves |
| Phosphorus | Purple or violet leaves, weak roots |
| Potassium | Leaf tips yellow then brown and burnt |
| Iron | Upper leaves yellow with green veins |
Part Seven
Five Common Fertilization Mistakes
From following hundreds of farmers, these are the five most common mistakes I see them repeating:
From following hundreds of farmers, these are the five most common mistakes I see them repeating:
Mistake 1: Applying Fertilizer and Leaving It on the Soil Surface
Nitrogen fertilizer especially evaporates if left on the surface under the sun. Always mix fertilizer with the soil.
Nitrogen fertilizer especially evaporates if left on the surface under the sun. Always mix fertilizer with the soil.
Mistake 2: Watering Immediately After Applying Dry Fertilizer
Fertilizer needs time to dissolve. Immediate watering may wash it away from the root zone.
Fertilizer needs time to dissolve. Immediate watering may wash it away from the root zone.
Mistake 3: Excess Nitrogen Late in the Season
As we said with garlic, this causes dense leaves and small fruits.
As we said with garlic, this causes dense leaves and small fruits.
Mistake 4: Neglecting Micronutrients
Iron, zinc, and manganese are very important, especially in calcareous and sandy soils.
Iron, zinc, and manganese are very important, especially in calcareous and sandy soils.
Mistake 5: Using the Same Fertilization Program Every Year
The land changes. Each crop pulls different elements. Test the soil every year and adjust your calculations.
The land changes. Each crop pulls different elements. Test the soil every year and adjust your calculations.
Part Eight
Practical Tips from Real Experience
Tip 1: Start with Less Then Increase
It is better to start with a quantity lower than recommended, then observe the plants and increase if needed. Excess fertilizer cannot be recovered.
Tip 2: Observe Your Plants
Plants talk. Yellow leaves, slow growth, deformed fruits are all messages. Learn their language.
Tip 3: Keep a Record
Write everything down. Planting date, fertilizer quantities, application times, results. After two seasons you will have your own guide specific to your land.
Tip 4: Distribute Fertilizer Evenly
Do not put all the fertilizer in one row. Distribute it along the line or field. Uneven distribution means strong plants here and weak plants there.
**Tip 5: Do Not Forget Organic Fertilizer
Animal manure or compost is not a replacement for chemical fertilizer, but it is an excellent supplement. It improves soil properties and helps retain water and nutrients.
Tip 1: Start with Less Then Increase
It is better to start with a quantity lower than recommended, then observe the plants and increase if needed. Excess fertilizer cannot be recovered.
Tip 2: Observe Your Plants
Plants talk. Yellow leaves, slow growth, deformed fruits are all messages. Learn their language.
Tip 3: Keep a Record
Write everything down. Planting date, fertilizer quantities, application times, results. After two seasons you will have your own guide specific to your land.
Tip 4: Distribute Fertilizer Evenly
Do not put all the fertilizer in one row. Distribute it along the line or field. Uneven distribution means strong plants here and weak plants there.
**Tip 5: Do Not Forget Organic Fertilizer
Animal manure or compost is not a replacement for chemical fertilizer, but it is an excellent supplement. It improves soil properties and helps retain water and nutrients.
Frequently Asked Questions
Q: Do the same calculations apply to greenhouse cultivation?
A: No, greenhouses are different. Planting density is higher, and water is limited, so you need more precise calculations. Requirements are usually 20 to 30% higher.
Q: How do I know the right fertilizer type for my soil?
A: Soil testing is the only accurate method. Without it, you are only guessing.
Q: What should I do if I applied too much fertilizer?
A: Wash the soil with plenty of water to flush out excess salts. In sensitive crops, you may lose the plants if the damage is severe.
Q: Can I mix different types of fertilizers?
A: Yes, but be careful of reactions. Do not mix nitrogen fertilizers with lime for example. Ask an agricultural engineer before mixing.
Q: How often should I test my soil?
A: At least once every year. If you grow intensive crops, every 6 months is better.
Q: Do the same calculations apply to greenhouse cultivation?
A: No, greenhouses are different. Planting density is higher, and water is limited, so you need more precise calculations. Requirements are usually 20 to 30% higher.
Q: How do I know the right fertilizer type for my soil?
A: Soil testing is the only accurate method. Without it, you are only guessing.
Q: What should I do if I applied too much fertilizer?
A: Wash the soil with plenty of water to flush out excess salts. In sensitive crops, you may lose the plants if the damage is severe.
Q: Can I mix different types of fertilizers?
A: Yes, but be careful of reactions. Do not mix nitrogen fertilizers with lime for example. Ask an agricultural engineer before mixing.
Q: How often should I test my soil?
A: At least once every year. If you grow intensive crops, every 6 months is better.
The Bottom Line
Calculating fertilizer quantities is not a difficult science, but it needs accuracy and observation. Start with a soil test, understand the needs of the crop you are growing, choose the right fertilizer, and split the quantities over the growth stages.
Tomatoes need balance between the three elements.
Potatoes need higher potassium to form large tubers.
Garlic needs fertilization split over long periods and less nitrogen in the second half of the season.
Always remember that the goal is not to apply the largest amount of fertilizer, but to apply the right amount at the right time. Excess fertilizer wastes your money, pollutes the environment, and harms the plants themselves.
God grant success.
Dr. Samir El-Zohiri
Researcher and Consultant in Plant Physiology and Crop Management
Over 15 years of experience helping farmers improve their production
Calculating fertilizer quantities is not a difficult science, but it needs accuracy and observation. Start with a soil test, understand the needs of the crop you are growing, choose the right fertilizer, and split the quantities over the growth stages.
Tomatoes need balance between the three elements.
Potatoes need higher potassium to form large tubers.
Garlic needs fertilization split over long periods and less nitrogen in the second half of the season.
Always remember that the goal is not to apply the largest amount of fertilizer, but to apply the right amount at the right time. Excess fertilizer wastes your money, pollutes the environment, and harms the plants themselves.
God grant success.
Dr. Samir El-Zohiri
Researcher and Consultant in Plant Physiology and Crop Management
Over 15 years of experience helping farmers improve their production
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