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Organic fertilizer versus chemical fertilizer

Organic fertilizer versus chemical fertilizer

Introduction: (Initial Observation)

The cost of fertilizer is one of the most important expenses for many farmers and gardeners. Adding fertilizer to soil will substitute for the nutrients that are consumed by plants or that are washed away by rain.

There are many different types of fertilizers; however, in general you can divide them in two main categories of organic and inorganic fertilizers. To have a cost effective and competitive product farmers have to decide which fertilizer is best for them. In this project we will compare an organic fertilizer with an inorganic fertilizer to see which one gives farmers a better bang for their buck. (or which one is more cost effective).

In this project you will compare an organic fertilizer with an inorganic fertilizer and compare their productivity per unit of investment.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Gather information about fertilizers, their variety and their cost. Find out how big the fertilizer market is and how different fertilizers are made. Find local sources for obtaining fertilizer samples for your experiment.

Keep track of where you got your information from.

Following are samples of information that you may find.

Looking up the WikiPedia Free Encyclopedia gives the following result.

Fertilizers are chemicals given to plants with the intention of promoting growth; they are usually applied either via the soil or by foliar spraying.

Fertilizers typically provide, in varying proportions, the three major plant nutrients (nitrogen, phosphorus, and potassium), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, manganese, iron, zinc, copper and molybdenum.

The three primary ingredients of fertilizers are listed on the fertilizer bags as nitrogen, phosphate and potash as three numbers, indicating the ratios in that order. Thus a 5-10-5 fertilizer would have 10 percent phosphate in its ingredients.

Manure was once the dominant fertilizer, and is still used, but its role is greatly diminished. Fertilizer can be created either from natural organic material such as manure or compost (see also organic gardening), or artificially as through the Haber-Bosch process which produces ammonia. This ammonia is used to produce nitric acid. A reaction product of ammonia and nitric acid already gives Ammonium nitrate which is a fertilizer product. The nitric acid and ammonia also can be used in the Odda Process to produce compound fertilizers such as 15-15-15.

The Haber-Bosch process uses about one percent of the Earth’s total energy supply in order to provide half of the nitrogen needed in agriculture. Organic material has the advantage of adding carbon compounds to the soil. A major source of soil fertility is the decomposing crop residue from prior years, though this is not considered “fertilizer.”

Justus von Liebig wrote in 1840 the law of the minimum required by the plant.

Over-use of fertilizer can lead to algal blooms in lakes and streams that receive run-off from crop lands, and lead to long-term degradation of the soil; see in this regard eutrophication and nutrients. For these reasons, it is recommended that knowledge of the nutrient requirements of the soil vis-a-vis the crop precede applications of commercial fertilizer. In short, excess nutrient elements can cause local soil and off-site damage, as well as waste money.

World Fertilizer Market:

Fertilizer consumption has increased substantially over the last 40 years or so. Nitrogen fertilizers are in most demand worldwide and N consumption has increased the most-20 fold or more since 1950.

In the urbanized rich countries of the world, fertilizer is often seen either as a smelly problem that can ruin a visit to the countryside or as a dangerous chemical best avoided. However the annual world trade in fertilizers in the mid-1990s amounted to approximately 120 million tones – representing some 8% of all sea-borne bulk trade. The international fertilizer trade is a very big business, ranking fourth after iron, coal and grain by value.
Source: http://www.woodhead


With the growing interest in organic gardening, many companies have brought what they call “organic” or “natural” fertilizers to market, and you are likely to find one or more of them available at your local hardware store or garden center. You may also be able to order it online. This is a sample website: http://www.heirloomseeds.com/fertilizer.html

As a part of your study, find some websites of organic fertilizer manufacturers to see what do they claim about their products. This is a sample.
Note: Don’t believe all claims and marketing tactics.

Humus is a complex organic substance resulting from the breakdown of plant material in a process called humification. This process can occur naturally in soil, or in the production of compost. Humus is extremely important to the fertility of soils in both a physical and chemical sense (see below). Physically it helps the soil retain moisture and encourages the formation of good soil structure. Chemically, it has many active sites which bind to ions of plant nutrients, making them more available. Humus is often described as the ‘life-force’ of the soil. Yet it is difficult to define humus in precise terms; it is a highly complex substance, the full nature of which is still not fully understood. Physically humus can be differentiated from organic matter in that the latter is rough looking material, with coarse plant remains still visible, whilst once fully humified it become more uniform in appearance (a dark, spongy, jelly-like substance) and amorphous in structure. That is, it has no determinate shape, structure or character.

Compost is the decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture, mixed in with the soil. It improves soil structure, increases the amount of organic matter, and provides nutrients.

Compost is a common name for humus, which is the result of the decomposition of organic matter. Decomposition is performed primarily by microbes, although larger creatures such as worms and ants contribute to the process.

You may choose to grow tomato in the experiment section of this project. Following information may help.

Growing Tomato at home

1. Soil Preparation: Tomatoes are a delicate crop, so choose a warm spot in front of a south facing wall or fence to plant your tomatoes for the best results. During the winter, dig up your plot thoroughly (being careful not to bring clay or granite to the surface) and incorporate a good compost into your soil. Shortly before planting add a good source of fertilizer to the plot. If you lack ground space, you can easily grow excellent tomatoes in 2 gallon sized pots or grow bags, but remember to water them regularly. In addition, regular feeding with a good fertilizer will be necessary.

2. Sowing & Planting: Sow the seeds into a standard sized propagator filled with a good seed starting mix or compost. Before you sow your seeds dampen the soil in your propagator and allow it to sit overnight.

Sow one seed in each cell of the propagator by placing the seed on top of the soil in the center of the cell. Sprinkle a light cover of compost or seed starting mix over the seed. Cover the propagator with a cloak. Alternatively if only a few plants are required you may use a pot of any size and a home-made cloak.

To make a home-made cloak take a small, clear-plastic bottle and cut off the top part of the bottle. Small soda bottles cut at the top of the label are ideal for this purpose. Place the cloak over the sown area. Keep the soil moist, but not wet, for the best results. Keep the newly sown seeds at around 65 degrees for the most rapid growth. When the seeds have sprouted and matured into seedlings that are 6 inches high, transplant the seedlings into your plot, 2 gallon pots or grow bags.

3. Looking After the Plants : Tie the main stem of each plant to a cane or provide a cage for each plant. Water and feed the plants regularly, especially in hot weather, to keep the soil moist. Alternating dryness and flooding will lead to many problems, primarily split-fruit and blossom-end rot.

4. Harvesting : In about 90 days, pick the fruits when ripe and fully-colored. Always harvest the fruit with a sharp knife or pruners to avoid damaging the plant.

Tomato Culture
Tomatoes require a lot of fertilizer for best production. Work in 2-5 lb (0.9-2.3 kg) of 5-10-5 per 100 sq ft (9.3 sq m) before planting. Add lime if the soil pH is less than 6.0. (Call your county extension agent to find out how to get a soil pH test.)
Light: Tomatoes should be grown in full sun.
Moisture: Tomatoes should be watered before the soil dries out completely. Irregular watering can cause the fruit to split or crack and can also contribute to blossom-end rot.
Hardiness: Tomatoes are actually perennials in tropical climates, but gardeners in temperate climates grow them as warm season, frost-tender annuals. Tomato foliage is damaged by frost and freezing temperatures will kill the plant. Most varieties will not set fruit if nighttime temperatures fall below 50º F (10º C) or if daytime temperature stay above 90º F (32 ºC).
Propagation: Tomatoes are grown from seed and usually germinated indoors under controlled conditions, then grown for 5-8 weeks before setting out in the garden.

What is N-P-K?

  • When you look at a bag of fertilizer the label will have 3 numbers printed on the bag. They represent the combination of Nitrogen, Phosphorus and Potassium in the fertilizer.
  • Each number represents how many parts of each mineral is mixed in to produce the type of fertilizer in the bag. For example 5-10-5 means 5% Nitrogen, 10% phosphate and 5% potassium.


  • Nitrogen helps plants grow faster but too much of it will burn the roots and prevent flowering.
  • Too little nitrogen will make green leaves turn a lighter shade and cause the older leaves to turn yellow.
  • The best type of nitrogen-rich fertilizer should have Slow Release Formula printed on the bag label. It dissolves slowly so the plants don’t get too much nitrogen at once.


  • Phosphorus helps plants form new roots, develop seeds, fruits and flowers. It also increases a plant’s ability to resist diseases.
  • Plants that aren’t getting enough phosphorus will have darker old leaves or develop a reddish color.
  • The plant will start to produce poorer flowers and fruit when the soil needs more phosphorus.
  • It should be added to the soil when you are tilling because it tends to stay put in one spot.


  • Potassium helps increase a plant’s disease resistance and make the stems strong and keep it growing vigorously.
  • Too little potassium will show up as a general slowing of growth and leaves that are smaller than usual.
  • Potassium mixed into fertilizer will give plants the boost they need.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
Compare an organic fertilizer with an inorganic fertilizer to determine which one is more cost effective. Being cost effective means produce a better result while keeping the cost constant.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the type of fertilizer. Possible values are organic and inorganic. (While defining this variable, you may be more specific and specify the exact type and brand names as well)

Dependent variable (also known as responding variable) is the rate of plant growth. Factors such as plant height, number of leaves, size of leaves, color of leaves, size of fruits, number of fruits and the total dry mass of plant may be used as indications for plant growth. (you may select one or more factor).

Controlled variables are temperature, light, water and the cost of fertilizer.

Constants are plant type, soil type, soil volume.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Following is just a sample hypothesis:

Inorganic fertilizers are the most cost effective type.

My hypothesis is based on my gathered information about the large volume of production and market growth of inorganic fertilizers.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment: Tomato plants and fertilizers (organic and inorganic)

In this experiment you will grow two identical groups of tomato plants and use a different type of fertilizer for each group. One group will only use organic fertilizer and the other group will only use inorganic fertilizer.


Before you start planting tomato seeds or any other seeds, you need to have some basic information about planting seeds and the plant that you want to grow. Review some books or use the information provided in “Gathering Information” section (above) to familiarize yourself with this process.

Material Selection:

You will need one organic and one inorganic fertilizer to compare.

  • The organic fertilizer that you buy may be made of poultry feathers, manures and treated sewage sludge. Buy any one that is available to you and make sure that you know the weight, the coverage area and the price. You need about one pound organic fertilizer for your experiments.
  • The inorganic fertilizer that you select can have the N-P-K of 5-10-5 or any similar values. It does not matter if your fertilizer is solid or liquid. Again you need to know the weight, the coverage area and the price of the inorganic fertilizer that you purchase.


  1. Get 15 pots and place them in 3 groups of five.
    Label 5 pots with “Organic fertilizer” and number them from 1 to 5.
    Label 5 pots with “Inorganic fertilizer” and number them from 1 to 5.
    Label 5 pots with “Control group” and number them from 1 to 5.
  2. Fill up all 15 pots with low nutrient soil.
  3. Apply organic fertilizer to all the pots in organic fertilizer group as instructed by the manufacturer of fertilizer. Such instructions are usually printed on the packaging. The instructions may suggest to mix some fertilizer to the soil and add some additional fertilizer every week.
  4. Apply inorganic fertilizer to all the pots in inorganic fertilizer group as instructed by the manufacturer of fertilizer. Such instructions are usually printed on the packaging. The instructions may suggest to mix some fertilizer to the soil and add some additional fertilizer every week.
  5. Do not apply any fertilizer to the pots in the control group.
  6. Water all pots to moisten the soil. Cover the pots with plastic and let them stay in moist form for about one day.
  7. Plant one seed in each pot about 1/2″ deep.
  8. Continue daily observations, watering and adding fertilizer as suggested by the manufacturer for the period of your experiment. Record the condition of seedlings or young plants every day. Also keep track of the amount of fertilizer that you add to the pots. Make sure your plants get enough light and temperature of about 70º to 90º Celsius.
  9. At the end of your experiment period compare the size, and overall conditions of the plants in all 3 groups. Record your results and used them to draw your conclusion. Explain which fertilizer produced a better result. Which fertilizer costs more. Does the more expensive fertilizer produce a better result? Following is a sample results table for plant height.

Plant height in different groups in days 7, 14 and 21 after the experiment start.

Group Pot # Day 7 Day 14 Day 21
Organic Fertilizer 1
Inorganic Fertilizer 1
Control Group, No fertilizer 1

Variations/ suggestions:

Variations/ suggestions:

  • Use same strength fertilizer: Try to purchase same strength organic and inorganic fertilizers. For example you may purchase organic 5-10-5 and inorganic 5-10-5. Inorganic fertilizers can be found at higher strengths as well. For example you may find 10-20-10 fertilizer that is double strength as 5-10-5 fertilizer. In other words one pound 10-20-10 has the same amount of nutrients as two pounds 5-10-5.
  • Use same cost fertilizer: Using the instructions suggested by the manufacturer calculate the cost of each fertilizer per square foot. Find out which fertilizer will cost more if used according to the instructions. Reduce the use ratio of the more expensive fertilizer to bring the cost down and make it equal to the less expensive fertilizer. In this way dollar amount of fertilizers used in two main experiment groups will be equal.
  • If you are doing this experiment in winter, you must do it indoor and control the temperature in about 70º to 90º. Fluorescent lights is a good source of light for plants. Light should be placed about 10 inches above the plants.

Note: if you really have a few months for your experiment and want to grow real tomatoes, you will need to transplant the seedlings to larger pots when they are about 7″ tall. Each mature tomato plant need a 10-gallon or larger pot. Transplanting must be done with enough care and without any damage to the roots of young plants. Most students may compare the effect of fertilizer in about 2 to 4 weeks and that will not be enough for tomato plants to fruit.

Materials and Equipment:

Following are suggested list of material. You may change this list based on the material and equipment that are available to you.

  • 15 same size ceramic or plastic pots. 1/2 Gallon pots are good for start. If you don’t have access to pots, use Styrofoam cups or use the bottom half of 2-Liter soda bottles instead. Pots must have a hole at the bottom to drain excess water.
  • 15 plates to be placed under the pots.
  • Low nutrient soil. A mixture of sand and clay may be used as a low nutrient soil. A low nutrient soil is free from organic mater. A mixture of sand and paper towel may simulate a soil that is free from nutrients. Clay and paper towel are material that can hold moisture needed for the plant to grow. Calculate the amount of soil based on the size of your pots.
  • Any organic fertilizer. Try to find a 5-10-5 mix.
  • Any inorganic fertilizer. Try to find a 5-10-5 mix or 10-20-10 mix.
  • Tomato seeds.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


If you do any calculations to determine the amount of fertilizer or the cost of fertilizer, write your calculations in this section of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find books related to botany, gardening or farming with information about soil quality and fertilizers. You may also use some Internet resources such as the following two websites.