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Effect of Fertilizers on the Environment

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Since the rising problem in our environment involves water contamination and unhealthy water, which mainly occurs due to the washing away of fertilizers. However there are two different types of fertilizers: Organic and Inorganic fertilizers, both of many kinds, with different effects. Thus, I decided to research on this question: "How is the effect of the nitrogen and phosphorus ions in organic fertilizers different from the effect of nitrogen and phosphorus ions contained in inorganic fertilizers on the environment, with respect to their contribution in water contamination and oxygen reduction?" I will analyze how the effect of the nitrogen and phosphorus ions on the environment is different when they are in organic fertilizers compared to the case when they are contained in inorganic fertilizers. We will make our evaluation based on their respective contributions in water contamination and oxygen reduction.

To carry out this research, first of all I had to find out what causes oxygen reduction in the water, and how it is caused. Then I had to check whether and to what extent the fertilizers could be responsible for oxygen reduction. Moreover I had to figure out that in which fertilizer water bacteria could convert into their nutrients more effectively. This whole research led me to conclusion that natural (organic) fertilizers are much better than inorganic ones, because inorganic fertilizers have more amounts of phosphates and nitrate ions, which are the main causes of deoxygenation of water.

To understand the topic and write this article, I did extensive study of the available resources, including relevant websites, Wikipedia, and the published articles and a few books covering this topic. I also gained some information while in discussion with my supervisor and conducted an experiment for primary data. I also used a few books for the research.


Importance of Water

Water is an important substance which we need in our daily lives. It is the basic need of every living thing. We use it for different purposes, such as drinking, cooking, cleaning, farming, while industries use huge amounts of it of it to produce products. Most of the water we use is fresh water; however 97% of the Earth's water body is saltwater. The rest being fresh, comes in the form of Surface water (rivers, lakes and streams), ground water (springs), and mainly glaciers and ice caps. Fresh water can also obtained by a process called desalination, in which salt water is converted to fresh water; however because this process is quite expensive ("Water Resources," 2013, para. 2), we tend to use the water from other alternate and natural sources of fresh water, especially the surface water.

Fresh water, however, is becoming less and less clean. It is being contaminated in several different ways, such as industrial waste being drained into water, DDT being sprayed into water for pest control reasons, and the running off of fertilizers in the water bodies. Ongley (1996) mentioned that the statistical studies conducted by Czechoslovakia found agriculture as the single largest contributor, with a share of 48%, of the overall pollution of the surface water (p.3).

Consequences of Water Pollution:

This pollution of water results in harmful effects to the environment and human health. As water becomes deoxygenated and contaminated, marine life is affected and many of it dies. People also drink that water, and so do their livestock and this can have adverse health effects on both as they are exposed to different chemicals.

Types of fertilizers:

There are two main types of fertilizers: Organic and Inorganic. Organic being natural origins of either plant or animal, while inorganic being produced through chemical processes or originated from minerals. (International Rice Research Institute, 2009).

Fertilizers are used in certain amounts for agriculture to increase crop yield and for healthy growth. However excess amounts can be leached off and drained into the surface water and /or groundwater. This causes problems such as eutrophication which results in algal blooms and later loss of oxygen in water which is a threat for aquatic life and the later users of this water. The main components of both Organic and Inorganic fertilizers are Nitrogen and Phosphorus, however inorganic fertilizers have controlled amounts of specific ions, whereas in organic fertilizers the amount/ levels of every compound varies and has different ions available in it.

In next section of this report, I will give a comparison of the both types of fertilizers mentioned above in terms of their impact on the environment. In particular, I will find how the effect of the nitrogen and phosphorus ions in organic fertilizers (in particular potting soil/ compost and manure) is different from the effect of nitrogen and phosphorus ions contained in inorganic fertilizers (NPK) on the environment, with respect to their contribution in water contamination and oxygen reduction?"

For this essay I am first going to find direct effect of bacteria on water and how it especially contributes to the deoxygenation of water. In order to be able to find that out, I carried out an experiment.


What is the effect on the BOD (Biological Oxygen Demand) of distilled water when treated with organic or inorganic fertilizer directly?


The DO concentration less for inorganic fertilizers than organic fertilizers, as organic fertilizers tend to settle down and have less amounts of nutrients in them as compared to inorganic fertilizers. So more bacteria will consume more nutrients from the inorganic fertilizer, and therefore more respiration will occur, resulting in the deoxygenation of water.

Control Variables:

The mass of the fertilizers (in grams) was a control variable, and so is the amount of water (volume in ml). I took 1.5 grams of fertilizer, and the water was filled to brim of the flasks. The control temperature was around 30.

Dependent variable:

The dependent variable in this experiment was the Dissolved oxygen (DO) concentration in the water after the fertilizer had been added.

Independent variable:

The independent variables are the fertilizers. I am going to be comparing their effect on the water and its deoxygenation.


  • Conical flasks (4) [500ml]
  • Organic Fertilizer, compost
  • Inorganic Fertilizer, NPK(14:14:14)
  • DO sensors (measures in mg/L)
  • Data logger
  • Distilled water
  • Measuring balance
  • Corks (4)
  • Beaker [500 ml]


First I set up the DO sensor and data logger and put in the beaker filled with distilled water for warming up. We have to keep it in there for ten minutes before being able to get the final result. We will use this value as the control value.

First I put a piece of tissue on the measuring balance. Then I calibrate the measuring balance to zero. Then I add the inorganic fertilizer on top of the tissue till it reads 1.5 grams. Then I add the fertilizer into one of the flasks.

I do the same for another 1.5 grams of organic and for two 1.5 grams of inorganic fertilizers.

Then I fill all the conical flasks to brim with distilled water (to make sure no air is left trapped). Then I stirred the water in the flask to mix the fertilizer as properly as possible. Then I took the DO measurement of the distilled water by stirring the DO sensor in the beaker filled with water. Then I stirred the DO sensor into the flasks to take down the initial readings.

Then I put the cork on and place all of the flasks in the cupboard. This is done to prevent the bacteria from having sunlight, this to prevent algal growth in water (so that no photosynthesis occurs, and no oxygen is produced; which is done to determine the value of oxygen depleted). The control water in beaker is also kept into the dark.

Then I took the final reading of all the flasks five days later, to check how much oxygen each of it had lost. I opened the corks and set up the DO sensor, that is warmed it up for ten minutes in a beaker of distilled water).

Then I took down the final DO concentration of the water in each flask.

The time taken to do this experiment was 20 minutes, plus 5 minutes for clearing up stuff, excluding the 5 days. So, in total the time taken was 5 days and 50 minutes. Also we have to make sure that when we stir the sensor in each flask or beaker, we have to clean sensor before putting it in the other.

Data collection and processing:


As we can see by comparing these graph that the average final value is way less than the average DO value needed for the water. The DO value needed for water to be stable is 7.56 mg/L at 30. However, water suffering from hypoxia (dangerously low level of dissolved and thus is not able to support life) has to have a DO value below 2 mg/L. This characteristic can only be noted in the flasks that contained the organic fertilizers. The other flasks also experienced a decrease in the DO concentration, however the change was not as significant as that of the organic fertilizer, and it certainly does not show signs of hypoxia. We can also notice from the graphs that the some of the oxygen is also lost naturally, but it is not a very huge amount and it usually maintains its balance.

Conclusion and Evaluation:

What is the effect on the BOD (biological Oxygen Demand) of distilled water when treated with organic or inorganic fertilizer directly?

As we can see that the results are completely opposite to that of the Hypothesis. I hypothesized that the inorganic fertilizer would lead to lower concentrations of DO, rather the organic one. In fact, an opposite pattern was observed. This experiment shows little support for my hypothesis. There could many reasons for this, but the basic and main reason could be presence of bacteria in the compost itself. The compost may already be present with a lot of bacteria and therefore because of the abundance of bacteria, more nutrients and food was consumed and it was consumed faster (It was consumed faster because of the amount of competition was more and they were competing for survival reasons). With the consumption of food by so many bacteria, more respiration took place and thus more oxygen was used up. This may have been the main of oxygen decline in the water. Also in the flask containing inorganic fertilizers, there were fewer bacteria, causing there to be enough food and thus the oxygen consumption was not as low.

Another reason might be that they weren't put under normal conditions and also that there was not much time to check for all different conditions over a long period of time. That would have given us better results. For example, if we had also put two more sample flasks out in the open that would have shown us algal growth, increase in oxygen and then its decrease. This would have given us the more appropriate result. Secondly these are the results of the effect of fertilizers directly on water. Fertilizers are not directly thrown into water. They are leached into it. So we do not exactly know how much is leached into the water and that's another factor that is needed to be considered.

So it seems, in the short-term, organic fertilizers contribute much more to the deoxygenation of water than inorganic fertilizer (given that no photosynthesis has taken place, and/or no sunlight has been given).

As mentioned already, fertilizers are not thrown into the lakes and/or water bodies directly. They are put onto the land with the intention of providing the crops, or fields with appropriate nutrients, in order to ensure good crop yield and healthy plants. This however leads to the leaching of the fertilizer, that is the fertilizer is drained into the water bodies. This means that leaching is directly proportional to solubility of the object.

We are all also well aware that farmers usually spray the fields' land with water, with the rare exception of occasional urine sprays. In the case of the rare exception they still use water and use urine occasional rather than regularly. As we know, organic compounds are not soluble in polar liquids and while inorganic compounds are.

This shows that due to water being a polar compound, inorganic fertilizer is more easily leached into the water bodies. This thereby increases the risk of the water bodies being more contaminated through inorganic than inorganic. According to Inckel (1999), compost plays a big part increasing the soil quality, which makes the more able to retain water.(p. 41-42) This means that less water is leached due to more water being retained, which also means that organic fertilizer is leached into the water body.

However, farmers mostly tend to use inorganic fertilizers to obtain quicker results and higher yields, as inorganic can be easily applied while using the organic takes time. Obviously a fertilizer has to be soluble in order for the plants to be able to consume it.

So therefore when compost is applied on to the soil, bacteria decompose it slowly, releasing the nutrients. That's why compost is supposed to be kept wet, so that as soon as the nutrients are released they could be absorbed by the plant quickly. This slow process of nutrients being released ensures that fewer nutrients are leached away, because as soon as the nutrients will be released from the inorganic compound, they would be directly taken in by the plant, as the process of decomposition is slow. Also if it some is leached, it would be very little, quite an insignificant amount. Because as the nutrients are slowly released in organic fertilizers, and plants are in continuous need of nutrients, they would quickly absorb the little that is produced due to the slow decomposition of the compounds, therefore there is a lesser chance of the nutrients being leached away.

While, on the other hand, inorganic fertilizers are quickly leached because they do not need to be decomposed and when in contact with water, some of it is absorbed by the plant, while some is leached away.

This shows that inorganic fertilizers are more prone to being leached into the water bodies, thus being more of a threat to the water.

Also according to my research question I am going to be looking specifically at the effect of Phosphorus and Nitrogen compounds of each fertilizer on the water.

In order to do that, first I will explain how and what causes the waters contamination and/ or decrease in oxygen. "Water becomes contaminated when pollutants such as fertilizers are discharged into the water, without adequate treatment to remove them" ("Water Pollution," 2013, para. 1). Water can be contaminated by fertilizers through many ways, but happens mainly through leaching. Then comes the process of eutrophication.

In this process, the water bodies are enriched with excessive nutrients, causing an overgrowth in the plant life and algal blooms. As algal blooms and water plants increase great amounts of oxygen is used up. This therefore causes a decrease in the amount of oxygen. Soon when they die, the bacteria decompose them and more oxygen is used up (Mackean, 2002, p. 238). This causes the water to be deoxygenated.

The condition of hypoxia occurs when the water has too low oxygen levels, usually at the amount of 2mg/L. (Committee on Environment and Natural Resources, 2000).

We know that in water, originally, phosphate and nitrate ions occur in small amounts and algae only need small amount to survive. However, when given increased amounts of nutrients, they get more to feed on, thus resulting in their growth and then they multiply.

"At sea level, typical DO concentrations in 100-percent saturated fresh water will range from 7.56 mg/L (or 7.56 parts oxygen in 1,000,000 parts water) at 30 degrees … Low dissolved oxygen (DO) primarily results from excessive algae growth caused by phosphorus…. Nitrogen is another nutrient that can contribute to algae growth. As the algae die and decompose, the process consumes dissolved oxygen…. , a zone of less than 2 ppm of DO covers an area about the size of New Jersey for much of the year, where aquatic life can't survive. The condition is primarily caused by excessive nutrients, primarily nitrogen and phosphorus" ("Integrated Assessment of Hypoxia in the Northern Gulf of Mexico," 2009, p.1-2).

Due to this resource we can conclude that excess nitrogen and phosphorus are the main causes of oxygen depletion in water. It also shows at normal levels the water would contain about 7.56 mg/L DO at 30 degrees in water, while also implying that contaminated and deoxygenated water would contain less than 2 ppm of DO.

The question that arises next is what levels of phosphorus and nitrogen ions are needed in order to cause the water to be deoxygenated or contaminated?

According to the Pond Ecosystem Chapter 3 of the Guide to Optimum Pond Dynamics (2008), in the section Nutrient levels, for a water body to be contaminated phosphate levels have to reach 0.05 to 0.01 ppm and /or nitrates have to be about 5 to 7 ppm for the water to be contaminated (para.1). This also shows that phosphorus is more of the cause of algal blooms. This shows that even the addition of a little phosphorus can cause low levels of oxygen in water, while it also shows the addition of some nitrogen could be dangerous too.

Now we will look and compare the values of average phosphorus and nitrogen content in organic and inorganic fertilizer in order to analyze which would be greater cause in the production of algal blooms. According to Sources of Nitrogen for Organic Farms (n.d.), the maximum amount of nitrogen poultry manure compost can have is 4%. The maximum amount of phosphate is also 4% (Walls-Thumma, n.d., para.2).

According to the Food and Agriculture Organization of United Nations [FAOUN] (n.d.), minimum amount of Nitrogen compound in the NPK fertilizer would be 15%, while the minimum phosphate level would be 15.2%.

As we can see there is about 2.5 times the amount of each compound in inorganic fertilizer than in the organic fertilizer. This means that the effect of the inorganic fertilizer would be than that of organic fertilizer.

We can see that as due to having no retaining abilities like the organic fertilizer, and due being more easily leached and having higher amounts of nitrogen and phosphorus levels,

Inorganic fertilizers are a greater cause of water contamination, algal blooms and thus the oxygen reduction in water.

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