Macronutrients and Micronutrients in Soil

The primary macronutrients of soil include: nitrogen, phosphorus, and potassium.

Nitrogen provides energy to the plant to allow vegetative growth. Plants that can grow fruits need plenty of nitrogen in the beginning of their growth cycle. Phosphorus makes plants more stress resistant, allows for fast growth, and encourages bloom and root growth. Potassium helps with the photosynthesis process and increases the quality of the fruit the plant produces.

The secondary macronutrients plants need include: calcium, magnesium, and sulfur.

Calcium helps with strengthening the cell wall structure. One can get calcium into plants from limestone, gypsum, eggshells, and antacids. Magnesium is required as part of the chlorophyll in order to do photosynthesis. One can get magnesium from Epsom salt or limestone. Sulfur is needed to allow plants to create protein, enzymes, and vitamins. It also helps with seed and root growth, and strengthens a plant’s resistance to cold.

Then there are the micronutrients, which plants consume in small amounts. These micronutrients should already exist in the soil, so they rarely need to be supplemented. They are important for plant growth. The micronutrients include: boron, copper, chloride, iron, manganese, molybdenum, and zinc.
Boron helps in the production of sugar and carbohydrates. It is essential for seed and fruit development. Copper helps in plant reproduction and can be derived from copper sulfate. Chloride helps with plant metabolism. Iron helps in the formation of chlorophyll in the plant’s chloroplasts. Manganese helps in the breakdown of carbohydrates and nitrogen. Molybdenum helps in the break down of nitrogen. Zinc regulates growth and consumption of sugars by the plant.

A way to determine whether or not one’s soil has the appropriate amount of soils is to do a soil test. Simple soil test kits are available, which will measure the pH of the soil as well as the amount of nitrogen, phosphorus, and potassium present in the soil.

Pros and Cons: Organic versus Inorganic

Organic food is food that is produced using methods that do not involve modern synthetics inputs such as pesticides an chemical fertilizers, do not contain genetically modified organisms, and are not processed using irradiation , industrial solvents, or chemical food additives.

The pros of organic food:

• Organic food contains more nutrients than that of non-organic.
• It does not contain poisons found from pesticides.

The cons of organic food:

• Critics say that organic farming leads to the risk of contamination with potentially dangerous bacteria and mold toxins.

Non-Organic food is food that uses pesticides and other things to help the plants grow and so they wont be attacked and destroyed by predators.

The pros of non-organic food:

• Non-Organic food is cheaper and more easy to make. Therefore, it is more easily available to others.

The cons of organic food:

• There are over 450 pesticides used in Non-Organic food, many of which are toxic.
• Non-Organic food is irradiated to kill bacteria; the radiation can cause diseases in humans. 

There are a number of pros and cons for both organic and non-organic foods. Which one do you think is better?

Ethylene Gas and its Effects on the Fruit Ripening Process

Ethylene gas has a structural formula of C2H4, categorizing it as an alkene. This colorless and odorless gas is found in nature and is also man-made. Naturally, it is produced by all plants but mainly agricultural companies use this hydrocarbon to catalyze the vegetable and fruit ripening processes. Fruits, vegetables, and flowers contain receptors which serve as bonding sites to absorb free atmospheric ethylene molecules. Adding ethylene gas to a closed-container of any kind, along with a fruit or vegetable, will hasten ripening, aging, and eventually cause spoilage. Ethylene has been known to be harmful to vegetation—decreasing product quality and shelf-life. Albeit helpful, ethylene is flammable and in certain conditions know to be explosive. Along with its other stigmas this gas has also been know to have a slightly carcinogenic effect when synthesized with oxygen. To plants, its worst effect is depleting post-harvest life by approximately 46%. This then causes companies to spend more money on growing and shipping food, which can hurt the agricultural economy. Man-made ethylene gas has many effects good and bad, but ultimately shares the same qualities as natural ethylene. A good way to induce the ripening process is to place the fruit or vegetable with a banana. The banana produces the greatest amount of ethylene among all of the fruit and vegetables, and hastens ripening in an eco-friendly, productive, and sustainable manner.

Organic Pesticides

Organic pesticides are commonly regarded as a healthier and more “natural” alternative to conventional pesticides. However, they are less efficient, meaning a larger dosage of pesticide is required for the same effect. Organic pesticides are largely unstudied and longterm effects may be unknown.

“The consumer demand for organic products is increasing partly because of a concern for the environment,” said Hallett. “But it’s too simplistic to say that because it’s organic it’s better for the environment. Organic growers are permitted to use pesticides that are of natural origin and in some cases these organic pesticides can have higher environmental impacts than synthetic pesticides often because they have to be used in large doses.”

In the context of a small scale garden, such as the Santa Monica High School garden, there are a number of novel organic “pesticides” that may, or may not, ward of pests. This includes different foul-smelling substances that would dissuade aphids and other pests from the crops. 

If you’re looking for natural alternatives to the synthetic killers on the market, try using non-toxic household substances already in your pantry.

Chemistry Composting Part 2

Oxygen is an important factor to consider when composting.
Aerobic Composting: An aerobic process in the decomposition of organic materials in the presence of oxygen. Composting can be an aerobic process. As compost is consumed, the carbon to nitrogen ratio goes from 30:1 to 10-15:1. This is because two thirds of the carbon is released as carbon dioxide gas. The carbon is oxidized and carbon dioxide is produced. The remaining third is combined with nitrogen in living cells. The oxidation of carbon is an exothermic process. For every gram of glucose 484-674 kcal of heat are produced. This means that compost heaps can have temperatures above 170 degrees Fahrenheit. The atmosphere is twenty-one percent oxygen, but a compost heap only needs to maintain an oxygen percentage of ten percent to be aerobic. Some compost mixtures naturally maintain healthy oxygen levels by diffusion and convection, while other require active aeration. Blowers or periodic turning and mixing can aerate composts. Compost that is not aerated will become anaerobic. Aerobic composting takes place in bins, pits, or stacking piles.
Anaerobic Composting: Another type of composting is anaerobic- the decomposition of organic matter without the presence of oxygen. Unlike aerobic composting, anaerobic composting is a reduction process. Carbon is reduced to methane gas. Hydrogen sulfide gas is another byproduct of anaerobic composting.
As a result anaerobic composting releases pungent odors. The final product in the reduction process is humus. Some minor aerobic oxidation takes place at the end, but it is negligible. Therefore, anaerobic oxidation releases significantly less heat than aerobic. As a result, pathogens are not destroyed by heat but disappear naturally due to unfavorable condition- a much slower process. Nitrogen is reduced to organic acids and ammonia. Anaerobic compost must sit for up to six months to a year to insure pathogens are no longer present. Anaerobic composting takes place in large well packed stacks. It requires much more water than aerobic so that oxygen cannot penetrate the mixture. When the mixture is eighty to one hundred percent saturated, the organic material becomes suspended in a liquid.
Whether the gardener chooses aerobic or anaerobic composting, there are some basic dos and don’ts of composting. A good balance of green and brown materials will lead to an ideal balance of nitrogen and carbon. However do not include any meats, cooked vegetables, dairy, animal waste, perennial weeds or salad heads.

The Fertilizers in our Gardens

Another way chemistry is connected to gardens is through fertilizers. Fertilizers are commonly regarded as materials that are added to the soil or plant to supply one or more elements that are essential for plant growth. Most people are unaware that fertilizers are chemicals, so treat them with care and use protective gloves. Make sure to avoid inhaling odors. The standard fertilizer will have a label reading “20-20-20”, which means that that particular fertilizer has 20% Nitrogen by weight, 20% Phosphorous by weight, and 20% Potassium by weight.
Higher concentrations of Nitrogen should be applied in the early growth stage, as it contributes to leaf root growth which results in a lush, green plant. However, too much Nitrogen can reduce or delay the growth of flowers and fruit, so if your plant is a healthy green, seems to growing well, but doesn’t have flowers, stop adding Nitrogen. You should start using fertilizers that have a higher concentration of Phosphorous when the season moves towards the flowering and fruit set stage. Phosphorous promotes flower growth, root growth, and fruit set and development. Potassium promotes fruit growth. After fruit set, you should start using a high potassium fertilizer. Below is a chart demonstrating possible fertilizer variations.

As mentioned above, there are nitrogen, phosphorous, and potassium fertilizers. There are also quick release/slow release fertilizers, and stabilized nitrogen fertilizers. Anhydrous ammonia is the main component in nitrogen fertilizers, and is produced by the Haber-Bosch process:
3H2+ N2 + heat, pressure, & catalyst = 2 NH3(g) (anhydrous ammonia)
Anhydrous ammonia (82-0-0) is sold as a liquid under pressure and when injected into the soil, undergoes the following reaction:
NH3(g) + H2O <— —> NH4OH <— —> NH4 + OH- —> NO3
The raw material in phosphorous fertilizers is rock phosphate or apatite. They create a superphosphate through the following reactions.

• Apatite + sulfuric acid —> superphosphate.

• Apatite + phosphoric acid triple —> superphosphate

KCl (0-0-60) or K2SO4 are the main raw materials for potassium fertilizers.
Quick release fertilizers are readily available and are very water soluble. Slow release fertilizers, on the other hand, are less soluble due to the fact that a coating is added to the fertilizer in the granule that delays the rate of dissolution. The advantages of slow release fertilizers include: lower potential to cause injury to plants, higher Nitrogen use efficiency by plants, less subject to volatilization. One disadvantage of slow release fertilizers is that they are fairly expensive. Stabilized nitrogen fertilizers are products mixed with or added to Nitrogen fertilizer materials that either act as a urease inhibitor or a nitrification inhibitor. The fertilizer is said to be stabilized because it is not as subject to losses from volatilization or leaching. This fertilizer is used widely in corn producing areas of the U.S. It is a liquid that is mixed with anhydrous ammonia. In places where the microbial reactions in the soil are already slowed down (perhaps due to cool soil temperatures, as in Alaska) the use of this fertilizer may reduce Nitrogen availability to crops.)

Chemistry Composting

In researching the links between chemistry and gardening, composting arose as a key component. While composting merely entails the accumulation of waste outdoors, there is a surprising amount of chemistry involved.
The decomposition of organic materials is rich in nutrients that promote plant growth. When organisms die their stored carbon and nitrogen becomes available to other organisms. Any compost will have a balance between bacteria and plant materials. This is to maintain a healthy carbon to nitrogen ratio. Bacteria typically have a ratio of 4:1, while plant material has 30:1. Carbon and nitrogen are both important elements in plant growth. Carbon is an essential energy source and a building block for plants, as it composes fifty percent of microbial cells. Nitrogen is an important component of proteins, nucleic acids, amino acids, and enzymes. While carbon and nitrogen are both essential, neither is useful independent of the other. Diamonds would be detrimental to a compost heap. The ideal carbon to nitrogen ratio for composting is thirty to one. An excess of nitrogen will cause it to form ammonium gas, toxic to plants, and releasing pungent odors. Conversely, a compost heap deficient in nitrogen will restrict plant growth.

Below is a table of a variety of different plants and their carbon to nitrogen ratios.                                          

Soil and its pH

We continued to discover the connections between chemistry and gardens, and found out quite a lot about soil pH. At first, we didn’t think there’d be a way to take the pH of the soil, or if it was even important. After doing some research, we discovered that there are several different ways to take the pH of the soil, some of which are listed below.

• Use an inexpensive pH testing kit based on barium sulphate in powdered form. When a small sample of soil is mixed with water, the color will change according to the acidity or alkalinity.
• Use litmus paper. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acidic the paper turns red, if alkaline, blue.
• Use a commercially available electronic pH meter, in which a rod is inserted into moistened soil and measures the concentration of hydrogen ions.

Now that you know what to use to discover what the pH of the soil is, you need to know why it’s important! Its main importance is that certain plants can grow the best only at certain pHs. A list of plant pH preferences is listed below.

• pH 4.5-5.0: blueberry, cranberry, orchid, blue hydrangea
• pH 5.0-5.5: parsley, potato, radish, ferns, sweet potato
• 5.5-6.0: beans, carrot, brussels sprout, peanut
• 6.0-6.5: broccoli, cauliflower, cabbage, cucumber, tomato, strawberry
• 6.5-7.0: asparagus, beet, celery, lettuce, spinach, onion
• pH 7.1 - 8.0 lilac, brassica

To increase the pH of the soil (make it more basic), use a process calling liming. To decrease the pH of the soil (make it more acidic), use iron sulphates or aluminium sulphates, ammonium nitrate, decayed vegetable matter, compost, or stable manure.

Be sure to check back at our blog for more information on the incorporation of chemistry in gardens!

The Beginning!

Santa Monica!

We are students in AP Chemistry at Santa Monica High School. Our class has decided to take on a service learning project. In this month and next we will be turning gardening into a community effort. Our goal is to sustain a school/community garden at Santa Monica High School that can effectively make an impact on education and the school. In addition, we will incorporate Chemistry into helping the garden and growing produce.

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Thanks for the support and check back soon,

The Samohi Garden