This is a short piece I wrote after learning more about the limits of plant nutrient yields and how different method of growing effect output. It was a short rumination on how plants and their food yields are limited by the laws of chemistry and looking back on it now I would be and interesting topic to revisit now the GMO's are a much more popular topic of discourse. 

The effects of chemistry on plants


Around 10,000 plant species have been used for human food since the origin of agriculture. Today, only about 150 plant species make up the diets of the majority of the world's population. Of these, just 12 species provide over 70 percent of food, while four – rice, maize, wheat and potatoes – make up over 50 percent of the food supply and only 30 crops provide 90 percent of the world's calorie intake. This is a staggering statistic, which I could talk about all day, but what I am going to show is how much the plants we rely on rely on the chemistry. Plants are at the mercy of the simple rules of chemistry, through nutrient concentrations in their growing medium, pH levels in soil solutions, and what humans do to make them “safe” to eat.

A good example of how plants are at the mercy of chemistry is demonstrated by the hydroponic solution system. A hydroponic growing system supply nutrients to the crop in a solution of irrigated water. The nutrient solution is still, or it is re-circulated using a pump. All hydroponic systems need to provide plant roots with enough nutrients, water, and oxygen for good growth. Plants require large amounts of the macronutrients: nitrogen, potassium, calcium, magnesium, phosphorus and sulphur, and smaller amounts of the micronutrients: chlorine, iron, boron, manganese, zinc, copper, nickel and molybdenum. This is reflected in the concentrations of macronutrients and micronutrients that are found in commercial hydroponic solutions.

Hydroponics take complete advantage of the process of concentration gradient, and solutions. Diffusion gradient is the “slope” of the concentration of a solution. If a solution has a very large amount of solvent and a small amount of salute, then the concentration gradient will be very steep. The plant’s cell membrane allows water and nutrients to pass through the process of concentration gradient. There is a far higher concentration of nutrients with in the hydroponic growing solution than in the plant’s root system. Since nutrients will move from high to low, they are drawn into the roots of the plant in order to maintain homeostasis with the environment. The solutions the plants grow in must be perfectly balanced in order for the plant to grow properly. If there is excessive concentration of magnesium to iron – for instance - then the plant will suffer the consequences of iron deficiency and could possibly die or develop a disease.

Another example of how plants exist within the confines of chemistry, is in their response to pH of solutions. For instance, when a clay particle breaks down in soil, aluminum is released.  Often this aluminum ion will bind to another negatively charged clay particle.  When the conditions in the soil solution are favorable, the bound aluminum ion will react with water in the soil solution and form a number of aluminum hydroxides.  When this occurs, hydrogen is released into the soil solution, which increasing the acidity. When there are a high number of hydrogen ions in solution, this reaction will not form a hydroxide, but instead will simply stay in solution.  This in itself is not a suitable, because aluminum is toxic to plants and when it is present in high amounts in the soil solution plants will take it up (because of the concentration gradiant) and this can weaken or even kill them.  In addition, aluminum can bind to plant nutrients, thus making them unavailable to plants. 

Aside from hydroponics traditional agriculture relies on soil solutions. In the case of pH, the amount of hydrogen ions and aluminum greatly affect how acidic the soil is and how the plant will fair. If the soil is acidic then most of the plants that are in that patch of soil will not do well. Most plants need soil that is 6.0- 7.0 on the pH scale. However, there are some plants that love acidic soil: blueberries, sweet potatoes, and watermelons prefer a soil pH of 5.0-6.0.

Chlorine concentration is another aspect of chemistry that has large effect agriculture. Many manufactures of processed foods use chlorine and water to clean the produce, but it can have some nasty effects. It is an effective sanitizer but can easily damage the quality of processed foods if not used in the proper concentrations. According to federal regulations the concentration of sanitizer in the wash water must not exceed 2000-ppm hypochlorite, and the produce must be rinsed with potable water following the chlorine treatment. Chlorine solutions are by nature highly corrosive; they should not be used on surfaces that are prone to rust. Chlorine solutions are irritating to the skin and the fumes irritate the respiratory tract.

This system like hydroponics is all about proper solutions and concentrations. If there was even the smallest excess chlorine it could possible leach into the produce through diffusion across the cell membrane, make a factory worker very ill or possibly kill someone. It would certainly make the food have a very unpleasant taste.

Plants are at the mercy of the simple rules of chemistry, through concentrations of nutrients in their growing medium, pH levels in soil solutions, and what humans do to make plants “safe” to eat. Chemistry is all around us in the world. Without Chemistry there would be no plants, no Earth, no life or non-life, as we know it. It is not very surprising that plants rely so heavily on the rules of chemistry in order to survive. We all do.