Our Little Lesson in Plant Chemistry

Sometimes as we try to understand plant science it becomes so complicated we give up. In this article and future ones, I am going to keep it so simple that even I can understand it. When I turn the key to start my engine in the morning, my engine rumbles, comes to life and away I go. I really do not know how it works but I do understand the basics. If you do not keep the proper level of oil topped up and the gasoline above empty, then turning that key won't do very much. Lets understand the basics and then "grow" from there.

What do plants need? Well, they need air (oxygen) and light (natural or artificial) and food (like gas in the tank).

Today's chemistry lesson is on food or nutrients as we often call them. On most bottles or bags of fertilizer you will see three numbers. These are called N-P-K. N - being nitrogen, P - being phosphorus and K - being potash or potassium. Further on down the label you will see a list of micro elements or "trace elements". These are included in the feed mix but in minute amounts.

Just as eating a balanced diet on a consistent basis is healthy for the human body, a "balanced" nutrient on a consistent basis is good for plants. The body can go for several days without certain foods, and the vitamins and minerals that they contain, because the body stores a certain amount. In time though, without those vitamins, minerals or elements, our body will certainly become unhealthy, even become ill.

Let's start with the really important one, nitrogen. Nitrogen is so important that it accounts for about six% of a plant's dry weight. Our atmosphere generally contains about 80% nitrogen but most plants are unable to use this form of nitrogen because they feed through the roots and take in two particular types. Plants use nitrate nitrogen (N03) and ammoniacal nitrogen (ammonia) (NH3).

In most soils the ammoniacal nitrogen is quickly converted by a process called nitrification. This is where bacteria and heat change the ammonia into a useable form. In soil with poor drainage and aeration, the bacteria cannot reproduce quickly and ammonia begins to build up. This build up of the ammonia form of nitrogen is not good.

Nitrate nitrogen is the main or principal form of nitrogen available to plants under normal field or greenhouse conditions. This type of nitrogen is the best source and in this form provides the quickest way for inorganic nitrogen to change into an organic compound.

There are many other chemical processes that are involved in breaking down composted material into a useable nitrate form. Included are amino acids, nitrosomas bacteria, fungi and humic substances. Lets skip all the heavy chemistry and just say that plants want the "nitrate" form of nitrogen. Out in the field this is simple because you have a) bacteria and b) heat or warm temperatures to create this reaction or change.

What if you do not grow your crop outside in the field, what then? This, my friend, is why you want a fertilizer with a reasonably high form of nitrate (NO3) nitrogen. There is NO bacteria or "nitrobacteria" normally present in a soiless medium or water culture system. Growing hydroponically changes the game.

All these organic plant foods need to break down to useful or useable compounds. As Dr. Cal Herman said to me not long ago, "Organics was created to feed the soil, not to feed the plants". Oh, yes! By feeding the soil we provided a regenerating or renewing of the nutrients in the soil for the plants to then assimilate or feed themselves. Hydroponics is NOT soil gardening, is it? No, it is not, because we the caretaker of the greenhouse or hydroponics system are the only ones who can provide the proper useable form of nutrition for those plants. They cannot take nutrients from an inert media like peat, coco earth, clay rock or rockwool.

Is all ammoniacal nitrogen a problem? No a certain amount can be slowly converted and some ammonia does have a purpose. Some plants that thrive in low pH soils or crops, such as rice, seem to favour some ammoniacal nitrogen but the normal preference is a nutrient high in nitrate nitrogen.

Plants weight of nitrogen, when measured from a dried point, usually ranges from about three to five%. When the supply of nitrogen is low, plant growth is slowed and even retarded. The nitrogen is moved to the new growth area away from the older part of the plant and the leaves begin to age and die off.

When too much nitrogen is present you will have a different set of problems. Typically the plants exhibit stem and shoot elongation, thinner leaves and root inhibition. The roots being not well developed, cannot uptake and assimilate the nutrients properly. This plant will be lush, but "droopy" and is often called "soft growth" as opposed to a plant with the proper amount of nitrogen, which exhibits "sturdy" growth.

Plants that have had an excess of nitrogen and experienced stem elongation can often produce lower yields.

Nitrogen changes the composition of a plant more than any other nutrient. In cereal and grain crops an excess of nitrogen reduces the amount of sugars, fructose and carbohydrate storage that the plant would bank.

If you increase the nitrogen level the plant will increase its protein content and leaf area, but only to a certain amount. A minimal increase in nitrogen will not change the make up of the plant very much, but will increase the crop yield. Too much nitrogen actually inhibits other minerals from working properly.

Inordinate amounts of nitrogen at harvest time can affect the value and nutritional level of that crop. Sometimes nutrients are formed during vegetable storage or processing. Possible risks include blood problems in children, food with high nitrite levels and the formation of nitrosamine which can be carcinogenic.

What we are really saying is:

A) Use a balanced fertilizer and the recommended amount and B) don't over- do the grow formula or nitrogen use at the beginning.

What are the minerals for?

Nitrogen - controls oxygen levels in plants and controls the rate of use and breakdown of carbohydrates for energy and growth.

Phosphorus - helps promote root growth and is concentrated in seeds, fruit growing cell tissue.

Potassium - is concentrated in the actively growing part of the plant. Roots, young leaves and buds. Potassium is the catalyst and acts like the gas pedal and the brake pedal.

Calcium - is the foundation for cells in both animals and plant structures, just like bones in animals and people.

Magnesium - used in making chlorophyll and is essential for the uptake of CO2. Magnesium is a carrier for phosphorus in a plant.

Iron - regulates photosynthesis and is a carrier of oxygen. Iron is a also found in enzymes.

Manganese - is also a catalyst that speeds up plant reactions and works in conjunction with calcium.

Zinc - acts as a catalyst as well and is partially controlled by the amount of light that a plant receives.

Copper - is important in the production of chlorophyll, enzymes, and is an electron carrier.

Molybdenum - is a catalyst for many enzymes, assists in the nitrogen activity and also has some effect on the carbohydrate usage in a plant.

Summary:
A. There are a number of supplements or additives available but nothing replaces a well-balanced plant food.

B. Should we use a special fertilizer designed for hydroponics use? Absolutely. Choose a plant food that is complete and balanced.

C. Many other factors govern nutrient usage, but a well formulated plant nutrient, used in the proper amount is the real "lesson" here.

Next month we will talk about "Bio Stimulants and Vitamins".