Plants use several basic processes for their development. The first one is photosynthesis, which uses light and the atmosphere to transform water and minerals into energy and plant tissue. It is performed by plants in all their green bodies, where chlorophyll is. In this process, photosynthetic organisms capture and use solar energy to oxidize water, releasing oxygen and reducing carbon dioxide; this makes them produce organic compounds consisting primarily of sugars.
Another basic process is breathing, in which organic substances decompose into carbon dioxide and water and release energy.
As photosynthesis does no consume any existing water in the plant, what remains is removed as water vapor through the leaves; this is process of transpiration. The factors that have influence on it are the surface of the leaves and the number of stomata, the temperature, humidity and air agitation.
Summarizing some of the processes involved, we can say that, during photosynthesis, the plant breaths in carbon dioxide and releases oxygen. Breathing is an inverse process: the plant releases carbon dioxide and breaths in oxygen and in the transpiration phase it releases water.
The plants and the Soil
Soils consist of 3 states: solid, liquid (soil solution) and gaseous (air). They are a mixture of organic matter and minerals that form a porous structure, containing large as well as small pores filled with water. The concentration of nutrients in the soil depends greatly on the water content in the soil, its pH, microbial activity and the use of fertilizers.
The movement of nutrients in the soil and their approximation to the roots (where radicular absorption occurs) are performed by mass flow, root diffusion and interception. Mass flow is the movement of nutrients up to the roots in the water mass that is absorbed and transpired by the plant, and is influenced by the water content in the soil so, whenever there is a lack of water in the soil, that movement of water and nutrients decreases. Diffusion is the movement of nutrients from higher concentration to lower concentration areas and is, for instance, the main mechanism for the movement of phosphate towards the roots and is also very important for potassium. As the roots grow and occupy positions in the soil, they find nutrients. This is the root interception process.
When the plant absorbs this solution of water and mineral salts, the solution passes from cell to cell, reaching the xylem vessels and going up through them up to the leaves, where photosynthesis is performed. This is a bottom up movement and is referred to as crude sap or xylem. However, that movement also occurs top down, especially by action of gravity and is the result of organic products generated by photosynthesis (water and other substances) and some mineral salts. That movements is called elaborated sap or phloem.
Essential Elements and Minerals
There are 94 known elements altogether; only 60 were found in varied plants and not all of them is considered essential to the development of the plant. A plant’s root probably absorb any existing element in the soil, as long as it is soluble. Nevertheless, plants have some ability to select the ratio at which they absorb those varied elements, and different species vary their ability to select them. Thus the absorption is not directly proportional to the availability of nutrients.
Each element must correspond to 3 criteria in order to be considered essential to plant growth:
1. The plant cannot complete its life cycle without it;
2. Its action is specific and irreplaceable;
3. It is directly related to the feeding of the plant.
Only 20 elements are considered essential for plants and are divided into MACRONUTRIENTS and MICRONUTRIENTS, used in a large and small scale, respectively. MACRONUTRIENTS include Carbon [C], Hydrogen [H], Oxygen [O], Nitrogen [N], Phosphorus [P], Potassium [K], Calcium [Ca], Sulfur [S] and Magnesium [Mg]. MICRONUTRIENTS include Iron [F], Chlorine [Cl], Manganese [Mn], Boron [B], Zinc [Zn], Copper [Cu], Molybdenum [Mo], Nickel [Ni], Silicon [Si] and Cobalt [Co].
Nutrients are essential in hydroponic cultivation. They can be prepared at home but are also commercially available and, if you are a beginner, we recommend that you use the nutrients available in the market. Those fertilizers contain an ideal mix of both macro and microelements, and so can be adjusted according to the plant’s needs. The amount of nutrients is identified with 3 digits separated by a hyphen (e.g., 10-10-10). These numbers represent the percentage by weight of the 3 main elements present – nitrogen [N], phosphorus [P] and potassium [K]. there are several solutions with these nutrients in the market and are usually well-balanced, despite the differences in the ratios.
Some common chemicals used in the preparation of nutritional formulas are: