We need to know how plants grow in soil in order to understand how hydroponics differs from soil. A plant has three main parts, namely the root system, the stem and the leaves. The root system anchors the plant in the soil and takes up water and nutrients from the soil.
The soil itself consists of 5% organic matter, which is plant remains and animal residues. These are broken down by bacteria to form humus. This mixture increases the water-holding capacity of the soil and fixes inorganic plant nutrients as well as being a source of nitrogen. The inorganic part of the soil, comprising 45% by volume, is made up of minerals released from broken-down rock particles, mainly sand and clay. This provides the chemical nutrients for plants. The remaining 50% of soil is made up in equal parts of water and air.
Air is essential for the supply of oxygen to the roots of a plant. The stem connects the roots and the leaves. It is responsible for getting water and nutrients from the roots to the leaves.
The leaves, in the sunlight, turn carbon dioxide and water from the atmosphere into chlorophyll. This is the green substance which is the source of energy to help the plant grow. Another function of the leaves is to act as an air-conditioner to cool the plant on a hot day.
Now we come to the common denominator between growing in soil and hydroponics, which is the availability of mineral elements. These are absorbed by the plant from the soil (or nutrient solution in hydroponics) and are essential for the growth of the plant.
There are six major elements and six trace elements. The major elements are nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. The trace elements are iron, mangenese, boron, copper, zinc and molybdenum. There are other trace elements, but they do not have any effect on plant growth. We don’t want to frighten you with too much science, but it is important that you have the basics.
An interesting fact is that the mineral elements mentioned above form only about 2% by weight of a tomato fruit, with 95% made up of water!