Nutrient Elements of Plants
Let us first find out the chemical composition of plants and see which element nature has selected to support their healthy growth. Only then we will be able to know the nutritional requirement of plants. As you know a major part of plant tissue is comprised of water. This we can demonstrate by taking a known amount of plant tissue and drying it for a few hours in an oven at a temperature of 65-80°C. If we condense and analyse the vapours coming out from the plant tissue we will find that it is nothing but water. In fact, about 85-90 per cent of the tissue is composed of water. The part of the tissue which is left behind is called the dry matter and typically it is about 10-15 per cent of the original weight.
The dry matter consists mainly of organic compounds. About 90% of the dry matter consists of plant cell walls, primarily cellulose and related carbohydrates. This can be eliminated in the form of gases on combustion at 600°C. The residue now left is the ash which varies in different plant tissue from about 1 per cent to 0.15 per cent of the dry weight. Interestingly, a careful analysis of the ash shows that it contains almost all of the chemical elements present in the soil surrounding the plant.