Soil has following four ingredients: 1. Mineral Matter-Minerals are part of rocks which constitute soils. Every mineral has some specific quality whose deficiency impairs soil-quality. For example, calcium strengthens the plant roots and its deficiency affects root development and plant growth.
Phosphorus helps in the development of tissues and cell-division. In its absence plants will not grow. Sodium provides oily protein for the formation of joints and its deficiency causes retardation of plants. Potassium prevents premature falling of leaves. Lack of this mineral leads to loss of chlorophyll (greenery) in leaves and their untimely falling. That is why for improving crop-yield the first thing one has to do is to go for soil test, ascertain the deficient mineral and recoup the same through artificial fertilisation.
1. Organic Matter-it is a plant material derived from the roots of the grasses and rotten leaves of the trees. It is also called amorphous material (nitrogen or humus). It provides strength to the soil and improves its quality.
2. Soil Air-the intervening space between soil-particles is filled with soil air which contains higher amount of carbon-di-oxide than in the atmosphere. This air helps in the growth of plants. Its amount depends upon the depth and compactness of the soil. For example, clay contains less air than sand.
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3. Soil Moisture-the soil moisture is largely in the form of vapor. Its deficiency retards the germination and growth of the plants. Similarly excess of moisture dries down soil-air, promotes soil leaching and withers down roots.
Soils generally restore their fertility through self-fertilising methods. There are various bacteria, actinomycetes, and fungi which help in this process. Rotation of crops and leaving fallows are other methods to allow soil to restore its fertility. Besides there are natural (compost, green manures) and artificial (sulphate, phosphates, nitrogen’s) and bio fertilisers which are utilised by farmers to improve soil-fertility.