Soil is a complex system that is composed of four components, namely minerals, organic matter, air and water. Mineralized material contained in a variety of shapes and sizes, consisting of fragments of rocks, minerals and various compounds result of weathering of rocks. The organic material consists of the remains of plants, animals and micro and macro bodies that live in the soil and the dead and decomposing. Part of groundwater that fills most or all of the pores that exists between soil grains, is a solution of various types of salts and compounds that dissolve in water.
Air section of land is a mixture of air in the soil that fills the pores of the soil grains that are not occupied by water. The combination of all four components of the soil will form a distinctive physical soil properties. Some of the physical properties of soil that are important to study, among others, the texture, structure, permeability, water power savings, future soil type, soil color and soil temperature. Mineral soil as a growing medium is an ideal plant material is composed of four components, namely solids (minerals and organic matter), water and air.
Based on the volume, then the soil is generally comprised of (1) 45% solids in the form of minerals, (2) 5% organic matter, (3) 25% of water and 25% air, as in Figure 1.3 below.
Picture. 1.3. Mineral soil components
The special thing occurs in soil organic soil (peat) in which the part 100% solids can be any organic material, whereas 100% pore space can be filled with water. Therefore all parts of the pore space filled with water, then no parts of air in this land, this will cause the peat soil can not be used as productive agricultural land, unless done engineering in accordance with the conditions of peat through drainage improvements and the addition of mineral matter.
Figure 1.4. Organic Soil Profile
Naturally the percentage or proportion of the components of the soil depends on the following matters:
1. The size of the particles making up ground. The finer the particles making up ground means more solid ground, so that the pore space will also be narrowed and vice versa.
2. Sources of soil organic matter. In vegetated land will have a high percent of organic matter, and vice versa soil contains little organic material if the conditions are not vegetated.
3. The climate, especially precipitation and temperature factors. At the time of irrigable land (irrigation) or when it rains, the water component of the soil will increase, and the air component decreases, otherwise when no rain and high evaporation, the water content decreases while increasing air.
4. Sources of water. Land close to water sources, such as rivers, lakes will contain more water than those far from water sources.