There are a lot of meaning or definition of the land developed in the communities are very diverse definitions must be adjusted to just the interests of each. But the definition of the public about the land is as follows, namely land is accumulated body of the outdoors, a three-dimensional, occupied most (large) surface of the earth, which was able to grow crops, and has properties as a result of climatic influences and the bodies of living that acts against the parent material on topography / specific relief and for a certain time.
In agriculture, the soil is more specifically defined as a medium for the growth of plants. Soil derived from the weathering of rock mixed with the remnants of organic material from the organism (vegetation and animals) that live on it or in it. In addition, in the ground there is also air and water. Ground water comes from rain water retained by the soil so it does not seep into other places. In this sense, there are two variables that distinguish the notion of land in the field of agriculture with other sectors, namely soil depth and size of the particles.
The depth of the soil in terms of agriculture is limited to the top of the earth’s crust that have experienced weathering or their biological activity. If the part has undergone weathering is shallow, then the tersebutlah used as soil depth limit. Conversely, if the part that has undergone very deep weathering (4-6 m), then not all of the weathered material called ground, but to a depth where there is biological activity.
In general, the discussion of land in agriculture is limited to a depth of about 2.0 m. Depth is far different from the depth of the soil in the field of engineering that can reach tens of meters. In connection with the particle size, soil limit agricultural experts on particle size (0.02 to 2 mm), compared with engineering experts who are also interested in the size larger than 2 mm such as gravel and even rock, or expert in the fields of ceramics are only interested in particle size of 2 lm.
If we make a vertical incision ground by making a hole (1.0 x 1.5 m with a depth of about 2.0 m) and further examined at the cross upright, will be visible layers in the direction parallel to the surface of the earth’s crust is relatively easy to distinguish one each other. These layers in soil science called horizon. Horizon is above the soil parent material called solum.
Figure 1.2. Observation of soil profile hole
Topsoil generally contain organic material that is higher than its subsoil. Because of the accumulation of organic matter, the dark layer of soil and a layer of fertile soil so it is a very important part of the soil to support plant growth. A layer of soil is called topsoil (top soil) or also referred to as topsoil, and has a depth of about 20 cm.
Subsoil called subsoil (subsoil) lighter color and is relatively poor. This does not mean that the subsoil is not an important role for the productivity of the land, because although it may be the plant roots can not reach the deeper soil layers, but soil properties such as permeability and chemical properties of the subsoil will greatly affect the topsoil in its role as a medium to grow plants.