Fourth soil-forming components have an important role in supporting the function of soil as a growing medium. The fourth difference component of this land will have an impact on the versatility of the soil as a growing medium. Eg soil air serves as a source of gas needed by plants, among others:
1. As a source of oxygen (O2) that is needed by the cells of the plant roots for respiration activity. The results of the activity of respiration releases CO2. For autotrophic microbes that utilize organic materials, then the CO2 would be used as a source of energy for the process of enzymatic oxidation decomposition of organic matter and release nutrients.
2. Carbon dioxide (CO2) released the roots of the plant will be utilized by photosynthetic microbes.
3. Nitrogen (N2), will be utilized by microbes fastener N, and can supply N in the soil to improve fertility.
4. Some types of gases in the soil such as CO2, N2, NH3, H2 and other gases, both derived from the decomposition of organic matter or derived from the remnants of pesticides or industrial waste, if its content can be toxic to plant roots, and for soil microbes. If the condition of good soil aeration, then good air circulation will allow the exchange of gases with O2 from the atmosphere, thus autotrophic microbial activity plays an important role in supplying nutrients be guaranteed and the danger of poisoning gases are neutralized.
Groundwater is an important part of land plants and living creatures. Most of the availability and uptake of nutrients by plants is influenced by the availability of water, even the elements could move like N, K and Ca can be absorbed by plants through the aid mechanism mass flow of water to the surface of the roots and transported to the leaves. Therefore, if crops suffer from lack of water, the plant will wilt and will also experience a lack of nutrients.
To produce 1 gram of dry biomass, the plant needs about 500 grams of water, where 1% of its charge per unit of plant cells. Organic matter and mineral soil is a storehouse and provider of nutrients for plants and creatures living in the soil. Mineral materials in the form of a constituent particles of soil pore space that not only serves as a storehouse of air and water, but also as a space for entry of plant roots into the ground deeper, so that the roots develop properly.
If the condition of the soil pore space decreases, then the development of the root system of the plants do not develop normally, resulting in impaired plant growth. The organic material is a source of energy, carbon and nutrient for living beings who served as decomposers of organic compounds, resulting in the presence of organic materials will largely determine the population and activities in liberating the nutrients in organic materials.
In ideal conditions the plant roots can grow and develop well in horizontal and vertical direction as far as a few centimeters per day, so that the mature corn crop planted within 100 cm can have root systems that are touching each with a depth of more than 2 meters. Even alfalfa plants are known to reach depths of up to 7 meters. Soybean plant roots can get into the soil up to 35 cm to the side and 1 meter vertical direction.
The increasing development of the root system, the more nutrients and water that can be absorbed by plants, so that more secure needs during the process of growth and production, and ultimately more productive farmland. The productivity of agricultural land is defined as the ability of plants cultivated in an area with a certain area under good management to generate production in a certain time, which is expressed in units of weight per area per time.