Chemistry Assignment代写:腐殖质分解材料

The surface layers of soil contain the highest numbers and variety of microorganisms [10]. These microorganisms in soil play the important role of breaking down both, organic and mineral materials partly by enzymatic action and partly by taking the materials in as nutrients and metabolizing them further. Most of the breakdown products are used by the plants as nutrients or are lost into the soil environment. However, the rest of these breakdown materials are used to generate humus. Humus plays an active role to further enhance soil property, e.g. it improves the water-holding capacity of soil which makes more water available to the plants, a supply plant with nutrients, increases the adsorption of minerals, and contributes to soil aggregation [9]. Moreover humus increases the soil buffering capacity and stabilizes the soil's pH to further help the plants to take up mineral nutrients. Additionally, it darkens the soil color which increases the soil's absorption of solar energy

In addition, the decomposition of the plant and animal tissues by microorganisms can recycle energy and convert nutrients to forms that are usable for plants. Also, very importantly, microorganisms play vital roles in cycling of sulfur, phosphorus, iron, and many micronutrient trace elements [11]. The transformations of elements to various forms are described as cycle. In the carbon cycle, microorganisms transform plant and animal residues into carbon dioxide and the soil organic matter known as humus. In the nitrogen cycle, nitrogen is made available to plants only when it is transformed to ammonia (NH3) either by soil bacteria such as (N2 fixation) or by humans such as (manufacture of fertilizers) Soil bacteria also can return the nitrogen to the atmosphere by transforming NO3- to N2 or (N2O) gas

Another very important element found in soil is Phosphorus, which is critical for improving the soil fertility [13-14], thus increasing the forest and agriculture production. As shown in fig: 1.1 Phosphorus is usually found in rocks and it becomes available for plant after weathering and dissolving in the soil water. It is then absorbed by plants and then gets transferred to animals, the animal and plant residues containing this phosphorus can be recycled again by microorganisms. Additionally, fertilizers are also an important source of phosphorus in the soil