Organic matter, as its name implies, is made of organic material, the original source is photosynthetic products, the energy from solar power, required synthetic materials from nature. Organic matter or organic matter in the soil of cultivated land, which is present in all carbon-containing organic material in the soil, includes a variety of plant and animal residues, microbial decomposition and composition of organic matter. Composition of the soil solid phase is an important part of soil organic matter, soil accounted for only small part of the total soil organic matter content, but it's on the formation of soil, soil fertility, environmental protection and Agriculture and forestry plays an important role in sustainable development.
Since its rural land contracting and management, due to land yangdi, and organic matter of farmland showing a decreasing trend in China, directly affecting the quality of arable land. If unable to control, will also affect food supply, affecting the health and even the life of the nation. 1999-2014, by the China geological survey Bureau, in conjunction with the provincial-level people's Governments and their departments of land and resources, national coordination of 77 units of more than 100,000 people conducted a comprehensive survey on the quality of cultivated land situation throughout the country. Investigation of the total land area of 1.507 million square kilometers, which surveys 1.386 billion mu of arable land, accounting for 68% of the country's total cultivated land area. By 60duowanjian of soil, water, biological samples, such as 54 elements precision test indicators, access to the 3000duowange data are established and 31 provinces of the country (district, municipal) land of the geochemical database, and on the general situation of cultivated land in China formed a preliminary knowledge and judgment.
Survey, China, Fujian, Guangdong and Hainan area, North West and part of the Tibetan district of arable land compared to the organic carbon content in the 1980 of the 20th century showed a downward trend, Northeast organic carbon of arable land fell by 21.9%, which reduces soil fertility. Survey arable land range within has 29.3% of soil alkalization trend increased, pH value rose has 0.64, main distribution in North area; 21.6% of arable land acidification serious, pH value reduced has 0.85, main distribution in heavy metal pollution problem highlight of min Guangdong Joan district and Hunan e Wan Gan district, in reduced arable land quality of while increased has heavy metal pollution, increased has arable land ecological and groundwater quality deterioration risk. Ph decrease of arable land, soil compaction, soil fertility decline is not conducive to crop nutrient absorption. Meanwhile, chemical inputs too big for a long time, against the formation of soil organic matter.
Despite straw practices in some regions of China, cultivated organic matter decline has slowed, but relative to the health of soils, organic matter content was very low. In addition to the heavy use of chemical fertilizers and pesticides, burning straw, waste water irrigation, plastic sheeting covering, use herbicides to control weeds, caused a decline in organic matter, soil fauna and microbial diversity decreases.
Healthy soil organic matter content. Soil organic matter content varies in different soils, with high content of up to 20% or 30% (such as peat soils, fertile forest soils, etc), low levels of 1% or 0.5% (like the desert soil and sandy soil, etc). In soil science, generally over 20% of the organic matter in the soil called topsoil soil organic matter, organic mineral soil following soil called 20%. In healthy soil, topsoil soil organic matter is usually 5%. Second, source of soil organic matter
Soil organic matter sources are extensive. Soil organic matter into humus and non-humic substances. Microbe is the earliest source of soil organic matter. Several ingredients are an important source of organic matter in soils:
1) plant residue: includes all types of plant litter, dead plants and roots. The main sources of soil organic matter in it's natural state. Forest soils for agricultural soils, with lots of litter and roots of huge trees and so on. Tropical rain forest leaf litter dry weight of up to 16700kg/(km2 a), and desert vegetation litter dry weight is only 530kg/(hm2 a). 2) animal, microbial debris: include soil animals and non-soil residues and residues of various microorganisms. This part is relatively small. But the original soil, microorganisms are the earliest source of soil organic matter. 3) animal droppings and secretions: that some sources even though the amount of soil organic matter are few, but the transformation of soil organic matter plays a very important role. 4) waste: applying organic fertilizer in the soil (green manure, compost,
composting, etc), industrial and domestic waste water, waste, there is all kinds of micro-biological products, organic pesticides, and so on. In the traditional agricultural production, farmers collected a vast amount of human and animal waste to meet the plant nutrition of organic matter and maintain cultivated land.
Generally 3 types of organic matter into the soil in the State. 1) fresh organic matter: who has not broken down by the microbes in the soil plant and animal residues, which still retains its original shape and other characteristics. 2) decomposition of organic matter: by microbial decomposition, has entered the soil, litter lost its shape and other characteristics. Partially decomposed organic matter, and tangled with each other, Brown. Includes organic matter decomposition products and new synthesis of simple organic compounds. 3) humus refers to organic matter after microbial decomposition and synthesis of a brown or dark brown macromolecular colloidal substance, and soil mineral particles are combined together, are the main types of soil organic matter, accounting for 85-90% of the total organic matter in soils.
Rather complex composition of soil organic matter, soil organic matter composition depends on the composition of organic matter into the soil. Variety of plant and animal residues of the chemical composition and content by animal and plant species, organ, age, there is a big difference. Under normal circumstances, plant and animal residues main organic compounds are carbohydrate, lignin, protein, resin, wax, etc. Major element composition of soil organic matter is c, o, h, n, respectively, 52%-, 34%-9%, 3.3%-4.8%,3.7%-4.1%.
Only organic matter into the soil can become stable components of the natural, the process is done through a process of mineral, must have the participation of microbes. Mineral process of organic matter into chemical conversion process, animal and microbial transformation of the transformation process. This procedure enables the transformation of soil organic matter into carbon dioxide, water, ammonia, and mineral nutrients (phosphorus, sulfur, potassium, calcium, magnesium and other simple compounds or ions) and release energy. This process provides nutrients and energy for plants and soil microorganisms, and directly or indirectly affect soil properties, but also provides the material base for synthesis of humic substances.
Arable land is in the destruction of natural ecosystems, cultivated land was originally from natural soil sequestration of organic matter. Chinese people have long "yangdi" good habits, central region a lot of continuous cultivation of arable land over four thousand or five thousand years, little degradation, is to use measures of eco-agriculture yangdi. Throughout today, mainland arable land used fertilizer, pesticides herbicides, agricultural film, just less than 40, a serious degradation of cultivated land reclamation of grasslands, deserts and oases, at first a high organic matter (>5%), but uses less than 10 severely degraded, until becoming desert. Our ancestors is certainly not in a draught for land reclamation, only those excesses of capital can be capricious to mess things up.
Third, the important role of soil organic matter
The content of soil organic matter and soil fertility levels are closely related. Although it accounted for only a small fraction of the total soil organic matter, but it played a multifaceted role in soil fertility are significant. Usually under the same or similar conditions, organic matter content was positively correlated with soil fertility.
First, soil organic matter provides nutrition for plants. Soil organic matter contains large amounts of plant nutrients such as n, p, k, Ca, Mg, s, Fe, and other important elements, and some trace elements. Mineral process of releasing large amounts of nutrients in soil organic matter provides nutrients for plant growth; synthesis the humification process of humus, saving nutrients, humus and they were released again the process of mineral nutrients, so as to ensure plant growth, nutrient demand of the entire process.
Mineral process of organic matter decomposition of plant carbon CO2 is an important source of nutrition, it is estimated that soil organic matter decomposition and microbial biomass and root respiration produces CO2, up to 13.5 billion t per year, roughly equivalent to the requirements of terrestrial plants. This shows that the CO2 produced by the process of mineralization of soil organic matter is an important source of CO2 in the atmosphere, but also important carbon source for photosynthesis and plant. Soil organic matter is the most important soil n and p nutrition, is the source of available n and p in plants. Total soil n 92%-98% is the storage of organic n in soils. According to studies, plant uptake of nitrogen known as 50%-70% from the soil. Organic p in soil organic matter content of soil total phosphorus 20%-50%, with the decomposition of organic matter releases phosphorus supply plant nutrients. In most non-calcareous soil, organic the organic sulfur from sulfur 75%-95%, with the release of mineral process of organic matter, is absorbed by the plants.
Second, the absorption of other nutrients in the soil organic matter plant. In the process of decomposition and transformation of soil organic matter, organic acids and humic acid on soil mineral part has a certain degree of solvency, can contribute to mineral weathering, in favour of certain nutrient availability. Some organic acids and fulvic acid complexes the metal ion can remain in the soil solution, will not affect its validity precipitation. Soil humus and some compounds of iron in acidic or alkaline in soil, on plants and micro-organisms are effective.
Soil humus is a colloidal, with high specific surface area and surface, negatively-oriented colloidal humus, thus adsorption in soil solution and exchangeable cations such as k +, NH4+, Ca2+, and Mg2+ etc, it will prevent water loss, on the other hand, can be exchanged for plant uptake and use. Its fertility is very significant. In terms of water conservation, soil humus and clay minerals, has strong adsorption capacity, but humus ability to save cation nutrients per unit mass several times to dozens of times larger than the clay minerals, so fertility of soil organic matter has a huge capacity.
Third, soil organic matter of plant growth and development. Soil organic matter, humic acids, polyphenols with aromatic groups, strengthening the process of plant respiration, increase the permeability of the cell membrane, promoting nutrients into plant cells. Humic acid sodium salt on the growth of plant roots promotes, humic acid sodium salt on corn, grasses and grass root growth has a great role. Soil organic matter also contains vitamins B1, B2, h-acid and Nicotinic Acid, hormones, different Auxin (β-indolylacetic acid), antibiotics (streptomycin, penicillin), promotes the growth of plants, and plant resistance to disease. Finally, improvement of soil physical properties. Effect of physical properties of organic matter in the soil is in many aspects, is one of the most important and direct role in improving soil structure, and promote the formation of granular structure, so as to increase the porosity of the soil, improve soil aeration and permeability. Humus is the main cement soil aggregates,
humus in the soil is rarely free, and most of the mineral soil particles and combined, through mechanisms such as functional groups, hydrogen bonds, van der Waals force, in the form of film coating in the mineral soil surface, formation of organic-inorganic composite body.
The formation of aggregates, small and large pore distribution is reasonable and has good water stability, is a better structure. In the dry zone, organic matter through improving stickiness, reduce the swelling and shrinkage of soil, prevent large fissures in the soil drought (the crack).
Soil humus is hydrophilic colloids, with high specific surface area and hydrophilic groups, determination of water absorption is about 500% humus and clay mineral water absorption rate of only about 50%, so can increase the effective water-holding capacity of the soil, the sand is of great importance. For the Brown, dark brown or black humus substances, is surrounded by soil soil after dark, so as to increase the soil's ability to heat and raise the soil temperature, this spring to promote seed germination characteristics on the North are particularly important. Heat capacity than air, minerals, humus, and as water, thermal centers and, therefore, higher soil organic matter content in the soil the soil temperature is relatively high, and the amplitude is small, good thermal insulation.
Finally, soil organic matter is a major source of soil bio-energy. No soil micro-organisms will not have all the biochemical processes in the soil. Soil microbial populations, quantity and activity increase with increasing organic matter content, with a highly significant positive correlation. Low level of mineralization of soil organic matter, not as fresh plant residues rapid excitation effect on microorganisms but lasting stability to provide energy to microbes. Therefore, the soil is rich in organic matter and fertility of smooth and less prone to persistent plants long and fat removal.
Soil macrofauna (earthworms) with organic matter as food and energy source; can improve the physical environment of soil organic matter, increasing the degree of osteoporosis and increased permeability (for sand, reducing permeability), which provides good conditions for activity of soil animals and animal itself accelerates the decomposition of organic matter in soils (especially those of fresh organic matter decomposition). Further improve soil permeability, soil microbes and plants to create a good environment. Vermicompost is very good crumb structure, has the characteristic of water does not come loose. Natural reproduction of earthworm population size are important indicators of a healthy soil.
Last, with the activation of soil organic matter and phosphorus, potassium and other nutrients. Soil phosphorus is generally not available in the library exists, often with efficiency-State moderate activity States. Low p availability in soil. Soil organic matter with insoluble phosphorus response characteristics can increase the solubility of phosphorus, so as to improve the effectiveness of phosphorus in soil and phosphorus utilization. In addition, soil humic acid is a physiological active substances, it can speed up germination, enhance root activity, promote plant growth, soil microbes, humic acid is a physiological active substances to promote growth. Some microorganisms have the function of potassium, these microbes must exist with lots of organic matter.
Four sources, human health, soil organic matter
Soil is made up of solids, air and water, mainly from solid part of the rock matrix which native minerals and particles as well as from biological (animals, plants and micro-organisms) living and organic residue left behind. Soil organic matter is to provide crop growth and nutrient storage. Status and amount of organic matter in the soil, must maintain a relatively stable enough. Soil organic matter content in the dry land 0.5%~3.0%, 1.5%~6.0% in paddy field. Because organic matter decomposition and conversion are ongoing. In the process of growth and decline of soil organic matter, soil fertility also correspondingly with the ever-changing.
According to the Guangdong Institute of eco-environment and soil researcher Chen Neng presentations, ideal soil, solid 50%, air and water 25%. Solid minerals section 45% and 5% of organic matter, activities 10% of the bio-organic root organic matter accounts for 10%, has been transformed into a stable polymer "dead" organic matter accounts for around 80%.
Cultivated organic matter itself is the nutrient storage, and profoundly affected the physical, chemical, and biological properties of the soil. Assume that a surface soil organic matter content of the soil 4%, organic matter and nitrogen content of 5%, a crop
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