First, what is the role of soil organic matter:

Soil organic matter plays an important role in soil fertility and plant nutrition. It mainly includes the following aspects:

1. Provide various nutrients needed for crops

Soil organic matter is not only a stable and long-lasting nitrogen source, but it also contains almost all the nutrients needed for crops and microorganisms. A large amount of data indicates that about 80% of nitrogen and 20%~76% of phosphorus in the main soil topsoil in China exist in organic form. In most non-calcium soils, organic sulfur accounts for 75%~95% of total sulfur. With the mineralization of organic matter, these nutrients become mineral salts (such as ammonium salts, sulfates, phosphates, etc.) and are continuously released at a certain rate for use by crops and microorganisms.

In addition, it is estimated that the decomposition of soil organic matter and the CO2 produced by microbial and root respiration can reach 1.35*1011t per year, which is roughly equivalent to the demand of terrestrial plants. It can be seen that the mineralization decomposition of soil organic matter is an important source of CO2 in the atmosphere. It is also an important source of plant carbon nutrition.

In addition, in the process of decomposition of soil organic matter, a variety of organic acids (including humic acid itself) can be produced, which has certain solubility in the mineral part of the soil, promotes weathering, is conducive to the effectiveness of certain nutrients, and can also complex Some polyvalent metal ions increase their effectiveness without causing precipitation in the soil solution.

2. Enhance soil water retention and fertilizer retention capacity and cushioning

The humus is porous and porous, and it is a hydrophilic colloid. It can hold a large amount of water, so it can greatly improve the water retention capacity of the soil. In addition, humus improves soil permeability, reduces water evaporation, and provides more effective water for crops.

Humus has positive and negative charges, so it can absorb yin and cation; and because its chargeability is mainly negative, it has strong ability to absorb cations, among which K+, NH4+, Once cations such as Ca2+ and Mg2+ are sucked, they can avoid loss with water, and can be exchanged by other cations near the roots for absorption by the crops without losing their effectiveness.

The ability of humus to retain cationic nutrients is many times to several dozen times greater than mineral colloids. Generally, the absorption of humus is 150~400 cmol(+)/kg. Therefore, the addition of organic fertilizer to the sand with weak fertility not only increases the nutrient fraction in the soil, improves the physical properties of the sand, but also improves its fertilizer retention capacity.

Humus is a weak acid containing a multi-acid functional group, and its salt has an amphoteric colloidal action, so it has a strong ability to buffer acid-base changes. Therefore, increasing the soil humus mass fraction can enhance the performance of soil buffer acid-base changes.

3. Improve the physical properties of the soil

The humus is mainly coated in the form of a film on the surface of the mineral soil. Since it is a kind of colloid, the cohesive force and the adhesive force are larger than the sand particles. After being applied to the sand soil, the viscosity of the sand soil can be increased, and the formation of the agglomerate structure can be promoted. Because it is soft, flocculent, porous, the adhesion is 11 times smaller than the cosmid, and the adhesion is less than half of the cosmid. Therefore, after the cosmid is coated, it is easy to form scattered agglomerates, making the soil softer. And no longer form a hard block. It shows that the organic matter can make the sand compact, the clay becomes loose, and the soil retains water, water permeability and ventilation. At the same time, the soil ploughing is also improved, the ploughing and labor saving, the long tillage period, and the quality of farming are correspondingly improved.

Humus also has an effect on the thermal state of the soil. Mainly because humus is a dark brown substance, its presence can significantly deepen the color of the soil, thereby increasing the heat absorption of the soil. At the same time, the heat capacity of humus is smaller than air and minerals, but smaller than water, and the thermal conductivity is middle. Therefore, under the same sunshine conditions, the soil temperature with high humus mass fraction is relatively high, and the variation is not large, which is conducive to the early growth of heat preservation and spring sowing crops.

4. Promote soil microbes and activities

The energy substances and nutrients required for soil microbial life activities are directly and indirectly derived from soil organic matter, and the humus can regulate the acid-base reaction of the soil and promote the improvement of physical properties such as soil structure, which is beneficial to the activities of microorganisms. This promotes the ability of various microorganisms to convert substances. Soil microbial biomass increased with the increase of soil organic matter mass fraction, and there was a significant positive correlation between the two. However, due to the low mineralization rate of soil organic matter, it does not have a rapid stimulating effect on microorganisms like fresh plant residues, but provides energy for microorganisms in a stable and stable manner. Because of this, soil fertility with a lot of organic matter is stable and long-lasting, and it is not easy to produce crops that are violent or de-fertilized.

5. Promote the physiological activity of plants

Humic acid can promote the physiological activity of plants at a certain concentration.

(1) The dilute solution of humate can change the sugar metabolism in plants, promote the accumulation of reducing sugars, and increase the osmotic pressure of cells, thereby enhancing the drought resistance of crops. Fulvic acid is also a major component of certain drought-tolerant agents.

(2) It can increase the activity of catalase, accelerate seed germination and nutrient absorption, thereby increasing growth rate.

(3) It can enhance the respiration of crops, increase the permeability of cell membranes, thereby increasing their ability to absorb nutrients, accelerate cell division, and enhance root development.

6. Reduce pollution of pesticides and heavy metals

Humus helps to eliminate pesticide residues and heavy metal pollution in the soil and the toxicity of Al, Mn and Fe in acidic media. In particular, brown humic acid can increase the solubility of certain pesticides such as DDT and triazabenzene remaining in the soil, accelerate the leaching of the soil, and reduce pollution and toxicity. Humic acid can also complex with certain metal ions. Due to the water solubility of the complex, toxic metal ions may be discharged with water, reducing crop damage and soil pollution.

Second, the adjustment of soil organic matter

1. Regulation principle Soil organic matter

The amount of humus mass fraction is an important indicator of soil fertility. Within a certain range of organic matter mass fraction, soil fertility increases with the increase of organic matter mass fraction, and crop yield also increases with the increase of organic matter mass fraction, but the soil organic matter is not as good as possible. When it exceeds a certain range, the correlation is Not obvious. Excessive organic matter quality fraction is neither economical nor beneficial to improving soil fertility. For example, some low-humidity paddy soils have a high organic matter mass fraction, which is caused by the slow decomposition of the soil due to excessive soil moisture. symbols of.

The main measures to increase the organic matter in the soil are: on the one hand, it is necessary to increase the source of soil organic matter; on the other hand, it is necessary to understand the factors affecting the accumulation and decomposition of organic matter, in order to regulate the accumulation and decomposition process of organic matter, so that the accumulation and consumption of soil organic matter can be achieved. dynamic equilibrium.

2. Ways to increase soil organic matter

The organic matter quality fraction of agricultural soils in China is mostly low, especially in the North China Plain and the Loess Plateau. Increasing the quality of soil organic matter in these areas will effectively increase soil productivity. Ways to increase soil organic matter are:

1. Planting green manure crops

Planting green manure and implementing green manure and grain crop rotation have always been an important source of fertilizer for replenishing soil organic matter in agricultural production in China. High green manure yield, high organic matter mass fraction (generally 10% to 20%), rich in nutrients (generally containing NO 5%, P2O50.1%, K2O 0.5%), decomposition is also faster, and humus formation is faster. Continuously update soil humus.

Compared with single crop continuous cropping, the implementation of green manure or pasture and crop rotation can significantly increase the quality of soil organic matter. According to the results of the positioning test conducted by the National Green Fertilizer Experiment Network in 16 provinces (regions), whether it is in the south or north of China, dry land or paddy field, the green manure is turned over for 5 consecutive years, and the soil organic matter is obviously improved. 1-2 gÂ·kg-1 soil. However, soil fertility is different, and the effect of cumulative organic matter is quite different. On soil with high fertility, green manure can only play a role in maintaining soil organic matter level; while soil with low fertility, green manure has a good effect of increasing soil organic matter mass fraction.

In order to prevent the massive consumption of the original organic matter in the soil and the toxic substances that may be produced when the green manure is decomposed, the method of manure can be adopted. First, the green manure and the straw, river mud, etc. are smashed together, and then applied to the soil, or the method of changing the fertilizer. Part of the green manure is cut for use as feed, and then part of the manure is used instead of green manure.

2. Add organic fertilizer

Chinese farmers have the habit of applying organic fertilizer, and there are many types and quantities of application, such as manure, manure, compost, grass, young leaves, cake fertilizer, silkworm, fish fertilizer, etc., in which manure and manure are commonly used. The main organic fertilizer. This should encourage farmers to develop organic fertilizers while vigorously developing animal husbandry. The accumulation of livestock and livestock is generally based on raising pigs. If the average pig is 30 pigs per hectare and 22,500 kg of manure per hectare, the increased dry weight per hectare of soil can reach more than 750 kg.

3. Straw returning

Returning straw directly to the field is an effective measure to increase soil organic matter and increase crop yield. Crop straw contains more cellulose and lignin. In the process of decomposition, humification is slower than that of legumes, but more humus can be formed. For soils with more nitrogen, the effect of returning straw to the field is better. When the straw is used for returning to the field, the quick-acting nitrogen fertilizer should be applied appropriately. Otherwise, the straw decomposition will be slow or the crop will be decomposed and the crop will produce yellow seedling and nitrogen deficiency. phenomenon. When the straw is returned to the field, it is best to use the straw or manure of the gramineous plant in combination, which can adjust the C/N ratio, accelerate the decomposition of the residue, accumulate humus and prevent the occurrence of nitrogen deficiency in the crop. The yield increase effect of undergraduate straw or legume straw is good. It should be pointed out that the way to increase organic matter should be adapted to local conditions. For example, in areas where animal husbandry is the main area, grain and grass rotation can be used; in mountainous areas, comprehensive management of mountain areas should be combined to develop forestry and animal husbandry; in the plain area, in addition to developing green manure, forestry should be actively developed, greening should be carried out, and straw should be returned to the field. The number is constantly increasing.

3. Adjust the decomposition rate of soil organic matter

The decomposition rate of soil organic matter is closely related to soil microbial activity, so we can control the rate of decomposition of soil organic matter by controlling the factors affecting microbial activity. The main ways of regulation are as follows:

1. Regulate soil water, gas and heat conditions and control the conversion of organic matter

Soil water, gas and heat conditions affect the direction and speed of organic matter conversion. In production, the water, gas and heat conditions of the soil are often improved through irrigation, drainage and cultivation, so as to promote or regulate the transformation of soil organic matter.

2. Reasonable farming and rotation

Reasonable tillage rotation can not only regulate the types and quantity of organic matter entering the soil and its distribution in different depth soil layers, but also regulate the water, gas and heat conditions of organic matter conversion. Maintaining and increasing the quality and quantity of soil organic matter is often a powerful measure to influence the overall situation. The good grain and fertilizer rotation, water and drought rotation system formed by the Chinese people in the regular production practice are all good agricultural farming measures for land conservation, which not only helps to exert the soil fertility, but also improves the organic matter quality score and fertilizes the soil.

3. Adjust carbon to nitrogen ratio and soil pH

According to the composition of organic matter, adjust its carbon to nitrogen ratio to regulate the mineralization and humification process of soil organic matter. When applying organic fertilizer with a large carbon to nitrogen ratio, some fertilized organic fertilizers and chemical nitrogen fertilizers with high nitrogen content can be appropriately added at the same time, and the carbon-nitrogen ratio is reduced to accelerate the conversion of organic matter. Soil microorganisms are generally suitable for living in the neutral to slightly alkaline range. By improving the acidity and alkalinity of the soil, the microbial activity is enhanced to improve the conditions of soil organic matter conversion.

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