What is soil salinization? What are the hazards of soil salinization?

Soil salinization refers to the fact that the soil salt content is too high (exceeding, and the crops are low or cannot grow.

There are two conditions for the formation of saline-alkali soil: first, the climate is arid and the groundwater level is high (above the critical water level); The other is low-lying and there is no way to drain the water. Groundwater contains a certain amount of salt, and if its water surface is close to the ground, and the area is relatively arid, the water that rises to the surface due to capillary action evaporates, leaving salt

Over time, the salt content of the soil gradually increases, forming saline-alkali soil. If it is a depression and there is no drainage outlet, the water in the depression will evaporate, leaving salt and forming a saline-alkali land.

Adverse effects: 1. Soil compaction and fertility decline.

2. It is not conducive to the absorption of nutrients by crops and hinders the growth of crops.

Prevention and control: The measures to control saline-alkali land include water conservancy improvement measures (irrigation, drainage, dredging, rice planting, seepage prevention, etc.); agricultural improvement measures (land leveling, improved tillage, soil application, fertilization, sowing, crop rotation, intercropping, etc.); biological improvement measures (planting salt-tolerant plants and pastures, green manure, afforestation, etc.); and chemical improvement measures (application of improved substances such as gypsum, phosphogypsum, calcium sulfite, etc.). Four aspects.

Since each measure has a certain scope of application and conditions, it is necessary to adapt measures to local conditions and comprehensively deal with them.

The pH value of the soil due to acid rain or environmental pollution is acidic or alkaline, which is not conducive to the growth of plants.

The harm of salt to crop growth is mainly twofold:

The first is the high salt osmosis, which affects the absorption of water by crops.

The second is single salt toxicity, which will also affect the structure of the soil, and soil microorganisms will indirectly affect the growth of crops.

China's saline soil, or saline-alkali soil, has a wide distribution range, a large area, and many types, with a total area of about 100 million hectares. It occurs mainly in arid, semi-arid and sub-humid regions. The soluble salts of saline-alkali soils mainly include sulfates, chlorides, carbonates and bicarbonates such as sodium, potassium, calcium, magnesium, etc.

Sulfates and chlorides are generally neutral, and carbonates and bicarbonates are alkaline salts.

Agricultural measures. Agricultural technical measures are irreplaceable for consolidating the effect of improving and utilizing saline-alkali soil and improving its economic benefits. Therefore, on the basis of water conservancy engineering measures, the timely implementation of agricultural technical measures can not only speed up the improvement process, but also improve the improvement effect. The main agricultural technical measures for improving and utilizing saline-alkali land include rational farming, combining use and reform, carrying out micro-area soil modification, large hole land preparation and increasing organic fertilizer.

Saline-alkali soil compaction, deep tillage is not only conducive to loosening the surface layer, breaking the bottom layer of the plow, improving soil permeability, changing the distribution of salt in the soil profile, but also cutting off the capillary, reducing water evaporation, and inhibiting salt return.

The application of organic fertilizer can increase soil organic matter, promote the formation of aggregate structure, improve the physical properties of soil, and also improve the water storage capacity and temperature status of soil, so as to improve the ability of soil to store and regulate nutrients.

Moreover, the organic acids produced in the process of organic matter decomposition can not only neutralize alkalinity, but also activate calcium in the soil, which can play a role in reducing or eliminating alkali damage. The main sources of organic fertilizer are: green manure (which can be obtained through a large number of planting, varieties such as field cyanine, grass and tree trees, etc.); excrement such as manure, urine and other excretions from people, livestock and poultry; Domestic garbage crop straw crushed and returned to the field.

The typical sign of direct damage to crops caused by soil salinization is that the plant grows delicately and is diapaused. Under the premise that there is not much deficiency in temperature, moisture and fertilizer, the root system of vegetable plants in the shed is poorly developed;

The proportion of old roots and new roots is unbalanced, and the ability to absorb fertilizer and water is poor, which significantly delays the growth and development period, especially the yield in the early and middle stages, and the yield will be reduced by 10%-30% if the damage is serious, which directly affects the cultivation efficiency.

In the field diagnosis, if other harmful factors have been ruled out, and the crop plants are still showing poor growth and the root system is not developing well, it is basically the consequence of this soil salinization.

There are four causes of soil salinization:

First, the salt accumulated in the soil cannot be leached into the groundwater, but accumulates on the surface of the soil;

Second, the protected land is often irrigated, the soil is in a moist state for a long time, the crops grow vigorously, and the evaporation of soil moisture and the transpiration of crops are very large, which promotes the accumulation of salt to the soil surface.

Third, excessive fertilization increases the salt content of the soil, especially the excess of acid ions of nitrogen fertilizer, which acidifies the soil and activates some cations, which accumulate on the soil surface with the movement of water.

Fourth, the special environment formed by continuous cropping for many years restricts the activities of beneficial microorganisms, while harmful bacteria become active, so that the activities of beneficial microorganisms are restricted, while harmful bacteria are active, destroying the natural balance of soil microorganisms and inorganic nutrients, and affecting the decomposition of fertilizers.

1. Affect the growth of crops.

Due to the high salt concentration of the soil, the crop roots can not effectively absorb the water and nutrients in the soil, and the symptoms of nutrient deficiency appear, which are manifested as weak plant growth, yellowing, wilting, weak root system and other symptoms, and in severe cases, the root system dies, resulting in the death of the whole plant.

2. Prone to diseases and pests.

Soil salinization leads to crop dehydration, affects normal respiration, reduces immunity, and water nutrients do not go up, the epidermal cells of the leaf and fruit are not robust, and the wound is affected by the external environment, which is easy to be infected by pathogenic bacteria and cause leaf and fruit diseases.

3. Reduce the yield and quality of agricultural products.

Crops grown in salinized soil, fruit yield and quality will be affected, crop root growth is inhibited, can not normally absorb water, inorganic salts for aboveground utilization, leaf photosynthesis is inhibited, the production of amino acids, organic acids, sugar and other nutrients and flavor substances are reduced, resulting in small fruits, poor taste, reduce fruit yield and quality, some particularly serious salinization plots, so that crop yield is greatly reduced or even no harvest.

Causes: 1. Excessive application of chemical fertilizers. The absorption and utilization rate of ordinary compound fertilizer is about 30%, and the remaining fertilizer will be fixed in the soil in large quantities, so that the chemical properties of the soil will change, resulting in the decline of the soil's fertilizer supply capacity. Excessive application of livestock and poultry manure (especially chicken manure, duck manure, pig manure) will also have a certain impact on the soil.

2. Long-term use of flood irrigation will cause adverse effects on soil compaction and leaching. To a certain extent, flood irrigation has a heavy compaction effect on the soil, especially for cohesive soil, the soil cultivated layer is in an anaerobic state after flood irrigation, which inhibits the absorption of nutrients by roots and aggravates the soil salt concentration.

The main salts in the soil are weathering products and saline groundwater. The salt content of irrigation water and the application of physiological alkaline fertilizers can also increase the salinity in the soil. After soil salinization, the osmotic pressure of the soil solution increases, the soil aeration and permeability deteriorate, and the nutrient availability decreases, resulting in the normal growth of plants.

(1) Physical and geographical factors.

1.The arid climate is an important condition for the formation of saline-alkali soils.

The arid climate and strong evaporation in Xinjiang determine the water movement dominated by the upward flow of water in the soil, which causes the soluble salt of the soil to rise and accumulate on the surface of the soil, resulting in the general accumulation of salt in the soil. The high salt content of the strata and soil parent material also provides a salt source for the formation of saline-alkali soils.

2.The closed geomorphological and hydrological characteristics are the strengthening factors for the formation of saline-alkali soils.

Most of Xinjiang's rivers are inland rivers surrounded by high mountains, and they all end up in the low-lying areas in the center of the basin, so that salt is constantly collected in the basin.

3.Surface and subsurface runoff are the main driving forces for the formation of saline-alkali soils.

Surface and underground runoff flows through the saline highland layer, dissolves and carries a large amount of salt, causing the soil salinization in the flowing area or the accumulation of salt in the surface layer of the soil through strong evaporation, forming a large area of saline soil.

4.Halophytes are a contributing factor to the formation of saline-alkali soils.

Its roots absorb water and nutrients while bringing salt from deep soil or groundwater into the body, and when the residue decomposes and scatters, the salt accumulates in the topsoil.

2) Human factors.

The rise of groundwater level caused by improper irrigation is the root cause of secondary salinization of oasis soil.

1) The groundwater level rises due to large leakage from canals and plain reservoirs and the use of flood irrigation for farmland irrigation.

2) Heavy irrigation and light drainage, the drainage outlet is not smooth, so that the groundwater level is difficult to lower.

3) Irrigation from the top to the bottom, and the deterioration of water quality enters the farmland. The upstream drainage is discharged into the nearby river, and the downstream irrigation is redirected, so that the salt is brought back into the farmland.

The causes of soil salinization are: the influence of climate, the influence of temperature, the influence of water level, the influence of vegetation and the influence of topography.

1. The impact of climate. The dryness of the climate and the ratio of ground evaporation to precipitation are closely related to soil salinization, and soil freezing exacerbates the process of soil salinization.

2. The influence of temperature. Under the influence of the geothermal gradient, soil water moves from the bottom to the freezing front, and the salinity migrates upward. When the local temperature gradient is large or the groundwater level is high, the migration of water and salinity increases, and when the soil contains salt, the freezing depth decreases correspondingly, the water and salt are lifted close to the surface, and the soil salinization enters the gestation and destruction period.

3. The influence of water level. Surface and groundwater runoff and water quality directly affect soil salinity.

4. The influence of vegetation. Meadow plants and desert plants grow in arid and semi-arid areas, halophytes have a salt content of up to 10% to 45%, absorb water and salt from the bottom through a strong root system, and retain the ground in the form of fibrids, and the calcium and sodium salts formed by the decomposition of plant debris are returned to the soil, which plays a role in contributing to the salt evolution of the soil.

5. The influence of terrain. The topography and landform directly affect the runoff of surface water and groundwater, and the degree of soil salinization gradually increases with the topography from high to low and from upstream to downstream.