Saline alkali land is a kind of salt accumulation, which means that the salt contained in the soil affects the normal growth of cropsUNESCOAccording to incomplete statistics from FAO, the area of saline alkali land in the world is 954.38 million hectares, including 99.13 million hectares in China.China's alkaline soil andAlkalized soilThe formation of is mostly related to the accumulation of carbonate in the soil, sobasicityGenerally higher, plants can hardly survive in severe saline alkali soil areas.
From September 23 to 24, 2022, the 4th International Delta Forum and Saline alkali Land Seed Industry Innovation Forum academic conference was held in Dongying City, Shandong Province.[3]
In the process of utilization, saline alkali land can be divided into light saline alkali land, medium saline alkali land and heavy saline alkali land.
Saline alkali land
Light saline alkali land means that its emergence rate is 70% - 80%, and its salt content is less than 3 ‰;Heavy salt alkaline land means that its salt content is more than 6 ‰, and its emergence rate is less than 50%;The middle part is moderately saline alkali land (withPH valueIt is expressed as: pH value of slightly saline alkali land is 7.1-8.5, pH value of moderately saline alkali land is 8.5-9.5, and pH value of severely saline alkali land is above 9.5).
All kinds of saline alkali soil are formed under certain natural conditions, and the essence of its formation is mainly the redistribution of various soluble salts in the horizontal and vertical directions on the ground, so that salt gradually accumulates on the surface of the soil in salt collecting areas.The main factors affecting the formation of saline alkali soil are:
1. Climatic conditions
In the arid and semi-arid areas of northeast, northwest and north China, the precipitation is small, the evaporation is large, and the salt dissolved in water is easy to accumulate on the soil surface.In summer, there are many concentrated rainwater, and a large amount of soluble salt seeps into the lower layer or flows away with the water, which is the "desalting" season;In spring, the evaporation of surface water is intense, and the salinity in groundwater increases withCapillary waterIt rises and gathers in the soil surface, which is the main "salt return" season.Saline alkali soil in Northeast China, North China and semi-arid areas has obvious "desalinization" and "salt return" seasons, while in Northwest China, the seasonal change of soil salinity is not obvious because of little precipitation.
2. Geographical conditions
The height of terrain has a great impact on the formation of saline alkali soil. The height of terrain directly affects the movement of surface water and groundwater, which is closely related to the movement and accumulation of salt. From the perspective of large terrain, water-soluble salt moves from high to low with water, and accumulates in low-lying areas.Saline alkali soil is mainly distributed inInland basin, intermountain depressions and flat plain areas with poor drainage, such asSongliao Plain。From the perspective of small terrain (local scope), the situation of soil salt accumulation is opposite to that of large terrain, and salt tends to accumulate in local small bumps.
3. Soil texture and groundwater
Texture can affectSoil capillary waterThe speed and height of movement. Generally speaking, the capillary water of loam soil rises faster, and the height is also higher. The salt accumulation of sand and clay is slower.The key problem of groundwater affecting soil salinity is the height of groundwater level andGroundwater mineralizationSize of,High groundwater level, high salinity, easy to accumulate salt.
4. Impact of rivers and seawater
The ground water level of the river and the land on both sides of the channel is raised due to the lateral seepage of the river, which promotes salt deposition.Coastal saline alkali soil can be formed in coastal areas due to seawater immersion.
5. Improper farming management
Some places are flooded with water when watering, or low-lying areas are only irrigated without drainage, so that the groundwater level rises quickly and salt accumulates, turning the original good land into saline alkali land. This process is calledsecondary salinization 。In order to prevent secondary salinization, water conservancy facilities should be equipped with drainage and irrigation facilities. Flooding irrigation is strictly prohibited. After irrigation, plowing and hoeing should be carried out in time.
Land improvement
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The basic reason for the formation of saline alkali soil is poor water condition, so in the initial stage of improvement, the focus should be on improving the soil water condition.Generally, it is carried out in several steps. First, salt is discharged and washed to reduce the salt content of soil;Then plant salt tolerant plants to fertilize the soil;Finally, plant crops.The specific improvement measures are: drainage, irrigation and salt washing, silting improvement, rice planting, fertilizer improvement, land leveling and chemical improvement.
amendment
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Saline alkali soil is the general name of saline soil and alkaline soil.Saline soil mainly refers to saline soil with high chloride or sulfate content. The soil is alkaline, but the pH value is not necessarily high.Alkaline soil refers to the soil containing carbonate or diphosphate. The soil is alkaline with high pH value, low organic matter content, low soil fertility, poor physical and chemical properties, and many negative and positive ions harmful to crops, making it difficult for crops to promote seedlings.The fertilization principle of saline alkali soil isOrganic fertilizerAnd high efficiency compound fertilizers, and control the use of low concentration fertilizers.Organic fertilizer contains a large amount of organic matter, which can buffer harmful anions and cations in the soil, and is conducive to rooting and seedling promotion.High concentration compound fertilizerThere are few invalid ingredients and residues, but the amount of chemical fertilizer should not be too much each time to avoid aggravating the secondary salinization of soil. After applying chemical fertilizer, irrigation should be combined to reduce the concentration of soil solution.
The improvement methods of saline alkali land are as follows:
1. Wash salt.Salt washing is to irrigate water into saline alkali land to dissolve the soil salt, drain the soluble saline alkali in the topsoil layer into deep soil or leach it out through infiltration, and then drain it into the drainage ditch.
2. Land leveling.Leveling the land can make the water infiltrate evenly, improve the effect of rainfall salt spraying and irrigation salt washing, and prevent the soil from porphyritic salinization.Deep ploughing and deep ploughing.The distribution of salt in the soil is that there is more salt in the surface layer than in the lower layer. After ploughing, the salt in the surface soil can be turned over to the lower part of the plough layer, and the soil with less salt in the lower layer can be turned over to the surface.Tillage can loosen the plough layer, cut off the soil capillary, weaken the soil water evaporation, and effectively control the soil salt return.The best time for plowing in saline alkali land is spring and autumn.Spring and autumn are the seasons of heavy salt return.Autumn ploughing is especially beneficial to killing disease and insect eggs, removing weeds, deeply burying roots, strengthening the decomposition of organic matter and the release of delayed nutrients, so it is worth advocating.
3. Rake the land timely.Raking can loosen the topsoil, cut off the capillary water of the soil to transport salt to the surface, and prevent salt return.The land shall be harrowed in a timely manner, with shallow spring ploughing, rush ploughing, early autumn ploughing, and dry ploughing instead of wet ploughing.
4. Increase the application of organic fertilizer and apply chemical fertilizer rationally.Saline alkali land is generally characterized by low temperature, thin soil and poor structure.Organic fertilizer can be decomposed and transformed into humus by microorganisms, which can improve the buffer capacity of soil, and can react with sodium carbonate to form sodium humate, reducing soil alkalinity.Sodium humate can also stimulate crop growth and enhance salt tolerance.Humus can promote the formation of aggregate structure, thus increasing porosity and water permeability, which is conducive to salt leaching and inhibiting salt return.Organic matter produces a large amount of organic acids during decomposition, which can neutralize soil alkalinity on the one hand, accelerate nutrient decomposition on the other hand, promote the transformation of delayed nutrients, and improve the availability of phosphorus.Therefore, increased applicationOrganic fertilizerIt is an important measure to improve saline alkali land and improve soil fertility.In addition, people also attach importance to the role of chemical fertilizers in improving salinity. Chemical fertilizers increase nitrogen, phosphorus and potassium in the soil, promote crop growth, and improve the salt tolerance of crops.Applying chemical fertilizer can change the soil salt composition and inhibit the adverse effects of salt on plants.Inorganic fertilizer can increase crop yield, increase straw, expand organic fertilizer source, and promote organic production with inorganic fertilizer.Of course, alkaline fertilizers, such as ammoniaAmmonium bicarbonate, lime nitrogen, calcium magnesium phosphate, etc., and neutral and acid fertilizers should be preferred.Potassium sulfate compound fertilizerIt is a slightly acidic fertilizer, suitable for use on saline alkali land, and has a good effect on improving saline alkali land.
5. It can be controlled by non chemical means, and can be used exclusively for saline alkali landSoil conditioner"Alkali control" can effectively improve the soil. First, it can promote the exchange and release of metal ions in the soil and reduce the salt content;Second, it contains a kind of plant derived acidic substance, which can effectively neutralize the alkaline components in the soil, and does not cause any harm to plants and soil itself, which is in line with the development direction of green agriculture in the future;Third, this kind of plant derived acid itself has a great impact onPlant virus diseaseIt has good prevention and treatment effect, and can effectively prevent and control the occurrence of plant seedling diseases.The specific usage is as follows:
Flooding irrigation: first, the land to be used for alkali treatment shall be deeply turned over and raked, then the quantitative alkali treatment shall be diluted with water (the dilution multiple is unlimited, and it is better to save time and labor), and then the water shall be sprayed evenly on the surface before irrigation, and water leakage and cross irrigation shall be prevented.
Drip irrigation: add alkali treatment directly into the fertilizer tank and drip with water.First drip clean water for about 3 hours, and then add alkali treatment to drip with water.
Sprinkler irrigation: if there is a reservoir, alkali treatment can be added;If there is no water reservoir, the alkali treatment can be sprayed on the ground first and then sprayed for irrigation.The duration of sprinkling irrigation should be properly extended, at least 30 cm above the wet plough layer, and the deeper the wet layer, the better.
Application time:
Cotton: applied during winter irrigation or spring irrigation;Drip irrigation can be applied when the seedling water is dripping to increase the emergence rate, or it can be applied with water at the seedling stage. The earlier the application time at the seedling stage, the better;It can be applied at acupoints in areas lacking water.
Rice: when raising rice seedlings, spray on the seedbed to make the seedlings neat and strong;Spraying in paddy fields before and after transplanting, the seedlings turn green quickly, the tillering rate is greatly improved, and the maturity is about a week earlier.
Corn, wheat, soybean, etc.: treat the soil before sowing to improve the emergence rate;It shall be applied when watering at seedling stage.
Economic forest: after the seedlings are planted, they shall be applied in holes along with the water;Application during seedling growth period;The application at flowering or fruit expansion stage can increase yield and improve quality.
national standard
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National standards《General technology of saline alkali land improvement》(GB/T 42828-2023), under the jurisdiction of TC105 (National Technical Committee for Standardization of Fertilizers and Soil Conditioners), and the competent department is the China Petroleum and Chemical Industry Federation.
GB/T 42828.1-2023 General Technology for Saline alkali Land Improvement Part 1: Iron Tailings Improvement[7]
GB/T 42828.2-2023 General Technology for Saline alkali Land Improvement Part 2: Rice Field Pond Fishery and Agriculture Improvement[6]
GB/T 42828.3-2023 General Technology for Saline alkali Land Improvement Part 3: Biological Improvement[5]
Frequently planted trees
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There are more than 99 million hectares of saline alkali land in China. As a valuable land resource, saline alkali land has been wasted due to the lack of suitable tree species.Planting trees on saline alkali land can not only improve soil, but also increase farmers' income.Several trees that can be planted in saline alkali land are recommended.[1]
oleaster
oleasterIt is the most common tree species in northwest China. It can tolerate sulfate dominated saline soil.Elaeagnus angustifolia also reduces soil salinity.It is determined that Elaeagnus angustifolia has a strong salt tolerance. Although its growth is inhibited, it can still become a forest after good tending and management.Therefore, according to the salt tolerance of Elaeagnus angustifolia, it can be planted on the unimproved medium and heavy saline soil.The high salt tolerance of Elaeagnus angustifolia makes it a saline alkali landFarmland shelterbeltThe main tree species.
Eurya littoralis
Eurya littoralisIt is an evergreen shrub belonging to Eurya of Theaceae, and is mostly distributed in the southern coastal areas of China.Its leaves are thick leathery, obovate or obovate lanceolate, with fine serrated edges, dark green and glossy.The tree crown is compact, and in natural state, the tree crown is more flat, and the tree posture is beautiful.Its growth environment is mostly in the seaside crevices or seaside hillsides, so this tree species is extremely resistant to barren, drought, strong wind resistance, and certain salinity.
Ulmus pumila
In the soda alkali soil zone of northeast China, when the soluble salt content of 0-30cm soil layer reaches 0.54%,Ulmus pumilaIt can not grow, but it grows well when the soluble salt content is 0.38% in 0-37cm soil layer.On the chloride saline alkali soil along the coast of Shandong Province, Ulmus pumila is suitable for clay loam with a soil salt content of about 0.3%.In desalted saline alkali land, soil alkalinity is the limiting factor that directly affects the growth of Ulmus pumila.When the soil alkalinity reaches 13%, Ulmus pumila can still grow normally. When it reaches 20.1%, the growth is poor. When it reaches 25%, the growth is very poor or dead.Therefore, Ulmus pumila can be planted on saline soil with salt content below 0.8%.
Willow
WillowIt can grow on saline soil with about 0.3% salt content in the coastal area of Shandong Province.Salix bungeana is resistant to moisture and has large leaf transpiration, which can effectively reduce the groundwater level and prevent secondary salt debt in the soil.Salix bungeana can be used as a common tree species for greening and shelter belt on saline soil with low humidity and soil salt content below 1.0%.
white wax
white waxFor deep and fertile soil, afforestation can be conducted on fertile soil with salt content below 0.5%.
desert false indigo
desert false indigoIt is not a halophyte in itself, but it has the ability of salt resistance and strong resistance to salt and alkali.In the coastal saline alkali area, Amorpha fruticosa can survive and grow in the soil with salt content of 0.4471% and the rhizosphere soil with salt content of 0.3%;However, when the salt content of soil is 0.7134%, and the salt content of rhizosphere soil reaches about 0.5%, it is obviously damaged, and the leaves turn yellow and fall off.Amorpha fruticosa has a strong ability to resist floods and tsunamis. It is not only resistant to alkali, but also can improve saline and alkaline land.The planting of Amorpha fruticosa forest on the inland saline alkali land of Hebei Province can reduce the soil salt content from 6 ‰ to 1/2 ‰ within five years, and can also obtain a large amount of fertilizer, feed, fuel and weaving raw materials at the same time.Generally, Amorpha fruticosa grows normally when the soil salt content is below 0.56%.The construction of Amorpha fruticosa forest is an effective way to transform heavy saline alkali land.
Populus euphratica
In China, it is mainly distributed in Xinjiang, Gansu, Inner Mongolia, Ningxia, Qinghai and other provinces (regions) with 37 ° - 47 ° north latitude. The altitude along the river valley is about 2500 meters to 150 meters, and the highest altitude in eastern Pamir is about 2300 meters.Populus euphraticaIt has strong adaptability, salt and alkali resistance, cold and cold resistance, weather and drought resistance, developed roots and strong sprouting ability. It is a naturally distributed tall tree species in desert areas before sandstorms.Populus euphratica can be planted on the soil with pH value of 9.3 and salt content of 1.4759%, and it grows vigorously.Populus euphratica not only can absorb salt and alkali, but also has the special ability to eliminate salt and alkali.Populus euphratica can grow on sulfate soil, chloride saline soil and soda saline soil,[1]But the growth is slow.It can be seen that Xiaoxuhu hybrid grows faster than Populus euphratica, and is a promising tree species for afforestation on saline alkali land, which is worth popularizing.In a word, the development of Populus euphratica forests and the afforestation of Xiaoxuhu hybrids are effective measures to speed up the transformation of saline alkali soil quality and improve the harsh desert environment in the three northern regions.
a manchurian ash
a manchurian ashWith good quality, developed root system, easy afforestation, high survival rate, stable growth, disease and insect resistance, Fraxinus mandshurica is one of the precious tree species with a certain salt tolerance. On soda saline soil, when the pH value is less than 8.5, the salt content is less than 0.15%, and the total alkalinity is less than 1.10mg/100g, Fraxinus mandshurica grows normally, and when the salt content exceeds this limit,The growth of Fraxinus mandshurica was inhibited or died.In addition, the salt tolerance of Fraxinus mandshurica is also changed due to different soil moisture and soil nutrients, that is, when the soil moisture content is high and the soil fertility is high, the salt tolerance is high and the growth is increased.It is understood that Fraxinus mandshurica can grow normally on medium thick carbonate meadow chernozem, thin carbonate meadow chernozem and slightly saline alkaline carbonate meadow chernozem in Heilongjiang Province.
Tamarix chinensis
Tamarix chinensisIt is a salt secreting plant suitable for growing in saline alkali land.The natural forest grows well when the salt content of 0-10 cm soil layer is 1.025% and the pH is 8.21.When the salt content of 1 meter soil layer is 0.55%, the cuttings grow well.During the tsunami, Tamarix was soaked in seawater for ten days without obvious damage.It is reported that Tamarix plants in China have the strongest salt tolerance: Tamarix brevifloratamarix elongata , Tamarix hispida, Tamarix kansuensis.Under the condition that the average salt content of 1 meter soil layer is 3~12%, only by trenching and deep planting (50cm) to avoid salt, Tamarix chinensis can be successfully planted in heavy saline alkali land, which is an effective measure for afforestation in heavy saline alkali land in desert areas.
Chinese wolfberry
Lycium barbarum L. has important medicinal value. It is a true halophytic tree species suitable for growing in saline alkali soil. Its anti saline ability is close to that of Tamarix chinensis, and it grows vigorously in alkaline soil with pH value of 8.6.
Haloxylon ammodendron
Haloxylon ammodendronIt is a big shrub of Chenopodiaceae.Young trees grow well in fixed and semi fixed dunes with soil salt content of 0.2~0.396.
poplar
Poplar varieties suitable for afforestation on saline alkali land mainly include: Fargesia poplar, cooperative poplar, Xiaomeihan, Xiaomeijia, Liaoyang, Xiaoheiyang, Dendrolimus davidiana, etc.The practice has proved that the arrow stem poplar grows well in the Huzhou Baotou Plain, Inner Mongolia, and along the Yellow River in the breeding area, and its salt resistance is good. The arrow stem poplar grows well in the Wuyuan and Linhe saline alkali areas of the Pakistan League. The cooperative poplar, Xiaomeizao, Xiaomeijia, Liaoyang, etc. have been tested to grow well in the moderately saline alkali areas of the Pakistan League;Populus deltoides can grow under the condition that the soil salt content does not exceed 0.4%.
ailanthus
Ailanthus altissima is a good timber tree species, which is relatively resistant to salt and alkali, but not to waterlogging. The newly planted young forest will die after 7 days of blistering.The tree species can be planted in dry places where the soil salt content is about 0.3%.
Mulberry
Mulberry trees can be planted on saline alkali land with soil salt content below 0.3% and pH value of 8.1, and are relatively resistant to waterlogging. They can still recover their growth after soaking in seawater for 20 hours.
Mulus zhumei
This is a newly cultivated salt tolerant tree species, which can be used not only as a general greening tree species, but also as a rootstock for grafting apple trees.Mulus zhumei It can still grow normally in the soil with a salt content of 0.5~0.6, and its salt tolerance is similar to that of Tamarix chinensis, providing a good tree species for greening and developing fruit tree production in saline and alkaline areas.
Platycladus orientalis
Platycladus orientalisThe ability to tolerate salt and alkali is strong. When the soil salt content is 0.2, the growth is good, and when the soil salt content is 0.2-0.3%, the growth is inhibited.
Of course, the key to choose the trees that can be planted in saline alkali land is to choose according to the amount of salt in the soil.It varies with the growth conditions, soil and fertility of trees. In order to improve the survival rate of plants suitable for saline alkali land, different planting methods can be used to create a suitable growth environment for young trees.
comprehensive utilization
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Central No.1 Document in 2022《Opinions of the CPC Central Committee and the State Council on the key work of comprehensively promoting rural revitalization in 2022》It is proposed to carry out the demonstration of planting soybean in saline alkali land.It is proposed to actively tap the potential to increase cultivated land and support the moderate and orderly development of qualified saline alkali land and other reserve resources into cultivated land.Study and formulate the comprehensive utilization plan and implementation plan of saline alkali land.Classify and transform saline alkali land, and promote the transformation from mainly controlling saline alkali land adaptive crops to more breeding salt tolerant plants to adapt to saline alkali land.Support the construction of national agricultural high-tech industry demonstration zones in saline alkali land, arid and semi-arid areas.[2]
In October 2022, the innovation team led by Professor Liu Peng of Shandong Agricultural University will improve 5 mu of saline alkali land in the demonstration field, with a yield of 911.9 kg per mu.[4]
In April 2024, the state announced to arrange 4 billion yuan to expand the pilot project of comprehensive utilization of saline alkali land from 2 provinces to 12 provinces, adhere to the combination of "planting suitable land" and "planting suitable land", and expand the agricultural production space.[9]
social influence
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In December 2023, Chinese scientists found the key genes that can promote food production in saline alkali land, which was selected as one of the top ten domestic science and technology news in 2023。[8]
