Do a good job of characteristic agriculture in saline-alkali land
Comprehensive transformation and utilization of saline-alkali land is an important aspect of cultivated land protection and improvement. There are many saline-alkali land in China, and the trend of salinization of cultivated land in some areas is intensifying, so it is of great significance to carry out comprehensive transformation and utilization of saline-alkali land. The second meeting of the Central Financial and Economic Committee held in July this year pointed out that it is necessary to fully tap the comprehensive utilization potential of saline-alkali land, strengthen the transformation and upgrading of existing saline-alkali cultivated land, effectively curb the trend of salinization of cultivated land, and do a good job in special agriculture in saline-alkali land. In this issue, invited experts will discuss relevant issues.
Saline-alkali land is an important reserve cultivated land resource.
How to understand the significance of saline-alkali land improvement?
Li Yuyi (Chief Scientist, Saline-alkali Soil Improvement and Innovation Team, China Academy of Agricultural Sciences):Saline-alkali land usually refers to soil with salt content exceeding 0.1%, including saline-alkali cultivated land, saline-alkali forest grassland and saline-alkali unused land. The essence of the formation of saline-alkali land is mainly the horizontal and vertical redistribution of various soluble salts on the ground, so that salt gradually accumulates on the surface of soil in salt-collecting areas.
There are many reasons for the formation of saline-alkali land, mainly influenced by natural conditions such as climate, topography, hydrogeology, unreasonable irrigation, excessive use of chemical fertilizers all the year round and other human factors. In the arid and semi-arid areas of northern China, soil evaporation is greater than rainfall, and salt dissolved in water is easy to accumulate on the surface of soil. Coastal saline-alkali soil is formed in coastal areas due to seawater immersion and high salinity of groundwater. The soil on both sides of rivers and canals will raise the groundwater level due to the lateral seepage of rivers, and the salt in groundwater will be evaporated and accumulated on the soil surface, thus forming saline-alkali soil. In some places, flood irrigation is used 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.
Soil salinization will not only make it difficult for crop roots to absorb water and reduce the efficiency of crop nutrient absorption, but also make soil fertility worse and reduce beneficial microorganisms in the soil. Saline-alkali soil often has poor air permeability and water permeability, and it is easy to stagnate water, thus delaying surface soil temperature rise, reducing soil enzyme activity, changing soil physical and chemical properties and reducing soil fertility to a certain extent, which has a negative impact on crop growth and its yield, and is not conducive to agricultural production. Generally speaking, when the soil salt content exceeds 0.1%, the growth of common crop varieties begins to be affected; When the soil salt content exceeds 0.3%, the yield of most crop varieties decreases obviously. Soil salinization has become a major factor limiting land resources in China, and it is also a major problem restricting the sustainable development of agriculture in arid areas.
China is the third largest saline-alkali land distribution country in the world, with more than 500 million mu of available saline-alkali land resources. Saline-alkali land is an extremely important reserve cultivated land resource and a "potential granary", and the improvement of saline-alkali land is of great significance to increase the quantity and quality of cultivated land. Saline-alkali land in China is mainly divided into five types: northwest inland saline-alkali land, northeast Songnen plain saline-alkali land, coastal saline-alkali land, Huanghuaihai plain saline-alkali land and irrigation area in the middle and upper reaches of the Yellow River. Among them, the saline-alkali area in the northwest inland and the saline-alkali area in the Songnen Plain in the northeast are the main distribution areas of saline-alkali land in China, with a large area and contiguous distribution; The saline-alkali area in the Huang-Huai-Hai Plain is a typical area where saline-alkali land has been successfully controlled in China. After continuous control, its saline-alkali land area has been greatly reduced, and it is only scattered at present.
In recent years, the Ministry of Agriculture and Rural Affairs, together with relevant departments, has actively promoted the improvement of saline-alkali land by strengthening the prevention and control of soil salinization in cultivated land, exploring comprehensive management models in different saline-alkali areas, and conducting a general survey of saline-alkali land. By the end of 2022, 1 billion mu of high-standard farmland had been built nationwide, which effectively improved the irrigation and drainage capacity of farmland and strengthened the prevention and control of soil salinization of cultivated land. From 2020 to 2022, the Ministry of Agriculture and Rural Affairs guided eight provinces to carry out pilot projects for saline-alkali farmland control, with a cumulative implementation area of 2.4 million mu in three years. After three years of pilot projects, more than 200 centralized contiguous comprehensive management demonstration zones have been built in various places, and the quality of cultivated land in the project area has improved by 0.11 to 0.51 grades on average. In terms of strengthening "planting suitable land", the Ministry of Agriculture and Rural Affairs has carried out accurate identification of salt-tolerant resources and approval of salt-tolerant varieties of crops such as rice, wheat, corn and soybean in major saline-alkali areas, continuously promoted innovative research on salt-tolerant crop breeding, and accelerated the breeding of breakthrough new varieties. At present, 6 varieties of wheat and 11 varieties of rice have passed the national examination and approval.
The technical path of saline-alkali land improvement is adapted to local conditions
How to improve different types of saline-alkali areas in China?
Ju Zhengshan (researcher, Land Consolidation Center, Ministry of Natural Resources):The main purpose of saline-alkali land improvement in agricultural application is to improve the physical and chemical properties of soil and provide a good growth and development environment for crops, so as to achieve high yield and high efficiency. There are two main technical ways to improve saline-alkali land. One is biological breeding technology with salt-tolerant crops as the core, and salt-tolerant crop varieties are selected for direct planting without soil improvement; The second is the engineering technology with soil improvement as the core. By adding irrigation and drainage facilities or applying soil improvers and other physical and chemical means, the soil salt is discharged and controlled, and the soil salt is reduced to a level that does not affect crop production, so as to achieve the purpose of improvement and management.
At present, China has comprehensively utilized saline-alkali land in many areas, and the improvement of saline-alkali land is still mainly based on engineering and technical measures, and more agricultural production practices have been carried out. Generally speaking, the traditional engineering technology mode of digging ditches and discharging salt in 1970s and 1980s is still used, but the breakthrough of some new technologies has provided important technical support for saline-alkali land treatment in different regions and promoted the development and utilization of moderate and severe saline-alkali land in a large area. According to different saline-alkali land types and soil and water conditions, China’s saline-alkali land can be basically divided into four distribution areas, forming technical models such as underground pipe salt drainage engineering technology in eastern coastal saline-alkali land, comprehensive improvement technology of rice planting in soda saline-alkali land in northeast China, comprehensive improvement planting technology of saline-alkali land in Hetao plain of central Yellow River, and drip irrigation technology under film in arid oasis area of western China.
The coastal saline-alkali land in the east is mainly distributed in the coastal beach areas with high groundwater level in Liaoning, Tianjin, Hebei, Shandong and Jiangsu provinces, and is mainly sodium chloride, which is a type of saline-alkali land formed by the influence of underground high salinity water. Except for local viscous deposits, the physical and chemical properties such as soil permeability are relatively good, which is beneficial to soil desalination. In terms of treatment technology, in addition to the traditional open ditch salt drainage and terrace field mode, the underground pipe salt drainage engineering technology mode has been widely applied in saline-alkali land in this area. Aiming at the high groundwater level and high salt content in coastal areas, this technical measure replaces the traditional way of digging ditches to drain salt with a series of underground pipes with holes buried deep underground, forming an underground drainage and salt drainage pipe network, and the salt in the soil flows into the underground pipe network with the water to discharge the soil, so as to control the groundwater level, drain salt and control salt. Compared with the traditional open ditch salt drainage technology, the underground pipe salt drainage technology has obvious advantages in saving water and land, the effect of salt drainage, the improvement efficiency of saline-alkali land and the prevention of soil secondary salinization. It can basically save land by 10% and water by more than 17%, increase grain production by 20% to 44%, and the average salt drainage rate of soil is about 50%.
Northeast soda saline-alkali land is mainly distributed in Baicheng and Songyuan in northwest Jilin, Qiqihar and Daqing in Heilongjiang, and it is one of the three largest soda saline-alkali land in the world. The soda saline-alkali land in Northeast China is mainly carbonate, with strong alkalinity, weak water permeability and poor physical and chemical properties, which is the most difficult type to control. At present, the comprehensive improvement technology model of rice planting has been widely used in soda saline-alkali land in Northeast China. Chemical improvement and agricultural measures of rice planting are combined, and acid soil improvers such as gypsum or organic acids are added to improve soil physical and chemical properties and soil permeability, and pioneer crops such as rice are planted for comprehensive improvement and utilization of saline-alkali land. The improvement technology of alkaline soil with rice planting as the core has become the core technology for the development and utilization of soda saline-alkali land, which has effectively promoted the large-scale development and utilization of saline-alkali land in this area. Northeast soda saline-alkali land has become an important reserve resource development zone of cultivated land in China and an important contribution area of Jilin’s "100 billion Jin of grain" productivity construction project, making the former "barren land" become today’s "land of plenty".
The saline-alkali land in Hetao Plain of Inner Mongolia is the product of the combined action of the Yellow River flood deposition and the secondary salinization of soil caused by artificial long-term agricultural irrigation and drainage under arid climate conditions. The soil conditions are complex, both salt and alkali are paid equal attention to, the soil is generally alkaline, the organic matter is low and the quality of cultivated land is not high. The causes of saline-alkali land in Hetao Plain are complex, with many types of saline-alkali land and many limiting factors. On the basis of irrigation and drainage system, different types of saline-alkali land and the degree of salinization are treated by classification. For example, for light and moderate saline-alkali land, the "five-in-one" management mode, that is, applying phosphogypsum, improver, adding sand to reduce capacity, increasing organic fertilizer, planting saline-alkali tolerant crops, etc., can make the seedling survival rate reach over 95% and achieve good results.
Saline-alkali land in arid oasis area of northwest China belongs to typical primary saline-alkali land type. After land development, irrigation and drainage measures are not matched, and secondary salinization of soil caused by irrigation with high salinity water all year round is very common. The soil salinity in this area is mainly sulfate and chlorate, which is one of the main limiting factors of land use in arid areas of northwest China. At present, drip irrigation technology under plastic film is mainly used to solve the problems of serious accumulation of soil salt on the surface due to drought and water shortage and large evaporation in the west. Plastic film mulching is adopted to inhibit soil water evaporation, and drip irrigation belt is laid under plastic film to accurately drip irrigation on the root system of crops, so as to ensure that crop growth is not harmed by salt, which has dual functions of water saving and salt control. At present, about 60% of the cultivated land in Xinjiang adopts drip irrigation technology under film, and the irrigation area with high efficiency and water saving accounts for about 59% of the total irrigation area in the whole region. Drip irrigation technology under plastic film has not only achieved remarkable results in water saving, but also is one of the mainstream technologies for saline-alkali land treatment in arid areas. In the next step, aiming at the saline-alkali land in the arid oasis area of northwest China, it will be a more ideal saline-alkali land treatment mode to combine the drip irrigation technology under the ground film with the salt drainage technology under the underground pipe.
Create a "salt-suitable and salt-using" agricultural development model
How to combine "planting suitable land" with "planting suitable land" to turn saline-alkali land into high-quality fertile land?
Sun Hongyong (stationmaster of Nanpi Ecological Agriculture Experimental Station of China Academy of Sciences):The breeding research of salt-tolerant crops in China has made positive progress. Salt tolerance is a complex quantitative trait controlled by many genes and involving many molecular and biological processes. Agricultural breeding has gone through domestication, hybridization, molecular breeding and design breeding. In 1950s, with the birth of molecular biology, crop breeding began to enter the era of molecular breeding, and its representative technologies were molecular marker-assisted breeding and transgenic breeding. At present, the main application is molecular design breeding or precision breeding, that is, through the precise change of genes or large-scale polymerization selection, so as to cultivate excellent varieties.
Traditional breeding methods improve the salt-tolerance and alkali-tolerance of crops through selection and hybridization, while molecular-assisted breeding uses modern genomics and molecular marker technology to select parents with salt-tolerance and alkali-tolerance genotypes for hybridization, thus accelerating the cultivation of salt-tolerance varieties. Next, more salt-tolerant alkaline marker sites should be developed to improve the screening efficiency and accuracy. By combining physiological and genetic methods, we can further study the genetic basis of salt and alkali tolerance, so as to screen and cultivate salt and alkali tolerance varieties more accurately.
In the aspect of seed precise design and creation, Chinese scientific research team used saline-alkali tolerant sorghum as the material, and discovered the major controlling base cause and its mechanism for the first time in the world. The field experiment in Pingluo saline-alkali land in Ningxia shows that the related breeding techniques can significantly increase the yield of sorghum, rice, wheat, corn and millet in saline-alkali land, and the comprehensive improvement and utilization of saline-alkali land has great application prospects. The genetic modification can increase the yield of sorghum seeds by 20.1%, the whole plant biomass for silage by nearly 30.5%, and the yield of millet by 19.5%. In the saline-alkali land of Da ‘an, Jilin, the annual yield of different crops increased by 22.4% to 27.8%. The researchers also found that transforming this gene can significantly improve the survival rate of corn in saline-alkali land.
In terms of safety, green and sustainability, some practical explorations have been made in the transformation and utilization of saline-alkali land in China, and remarkable results have been achieved.
The first is the scientific utilization of classification and grading. According to the characteristics of saline-alkali tolerance of plants and the characteristics of soil types, climate resources, water resources, plant resources types and distribution in saline-alkali areas, planting saline-alkali tolerant plants in mild, moderate and severe saline-alkali areas was carried out. In the mild saline-alkali area, develop the planting industry with high quality and high yield grain crops as the mainstay; In moderate saline-alkali areas, develop ecological grass animal husbandry with saline-alkali tolerant forage grass as the main feature; In the severe saline-alkali areas, we should develop the cultivation of characteristic high-value halophytes or ecological greening, or the facility agriculture that takes up space and the industry that focuses on characteristic aquaculture.
Second, the safe use of many water sources such as salt water and brackish water. Saline-alkali areas are mostly distributed in arid and semi-arid areas, and the shortage of water resources is the key factor limiting the comprehensive utilization of resources in saline-alkali areas. The available saline water resources in China are 20 billion cubic meters per year, and the brackish water exploitation resources are 13 billion cubic meters per year. The total exploitable salt water resources in northern China are about 13 billion cubic meters, of which 2.3 billion cubic meters are in North China, and 660 million cubic meters have been utilized. Multi-water source irrigation technology for farmland is an important breakthrough in Bohai granary science and technology demonstration project. During the jointing stage of winter wheat in Hebei Province, the average yield of wheat was increased by 12.5%, and the utilization rate of saline water resources was increased from less than 8% to 20%, achieving the goal of efficient utilization of multi-water sources for saving water and increasing production.
Third, the combination of agriculture and animal husbandry technology utilization. Give full consideration to the planting of saline-alkali tolerant feed crops, the breeding of characteristic livestock and poultry, and the fertilization application of breeding wastes, and develop a technical system for the utilization of saline-alkali land with the combination of planting and breeding and circular agriculture. Shanyin County, Shanxi Province, through planting silage corn and alfalfa in saline-alkali land to feed cattle, cow dung was processed into organic fertilizer to improve saline-alkali land, and then miscellaneous crops were planted in saline-alkali land. Dongying Modern Agriculture Demonstration Zone has established "Salt-tolerant Forage Planting in Saline-alkali Land — Healthy beef cattle breeding — Bio-organic fertilizer production — Saline-alkali land improvement and fertility improvement — Planting grass with high yield and high efficiency — Pasturing — Garden "coastal saline-alkali land management model. Shengwei Group established a saline-alkali land agriculture and animal husbandry industrial park model in Weifang.
The practical experience of saline-alkali land improvement in China shows that saline-alkali land improvement benefits from a perfect farmland irrigation and drainage system, and irrigation and drainage measures with fresh water as the core are the most effective way to control saline-alkali land. In order to transform saline-alkali land into high-quality fertile land, it is necessary to combine "planting suitable land" with "planting suitable land" and innovate the theory, technology and industrial system of efficient utilization of saline-alkali land resources according to the principles of "water saving first, ecological cycle, quality improvement and efficiency improvement, and green development" to create a new agricultural development model of "salt-suitable and salt-using" in saline-alkali land.
Deserted saline-alkali land turned into an "oasis of fish and rice"
What progress has been made in fishery and aquaculture in saline-alkali land in China?
Lai Qifang (Director, Culture Technology Research Office, Donghai Fisheries Research Institute, Chinese Academy of Fishery Sciences):China has 1.487 billion mu of saline-alkali land and 690 million mu of saline-alkali waters, which are widely distributed in Northeast China, North China and Northwest China. At the same time, in some areas, due to improper irrigation and drainage, the soil was salinized and returned to farmland. In the 1990s, Donghai Fisheries Research Institute of Chinese Academy of Fishery Sciences and Shandong Freshwater Fisheries Research Institute took the lead in developing and utilizing saline-alkali land fisheries. Donghai Fisheries Research Institute discovered the diversity of saline-alkali water quality, and found out the key factors that restrict the aquaculture in saline-alkali land. It successfully cultivated China shrimp in the inland saline-alkali waters of Dali, Shaanxi Province, which set a precedent for the inland aquaculture in saline-alkali land. Shandong Institute of Freshwater Fisheries and other units have succeeded in using Yellow River water to develop aquaculture in low-lying saline-alkali land. The barren saline-alkali land has become a cornucopia of increasing farmers’ income.
Although both saline-alkali water and seawater have salinity, the biggest difference is that seawater has the conservation ratio of main ions, that is, seawater around the world has only salinity, the composition ratio of main ions is constant, and there is only one type of water quality; However, saline-alkali water is influenced by geological landform and human activities, and its main ion composition is complex and diverse. At present, there are more than 10 types of water quality found, which brings difficulties to the cultivation and development of saline-alkali water. The publication of Water Quality for Aquaculture in Saline-alkali Land provides technical support for saline-alkali water to become aquaculture water, and promotes the high-quality development of aquaculture in saline-alkali land. China’s inland saline-alkali water resources are large, with low utilization rate and broad prospects for development and utilization.
In 2020, Donghai Fisheries Research Institute took the lead in tackling key problems of saline-alkali aquaculture technology, opened up new aquaculture space after fresh water and seawater, and also explored the establishment of a comprehensive utilization model of saline-alkali water and soil fishery, which made the abandoned saline-alkali water and soil become an "oasis of fish and rice" that can not only grow grain and vegetables, but also raise fish and shrimp. By December 2022, in 11 provinces, municipalities and autonomous regions in Northeast China, Northwest China, North China and East China, the demonstration area was 782,100 mu, with a total output value of 12.393 billion yuan and a total income of 3.367 billion yuan. The promotion area is 1,658,500 mu, with a total output value of 28.670 billion yuan and a total income of 6.944 billion yuan. The economic benefit is increased by more than 20%, and the comprehensive benefit is increased by more than 35%, forming a new aquaculture industry in saline-alkali land and creating a new fishery format in saline-alkali oasis.
In the No.5 Farm of caofeidian area, Tangshan City, Hebei Province, the total salt content in the topsoil is between 0.1% and 0.6% due to the influence of tidal current and groundwater. The salt content in the soil is high, so it is difficult to desalt, and the yield and income of saline-alkali paddy fields are low. In addition, paddy fields need to be soaked every year to produce a large amount of saline-alkali water. The fifth farm in caofeidian area used the waste water reuse project to introduce saline-alkali water produced by soaking rice fields into ponds to cultivate Litopenaeus vannamei and saline-alkali tolerant freshwater fish. The comprehensive utilization of fishery in saline-alkali land in paddy field has reduced the total salt content of topsoil by more than 20%, with the average yield per mu of rice reaching 750 kg, the average yield per mu of Penaeus vannamei cultured in ponds reaching more than 250 kg, the average yield per mu of saline-alkali freshwater fish reaching more than 1,000 kg, the economic benefit per mu in ponds reaching more than 3,000 yuan, and the average benefit per mu of saline-alkali land reaching more than 1,700 yuan. "Pond — The comprehensive utilization of paddy field fishery has found a new space for agricultural drainage, which can not only ensure the stable and increased rice production, but also increase the income per mu and promote the income of fishermen.
In Jingtai County, Baiyin City, Gansu Province, soil salinization is serious, spreading at the trend of 5000 mu every year. Through "digging ponds for precipitation, raising soil for farmland, paying equal attention to agriculture and fisheries, and controlling saline-alkali land" in low-lying saline-alkali land, the "pond — The comprehensive utilization of saline-alkali fishery in paddy field, the groundwater level in the surrounding area decreased obviously after the pond was excavated, and the soil salt gathered in the pond with the water, and the soil salt in the reconstructed Xintian tillage layer decreased greatly. Crops such as celery, cabbage, tomato, barley and oil sunflower planted in rice fields are growing well, and nearly 20,000 mu of land has been re-cultivated or re-used for agricultural planting. According to "salt comes with water and salt goes with water", "pond — The comprehensive utilization of fishery in saline-alkali land of paddy field provides a new way to prevent secondary salinization of soil.
In the severe saline-alkali land of Fumin Village, Shizuishan City, Ningxia Hui Autonomous Region, through the improvement projects of reducing salt and discharging alkali, such as trimming the water intake canal and digging the alkali drainage ditch, the heavy saline-alkali land was soaked and leached with brackish water or river water for many times, and the salt washing and discharging alkali water was collected, and intensive pond culture was carried out. The organic fertilizer water was collected through the bottom sewage system, and the solid-liquid was separated. The supernatant liquid was recycled by the ecological pond, and the solid organic matter was returned to the field after fermentation treatment, thus reducing the improvement cost. The soil salinity decreased from 21.01 to 3.55, and the yield of rice per mu reached 502 kg in the improved field, and 160 kg in the field with heavy saline-alkali soil, which changed the situation that nothing grows in the severe saline-alkali soil. The comprehensive utilization of fishery in saline-alkali land provides a new way for saline-alkali land management.
Practice has proved that the comprehensive utilization of saline-alkali fishery, which is based on aquaculture in saline-alkali land and aims at ecological improvement, not only does not compete with agriculture for water, but also opens up a new space for aquaculture, reduces soil salinity, revives abandoned saline-alkali soil and water, and constructs a diversified food supply system that is suitable for fishing and suitable for agriculture, which is of positive significance for ensuring the safety of agricultural food production, helping rural revitalization and reserving reserve cultivated land resources.