The problem of soil salinization and acidification in greenhouse is becoming more and more serious. How to improve them?

In recent years, with the rise of greenhouse, it not only brings economic benefits to farmers, but also inevitably causes the deterioration of soil environment. There are mainly soil secondary salinization, soil acidification, serious soil-borne diseases and unbalanced soil nutrition. How to change this situation and give crops a healthy growing environment?

Secondary salinization

With the increase of planting years, some greenhouse floors are white in some places, some are obviously dark red, and the phenomenon of dead trees is serious; Umbilical rot occurs on tomatoes that have already set fruit, which may be caused by secondary salinization of soil.

Secondary salinization of greenhouse soil is the most common soil problem in protected agriculture planting in China. After 3~5 years of greenhouse planting in general protected areas, the soil will be secondary salinized to varying degrees.

First, the causes of soil secondary salinization

Small environmental factors: compared with field planting, greenhouse planting is a relatively closed environment, and this closed environment lacks natural rainfall leaching, which is the fundamental reason. In addition, there is artificial irrigation, the water will not fall too deep, and the salt will remain on the soil surface.

Excessive fertilization: If the amount of fertilizer applied exceeds the amount taken away by crops, it will cause excessive nutrients in the root zone or deeper layer and accumulate in the soil.

Hydrothermal environment in the facility: there is a high temperature and high humidity environment in the greenhouse, and soil moisture evaporates strongly, and salt ions will move upward with the evaporation of water, resulting in salt accumulation on the soil surface.

Too many farming operations: Too many farming operations and serious trampling in greenhouse will cause soil hardening, damaged capillary gap and poor permeability, and will also aggravate the occurrence of secondary salinization.

Second, the consequences of soil secondary salinization

Overosmotic pressure of soil solution: salt ions in soil gather, which also leads to over-osmotic pressure of soil solution. Once the concentration of soil solution is higher than the concentration of plant cell sap, the water absorption of crop roots will be blocked, resulting in physiological drought of crops, and in severe cases, crop dehydration will cause death. Affect root absorption: Secondary salinization of soil will also cause poor growth and development of crop roots, affect the absorption of other elements by roots, destroy the nutritional balance of crops, cause element deficiency disease of vegetables, and reduce the disease resistance of vegetables. Third, the improvement measures of soil secondary salinization:

The secondary salinization of soil in protected land is a process of gradual accumulation. When improving, we should follow the principle of "preventing harm and controlling land" and adopt the method of comprehensive management.

Uncovering the film and leaving stubble: Uncovering the film can make the soil in the facility be irradiated and leached by sunlight, make the soil mature, increase the permeability of the soil and give the soil time to recuperate. Generally, stubble is cut off in the hot season from June to August every year, lasting about two months.

Deep tillage, irrigation and salt washing: after clearing the garden every year, deep tillage should be carried out to improve the soil and make the salt on the surface of the soil transfer to the lower layer. It is equivalent to distributing salt evenly in the soil below. After deep tillage, irrigation and salt washing should be carried out to make the salt in the soil fully enter the water, and then the salt water should be removed, thus reducing the degree of salinization.

Scientific fertilization: scientific and reasonable fertilization is also an important means to improve the secondary salinization of soil in protected areas. It is necessary to scientifically select fertilizer types, use less chemical fertilizers as far as possible, and increase the amount of organic fertilizers, especially straw organic fertilizers, which can improve the saline-alkali soil in greenhouses. Organic matter can loosen soil, restore soil structure, make soil form more granular structure, increase soil activity, increase humus in soil, thus promoting root growth and absorbing excess hydrogen ions to some extent.

Spray drip irrigation: to improve soil salinization, we should change the traditional irrigation method besides changing the types of fertilization. If possible, using drip irrigation, sprinkler irrigation and other irrigation measures with water can improve the integration level of water and fertilizer in greenhouse and improve the utilization rate of fertilizer, which can also effectively prevent soil salinization.

soil acidification

Soil acidification refers to the leaching of basic ions in soil, and the increase of hydrogen ions or aluminum ions, which leads to the decrease of soil PH value and the formation of acidic soil.

First, the causes of soil acidification

Long-term application of single chemical fertilizer: Different types of chemical fertilizers have different effects on soil acidification. Generally speaking, the effect of nitrogen fertilizer is the most obvious, especially ammonium chloride and ammonium sulfate. After applying urea, the soil can also be acidified after ammoniation and nitrification. Secondly, acid fertilizers such as diammonium phosphate and calcium superphosphate are widely used; Physiological acid fertilizers such as potassium sulfate and potassium chloride can also reduce PH value.

Insufficient oxygen content in soil: the air flow in the facility is limited, and the oxygen content in soil decreases. Carbon dioxide exhaled by roots and soil microorganisms accumulates in the soil and combines with water to form carbonic acid, which will also lead to the decrease of PH value in the soil.

Frequent irrigation: The soil in protected land is generally irrigated, and excessive irrigation will aggravate the loss of calcium and magnesium ions, which is also a major cause of soil acidification.

Second, the symptoms of soil acidification

The surface soil of acidified soil is hardened, the soil aggregate structure is destroyed, and the soil permeability will become worse and have more obvious characteristics. When the soil is airtight and acidified at the same time, and water cannot penetrate, some cations in the soil, such as iron and manganese, will rise to the soil surface. When there is water, it will show a green reduction state. After drying, it will oxidize and become trivalent iron ions, pentavalent or heptavalent manganese ions and other high-valent iron ions. Together, they turn yellow and red.

Third, the improvement measures of soil acidification

Reduce the application amount of chemical fertilizers: in the first year of improvement, reduce the application amount of chemical fertilizers, especially those with physiological acidity, and suggest stopping the application of fertilizers such as urea, diammonium phosphate and potassium sulfate. For soil, organic fertilizer and humic acid fertilizer should be re-applied, together with alkaline fertilizers such as calcium magnesium phosphate fertilizer or silicon calcium magnesium fertilizer. In the critical period of fruit development, appropriate amount of neutral instant fertilizer can be applied to the roots and some nitrogen and potassium fertilizers can be applied to the leaves.

Soil improvement: For severely acidified soil, lime or shell powder should be applied to improve it. But when choosing and using, we should pay attention to some problems. If lime must be used, it should be dolomite lime containing magnesium. If ordinary calcium carbonate lime or shell powder calcium carbonate lime is simply used, it should be used together with magnesium fertilizer and some trace elements. Otherwise, crops will have symptoms of lack of trace elements.

The specific method is to apply lime or shell powder together with organic fertilizer before soil preparation, and the dosage is controlled within 200㎏ per mu, and at the same time, apply a proper amount of medium and trace element fertilizer. Lime application can not only supplement calcium in soil, but also neutralize acidic soil.

Using drip irrigation, micro-sprinkler irrigation and other water-saving methods: improving soil acidification in protected areas, using drip irrigation, micro-sprinkler irrigation and other water-saving methods are also very effective measures. Improving the integration level of water and fertilizer in greenhouse can improve the utilization rate of fertilizer and effectively prevent soil acidification.

Soil-borne diseases in greenhouse soil

Soil-borne diseases in greenhouse refer to diseases caused by attacking crops from roots or stems under suitable conditions such as high temperature and high humidity, which have the characteristics of rapid spread and rapid onset. Common soil-borne diseases in production include clubroot, Sclerotinia sclerotiorum and soft rot of Cruciferae. Sheath blight, Fusarium wilt and root rot of eggplant, melon and other crops.

First, the causes of soil-borne diseases

Continuous cropping obstacle: that is, continuous cropping, which we often say, will cause various diseases and pests in the process of crop growth and development. In the process of occurrence, pests and diseases cannot be completely eliminated, and a large number of germs will be produced. With the accumulation of time, there will be more and more pathogens, the incidence index will be bigger and bigger, and the incidence will become heavier and heavier.

High multiple cropping index: the multiple cropping index in greenhouse is high, and the germs are hidden in the soil, especially in winter and summer, which leads to a large number of germs and more and more serious diseases.

Application of incompletely decomposed organic fertilizer: In protected cultivation, when growers apply incompletely decomposed organic fertilizer, the bacteria in the organic fertilizer will be brought into the greenhouse. These are the causes of soil-borne diseases.

Second, prevention and control measures

To prevent and control soil-borne diseases, the most important thing is to reduce the source of greenhouse bacteria.

Rotation: Planting practice shows that rotation is the most economical and effective measure to control soil-borne diseases. Such as solanaceae, cucurbitaceae and cruciferous or leguminous crops; Cruciferous crops, onions and leeks. Garlic rotation works well.

Improved cultivation method: deep furrow and high ridge cultivation is adopted to reduce water accumulation in the field, which is beneficial to inhibit the survival of pathogenic bacteria and reduce the occurrence of soil-borne diseases.

Eliminating pathogenic bacteria: eliminating pathogenic bacteria is an important means to prevent and control soil-borne diseases in protected areas. When changing stubble, it is important to clear the garden, thoroughly remove the fallen leaves of the previous crop, and then use the good sealing performance of the greenhouse to irrigate the closed greenhouse at high temperature, which can effectively kill a large number of pathogenic bacteria in the soil.

Soil disinfection: If the soil-borne diseases in greenhouses are serious, the soil should be disinfected in time. The most effective method is to use soil disinfectant. There are many kinds of common soil disinfectants in the market. Take lime nitrogen as an example to explain how to disinfect. Lime nitrogen is a mixture of calcium cyanamide, calcium oxide and other insoluble impurities. It is black-gray oily particles, containing about 20% nitrogen and also containing lime, so it is called lime nitrogen. It has dual functions of soil disinfection and fertility improvement. After decomposition, nitrogen fertilizer and calcium will be produced, which is very beneficial to the soil. In the market, lime nitrogen has two forms: solid and liquid. For convenience and safety, it is recommended to use liquid lime nitrogen.

Liquid lime nitrogen can be diluted after applying base fertilizer and rotary tillage in greenhouse. Every 1㎏ liquid lime nitrogen is mixed with 30㎏ water, and 60~80㎏ undiluted liquid lime nitrogen is used per mu. Conditional spray drip irrigation system with shed can be used; It can also be washed with water. It should be noted that the film should be covered in time after application and the shed should be closed 15~20 days. Before planting, open the plastic film and dry it for about 5 days. After the smell disappears, you can ridge up and plant crops.

Because soil treatment not only kills soil-borne pathogens, underground nematodes, pests and so on. But also kills beneficial microorganisms in the soil, and applying more biological agents during planting is beneficial to the growth of crops.

Soil nutrient imbalance in greenhouse

The imbalance of soil nutrients in protected land means that the inherent proportion of macro, medium and trace elements in soil is broken, and the contents of nitrogen, phosphorus and organic matter are greatly increased, while the proportion of medium and trace elements is reduced by human action.

First, the causes of soil nutrient imbalance

Continuous cropping for many years: in order to get high income, growers often plant a crop with high output value continuously, without paying attention to rotation. Therefore, the types of fertilizers applied every year are basically the same, and the nutrients needed by crops are different. Therefore, after being taken away every year, the lack of nutrients was not replenished in time, which aggravated the imbalance of nutrients in the soil and caused obstacles to continuous cropping.

The physical and chemical properties of soil have changed: on the other hand, due to perennial fertilization, some nutrients are excessive, which changes the physical and chemical properties of soil and reduces the effectiveness of some nutrients, thus destroying the balanced supply of soil nutrients.

Second, the influence of soil nutrient imbalance.

The direct consequence of the imbalance of nutrient elements in soil is that crops are prone to physiological diseases due to nutrient deficiency. Common ones are:

Potassium deficiency: plant disease resistance is reduced, crop yield is reduced, and quality will become worse; Calcium deficiency: the terminal buds and roots of plants develop slowly or not, and the growing points stop growing; Magnesium deficiency: the veins of leaves turn yellow, photosynthesis gradually weakens, and the whole leaf tissue turns yellow and brown until death. The symptoms of element deficiency in different crops in different regions are also different, depending on the actual situation.

Third, the improvement methods of soil nutrient imbalance

Balanced and efficient fertilization: the fundamental way to improve the imbalance of soil nutrition lies in balanced and efficient fertilization, combined application of organic fertilizer and inorganic fertilizer, and addition of medium and trace elements. The amount of nitrogen and phosphorus should be balanced when fertilizing, and the amount of trace elements such as potassium, calcium, magnesium and boron should be increased. In the use of organic fertilizer, we should change the types of organic fertilizer, reduce the use of chicken manure organic fertilizer, and increase the use of straw organic fertilizer. If possible, fertilization can be combined with soil testing formula, which can greatly improve the utilization rate of fertilizer.

Rotation and stubble replacement: combined with fertilization, rotation and stubble replacement have different requirements for fertilizer, which can also reduce the imbalance of soil total nutrients.

For the soil problem in facility agriculture, farmers should always pay attention to the soil condition of facility agriculture in actual production. Only through scientific and reasonable management methods can the soil productivity of facility agriculture be improved and the sustained and healthy development of facility agriculture be ensured.