Prevention Control Secondary Salinization In Greenhouses

Secondary salinization refers to the process in which good cultivated land becomes "salinized" due to unreasonable human cultivation and irrigation measures, as well as changes in vegetation.

Saline alkali land is divided into two types of saline alkali soil: saline soil and saline soil, alkaline soil and alkaline soil, based on soil salt content and pH value. Soluble salts (chloride, sulfate, and carbonate) accumulate too much on the surface of the soil, and if the salt content is too high, they are saline soil and saline soil; The surface salt content of soil may not be high, but when the adsorbed sodium ions on soil colloids exceed a certain amount and the pH value exceeds 8.5, it becomes alkaline soil or alkaline soil. In fact, saline soil and alkaline soil are coexisting in agricultural production, commonly referred to as saline alkali soil. Salinization occurs when the salt content in the surface layer of soil (0-20cm) exceeds 0.1% and the pH is greater than 7.5. With the increase of salinity and pH value, the soil surface will exhibit several typical characteristics such as "green", "white", and "red". "green" refers to the growth of green moss; "White" refers to the accumulation of a layer of salt frost on the surface area, while "red" refers to the appearance of "purple algae" on the ground, which is an indicator plant of saline alkali land. Its appearance indicates that the salt content in the soil is already high, reaching around 0.5%, which can cause serious yield reduction

The occurrence of the above three phenomena indicates that the soil has become saline alkali, and the reduction in production generally reaches 20%. At this point, the soil needs to be improved.

After soil salinization, it manifests as soil structural damage, sticky compaction, reduced ventilation and permeability, and slow water infiltration.

Prevention and Control Measures for Secondary Salinization in Greenhouses

（1） Scientific fertilization

Using formula fertilization technology, nitrogen, phosphorus, potassium, and trace elements are reasonably proportioned according to the fertilizer requirements of different crops and soil nutrient conditions, and promoting root dressing. The application of organic fertilizers, especially bio organic fertilizers made from high carbon raw materials, or the combination of microbial agents can achieve better results. Promote integrated water and fertilizer technology, improve fertilizer utilization efficiency, and reduce surface soil salt accumulation.

（2） Membrane removal and washing

According to the principle of "salt comes with water, salt goes with water", use the summer shed period to remove the film, wash with heavy rain, or irrigate with large amounts of water, with a depth of 5-7cm, soak for 3-5 days, and repeat 2-3 times.

（3） Soil conditioning

When applying saline alkali soil amendments, it is best to choose multifunctional saline alkali soil amendments that can increase soil organic matter, regulate soil pH, reduce soil salinity, and contain salt tolerant microorganisms.

（4） Deep plowing and deep plowing

Regular deep plowing and plowing can loosen the compacted soil in the deep layers of vegetable greenhouses, increase soil aeration, and improve the utilization rate of nutrients in the deep layers of soil.

（5） Biological desalination

Planting a crop of fast-growing vegetables or green manure during the summer break in a greenhouse can effectively absorb nutrients from the vegetable field, thereby achieving the goal of reducing soil salt content.

（6） Crop rotation

Select vegetables from different families and genera for rotation to prevent soil borne diseases. Adopting a deep root and shallow root vegetable rotation method to avoid excessive consumption of soil nutrients in the same soil layer.

（7） Plastic film coverage

By covering with plastic film, the evaporation of soil moisture is reduced, thereby reducing the salt content of the soil surface.