How to prevent and control salt damage in greenhouse flowers? Detailed explanation of causes and countermeasures

Greenhouse flowers receive relatively large amounts of fertilizer, and greenhouse soil cannot be leached by rainfall the way open-field soil is, so it remains in a year-round salt-accumulating state, making salt damage very likely. The main symptoms in the plants are stunted flower plants and dark leaf color; in some cases the leaves begin to dry out, or turn brown and curl inward or outward; some plants wilt, resembling fusarium wilt symptoms, and the root system develops poorly; or the roots that emerge gather around the main root, unable to spread out or grow downward, taking on a fist-like shape... All of these seriously affect the growth and quality of the flowers. The causes of salt damage in greenhouse flowers and the treatment methods are introduced below.

Causes of salt damage

1. Year-round cultivation of flowers in greenhouses removes excessive base elements such as potassium, calcium and magnesium from the soil, leading to excessive depletion of potassium and medium and trace elements in the soil and pushing the greenhouse soil toward acidification.

2. The application of large amounts of acidic fertilizers, together with high temperature and humidity inside the greenhouse and little leaching by rainwater, means that as the number of years of flower cultivation increases, acid radical ions accumulate in the plow layer, easily causing soil acidification.

3. The high multiple-cropping index of greenhouse flower cultivation and the large amounts of fertilizer used cause the organic matter content in the soil to decline year by year, and the buffering capacity of the soil solution declines, worsening the soil acidification problem.

4. The input ratio of the three elements nitrogen, phosphorus and potassium is too large, while base elements such as calcium and magnesium are easily displaced by hydrogen ions, thereby increasing soil acidity.

5. Soil microbial communities become abnormal and produce some biotoxic substances. In flower greenhouses, if a single flower species is grown continuously for a long time, the root exudates of the same crop are identical, causing certain soil microorganisms to multiply in large numbers while certain soil microorganisms are inhibited, making soil microbial abnormality likely. This is unfavorable for soil maturation and for the decomposition and differentiation of the nutrients in the applied fertilizer, causing soil acidity to increase sharply.

Measures to prevent salt damage

1. Increase the application of organic fertilizer. It is best to apply organic fertilizer rich in cellulose (with a high carbon-to-nitrogen ratio). During decomposition, organic matter forms organic colloids such as humic acid. Colloids have very strong adsorptive capacity and can adsorb soluble mineral nutrients such as ammonium ions, potassium ions, calcium ions and other cations around themselves. This adsorption is dynamic, and when the soil solution concentration is low, they are released into the solution. Increasing the application of organic fertilizer can enhance the buffering capacity (regulating capacity) of soil nutrients, prevent the accumulation of salt damage, and slow the process of secondary salinization of the soil.

2. Deep plowing of the soil. Salts in protected greenhouse soil are concentrated in the surface layer. Generally, the salt index of the 0-5 cm soil layer is 100, that of the 5-25 cm soil layer is 60, and that of the 25-50 cm soil layer is 40. After the flower crop is harvested, deep plow the land to turn the salt-rich surface soil to the lower layer and the lower layer soil with less salt to the upper layer, which can reduce soil salt damage.

3. Apply base fertilizer deeply and apply topdressing in limited amounts. When chemical fertilizer is used as base fertilizer, apply it deeply; when used as topdressing, apply it in small amounts many times. Mix chemical fertilizer with organic fertilizer, broadcast it, then plow and turn the fertilizer into the soil, so as to avoid excessive surface fertilization increasing the salt content of the surface soil. When applying topdressing, strictly control the amount applied each time; the number of applications can be increased to avoid raising the soil solution concentration.

4. Drain salt and wash salt. To drain salt, there should be a surrounding ditch 30-40 cm deep around each greenhouse. Where conditions permit, plastic corrugated buried pipes can be laid under the greenhouse soil; irrigation water seeps down through the upper layer, and salt flows with the water into the buried pipes and is discharged. This method has a high desalination rate and good effect. If there are no salt drainage conditions, water can also be used to wash salt. After the flowers are harvested in spring, uncover the greenhouse film so the soil can be plowed and harrowed into ridges and furrows, clear the drainage ditches, and let rainwater leach through so that salt is discharged with the water. The greenhouse soil can also be irrigated to a depth of 5-7 cm, soaked for several days and then drained, and this can be done 2-3 times.

5. Planting grass to remove salt. Taking advantage of the gap between crops during the high temperatures of midsummer, plant Sudan grass (which can be used to feed cattle and fish), which has very strong salt tolerance, on greenhouse soil with relatively high salinity. After 40 days of growth, the forage yield is 1500-3000 kg per mu, and the desalination effect is good.

6. Apply quicklime to improve acidic soil. Applying quicklime to the soil can neutralize acidity, raise soil pH, directly change the acidification status of the soil, and supply a large amount of calcium to the flower plants. Application method: crush the quicklime so that most of it can pass through a 100-mesh sieve; before sowing, broadcast the quicklime and organic fertilizer separately on the field, then plow and harrow so that the quicklime and organic fertilizer are mixed with the soil as evenly as possible. Application rate: for pH 5.0-5.4, use 130 kg of quicklime per mu; for pH 5.5-5.9, use 65 kg of quicklime per mu; for pH 6.0-6.4, use 30 kg of quicklime per mu (calculated based on regulating the 15 cm acidic plow layer soil).