How to determine and master the fertilization concentration of carbon dioxide gas?

It is generally believed that the suitable concentration of carbon dioxide for pepper is 800 ~ 1200ml/m3, but the specific concentration should be determined according to the light, temperature, plant growth and management level at that time. Specifically, the suitable concentration of carbon dioxide in seedling stage and growth stage is about 800 ~ 1000 ml/m3, and the fruiting stage is 1200 ml/m3. In winter, there is insufficient sunshine, low temperature and slow growth of plants. The concentration of carbon dioxide is lower, 800 ~ 1000ml/m3. In spring and autumn, the sunshine is abundant, the temperature is high, the plants grow fast, and the concentration should be higher, 1000ml/m3.

The concentration of carbon dioxide in protected areas is mainly controlled by controlling fertilization time and carbon dioxide consumption. Generally, fertilization should be started when the carbon dioxide concentration drops below 800 ml/m3 in the morning. The reference dosage of ammonium bicarbonate in the "ammonium sulfate" reaction method is about 2500 kg/day at low temperature and seedling stage when the concentration of carbon dioxide fertilization is low, and about 3500 kg/day at high temperature and fruiting stage when the concentration of carbon dioxide is high. Maintaining a high concentration of carbon dioxide for 2 hours a day can achieve better fertilization effect.

There are many methods to measure the concentration of carbon dioxide gas, mainly including detector measurement, sodium bicarbonate solution colorimetry, infrared carbon dioxide analyzer measurement, conductivity measurement and so on.

(1) detector method This method is based on the change of the color layer length of the special detector under different carbon dioxide gas concentrations, and compares it with the special temperature correction table to find out the local carbon dioxide gas concentration at that time. (2) Colorimetry of sodium bicarbonate solution This method uses sodium bicarbonate solution with molecular concentration of 0.00 1 to absorb carbon dioxide gas in the greenhouse, and adds a small amount of cresol red indicator to the sodium bicarbonate solution. According to the principle that the color of sodium bicarbonate solution changes differently under different carbon dioxide gas concentrations, compare the color of the measured solution with the standard color or look up Table 9 to determine the local carbon dioxide gas concentration at that time.

Table 9 The corresponding relationship between the color of sodium bicarbonate solution and the concentration of carbon dioxide gas. The colorimetric range of the test solution is deep red, orange yellow, orange yellow and light yellow. The concentration of carbon dioxide gas ranges from pH 7.97.8 ~ 7.77.65 ~ 7.67.47.357.3 (mL/Mi3) 310430 ~ 570670 ~1001274/kloc-0. Conductivity method This method uses the principle that the conductivity will change after the reaction between caustic soda and carbon dioxide, and calculates the concentration of carbon dioxide gas by measuring the change of conductivity before and after caustic soda.

Among the above methods, infrared carbon dioxide analyzer is the most accurate, but the instrument cost is relatively high. Other methods are relatively low in cost, but more troublesome and inaccurate.