How to adjust the light and gas composition in watermelon greenhouse?
Watermelon requires light intensity. However, due to the dew condensation or unclean surface of the shed film, the light intensity injected into the shed is reduced, especially in the case of multi-layer coverage. Therefore, we should pay attention to keep the shed film clean, and don't use the old film with poor light transmission. The light in the greenhouse mainly comes from the top (glass window) and the side (side light), and the plastic film also has a certain reflection effect in the early stage of growth. Under the condition of close planting in shed, the normal photosynthesis of leaf area above ground 1 meter has great influence on watermelon yield. Therefore, during the growth period of watermelon, the light from the top and both sides of the shed should always enter the shed unimpeded, so that the leaves above 1 m in the shed can get enough light in the middle and late growth period. Therefore, it is necessary to prune, split and top in strict time, so that the top leaf of the frame is 30 ~ 40 cm away from the roof film to prevent the row, top and edge from closing. When tying vines, pay attention to the leaf spacing of 20 ~ 30 cm to prevent overlapping.
(2) Gas regulation in the shed
The content of carbon dioxide in the air in a closed greenhouse is seriously insufficient, which affects the normal photosynthesis and the accumulation of assimilation products. Carbon dioxide fertilization is to artificially increase the carbon dioxide concentration in the greenhouse and supplement the insufficient carbon dioxide content in the greenhouse. The method is as follows: firstly, fresh horse manure is piled in the shed, and carbon dioxide can be released during the fermentation process, and 5-6 kg is piled up per 1 m3 space; Second, burning propane gas will produce carbon dioxide. In a greenhouse with an area of 600 square meters, burning 1.2 ~ 1.5 kg can make the carbon dioxide concentration in the greenhouse reach 1.3 ml/L. The amount of propane gas burned can be determined according to the area of the greenhouse. Thirdly, the application of coke carbon dioxide generator can release carbon dioxide when coke is fully burned; Fourth, the simplest method is to put concentrated hydrochloric acid in a container that has not been corroded, and then put a small amount of stone flow (calcium carbonate) to produce carbon dioxide through chemical reaction. The period of carbon dioxide fertilization is mainly in the peak period of watermelon growth, especially in the fruit development period; The optimum time is around 10 in the morning, and the optimum concentration is1~1.5 ml/L. Ventilation measures must be taken to keep the gas in the shed fresh and prevent the accumulation of harmful gases.