Detailed Explanation of Key Points of Watermelon Micro-Irrigation and Fertilization Technology

Micro-irrigation fertilization is a water-saving, fertilizer-saving, and efficient agricultural production technology that, under the condition of a pressurized water source, uses a fertilizer injection device to inject fertilizer solution into the micro-irrigation system and deliver it uniformly and steadily at a small flow rate to the soil in the crop root zone.

I. Watermelon Cultivation Characteristics

For spring greenhouse seedling raising, sowing is generally in late January to early February, with transplanting in mid-to-late March; for autumn greenhouse seedling raising, sowing is in late May to early July, with transplanting one month later. Density is 680-700 plants/mu, row spacing 105-110 cm, plant spacing 70-80 cm. Bed preparation: ridge height 18-20 cm, ridge width 40 cm, and after laying the drip irrigation tubing, cover with plastic film and seal well. Base fertilizer application: organic fertilizer 3500-8000 kg/mu, compound fertilizer (15:15:15) 50 kg/mu, potassium sulfate 15 kg/mu, and mix thoroughly and cover with soil.

II. Micro-Irrigation and Fertilization Facilities

The micro-irrigation system is generally drip irrigation, with one or two drip irrigation tapes (tubes) laid per bed, and the emitter spacing is comparable to the plant spacing. Installation and use shall refer to relevant specifications. The fertilizer injection device is generally a pressure-differential fertilizer tank or a Venturi fertilizer injector, and the fertilizer tank volume shall be no less than 15 liters.

III. Selection of Commonly Used Fertilizers

1. Fertilizer requirements: soluble in irrigation water at room temperature, with insoluble matter below 5% and low conditioner content; basically no precipitation when mixed with other fertilizers; will not cause drastic changes in the pH of irrigation water; low corrosiveness to the irrigation system.

2. Commonly used fertilizers: solid fertilizers with good water solubility or high-concentration liquid fertilizers, such as urea, monopotassium phosphate, potassium nitrate, ammonium nitrate, potassium chloride, etc., or water-soluble special compound fertilizers (special formula fertilizers); special formula fertilizers are recommended.

IV. Micro-Irrigation and Fertilization Scheme

1. Micro-irrigation scheme: After transplanting, water thoroughly once in time; generally drip irrigation should be more than 8 hours, or furrow irrigation may be used. After emergence, drip irrigation may be used depending on soil moisture. For protected cultivation watermelon, generally during the seedling stage, drip irrigate once every 5-7 days, 10-12 cubic m/mu each time; during the vine elongation stage, drip irrigate once every 5-7 days, 12-14 cubic m/mu each time; during the fruit enlargement stage, drip irrigate once every 6-8 days, 13-16 cubic m/mu each time. For open-field watermelon, generally during the seedling stage, drip irrigate once every 5-7 days, 10-15 cubic m/mu each time; during the vine elongation stage, drip irrigate once every 5-7 days, 13-16 cubic m/mu each time; during the fruit enlargement stage, drip irrigate once every 6-8 days, 15-18 cubic m/mu each time.

2. Fertilization scheme: The general principle is to apply fertilizer once every two drip irrigations. For protected cultivation watermelon, generally during the seedling stage, apply fertilizer once every 8-10 days, 10-12 kg/mu each time, with a fertilizer ratio (N:P2O5:K2O) of 20:15:15; during the vine elongation stage, apply fertilizer once every 8-10 days, 12-14 kg/mu each time, with a fertilizer ratio of 20:5:20; during the fruit enlargement stage, apply fertilizer once every 10-12 days, 15-18 kg/mu each time, with a fertilizer ratio of 20:5:25. For open-field watermelon, generally during the seedling stage, apply fertilizer once every 8-10 days, 10-12 kg/mu each time, with a fertilizer ratio of 20:10:15; during the vine elongation stage, apply fertilizer once every 8-10 days, 12-14 kg/mu each time, with a fertilizer ratio of 20:5:20; during the fruit enlargement stage, apply fertilizer once every 10-12 days, 15-18 kg/mu each time, with a fertilizer ratio of 20:0:20.

V. Micro-Irrigation and Fertilization Operation

1. Irrigation operation: During irrigation, close the valve on the fertilizer tank (injector), fully open the control valve of the drip irrigation system sub-main, and irrigate according to the micro-irrigation scheme. At the end of irrigation, first cut off the power, then immediately close the control valve. The wetting depth of drip irrigation is generally 30 cm. The principle of drip irrigation is small amounts and frequent applications; do not aim to apply more water by extending the drip irrigation time.

2. Fertilization operation

(1) Fertilizer preparation: According to the requirements of the fertilization scheme, first dissolve the fertilizer in water; the fertilizer may also be dissolved in water the day before fertilization. During fertilization, filter with gauze (mesh) and then pour the fertilizer solution into the pressure-differential fertilizer tank, or pour it into an open container and draw it in with a Venturi injector.

(2) Fertilization operation: Pressure-differential fertilization method: The fertilizer tank is connected in parallel with the pressure regulating valve on the main pipe, and the inlet pipe of the fertilizer tank shall reach the bottom of the tank. Before fertilization, irrigate for 20-30 minutes first. During fertilization, tighten the tank cover, open the tank inlet valve, and after the tank is full of water, open the tank outlet valve, and adjust the pressure difference to keep the fertilization speed normal. The fertilization time is generally controlled at 40-60 minutes to prevent uneven or insufficient fertilization. Venturi fertilization method: The Venturi injector is connected in parallel with the valve on the main pipe. Pour the previously dissolved fertilizer solution, after filtration, into an open container, place the suction head of the Venturi injector into the fertilizer solution; the suction head shall have a filter screen, and the suction head shall not be placed at the bottom of the container. Open the valve on the suction tube and adjust the valve on the main pipe so that the suction tube can draw the fertilizer solution uniformly and steadily.

Precautions: Each time fertilizer is added, the fertilizer solution concentration must be well controlled, generally adding 1 kg of fertilizer to 1 cubic m of water. The fertilizer dosage should not be too large, to prevent fertilizer waste and system clogging; after each fertilization, irrigate for another 20-30 minutes to flush the pipeline.

3. System maintenance

After the micro-irrigation and fertilization system has been running for a period of time, the drainage valve at the lower part of the filter should be opened to discharge impurities, and the residue at the bottom of the fertilizer tank should be cleaned frequently. In some areas, the water has a relatively high carbonate content. After each irrigation season, a 30% dilute hydrochloric acid solution (40-50 liters) should be injected into the drip irrigation tube, retained for 20 minutes, and then flushed with clean water.