Open-field Cultivation Methods and Technical Key Points for Onions
Onion is both a fine vegetable and has high health value; some developed countries even use onion in pharmaceutical production, where it plays a role in preventing cancer and combating cardiovascular and other diseases. According to the growth and development characteristics of onion, to achieve high yield and high efficiency in production, the following points should be mastered in cultivation techniques.
I. Variety and site selection. Qinghai Province is a high-latitude region, so long-day varieties should be selected. The variety used should be chosen according to climatic and environmental conditions and cultivation habits; the American hybrid variety "White Rock" can be selected. This variety has the characteristics of being large, tall, pure white in color, disease-resistant and high quality; varieties such as "Red Lantern" can also be selected. China's main export destination for onions is Japan. The cultivation site should be selected in river-irrigated areas with good soil fertility, flat terrain and good water and heat resources.
II. Sowing and seedling raising
1. Sowing at the right time. Onion sowing is generally around the Beginning of Autumn; the method can be drilling or broadcasting, and uniform sowing is required. The seeding rate is about 1.8-2.25 kg per hectare (increase or decrease as appropriate according to germination rate), and the seedbed per hectare can provide about 15 hectares of transplanting seedlings.
2. Seedling stage management. The onion emergence period is about 7-10 days. After most onions have emerged, irrigate according to soil moisture. After 2 leaves have grown, urea 105-108 kg/hectare can be applied as a topdressing combined with intertillage and weeding, then irrigate. Generally, irrigate once every 10 days.
3. Temporary planting of onion seedlings. Lift the seedlings in mid-November, tie onion seedlings of the same seedling quality into small bundles, remove seedlings without roots or that are too short, place the tied bundles of onions in rows in a shady place, and after a row is filled, cover the base to the middle-upper part of the onion seedlings with moist soil, then set up the second row and again cover with moist soil for temporary planting to overwinter.
4. Soil treatment. For the onion planting plot the following year, chemical soil treatment for underground pests and weeds should be carried out before winter, and thorough winter irrigation should be applied. For soil treatment of underground pests, phoxim emulsifiable concentrate 3750-6000 mL per hectare can be sprayed on the ground (because it is easily decomposed by light, it should be done in the evening), and evenly turned into the soil, or 5% phorate granules 22.5-33.75 tonnes can be evenly applied into the soil. For weed soil treatment, 2250 mL per hectare of Tianpu herbicide or 48% trifluralin can be sprayed, or 2250-3000 mL of 50% acetochlor or 1875-2250 mL of Caicaotong can be sprayed, and evenly turned into the soil.
III. Apply sufficient base fertilizer and plant at a reasonable density. The onion root system is a fibrous root system composed of string-like adventitious roots. The root system is not well developed and is relatively weak. The root mass is mainly concentrated in the soil at a depth of 20 cm, and its ability to absorb fertilizer and water is weak, so it has relatively high soil requirements. Onion is not suitable for continuous cropping; generally, a 3-year rotation is used.
1. Land preparation and fertilization. During land preparation, deep plowing should be carried out, and the plowing depth should not be less than 20 cm. The plot should be level to facilitate small-water irrigation (flood irrigation) without water accumulation, and land preparation should be very fine. Generally, for medium-fertility fields (bean stubble, corn and other dry stubble are better), apply 30 cubic meters of high-quality decomposed organic fertilizer per hectare, and 450-600 kg of diammonium phosphate and phosphorus-potassium compound fertilizer as base fertilizer. The planting method should preferably use flat beds; generally the bed width is 0.9-1.2 m (depending on the width of the plastic film), and the ditch width is 0.4 m for easy operation.
2. Film mulching. Film mulching can increase soil temperature and increase yield. Before mulching, irrigate the plot; after the soil is slightly dry, harrow and mulch immediately to help preserve soil moisture, and press the film edges tightly. After mulching and before planting, punch holes at a row spacing of 20 cm × 15 cm. The hole-punching tool can be homemade, punching 12 holes at a time.
3. Planting. In February of the following year, when the surface soil has thawed about 5 cm, onions can be planted. The planting depth should be such that the heart leaf is not buried and the seedlings do not fall over. Watering should be done so that seedlings do not fall over and the bed surface does not accumulate water. When planting seedlings, they should be planted straight and shallow (about 2 cm), with the roots and soil closely combined. If planted too deep, it easily affects bulb expansion. After planting, onions enter the seedling recovery stage. Where conditions permit, planting water can be applied; after the seedlings recover and grow new leaves, water again.
4. Reasonable dense planting. Density is an important factor constituting yield. Onion has few leaves and strong upright growth, so it is suitable for dense planting. Experiments show that reasonable dense planting can increase onion yield per unit area. The planting density depends on variety characteristics, soil conditions and production goals. Generally, medium-maturing varieties are 330,000-600,000 plants per hectare. If the row spacing is 20 cm × 15 cm, then 495,000 plants are planted per hectare.
IV. Field management. After planting, the relative soil humidity should be maintained at 60-80%. If it is below 60%, water is needed, with the soil becoming dry as the limit. Watering and topdressing should also depend on seedling conditions and soil fertility, and generally "frequent irrigation with small amounts of water" should be used. Fertilizer and water management should grasp the principle of "control before the year, promote after the year." During the growth period, in addition to base fertilizer, topdressing should also be carried out to ensure seedling growth. For plots with poor fertility, 105-150 kg of urea per hectare can be applied together with watering.
1. Vigorous leaf growth period. When onion has 6 leaves and 1 heart, it enters the vigorous growth period. At this time, the fertilizer requirement is relatively large. Per hectare, 300 kg of urea can be broadcast on the film surface, plus 300 kg of 48% nitrogen-phosphorus-potassium compound fertilizer, which can meet the nutrient demand of onion during the vigorous growth period.
2. Bulb expansion period. When the aboveground part of the onion reaches 9 leaves, it enters the bulb expansion period. The plant no longer increases in height, and leaf assimilates transfer to the bulb. The bulb expands rapidly. This period is another peak fertilizer demand period, especially the demand for P and K fertilizers increases significantly. Practice has proved that applying 450 kg per hectare of 48% nitrogen-phosphorus-potassium compound fertilizer can ensure normal bulb expansion.
3. Pest and disease control. Onion is susceptible to downy mildew, purple blotch and rust. In rainy and humid weather, downy mildew and purple blotch are more serious. For downy mildew and purple blotch, 75% chlorothalonil 600-fold solution or 64% oxadixyl-mancozeb 500-fold solution can be sprayed; 25% metalaxyl or 65% mancozeb 600-fold solution can also be sprayed for control. For rust, 15% triadimefon 1500-2000-fold solution can be sprayed for control, once every 10-15 days, for 3-5 consecutive sprays. The last use time of the above pesticides should be 7-10 days before the harvest period. For onion thrips, 40% omethoate 800-fold solution or 10% imidacloprid 300 g/hectare can be sprayed for control. These two insecticides may be used only once during the growth period, and should be separated from the harvest period by more than 15 days.
V. Timely harvest
1. Before harvest, when the leaves have not yet turned yellow, spray the leaf surface with maleic hydrazide (MH) 500 mg/kg, which can prevent sprouting during storage.
2. Do not water again 7-10 days before harvest, to prevent the onion bulbs from absorbing enough water in the field and thus being unsuitable for storage.
3. After 30% of the aboveground tubular leaves naturally lodge, this is the suitable harvest period. At this time, the first and second leaves at the base of the plant are yellow and withered, the third and fourth leaves still have green, the pseudo-stem loses water and becomes soft, and the aboveground part naturally lodges. Harvesting should be carried out on sunny days. The main plant is pulled out with roots, dried in the field for 1-2 days; during drying, use the leaves to cover the onion bulbs, drying only the leaves and not the bulbs. The yield per hectare is 60-90 t. To improve the commodity rate and get to market early, it can also be harvested early.
Onions sold on the market are required to have large bulbs, crisp and tender texture, fine and dense tissue, and excellent quality. For contract purchasing, grade according to the contract requirements. Generally, grade I bulbs have a transverse diameter of more than 8 cm, grade II bulbs have a transverse diameter of 6-8 cm, and inferior bulbs have a transverse diameter of less than 6 cm. Keep 1-1.5 cm of pseudo-stem on the bulb and cut it neatly. The onion bulbs are required to be intact, with a clean surface, free of disease and insect mold spots, free of mechanical damage, and free of shriveling or softening.