For good quality and high yield in Welsh onions, reducing nitrogen and increasing potassium fertilization is key
In recent years, in order to increase Welsh onion yields, many vegetable growers have blindly increased the use of chemical fertilizers, especially nitrogen fertilizers. According to surveys, on average, pure nitrogen applied to Welsh onions per mu is as high as 40-50 kg, and phosphorus pentoxide 10-15 kg, while potassium fertilizer is applied very little or not at all, resulting in Welsh onion yields not increasing but decreasing, and root rot becoming more severe...
In recent years, in order to increase Welsh onion yields, many vegetable growers have blindly increased the use of chemical fertilizers, especially nitrogen fertilizers. According to surveys, on average, pure nitrogen applied to Welsh onions per mu is as high as 40-50 kg, and phosphorus pentoxide 10-15 kg, while potassium fertilizer is applied very little or not at all, resulting in Welsh onion yields not increasing but decreasing, and root rot becoming more severe. Excessive nitrogen application and very little potassium application in Welsh onions can easily lead to an imbalance in nitrogen and potassium nutrition. Since 2011, the agricultural technology center of Sheqi County has organized scientific and technical personnel to set up Welsh onion fertilization trials at the Daiying Welsh onion base and the Xialaozhuang Welsh onion base. Based on the trial results and the nutrient balance principle of soil testing and formulated fertilization, the technical theory of "for good quality and high yield in Welsh onions, reducing nitrogen and increasing potassium is key" was proposed for Welsh onion fertilization. The promotion of this fertilization technique increased local Welsh onion yields by more than 20% per mu on average, achieving obvious results. The specific fertilization methods are described below:
1. Welsh onion is a vegetable crop of the Liliaceae family with a relatively long growth period. In the Huang-Huai River basin of China, Welsh onion cultivation generally uses two planting patterns: seedlings raised from September to October, transplanted from February to March, and the first onions or small onions harvested from May to June; seedlings raised from March to April, transplanted in June, and Welsh onions harvested in autumn and winter. During this period, it goes through different growth stages such as the seedling stage, the transplanting and seedling recovery stage, the leaf development stage, and multiple stages of root hilling and blanching (white stalk) formation. A Welsh onion yield of 3000-6000 kg per mu is considered high yield. The absorption ratio of nitrogen, phosphorus, and potassium nutrients by high-yielding Welsh onions is about 1:0.4:1.3, which shows that Welsh onions need more potassium and nitrogen, followed by phosphorus. Therefore, in the fertilization ratio, attention should be paid to the balanced supply of potassium fertilizer. Especially under high-yield cultivation and conditions where no organic fertilizer is applied, even more attention should be paid to supplementary potassium application. As for the appropriate amount of potassium to apply, the ratio of nitrogen to potassium fertilizer mainly depends on the following three aspects: first, the potassium supply capacity of the soil itself; for example, sandy soil has low potassium supply capacity, so the amount of potassium fertilizer used should be appropriately increased. Second, it depends on the target yield of Welsh onions; under high-yield levels, such as exceeding ten thousand jin per mu, the amount of potassium removed from the soil by each Welsh onion crop is greater, so potassium fertilizer should be increased accordingly. Third, the application amounts of other fertilizers, such as the amount of straw returned to the field and the amount of nitrogen fertilizer applied; if a large amount of organic fertilizer is applied, less potassium fertilizer can be applied, and especially the amount of chemical nitrogen fertilizer should be appropriate and applied in balance with the corresponding potassium fertilizer to achieve a good yield-increasing effect. Otherwise, blind input is not only unhelpful for high Welsh onion yields, but also causes a decline in Welsh onion quality, such as a small proportion of white stalk, many leaves, weak onion flavor, and even bitterness.
2. Generally, the recommended nitrogen rate for Welsh onion planting is about 20-26 kg of pure nitrogen per mu. Applying too much nitrogen fertilizer, combined with large amounts of irrigation water, not only wastes nitrogen fertilizer and increases costs, but also produces Welsh onions that do not store well and have reduced quality, and can also have negative environmental effects due to nitrogen loss. Therefore, the amount of nitrogen fertilizer should be appropriate. In choosing the type of nitrogen fertilizer, the most common is urea, but the most suitable nitrogen fertilizer type is ammonium sulfate, because Welsh onion is a sulfur-loving crop.
3. There are also particularities in Welsh onion fertilization methods. The whole-course fertilization should be divided into two parts: base fertilizer and topdressing. For the base fertilizer, it is best to apply 4000-5000 kg of thoroughly decomposed high-quality organic fertilizer per mu, spread on the ground during land preparation, and plowed into the soil. For the chemical fertilizer base fertilizer, all phosphate fertilizer, 40% nitrogen fertilizer, and 60% potassium sulfate fertilizer should be applied; compound fertilizer or single-element fertilizer can be selected. When choosing compound fertilizer, sulfur-based general-purpose or special-purpose types can be used, while high-nitrogen compound fertilizer is not suitable. The application depth of the base fertilizer must be about 15 cm. Welsh onion topdressing can be carried out in 2-3 applications, applying the remaining 60% nitrogen fertilizer and 40% potassium fertilizer from the base fertilizer as topdressing during the vigorous leaf stage and the early to mid-stage of white stalk formation. For the topdressing method, integrating fertilizer with water gives the best effect. Avoid heavy water and heavy nitrogen flushing, which not only causes low fertilizer use efficiency, but in summer, spreading urea on the soil surface also causes nitrogen volatilization, which can easily cause leaf scorch and seedling burn problems.