On August 7th, the season of Liqiu (End of Heat) begins, marking the official start of autumn. From this day on, temperatures gradually drop from their peak summer highs, and the weather becomes cooler, with more noticeable temperature differences between day and night. Although days remain warm, nights become relatively cool. This year, Liqiu falls during a period of economic downturn, so in many parts of China, after a brief period of heat, temperatures are still high, and humidity remains significant. From an agricultural perspective, farmers often say: “Planting Chinese cabbage at the beginning of autumn and picking cotton during the summer heat,†and “Floating radish on the head of radish.†These sayings highlight that autumn is an ideal time for planting Chinese cabbage.
Chinese cabbage is a staple leafy vegetable for many northern Chinese people throughout the year. The goal of fertilization is to achieve both high yield and quality. According to its nutritional needs, Chinese cabbage requires a ratio of NPK (nitrogen, phosphorus, potassium) of approximately 1:0.5:1.2, indicating a higher demand for potassium than nitrogen. However, in actual production, farmers often overemphasize nitrogen fertilizer while neglecting potassium balance. Based on recent fertilization practices, there are three key principles to follow this year.
First, apply an appropriate amount of nitrogen fertilizer. For high yields, how much nitrogen is needed? Practical experience shows that producing 1,000 kg of fresh vegetables requires about 2.0 kg of pure nitrogen. For 10,000 kg of vegetables, around 22–25 kg of nitrogen is needed. Nitrogen can come from soil, organic manure, or chemical fertilizers. In areas where large amounts of organic fertilizer are used, it’s wise to reduce the use of chemical nitrogen. Applying the right amount of nitrogen supports growth and enhances photosynthesis, which is crucial for achieving high yields. In some remote areas, insufficient nitrogen may result in thin, weak leaves and tough tissues, affecting both yield and quality. However, in most regions, excessive nitrogen application is common. Too much nitrogen can cause the outer leaves to grow too large, leading to poor head formation, lower yield, and reduced quality. It also increases water content, making the cabbage less storeable and more prone to pests and diseases later on. Therefore, not only the quantity but also the timing of nitrogen application matters. Throughout the growing season, the absorption of nitrogen varies: seedlings take up about 2%, rosette stage about 28%, and the filling stage accounts for as much as 70%. Thus, nitrogen should be applied in stages—light early and heavy later. Since Chinese cabbage has a long growing cycle, proper base fertilizer application is essential. In older fields with rich soil, organic fertilizer can be applied appropriately. Chemical compound fertilizers typically contain mainly phosphorus and potassium. In new fields, organic fertilizer should be combined with triple compound fertilizer, along with potassium. During top-dressing, from the seedling stage to the rosette stage, it's important to control nitrogen application. Only in special cases should seedlings be boosted. Usually, transplanting occurs during the rosette stage, allowing the outer leaves to develop strongly. This helps promote root growth and lays the foundation for nutrient and water absorption in later stages. The first top-dressing should occur during the critical rosette stage, applying nitrogen and potassium together, and combining it with irrigation to support the heart-filling phase. The second top-dressing takes place in the early to mid-stage of head formation, with controlled nitrogen application. Late-stage nitrogen application should be stopped to avoid overgrowth.
Second, increase the proportion of phosphorus and potassium fertilizers. Boosting potassium in both base and top-dressing improves the core development and disease resistance of the cabbage. Pay special attention to potassium application during the rosette stage. If phosphorus and potassium are insufficient during the head-forming period, the cabbage may not develop properly. Currently, potassium is often overlooked in vegetable farming. An appropriate amount of potassium is generally around 12 kg per mu of potassium chloride or 16 kg of potassium sulfate. The best method is to split the application into two parts—once as base fertilizer and once as top-dressing. Apply the base fertilizer when planting, and then apply the top-dressing after the seedlings have established, combining it with nitrogen and irrigation.
Third, ensure sufficient calcium supply. Adding calcium superphosphate to the base fertilizer helps prevent “dry heart†disease in Chinese cabbage. Cabbage is a calcium-demanding crop, and calcium deficiency, especially due to excessive nitrogen, can lead to dry heart disease. Controlling nitrogen and supplementing calcium are key technologies in preventing this issue. In addition to calcium-containing fertilizers, foliar applications such as spraying 0.3-0.5% calcium chloride or calcium nitrate can also help.
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