水稻种植需科学施用钾肥

Rice plants suffering from potassium deficiency exhibit several visible symptoms. The root system stops developing and is prone to root rot. The leaf color becomes very dark green, similar to the effect of excessive nitrogen, but the leaves are shorter in length. Early signs of potassium deficiency include stunted growth, with a dark green or bronze-like appearance of the leaves. Over time, the leaves turn yellow, starting from the older ones. The tips of the older leaves lose their green color first, followed by irregular brown spots beneath the discolored areas. These leaves age quickly and eventually die. The roots become thin, short, and fewer in number, often appearing dark brown or black and dying off in large quantities. The stems become weak and soft, leading to lodging. The flag leaf shows high rates of yellowing, and the flowering period occurs 5-7 days earlier than normal. The panicles are short and small, with high levels of empty grains, small and uneven grains, low milling yield, and poor quality. Depending on the planting season, variety type, and soil conditions, rice potassium deficiency can be classified into three main types: 1. Red spot type. Symptoms appear after tillering, with large red-brown irregular spots on lower leaves, which eventually become scorched and dry, forming a red-brown appearance. This condition is often accompanied by "black roots" and is referred to as potassium-deficient red spot disease or "bronze disease." 2. Mottled type. During the late tillering to early panicle differentiation stage, red-brown mottles appear, which are larger and darker compared to common leaf spot diseases. The boundaries between the affected and healthy tissues are clear. 3. Brown spot type. Symptoms appear around the time of panicle differentiation, characterized by scattered small brown spots or linear patterns. The leaf tips turn pale yellow and gradually turn brown and curl. This type is commonly observed in early rice due to excessive nitrogen fertilizer application. **Potassium Deficiency Diagnosis** Severely potassium-deficient rice plants show clear and recognizable symptoms. After heading, the leaves may appear red, as if burned, and the plant height decreases. Starting from the lower leaves, red-brown tips and spots appear, spreading upward. The edges of the leaves become scorched, and heading occurs 3-5 days earlier than normal. Another method for quick diagnosis involves testing the sap of the third to fifth leaves below the heart leaf during the tillering stage. When reacted with hexanitrobenzene reagent, potassium forms a hexanitrobenzene potassium precipitate, which turns orange-red under acidic conditions. By comparing the color intensity, if the potassium content is less than 1,500 mg/kg, it indicates a potassium deficiency. **Causes of Potassium Deficiency in Rice** Historically, China used organic fertilizers and wood ash, which helped replenish soil potassium. Since potassium levels were generally higher than nitrogen and phosphorus, the need for additional potassium fertilizer was low. However, over the past 30 years, increased crop yields have led to higher nitrogen and phosphorus consumption, along with reduced use of organic fertilizers. As a result, many regions have experienced potassium deficiency. Currently, about 70% of arable land in China is potassium-deficient, extending from coastal southern areas to the three northeastern provinces. Soil potassium deficiency is mainly caused by three factors: First, poor drainage or excessive drainage can lead to extreme pH levels, with the most significant issues occurring at a pH of around 7. At pH values between 7.5 and 8.5, excess calcium in the soil strongly interferes with potassium uptake. Second, climate conditions such as heavy rainfall followed by drought or consistently high humidity can affect potassium availability. Third, excessive application of nitrogen, calcium, and magnesium fertilizers, along with the removal of crop residues and overuse of fresh organic manure, can also contribute to potassium deficiency. **Potassium Fertilizer Application Techniques** Increasing organic fertilizer use is essential. Expanding sources of potassium and promoting straw return to the field can help recycle potassium within the agricultural ecosystem, addressing potassium deficiency effectively. Exploring biological potassium resources is also important. Although soils contain ample potassium, 90%-98% is in an insoluble form that rice cannot easily absorb. Developing green manure crops can help absorb and concentrate difficult-to-dissolve potassium, converting it into a usable form for plants. Implementing proper crop rotation can help alleviate potassium shortages. Different crops have varying potassium needs and absorption capacities, so rotating crops like rice-rice-fertilizer or rice-rice-oil can help balance soil potassium levels. Applying potassium fertilizers appropriately is crucial. First, determine the correct amount based on soil tests. Research shows that when available potassium is between 50-105 mg/kg, applying 5 kg of potassium oxide per mu (approximately 667 square meters) is suitable for a target yield of 500 kg/mu. Second, choose the right time for application. Since potassium is easily leached, it should be applied as both base fertilizer and top dressing. In fields with little organic fertilizer or severe potassium deficiency, more potassium should be applied as base fertilizer. In fields with sufficient organic fertilizer, especially those using rice straw return, at least 50% of potassium should be applied as top dressing. Due to the close relationship between nitrogen and potassium balance and potassium deficiency, it's important to apply potassium during the tillering and panicle formation stages in double-crop rice to prevent imbalances. In addition, integrated management strategies should be adopted. Winter plowing is recommended, nitrogen fertilizer use should be controlled, and water management should be improved. If potassium deficiency is detected, 4-6 kg of potassium chloride per mu can be applied.

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