水稻种植需科学施用钾肥

Rice plants lacking potassium exhibit poor root development and are prone to root rot. The leaf color resembles that of excessive nitrogen application, but the leaves are shorter. Early signs of potassium deficiency include stunted growth, dark green or bronze-colored leaves, followed by yellowing. Older leaves typically show yellowing first at the tips, with irregular brown spots appearing beneath the discolored areas. These older leaves age rapidly and eventually die. The root system becomes thin, short, and sparse, turning dark brown or black and dying in large numbers. The stems become weak and soft, leading to lodging. The flag leaf has a high rate of yellowing, and flowering occurs 5-7 days earlier than normal. The panicles are short and small, with a high percentage of empty grains, small and uneven grains, low milling yield, and poor quality. Depending on the planting season, variety type, and soil conditions, the symptoms of potassium deficiency in rice can be classified into three types: 1. Red spot type. Symptoms appear after the seedling stage and during tillering, with large red-brown irregular spots on lower leaves, which may turn necrotic and dry out, resembling "bronze disease" or "red blight." 2. Mottled type. Brown mottles appear during the late tillering stage to the early panicle differentiation stage, larger and darker than common leaf spots, with clear boundaries between diseased and healthy areas. 3. Brown spot type. Small scattered spots appear during the early panicle differentiation stage, often extending into lines. The leaf tips fade and turn yellow, then brown and curl. To diagnose potassium deficiency, look for typical symptoms such as reddish leaves, reduced plant height, and brown tips and spots starting from the lower leaves. The panicle emerges 3-5 days earlier than usual. Another method involves testing the sap of the third to fifth leaves from the center of the main stem during the tillering stage. When reacted with hexanitrobenzene reagent, it forms a potassium hexanitrobenzene precipitate, which turns orange-red in acidic conditions. If the potassium content is below 1500 mg/kg, the plant is considered potassium-deficient. Potassium deficiency in rice is influenced by several factors. Historically, organic manure and wood ash were widely used, replenishing soil potassium levels. However, in recent decades, increased crop yields have led to higher nitrogen and phosphorus consumption, along with reduced use of organic fertilizers, causing potassium deficiency in many regions. Approximately 70% of farmland in China is now potassium-deficient. Soil potassium deficiency arises mainly due to poor drainage or over-drainage, leading to extreme pH levels. A pH of around 7 is most favorable for potassium availability, while high pH (7.5-8.5) increases calcium concentration, hindering potassium uptake. Climate changes, such as sudden droughts after heavy rainfall, also contribute. Excessive application of nitrogen, calcium, and magnesium fertilizers, along with removal of crop residues and excessive organic matter, further exacerbate the issue. To improve potassium nutrition in rice, increasing organic fertilizer application, promoting straw return, and enhancing potassium cycling in the agricultural system are essential. Utilizing biological potassium sources, such as green manure crops, helps convert insoluble soil potassium into available forms. Crop rotation strategies, like rice-rice-fertilizer or rice-rice-oil rotations, can also help manage soil potassium levels. Proper potassium fertilizer application is crucial—determine the right amount based on soil tests, apply it as both basal and top-dress fertilizer, and ensure timely application during critical growth stages. Controlling nitrogen input, managing water properly, and applying 4-6 kg of potassium chloride per acre when deficiency is observed are effective measures to prevent and correct potassium deficiency.

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