钾在作物体中的存在形态与氮、磷不同，它主要是以离子态或可溶性盐类或被吸附在原生质表面上而存在，而不是以有机化合物的形态存在。所以钾的作用还没有完全弄清楚。现在已知它有下列几方面的作用：

Different from nitrogen and phosphorus, potassium exists mainly as ionic or soluble salts or adsorbed on the surface of protoplast, rather than in the form of organic compounds. So the role of potassium is not fully understood. Now it is known that it has the following functions:

(1)钾是许多酶的活化剂，酶是作物体中新陈代谢过程中的催化剂，没有酶的作用，许多生理过程无法进行。现在已知有60多种酶需要钾离子作活化剂。

Potassium is the activator of many enzymes, enzymes are used as catalysts in the metabolism process, without the role of enzymes, many physiological processes can not be carried out. It is known that more than 60 enzymes need potassium ion as activator.

(2)钾能促进光合作用，促进碳水化合物的合成和运输。民间有句农谚：“做瓦靠坯，番薯靠灰”。说明淀粉类(碳水化合物)作物施钾肥很重要；种甘蔗施钾肥可提高庶糖含量。施用钾肥往往会获得好的效果。

Potassium can promote photosynthesis, carbohydrate synthesis and transportation. There is a folk saying: "do tile by green, sweet potato by ash.". It shows that potassium fertilizer is very important for starch (carbohydrate) crops, and potassium fertilizer can increase sugar content in sugarcane. The application of potash fertilizer can get good results.

(3)钾能促进蛋白质的合成 根据研究，不管是饲料作物还是粮食作物，吸钾量多的作物其蛋白质含量也高。据测定：20克蛋白质中约有1克的钾。所以，缺钾影响蛋白质的合成，细胞的形成受抑制。这就是水稻缺钾时分蘖大受影响的重要原因之一。

Potassium can promote protein synthesis. According to research, whether it is feed crops or food crops, the protein content of crops with high potassium uptake is also high. According to the determination: 20 grams of protein in about 1 gram of potassium. Therefore, potassium deficiency affects protein synthesis and cell formation is inhibited. This is one of the important reasons that the tiller of rice is greatly affected by potassium deficiency.

(4)钾能增强作物茎秆的坚韧性，增强作物的抗倒伏和抗病虫能力。如水稻胡麻叶斑病、赤枯病、玉米茎腐病和香蕉凋萎病施用钾肥后病症都可减轻。

Potassium can enhance the tenacity of crop stem, enhance the ability of lodging resistance and insect resistance of crops, such as rice flax leaf spot, brown blight, corn stalk rot and banana wilt, and the disease can be alleviated after applying potassium fertilizer.

(5)钾能提高作物的抗旱和抗寒能力　这是由于钾能维持细胞的正常含水量、减少水分的蒸腾损失和提高作物的含糖量之故。如果缺钾，作物含水量下降，根细胞会很快衰老。所以干旱地区或季节，越冬作物，要考虑增施钾肥。

Potassium can improve the ability of drought and cold resistance of crops, which is because potassium can maintain the normal water content of cells, reduce the transpiration loss of water and increase the sugar content of crops. If potassium is deficient, the water content of crops will decrease, and the root cells will senescence quickly. Therefore, in arid areas or seasons, winter crops should consider increasing potassium fertilizer application.

作物缺钾.典型的症状是从老叶或植株下部叶片先开始，因为钾的再利用程度大，钾不足时，老组织中的钾可转移到幼嫩组织中去但如果严重缺钾，嫩叶也会发生此症状，田间表现为“黄金边”。其次是根系发育不良，根细弱，常呈褐色；在氮素充足时，缺钾的双子叶植物的叶子常卷曲而显皱纹，禾本科作物则茎秆柔软易倒伏，分蘖少，抽穗不整齐。

The most typical symptom of potassium deficiency in crops starts from the old leaves or the lower leaves of plants. Because of the high degree of potassium reuse, potassium in old tissues can be transferred to young tissues when potassium is insufficient. However, if potassium deficiency is serious, this symptom will also occur in young leaves, which is manifested as "golden edge". The second is the poor development of root system, the root is thin and weak, often brown; when the nitrogen is sufficient, the leaves of potassium deficient dicotyledons are often curly and wrinkled, while the stems of gramineous crops are soft, easy to lodging, few tillers and irregular heading.