Fate of Potassium in Crop Production

Potassium is the 3rd major nutrient after N and P. Its concentration ranges from 0.5-2.5 per cent in soil and in plants 0.5-6 per cent. It is an essential nutrient for crop production and is important for carbohydrate metabolism and it improves the water use efficiency. Potassium is taken up by plants as K⁺ cation. Potassium in soil is present in three forms i.e.; unavailable k (90-98%), slowly available K (1-10%) and readily available K (1-2%) (Mengal and Kirkby, 1987). Potassium from mica contributes a part of soil potassium (Mengal and Rahmatullah, 1994, Baeumler et al., 1997). Factors such as soil pH, organic matter, temperature and moisture are important determining factors for the availability of potassium (Fageria et al., 2001). Depending on the type of crop, the potassium requirement can be nearly as high as nitrogen requirement. Potassium deficiency resulted in a decrease in net photosynthetic rate and dramatic decrease in crop yield (Ding et al., 2006). Potassium fertilized plants were resistant to lodging but insufficient tissue potassium is known to increase lodging incidence. In recent years, however, deficiencies of potassium have been diagnosed more frequently by farmers due to greater potassium removal from soil by crops with enhanced yields, intensive cropping systems and so on (Scherer, 2001). Potassium deficiency is usually corrected by the addition of a potassium containing fertilizers such as potassium chloride (60%), potassium-magnesium sulfate (20%), potassium nitrate (44%), potassium sulfate (50%), potassium monophosphate (34%), potassium carbonate (68%) and potassium thiosulfate (25%). But muriate of potash is cheaper source of potassium and also contains more potassium as compared to sulphate of potash. Without adequate potassium, crops can not reach their full potential in terms of yield as well as quality. A dose of 36 kg k ha^-1 was ideal for wheat (Alam et al., 2009). Interaction effect of potassium and sulphur application significantly affected the protein, oil content and oil yield of Brown Sarson at the rate of 90 kg k ha^-1 and 60 kg k ha^-1 (Singh et al., 2013). Potassium is required in large quantities by the plants for their function. Since they are involved in various enzymatic activities, their deficiency causes malfunctioning of the plant activities. Response to potassium varies from crop to crop and depending upon the soil type and its potassium status. In addition to yield, it improves the quality of crops and has synergetic effect with other nutrients like sulphur and nitrogen (Bahmanyar and Mashaee, 2010).