- Potash deficiency is likely to occur on light textured soils but also on acid or strongly Potassium fixing soils (many loess soils with illitic clay minerals).
- All plants which need much light like fruit crops, tuber crops, root vegetables and beet and which accumulate large reserves (sugar and starch) require generous supply of Potash which can be usually assured only by the regular application of recommended doses of Potash containing fertilizers.
- A plant holds its Potassium salts from being washed or leached out as long as it is living. But as soon as it matures, the salts will move from the plant back into the soil.
- In cereals, the rate of absorption of Potassium is particularly fast between tillering and earing. Several plants and trees can also lose their Potassium content nearing to maturity.
- Excess amount of Nitrogen reduces the uptake of Potassium. Whereas excess of Potassium reduces the uptake of Calcium and Magnesium.
- Optimum doses of Nitrogen, Calcium, Zinc, Copper and Molybdenum increase the uptake of Potassium.
- Potassium requirement is more during pre-maturity, maturity and resting stages of plant growth.
- Potassium takes part in the process of starch conversion to sugars and soluble form.
- It is not a part of biochemical cycle, but it acts as a carrier.
- It functions in the process of photosynthesis, acting as a condenser.
- It is associated with protein activity, primarily in the maintainance of positive ion balance to satisfy negative ion charges on the protein.
- It is essential in the production of auxin – a growth regulator found in abundance in all meristimatic tissues.
- It imparts strength in the crop against stress, cold, diseases, abiotic stress and adverse climatic conditions, etc.
- It controls the mechanism of opening and closing of stomata on the leaves, in turn; keeps a check on the rate of transpiration, turgor pressure, ionic balance, etc.
GENERAL DEFICIENCY SYMPTOMS
- Restriction or early cessation of growth giving a thickset appearance (e.g. Celery and Carrots which develop rosette like growth).
- Leaves are smaller with narrow blades, often coloured dark green to blue green, since their chlorophyll concentration is higher because of the restriction in production of plant material.
- Death of tissue starting at the leaf margin owing to dehydration of the plasma and enrichment in toxic substances (e.g. Putrescine).
- Small necrotic spots/speckles at the leaf tips.
- Crumpling and cupping of leaf margins at the tips
- Dieback of fruit trees, fruits remain small and dull-coloured
- Potassium deficiency in vegetables leads to greater susceptibility to diseases, impaired growth, spots on the margins, marginal yellowing and browning, etc.
- Absence of Potassium results in straw stiffness and lodging of crops