Immobilization or fixation of a nutrient means that the nutrient becomes unavailable for plant. The process of converting exchangeable or water soluble potassium to its non exchange or water insoluble form is known as potassium immobilisation. Potassium is present in relatively large quantities in soil (averaging about 1.9%). Depending on the circumstances, soil potassium may be not easily available, slowly available or readily available. The first category accounts for 90 to 98% of the total soil potassium, which is only slightly soluble, the second category constitutes 2-10% of total mineral soil and third category makes up for about 1%.

The correct answer is option 'C': Potassium - Readily immobilisation.

Explanation:
Potassium is an essential macronutrient required by plants for various physiological processes, such as enzyme activation, osmoregulation, and protein synthesis. It plays a crucial role in plant growth, development, and overall health. Potassium is predominantly absorbed by plant roots in the form of K+ ions from the soil solution.

One of the significant challenges faced by plants in terms of potassium uptake is its availability in the soil. Potassium is primarily present in the soil in two forms: exchangeable (available for plant uptake) and non-exchangeable (bound to soil particles and unavailable for plant uptake). The exchangeable form of potassium is held in the soil solution and can be easily absorbed by plant roots.

However, the non-exchangeable form of potassium is tightly bound to soil particles and is not readily available for plant uptake. This immobilization of potassium occurs when it reacts with clay minerals, organic matter, or other soil components, leading to its fixation and limited mobility.

Once potassium is immobilized in the soil, it becomes unavailable for plant uptake, which can result in potassium deficiency in crops. This immobilization of potassium is a natural process that occurs in soils with high clay content or soils with a high organic matter content.

To overcome this immobilization and make potassium available for plants, various strategies can be employed, such as:

1. Soil management practices: Proper soil management techniques, such as incorporating organic matter, using cover crops, and practicing crop rotation, can help increase the availability of potassium in the soil.

2. Fertilizer application: Applying potassium-rich fertilizers can replenish the soil's potassium content and provide readily available potassium for plant uptake.

3. pH adjustment: Adjusting the soil pH to the optimum range for potassium availability can enhance its uptake by plants.

In conclusion, the correct match for the given statement is option 'C': Potassium - Readily immobilisation. Potassium can become readily immobilized in soils, making it less available for plant uptake. Therefore, it is essential to implement appropriate soil management practices and fertilizer application strategies to ensure an adequate supply of potassium for plant growth and development.

Active transport of nutrients require ATP. Symplast is translocation through plasmodesmata. Bakane disease of rice was found by Hori (1918) to be due to Gibberella fujikuroi.

•Option (c) is correct.