What characteristic of phosphorus leads to its low mobility in soil?

Phosphorus tends to have low mobility in soil primarily due to its tendency to bind with soil cations. This binding occurs because phosphorus can form complexes with positively charged ions (cations) such as calcium, iron, and aluminum, which are present in the soil. When phosphorus attaches to these cations, it becomes less available for plant uptake and movement through the soil. As a result, phosphorus does not leach easily through the soil profile, leading to its accumulation in the upper layers of soil and limiting its dispersal as compared to other nutrients that are more soluble or mobile.

The other options provided are less relevant to the mobility of phosphorus. For example, while high solubility might suggest a nutrient could move easily, phosphorus is not typically high in solubility in many soil types. Rapid uptake by plants implies that phosphorus is necessary for plant growth, but it does not directly influence its mobility in the soil. Finally, low nutrient demand does not correlate with the soil mobility characteristic, as it indicates merely how much the plants need phosphorus rather than how it behaves in the soil.