What factor can decrease phosphorous mobility in soil?

When considering how phosphorus mobility in soil can be decreased, cooler temperatures can play a significant role. Phosphorus, particularly in its dissolved form, is more mobile when the soil is warm because warm temperatures can enhance microbial activity and increase the solubility of phosphorus in water. Cooler temperatures can slow down these processes, leading to reduced microbial activity and lower solubility of nutrients, which collectively work to decrease the mobility of phosphorus in the soil.

Moisture content is also an important factor, as increased moisture can lead to greater phosphorus movement through leaching and surface runoff, thus increasing its mobility rather than decreasing it. Higher temperatures, similarly, promote nutrient cycling and can enhance the transport of phosphorus. The use of urease inhibitors is specifically aimed at delaying the conversion of urea to ammonia in nitrogen management, which does not directly affect phosphorus mobility. Therefore, among the options provided, cooler temperatures are the most effective factor in decreasing phosphorus mobility in soil.