Potassium is more easily mined from soil pool than phosphorus

An eight-year long-term field study conducted in Guanghan city, Sichuan province of China, revealed that severe K deficient symptoms occurred in the wheat plants (left) in the treatment that has not received K fertilizer application for eight years since 2004 compared to the normal wheat plants (right)receiving K for all seasons. As for P, however, there were no P deficient symptoms at all even in the treatment continuously omitted P application for eight years. Wheat yield was reduced by 10% with omitting P and 25% with omitting K, and rice yield was reduced by 6% with omitting P and 21% with omitting K based on the optimal fertilizer treatment. This further indicates that after P fertilizer is continuously used to a field for some years, the accumulated soil P reserves can support normal crop growth for a number of years without significant impact on crop growth and yield reduction. But This does not apply for K, significant yield reduction resulted in the minus K treatment.