The study looked at how potassium is held in paddy soils in northern Iran. By flooding the soils and testing different potassium levels, the researchers found that more clay and certain soil properties can predict how much potassium the soil can hold. They also discovered that a lot of potassium may be needed to improve soil fertility, and this may need to be added gradually over time. It's important to keep adding potassium to the soil to maintain its fertility for growing rice.