Potassium promotes the production of fruits and flowers on plants. At high levels, potash can block the uptake of foliage-boosting nitrogen. For that reason, plants that are grown for their flowering or fruiting potential rather than foliage most benefit from high-potassium soils. This group includes bushes and trees that produce edible fruit, as well as “fruiting” vegetables such as tomatoes (Solanum lycopersicum) and summer and winter squash (Cucurbita). It excludes edibles such as salad greens and cooking greens, because of their high nitrogen needs to maintain lush foliage. From SFGate.
Spray foliar zinc and iron on plants in high phosphorous soils. High phosphorous levels require additional zinc and iron treatments for plants to maintain their health. Texas A&M University suggests mixing a spray that contains water with 1 percent foliar zinc and iron, then applying that spray to plants every week if phosphorous levels are excessively high. You may apply it every four weeks if phosphorous levels are slightly high. Soils with 300 parts per million phosphorous will take up to five years to go back to acceptable levels. From SFGate.