Phosphorus is crucial for plant growth. It helps plants acquire, transfer and store the energy that helps them flourish. But, as is so often the case in plant biology, you can have too much of this good thing.
Phosphorus buildup is caused by excessive use of inorganic fertilizer or the use of composts and manures high in phosphorus. It can become water-soluble and mobile, entering surface waters and causing algae and other undesirable plants to grow.
Research has discovered that high inorganic phosphorus has a lasting negative impact, as microorganisms remain in decline and don’t fully recover. Microorganisms are critical to crop health. Microbes consume soil nutrients making them plant available, improve soil structure and contribute greatly to building soil organic matter (SOM).
Other problems from excessive phosphorus typically affect shallow-rooted plants. This is a significant issue as shallow roots have less access to nutrients and water.
Iron and zinc deficiencies are caused by excessive phosphorus. Iron deficiencies are characterized by yellowing between the leaf veins. Zinc deficiencies show a bleaching of the tissue. Both iron and zinc deficiencies occur in the youngest tissues and can occur at the same time, which makes it difficult to identify the actual problem.
Affected plants need additional iron and zinc. However, simply adding iron and zinc to the soil will not work. Research shows that soil-applied iron is rapidly tied up by alkaline soils and its availability to plants is limited. Under high-phosphorus conditions, both iron and zinc are quickly converted to non-available forms. Foliar iron and zinc applications, however, work well.
Over time, phosphorus is converted to increasingly stable forms. Phosphorus eventually will be converted into “rock phosphates” that have very limited solubility except in acidic soils. How long the problem persists depends on the type of plants being grown, the soil type and the initial level of phosphorus in the soil. Soils with extractable phosphorus levels of 150 to 300 ppm (parts per million) probably will have problems for 3 to 5 years. Soils with phosphorus levels above 330 ppm will require special treatments for much longer.
Andaman Ag sells a large array of foliar nutrient sprays and can make the appropriate recommendations depending on your past practices, current situation and whether you’re farming conventional or organic.