Phosphorus is important in plant metabolic processes, plays a vital role in energy transfer, and is critical for new plant development. Without phosphorus, plants appear to be weak, stunted, or less vigorous, and establishing a thick lawn would become very difficult.
Furthermore, plants deficient in P are likely more susceptible to pressure from weeds, insects, diseases, and decline from environmental stresses. In particular, drought stress becomes a greater issue as the root system is typically not well developed. This information should be more important for those that are managing turf or landscape ornamentals in areas where drought stress can be a larger problem.
How do we know when phosphorus is deficient? In most cases, a lack of available P is pretty tough to diagnose and can take on the look of a lot of other stress-related maladies.
Kevin Lewis of the Ewing Technical Services team tells this story: "I moved to a no phos fertilizer program on my lawn, and by year 4, I noticed that it was really not as vigorous as it had been in previous years. After scratching my head for a few minutes and a soil test, I could see that the soil was not supporting the needs of the lawn and I had my answer. The point is that the symptoms didn’t stand out as a specific issue, and I had to get down to the ….root of the problem."
This is where we stress the importance of soil testing. There is no other way to determine what nutrients are available in the soil than with the assistance of a soil test. Additionally, by performing soil testing, the property manager can solidify themselves as an industry professional who is a good environmental steward.
Another fact to keep in mind: under certain circumstances, phosphorus becomes unavailable to the plant even though it may be abundant. In lower pH soils, P can bond with iron, aluminum, or manganese, and in higher pH soils, bonds with calcium and magnesium will render P insoluble. So again, a proper soil analysis is crucial to determining these factors.
Lastly, many states have laws in place stating that phosphorus can only be applied at establishment or if a soil test shows the necessity. Be sure that you know your local and state laws.
While P is essential for proper plant health, there have also been studies that indicate that excess runoff can be partially to blame for surface water pollution and algal growth. The key is practicing responsible applications of all fertilizers and pesticides.
Phosphorus, when applied to soils with healthy plant material, tends to be fairly immobile and of little risk to leach into ground water due to extensive plant rooting and low surface erosion. The problem comes when it is applied to bare soils, directly into water, or left on hard surfaces after a lawn application. Rain and runoff can wash the materials offsite and ultimately into water sources where they become a problem.
Please make sure that you calibrate your spreader, read the label, and apply all fertilizers responsibly.
Please reach out to the Ewing Technical Services Team if there are any questions.