Phosphorus. The nutrient we’re not supposed to mention. Just sweep it under the rug, and forget about it. We can do without it.
But…we can’t, despite many folks outside of the industry suggesting that very thing to us over the past decade or so. We can’t, because when it comes right down to it, we know science. We know plants need phosphorus (P) perhaps as much as they need nitrogen and potassium. Maybe not in the same amounts, but take it away completely and, well, Houston we have a problem.
Phosphorus helps transfer energy from one point in a plant to another, and is crucial in root development and flowering.
Furthermore, superintendents (for the most part) have common sense. We know that phosphorus deficiencies (if left untreated) result in poor turfgrass. Poor turfgrass results in environmental problems.
Phosphorus deficiencies can go beyond just poor-quality putting surfaces. Phosphorus deficiencies can cause weakened and eventually dead turfgrass, which can lead to erosion and (here’s the rub) cause the very thing environmentalists are concerned about in the first place when they put bans on phosphorus.
But one of the problems is knowing when there is enough available phosphorus for the plants and when levels are actually at a level low enough where you need to address it. Soil tests for phosphorus can be a little tricky. They are not all created equal.
At the Golf Industry Show in San Diego in February, I attended a great seminar hosted by Dr. Elizabeth Guertal, professor at Auburn University. The class was “Phosphorus – Must It Always Equal Zero?” Professor Guertal’s research in phosphorus research may be unequaled in this country. Among the many things she discussed in regard to our use of phosphorus was those tricky soil tests. Reading soil tests and knowing exactly what they are saying (especially in regard to phosphorus levels and recommendations for those levels) can be more confusing than one would think.
Often, the parts per million levels that show up on various tests inform us if levels are low and need attention, but we are slowly finding out low does not always mean low enough to make corrections. The vast discrepancies between the different testing labs, the actual types of soils being sampled, as well as the opinions of what is low and what is acceptable, are, frankly, all over the place.
One thing we do know is to keep those roots as long and healthy as possible so the roots can find the available phosphorus they need. Making sure that phosphorus is there, but in levels that are not too high (environmentally speaking), is the key.
Much of Guertal’s emphasis was that it’s often OK for our soil tests to indicate low phosphorus levels. Many times we have to use common sense and determine for ourselves if those levels are truly low. But if they need correction, then how and when to correct?
Manganese use (or more correctly, lack of use) in our fertility arsenals was also discussed. A show of hands in our class indicated almost no one applies manganese as part of a regular fertility program. I did happen to be one of the few who raised a hand, as manganese use for us has helped with, among other things, keeping take-all patch away on our Poa annua greens.
There have been some studies that seem to indicate low levels of phosphorus could be less of a problem on bentgrass greens than those that are primarily Poa annua greens. But, again, so many other factors go into this. It cannot be used as a simple rule.
Walking the trade show the day after this class, I was amazed at how many products are out there (many of them new) to assist us with these low phosphorus levels. Miracle products – the cure all for all your phosphorus woes.
But proceed cautiously. Take soil samples and understand the tests. Ask questions. Know what the levels mean for you. Decide if you really need an application of phosphorus and, if you do, make sure to utilize the timing of the product you choose the very best you can.
Read more: A time for turf to revitalize