BEST MANAGEMENT PRACTICES
in cell structures and in energy transformations . It is especially important for root development with newly established sod and seedlings . However , excessively high phosphorus can result in poor plant health and encourage weed infestation , particularly annual bluegrass .
However , in contrast to nitrogen , phosphorus is rarely deficient in well-maintained and established turfgrass and is readily managed through soil testing . Plant response is well correlated to the proven soil tests , with no benefit to applying phosphorus when soil test values are sufficient . It is noteworthy that sports turfgrass tends to need relatively higher concentrations of phosphorus due to frequent overseeding and clipping removal . Despite this , there is no proven benefit , even in sports turfgrass , to continue to add phosphorus fertilizer when the soil test levels are very high . Doing so is a concern for water quality as it contributes to eutrophication . For this reason , fertilizer applications are regulated by some states / counties . In cases where phosphorus is not needed due to high soil test values and / or when prohibited , “ phosphorus-free ” fertilizer sources should be used . In most cases , uncoated / coated ureas , ammonium sulfate , and potassium chloride / sulfate suffice to provide the needed nutrients for turfgrass without application of any phosphorus .
More so than nitrogen , phosphorus fertilizer accumulates in the soil . Phosphorus is poorly soluble , especially at extreme alkaline and acid soil pH levels . Shortly after fertilizer is applied , the majority of the phosphorus precipitates into a solid form . Nutrients need to be dissolved into the soil solution for plant uptake and this solid phase phosphorus is temporarily not available for plants until it slowly solubilizes over time . This is not a concern if enough of these precipitates exist in the soil in proximity to the roots of each plant .
The forming of these solid phosphorus precipitates greatly minimizes phosphorus leaching , especially as compared with nitrate . However , phosphorus can be leached when soil test concentrations are high . Of greater concern is phosphorus loss due to surface water runoff when soil test values are excessive , especially in close proximity to surface water bodies . Fertilizer that lands on impervious surfaces ( e . g ., sidewalks ) that lead to stormwater drains should be minimized and removed .
The most common forms of phosphorus fertilizer are the ammonium phosphates . However , there are a wide variety of phosphorus fertilizers that can generally be categorized as follows :
Traditional inorganic phosphates – These are in granular ( such as monoammonium or diammonium phosphate ) or liquid ( ammonium polyphosphate ) form that quickly react in the soil to form precipitates .
Coated phosphates – These are similar to the coatings for nitrogen that are released slowly over time .
Organic complexed phosphates – These products have been reacted with organic acids or are bound in various plant and animal biosolids ( e . g ., animal or plant manures or treated sewage sludge ). These release nutrients into the soil as they are decomposed by microbes or chemicals . ( Note : The phosphorus described here is potentially different than the phosphorus found in “ organically certified ” fertilizers , which can include these materials or most other sources listed here .)
Specialty products – These include a wide range of products , which are primarily used for pathogen control and improvement of stress tolerance .
Recommended rates of phosphorus , when needed , are 1-4 lbs ./ 1,000 ft ², with the rate proportional to soil test values . Timing of phosphorus applications is not as critical as nitrogen . Typically , a single annual application is adequate , although more may be needed if the soil test is very low and / or with new sod / seed . It is recommended to apply phosphorus and incorporate into the soil ahead of establishing turfgrass if soil test values warrant its use .
POTASSIUM Potassium is essential for proper water relations in plants , as well as other functions , as it supports stress resistance . The overapplication of potassium is wasteful of maintenance costs and natural resources . As with phosphorus , there are good correlations with plant response and soil test values . Potassium is intermediary compared with nitrogen and phosphorus with regard to soil holding capacity . It is held loosely in the soil by clay and organic matter , which means that it is not easily leached in soils with higher levels of these soil components , but is readily leached in sandy , low-organic-matter soils . In these , it tends to need careful management similar to nitrogen to provide for season-long availability . Otherwise , a single annual application is generally adequate .
Rates of potassium , when needed , should be based on soil test results . The most common forms of potassium fertilizer sources are potassium chloride and potassium sulfate , although other sources are available and potentially useful ( e . g ., potassium nitrate , potassium thiosulfate , etc .). Coated sources are available and can be helpful , especially in sandy , low-organic-matter soils .
24 SportsField Management | January 2023 sportsfieldmanagementonline . com