Here are some facts that are worth considering before we apply phosphorus fertilizer on our lawns, landscapes, gardens, pastures, fields and forests.
- Phosphorus fertilizer comes from a relatively few mining operations around the globe (China, USA, are the major producers, in that order; Morocco is the largest global source). It is estimated that we will run out of domestic sources in two to four decades (pretty darn soon!, google ‘phosphorus crisis’ for more details).
from Scientific American, June 2009(1)
- Phosphorus is the middle number in the three-number label on bags of fertilizer. When you purchase a bag of fertilizer, the three numbers on it represent Nitrogen-Phosphorus-Potassium. All are required plant nutrients, and needed in fertilizer if not in adequate supply in the soil.
- Landscapes growing certain plants, like lawns and pastures, may not require any addition of phosphorus. If the soil contains adequate phosphorus already (naturally or from previous fertilizer applications), adding additional phosphorus is wasting a nonrenewable resource that is critical to food production.
- A landowner NEEDS to do a soil test to determine if the land needs any phosphorus. Take a soil sample and send that sample to a reputable laboratory for a soil analysis. Auburn University Soil Laboratory provides soil testing at a very low price (see www.aces.edu/anr/soillab for more information).
- Results from the AU Soil Laboratory indicate that nearly half of statewide soil samples analyzed in 2010 contained sufficient or excessive amounts of phosphorus, meaning that NO ADDITIONAL PHOSPHORUS was needed (see graph below). Results specific to Lee County indicated that from 40-44% of samples tested contained adequate to excessive phosphorus.
Percent of soil test results(2) for 2010 from the whole state of Alabama (blue bar) and from Lee County (orange bars) that contained adequate-to-excessive phosphorus (did NOT require additional phosphorus fertilizer).
*F+HO = Farms + Homeowners,
**HO = Homeowners only (lawn, garden, orchard)
- Don’t waste you money on ‘home’ test kits - they provide no useful information. If your soil phosphorus is too high simply stop applying it. Use fertilizers with analyses such as 10-0-10 or 15-2-10, ones in which the middle number (the phosphorus) is either zero or very low. Removing lawn clippings (normally not recommended) will keep phosphorus from recycling to the lawn as well.
- Unlike nitrogen, phosphorus is not prone to downward movement (leaching) in the soil. Instead it can accumulate readily, especially when over-applied (in fertilizers such as 10-10-10 or 12-12-12 products). Once phosphorus accumulates in the surface layers of soil it can move via runoff to surface water, creating a nonpoint source pollution issue. This is especially a problem when the soil is bare, with no vegetative cover to prevent erosion.
- High levels of soil phosphorus can also affect plant uptake of some needed micronutrients, especially iron (Fe) and may harm the very plants that one is trying to grow. Consider sprays of iron chelates or iron sulfates to help revive your plants’ green color (rather than over-applying nitrogen).
- If soil phosphorus is high in your garden (or area in which you till the soil) till the soil to a slightly deeper depth. This will help dilute the phosphorus with deeper soil that tests lower in phosphorus (personal communications, Elizabeth Guertal, Professor, AU Department of Agronomy and Soils).
- Phosphorus is detrimental to the aquatic environment, and is considered a major pollutant when its concentrations in the water exceed the very low levels that naturally occur (see www.aces.edu/waterquality/faq/faq_results.php3?rowid=2527 , http://water.epa.gov/scitech/swguidance/standards/criteria/library_index.cfm).
- Studies have shown that streams in the Auburn-Opelika area are excessively high in phosphorus concentrations, and that a large part of this phosphorus is from stormwater runoff in the urban/suburban headwaters (the Auburn-Opelika metropolitan area, see figure below(3)).
Average phosphorus concentrations (in µg/Liter) in tributary sub-watersheds in the Saugahatchee Watershed (outlined in red) from AU Fisheries study(3). Note, the phosphorus concentrations in urban/suburban sub-watersheds (in yellow) are much higher (three times higher) than concentrations in rural, mostly forested sub-watersheds (in green).
- Excess phosphorus from un-needed phosphorus fertilizer application is oftentimes detrimental to the environment. In the Auburn-Opelika area, excess phosphorus flowing into the Saugahatchee Creek is one of the two causes listed by the Alabama Department of Environmental Management for its placement on their 303(d) List of Impaired Streams (the other being Organic Enrichment; see http://adem.alabama.gov/programs/water/303d.cnt for more information).
- A growing number of local, county and state policy-makers have drafted and adopted various ordinances and regulations that limit fertilizer applications. Such policies have the potential of significantly reducing costs of land management and simultaneously reducing amounts of nonpoint source pollutants flushing into local surface waters. Policies restricting the use of fertilizers have been adopted in 11 states, including MN, ME, WI, MI, IL, NY, FL, MD, VA, NJ, and VT (source: EPA Watershed Academy Webcast - Nitrogen and Phosphorus Pollution Series: State and Local Policies to Restrict the Use of Phosphorus Lawn Fertilizer (September 21, 2011, http://water.epa.gov/learn/training/wacademy/archives.cfm ).
Heavy algae bloom in the Saugahatchee Creek near Reeltown, July 2000.
- Excess phosphorus in streams and lakes can, and oftentimes does generate algal blooms. Algae are tiny plants that grow in surface waters, the primary producers (along with aquatic plants) that form the base of the aquatic food chain. These algal blooms foul the water, interfere with recreational uses, can deplete the water of dissolved oxygen and lead to fish kills, make it more difficult and expensive to process potable water, and sometimes produce a variety of toxins (neurotoxins, hepatotoxins; see www.cdc.gov/hab for more information).
(1)Phosphorus: A Looming Crisis. 2009 (June). Scientific American, pp 54-59.
(2)Results from AU Soil Testing Laboratory (personal communications, Gobina Huluka, Director of the AU Soil Testing Laboratory, AU Department of Agronomy and Soils).
(3)Nutrient and Sediment Loading in Sougahatchee Creek and the Impacts on Aquatic Biota. 2004. www.aces.edu/dept/fisheries/natural-resources/riversandstreams.php