Several Factors Affect Phosphorus Availability in Lawn Soil
YESTERDAY’S ANNOUNCEMENT from Scotts Miracle-Gro that it will remove phosphorus from all of its synthetic chemical fertilizers in the United States has brought a flurry of media calls asking us to explain what that will mean to the health of American lawns. The company stated in its press release that it discovered that most existing lawns could get by just fine without additional phosphorus in the fertilizer and, while that’s technically true, many factors determine whether or not your lawn will receive an optimum amount of phosphorus.
Phosphorus is plentiful in many soils, but is often “locked up” in a form that is not usable by plants — which require phosphorus especially in root formation and for overall vigor. That was always the justification for why phosphorus was added to fertilizers in the first place.
By taking phosphorus out of fertilizers, it becomes incumbent to optimize the primary soil conditions: 1) the chemistry that includes the ideal pH of 6.5-7.2; 2) the structure and texture so that roots encounter minimal resistance for growth; 3) robust biology so that nutrient “cycling” within the soil delivers the natural phosphorus to the plants.
All of these attributes can be tested at laboratories, although you’ll rarely find one lab that will test all three. For the homeowner averse to spending a bunch of money on tests, he or she should at least determine the pH with a simple test from the local Cooperative Extension Service at the state university. Adjust the pH higher or lower with calcium or sulphur or other soil amendments depending on the results.
Get your organic matter as high as possible in the soil by the addition of compost and other natural soil amendments such as humates. This will improve soil structure and texture and enhance the soil biology so that the microbes in the can unlock that natural phosphorus most readily.
Failure to do any of these things could result in the long-term decline of your lawn from lack of phosphorus.