Turf - Soil pH and weather

Soil pH is affected by the weather received in a year. The following is an article on the subject.

In above average rainfall years there is increased leaching of nitrate nitrogen (N) along with calcium and magnesium (basic cations) from soils. Turf managers apply nitrogen fertilizer largely in ammonium or urea forms that are oxidized to nitrate in the soil releasing acidity. On wetter years often more of these acid forming fertilizers will be used. There may also be increased denitrification requiring higher N application rates (again, ammonium and urea based fertilizers reduce soil pH). In wetter years there is increased grass removal of basic cations, increased grass clippings that release acidity when they decompose, and numerous other factors that lead to higher acidity levels in our soils. Sandy soils that have a low cation exchange capacity are especially susceptible to loss of basic cations and sudden drops in soil pH (increases in soil acidity).

In below average rainfall years such as 2007 and 2008, there is reduced leaching of nitrate nitrogen (N), reduced calcium and magnesium loss (basic cations that help maintain higher pH), reduced use of nitrogen fertilizers that are acid forming, reduced denitrification requiring lower N application rates (less acidity released with nitrification), reduced grass removal of basic cations, and reduced grass clippings that release acidity when they decompose. As a result, soil pH will not drop as much in dry years.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County.