Soil pH in O'Brien, IA: Lime or Sulfur?

Typical topsoil pH in O'Brien, IA

Typical topsoil in O'Brien, IA is pH 6.29, already right for vegetable garden (6-7). Test before adding anything.

What O'Brien needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 2.7 lb/100 sq ft over 2 applications; blueberries 4.4 lb/100 sq ft over 3 applications; azaleas and rhododendrons 3.4 lb/100 sq ft over 2 applications; blue hydrangeas 3.4 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.29, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.

How mixed the soil is

Of the 365,552 surveyed acres in O'Brien, IA, 49% are near neutral (6.5-7.3), 46% are moderately acidic (5.5-6.5), 5% are alkaline (above 7.3). Mapped soils run from pH 5.7 to 7.9, a spread of 2.2 units across 106 soil components. No single class covers 60% of the county, so two gardens a few miles apart here can need opposite treatments. Test your own bed.

Clay, organic matter and rates

Topsoil here averages 33.5% clay and 5.13% organic matter, which this site treats as clay. At 5.13% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 6% of mapped components carry free carbonate (lime already in the ground).

O'Brien against the rest of Iowa

pH 6.29 is 0.07 below the Iowa median of 6.36. 29 of 99 Iowa counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Keokuk (6.27), Madison (6.27), Taylor (6.28), Warren (6.28), Poweshiek (6.29), Union (6.29), Clarke (6.3), Cedar (6.31).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; O'Brien sits 25% of the way up.