Soil pH in Polk, AR: Lime or Sulfur?

Typical topsoil pH in Polk, AR

Typical topsoil in Polk, AR is pH 5.46, too acidic for vegetable garden. Expect roughly 7 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Polk needs, by plant

• Already in range: potatoes, blueberries, azaleas and rhododendrons, blue hydrangeas.
• Just outside, test first: strawberries (off by 0).
• Lime: lawn (cool-season grass) 7 lb/100 sq ft over 2 applications; vegetable garden 7 lb/100 sq ft over 2 applications; tomatoes 7 lb/100 sq ft over 2 applications; roses 7 lb/100 sq ft over 2 applications; pink hydrangeas 5.6 lb/100 sq ft over 2 applications.

What to do next

If your test confirms pH near 5.46, spread about 70 lb of ground limestone per 1,000 sq ft of vegetable bed in 2 doses, ideally in fall.

How mixed the soil is

Of the 530,963 surveyed acres in Polk, AR, 62% are strongly acidic (below 5.5), 38% are moderately acidic (5.5-6.5). Mapped soils run from pH 5 to 6.2, a spread of 1.2 units across 144 soil components. 62% of the land falls in one class, so the county figure is a fair first guess for most yards here.

Clay, organic matter and rates

Topsoil here averages 15% clay and 1.33% organic matter, which this site treats as loam. Moving it one pH unit takes about 7 lb of lime or 2.3 lb of sulfur per 100 sq ft. None of the mapped components carry free carbonate.

Polk against the rest of Arkansas

pH 5.46 is right at the Arkansas median of 5.44. 40 of 75 Arkansas counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Clark (5.43), Ashley (5.44), White (5.44), Yell (5.45), Carroll (5.47), Lonoke (5.51), Conway (5.54), Cross (5.56).

The range in Arkansas runs from Madison at 5.02 to Desha at 6.33; Polk sits 34% of the way up.