Soil pH in Rapides, LA: Lime or Sulfur?

Typical topsoil pH in Rapides, LA

Typical topsoil in Rapides, LA is pH 5.68, too acidic for vegetable garden. Expect roughly 5.6 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Rapides needs, by plant

• Already in range: potatoes, strawberries, azaleas and rhododendrons.
• Just outside, test first: blueberries (off by 0.2), blue hydrangeas (off by 0.2).
• Lime: lawn (cool-season grass) 5.6 lb/100 sq ft over 2 applications; vegetable garden 5.6 lb/100 sq ft over 2 applications; tomatoes 5.6 lb/100 sq ft over 2 applications; roses 5.6 lb/100 sq ft over 2 applications; pink hydrangeas 4.2 lb/100 sq ft.

What to do next

If your test confirms pH near 5.68, spread about 56 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 765,298 surveyed acres in Rapides, LA, 49% are strongly acidic (below 5.5), 28% are near neutral (6.5-7.3), 22% are moderately acidic (5.5-6.5), 1% are alkaline (above 7.3). Mapped soils run from pH 3.6 to 8, a spread of 4.4 units across 99 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 22.8% clay and 1.79% 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. 0% of mapped components carry free carbonate (lime already in the ground).

Rapides against the rest of Louisiana

pH 5.68 is 0.14 above the Louisiana median of 5.54. 35 of 64 Louisiana counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Livingston (5.52), Lafayette (5.55), West Feliciana (5.6), Bossier (5.66), Caddo (5.75), Tensas (5.76), Natchitoches (5.77), Madison (5.82).

The range in Louisiana runs from Allen at 4.88 to St. Bernard at 7; Rapides sits 38% of the way up.