Soil Amendment Calculator

Enter your soil report and targets, and get exactly what to add (lime, gypsum, and fertilizer rates) to bring each field to your targets. Save and compare multiple tests side by side, and log each report to chart where your soil has been and where it is now.

About this tool: how to read a soil test
About this tool: how to read a soil test

pH and buffer pH are different numbers

pH is how acidic the soil is now. Buffer pH is how hard it resists changing, and it sets the lime rate: two soils can read 5.5 and need completely different amounts. Without one, the rate is estimated from texture.

Lime is slow

Six to twelve months for the full change. Only fine particles react, so compare bags on ENM, ECCE or CCE. Split anything over 50 lb per 1,000 sq ft. Lowering pH is much harder than raising it.

Gypsum does less than it is sold for

It supplies calcium and sulphur and does not change pH. It will not loosen ordinary compacted clay. It earns its place on sodic soil.

Salt and sodium are two different problems

ECe is how much dissolved salt is in the soil. Salt holds water against the root, so a plant on saline ground wilts in wet soil. It leaches out. SAR is sodium measured against the calcium and magnesium competing with it. Sodium on the exchange sites disperses clay, and dispersed clay seals the profile.

Above ECe 4 dS/m a soil is saline. Above SAR 13 it is sodic. Above both, saline-sodic.

The order is calcium, then water

A sodic soil is never leached first. Water with no calcium in it strips the salt that is keeping the clay flocculated and seals the ground, and the job gets bigger than it started. Gypsum goes on first, gets worked in, and the leaching water follows it.

P and K are an index, not an inventory

40 ppm phosphorus is what one extractant pulled out, not what is in your soil. Bray, Mehlich-3 and Olsen are not interchangeable, so stay with one lab.

The sample is the weakest link

  • Take 10 to 15 cores and mix them. One core is meaningless.
  • Consistent depth: 3 to 4 inches for turf, 6 to 8 for beds.
  • Different areas are different tests.
  • Not soon after liming, or you are testing the application.
  • Retest the same way every three years.