Søren Sørensen and the pH Scale

Measuring the hidden chemistry that governs life

As agricultural science moved deeper into chemistry, one persistent problem remained:

Soil reactions mattered—but they were difficult to describe with precision.

Farmers knew some soils were “sweet.” Others were “sour.” Certain crops thrived in one field and failed in another, even when nutrients appeared similar.

What was missing was a common language for acidity and alkalinity.

That language arrived in 1909 through the work of Søren Sørensen.

Why acidity mattered

Long before the pH scale existed, growers understood its effects.

They observed that:

• legumes struggled in sour (acidic) soils, while crops favoring sweet (alkaline) conditions performed better
• lime improved structure and crop performance
• nutrients behaved differently from field to field

But these observations lacked precision.

Without a way to quantify soil reaction, recommendations remained general and inconsistent.

Chemistry needed a...