Soil order

Molisol

Soil with a thick, dark surface horizon rich in organic matter (the mollic epipedon), with more than half of its exchange capacity occupied by calcium, magnesium, potassium and sodium. It forms under grassland.

What it means for farming

They are the soils agricultural lands par excellence: the Pampas grassland formed them and most of Argentine agriculture is done on them. They retain water and nutrients; its limitation, when there is one, is below: clay, sodium, calcareous hardpan or drainage.

Molisoles on the maps

Udol

Molisol humid climate (udic moisture regime): the profile almost never spends more than three months dry.

Ustol

Molisol from subhumid to semi-arid climate (ustic moisture regime): water is enough in the growing season but there are long dry periods.

Acuol

Molisol with excess water: saturated near the surface for part of the year, with redox depletions (gray, mottles) in the profile.

Albol

Molisol with a clear, washed (albic) horizon between the surface and the clay horizon, and water hanging over it in humid times.

Xerol

Molisol Mediterranean climate (xeric moisture regime): it rains in winter and summer is dry.

Rendol

Molisol shallow formed directly on calcareous material.

Borol

Molisol cold climate.

The definitions are a plain-language summary of the USDA Keys to Soil Taxonomy. The formal definition includes thickness, color and percentage thresholds that are left out here.

Sources