Water balance creates a threshold in soil pH at the global scale

Area of Science:

• Environmental Science
• Soil Science
• Ecology

Background:

• Soil pH is crucial for nutrient storage, supply, and terrestrial ecosystem productivity.
• Soil pH is primarily controlled by environmental factors, particularly water balance.
• Previous understanding of soil pH thresholds was limited by scale and confounding factors like topography and mineralogy.

Purpose of the Study:

• To globally quantify the relationship between water balance and soil pH.
• To identify the critical threshold where soil pH transitions from alkaline to acid.
• To investigate factors causing deviations from the global soil pH pattern.

Main Methods:

• Utilized a global dataset of 60,291 soil pH measurements.
• Extracted a spatially random sample of 20,000 measurements for analysis.
• Correlated soil pH with mean annual precipitation and potential evapotranspiration.

Main Results:

• Identified an abrupt global transition from alkaline to acid soil pH.
• This transition occurs when mean annual precipitation exceeds mean annual potential evapotranspiration.
• Seasonality, climate history, erosion, and mineralogy explain deviations from the global pattern.

Conclusions:

• Climate is a primary driver of global soil solution chemistry, creating a nonlinear pH pattern.
• The study reveals conditions where soil pH may not be in equilibrium with the modern climate.
• Understanding this threshold is vital for predicting soil fertility and ecosystem responses to climate change.