Long-term changes in mollisol organic carbon and nitrogen

Area of Science:

• Soil Science
• Agronomy
• Ecology

Background:

• Midwestern USA Mollisols have undergone land-use changes from prairie to agriculture.
• Crop production practices have evolved, impacting soil organic matter (SOM).
• Long-term studies using archived and resampled soils are crucial for understanding these impacts.

Purpose of the Study:

• To quantify changes in soil organic carbon (SOC) and total nitrogen (N) pools in Mollisols.
• To assess the impact of prairie conversion and cultivation on SOM.
• To document SOM changes over time, including the effects of synthetic fertilizers and drainage.

Main Methods:

• Resampling of soils to 1-meter depth across 19 sites in central Illinois.
• Utilizing archived soil samples from the early 1900s and mid-1950s.
• Comparing cultivated fields with adjacent virgin prairie remnants and grass borders.

Main Results:

• Cultivation of prairie resulted in 30-50% reductions in SOC and total N compared to virgin soils.
• No significant changes in SOC and N pools were observed between 1957 and 2002 under synthetic fertilizer use.
• Organic matter decline occurred primarily in the top 50 cm, with evidence of C and N translocation to deeper layers, potentially due to tile drainage.

Conclusions:

• Conversion of prairie to cropland led to substantial and likely irreversible losses of soil organic matter.
• Soil organic matter levels in cultivated Mollisols reached a steady state by the 1950s.
• Modern agricultural practices, including synthetic fertilizer use, have not significantly altered these stabilized SOM pools.