Chemistry and Mineralogy of Soil Aggregates in Soils From Temperate Continuous Corn System- Effects of Different Management Practices.

Agriculture could act as both sink and source of atmospheric carbon dioxide (CO₂) which has been estimated to reduce 15 % of global fossil fuel emission. Climatic factors as well as agricultural management practices (crop rotation, tillage intensity and fertilizer source) could influence the total organic carbon (C) content and chemical structure of C. The chemical structure of C determines the resistivity to degradation. This study was intended to understand the potential of C sequestration based on management practices and aggregate size fractions by determining the chemistry of humic substances, and mineralogy of soil aggregates.  

Soil samples (0-5, 5-15 and 15-30 cm depth) were collected from North Agronomy farm, Manhattan, Kansas, USA and soil was a moderately well-drained Kennebec silt loam (fine-silty, mixed, superactive mesic Cumulic Hapludoll). This site has been under continuous corn for 22 years and had two tillage treatments (tilled and no tilled) and two fertilizer treatments to supply 168 kg N ha^-1 (as compost or ammonium nitrate) with a control. 

Four aggregate sizes (> 2 mm, 2-0.25 mm, 0.25-0.053 mm and < 0.053 mm) were separated by wet sieving. Humic acid was extracted from all aggregate size fractions and was analyzed by Fourier transform infrared spectroscopy (FTIR). ¹³C Nuclear magnetic resonance (NMR) spectroscopy analyses are being conducted to further confirm the initial data determined by the FTIR.  Mineralogical information will be determined by x-ray diffraction analysis.