Management effects on the nature of organic matter in agricultural soils

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Soils cultivated for agriculture are generally depleted in soil organic matter (SOM) relative to their native counterparts (~50% less) so they in the past have been a major source of greenhouse gas emissions. However, agricultural soils also have the potential to be a sink provided they are managed appropriately to sequester C. Adoption of sustainable best management practices to protect and enhance SOM levels is currently actively promoted: reduced frequency and intensity of soil tillage, the planting of complex rotation cropping systems and cover crops to maximize quality and quantity of crop inputs, and maximizing return of crop residues and organic wastes. Despite the central role of SOM in soil functioning, the nature and dynamics of SOM constituents and how they are affected by agricultural management practices are poorly understood. Simply, the effects of these practices on SOM at the molecular level are unknown. Therefore, it is difficult to predict how SOM might respond to current pressures: (i) changes in land management due to agricultural intensification (which is essential for providing foodstuff to world's projected 9 million people), (ii) changes in cropping systems due to plant biomass use for bio-product and biofuel production, or (iii) changes in temperature and precipitation patterns under climate change.The goal of my research program is to determine how agricultural management practices affect the chemical nature and turnover of SOM. The research will consist of three pillars based on: (i) chemical characterization of SOM constituents in soils sampled from on-going, long-term field studies, (ii) controlled laboratory incubation studies to evaluate the formation and dynamics of persistent SOM, and (iii) biophysical modelling to evaluate predictions and test concepts of SOM. The research will identify at a molecular level the constituents of SOM most affected by agricultural practices and determine how quickly they change. For example it is well known that crop litter and residue accumulate on the surface soil under no tillage farming, but rapidly degrade if soils are tilled to manage compaction or crop residues. Can this pool of organic matter be better managed so as to increase its efficiency of conversion to SOM? This knowledge is critical for understanding the mechanisms controlling SOM storage to propose sustainable agricultural production strategies.