Sustainable De-Intensification or Intensification - Can We Assess Progress Using a Soil Organic Matter Based Index of Sustainability?.

Well-established measures of intensity and sustainability of agricultural production include assessments of water, energy and nutrient use and efficiency. More recently the species richness, abundance and diversity of wild bees in agroecosystems has been shown to be inversely related to an index of production intensity linked to nitrogen use, livestock density and pesticide use.  Such metrics of sustainability can also be applied to all organic agriculture production systems, which also vary significantly in intensity of production. However, while an appreciation of the fundamental importance of soil quality and health and their relationship to soil organic matter (SOM) dynamics are common to all of agriculture, much less effort has been devoted to developing an index of sustainability linked to factors influencing trends in these critical edaphic parameters.   Soil health and SOM levels are broadly influenced by inherent and dynamic soil properties, the former referring to the strong influence of soil type and texture while dynamic properties comprise those that are more sensitive to agricultural management (including tillage and crop rotation practices, cover crops and organic matter additions etc.). 

Throughout the Eastern US and Canada, crops such as soybean, corn and potatoes, which return little crop residue to soil, are often cropped at frequencies in rotation (i.e. intensity levels) which depletes SOM and soil health.  When situated on shallow soils on sloping land this further exacerbates risks of soil loss through tillage and water erosion.  In organic production, new developments in reduced tillage of green manures may allow for intensification of production (i.e. shorter rotations) once the net effect on SOM and soil health is better understood.  Drawing on results from ongoing replicated and on-farm cropping system trials the potential for development of an index of sustainable de-intensification and intensification linked to dynamics in SOM storage and soil health will be presented.