See more from this Session: General Soils and Environmental Quality: III
Maintenance of soil quality and productivity is very crucial to a sustainable agricultural production system. As the need to expand the use of agricultural biomass in the emerging bioenergy industry increases, the removal of crop residue could have serious implications to soil quality and production capacity. Indiscriminate removal of crop residues from the field represents a reduction in soil organic matter (SOM) input. Soil organic matter plays very essential role in soil health and quality, and therefore any attempt to remove residues for external uses should explicitly evaluate the SOM content and its dynamics. Two major process rates determine SOM levels: (1) the rate at which new SOM is formed from fresh organic inputs, and (2) the rate of mineralization/decomposition of the existing SOM. Both rates depend on the initial SOM level, climatic/weather conditions, and soil properties such as clay and silt contents. Sustainably removable residue would therefore depend on the minimum amounts of residues that should be retained in the soil to ensure new SOM formation and to offset decomposition of existing SOM. Total residue input consists of all carbon sources including belowground and aboveground residues. This total residue input less the minimum that should be retained provides the amount of residue that may be sustainably removed under a rotation. Earlier Canadian studies indicate that the cool and humid eastern agricultural ecoregion of Ontario are characterized by higher SOC decomposition rates compared to the semi-arid regions of western Canada. That implies that more residue C input is needed to maintain a certain SOM level in Ontario. The need for additional carbon input through effective rotation systems and the use of supplementary C inputs such as cover crops and manure therefore becomes very crucial if crop residue removal should play a major role in the expansion of the biofuel industry in Ontario. We developed a 5-step approach in estimating this sustainably removable residue. Sensitivity analysis shows that the net amount of residue to retain or remove are both very sensitive to the rate of new SOM formation from fresh residue inputs and the mineralization rate of existing SOM. Our 5-step approach allows for the estimation of removable residue under any type of cropping system in Ontario.