Agroecological impact of farming systems

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Certified organic production is a rapidly expanding sector within Canadian agriculture. We have documented low soil phosphorus (P) status across the major organic production sectors in Canada potentially critically constraining productivity. A core premise of organic agriculture is that this low-input farming system enhances soil biological diversity or soil health which in turn is suggested to improve cycling of nutrients including P. Our recent research, however, using molecular and soil biochemistry techniques, suggests a high degree of resilience of the soil microbial community diversity to farming system management. Mycorrhizal fungi (AMF) appear an exception and we have shown shifts in the AMF community even under perennial forage systems when managed organically. Legumes are an essential component in organic cropping systems and appear to influence these changes in AMF and soil P dynamics but the mechanisms are poorly understood. We have also shown how key functional properties, such as enhanced biochemical turnover of organic phosphorus, are enhanced by long-term organic farming but it is unknown whether this is sufficient to sustain crop P availability. In contrast to the soil microbial community we have found the abundance and diversity of higher tropic level soil organisms (beetles, earthworms) appear more responsive to organic farming systems and practices including novel reduced tillage systems for green manures. The overall research goal is to improve our understanding of the agro-ecological impacts of low-input and organic cropping systems, and inherent tradeoffs with productivity, that are linked to such farming systems or associated management practices. Proposed is a multi-scale (long-term experiment, paired farms) research program, which will apply novel techniques and feature interdisciplinary collaborations. Short-term objectives are: (i) to examine the relative impact of vegetative complexity versus soil P status, on soil microbial abundance, diversity and activity, and (ii) to link any observed shifts in soil biological community composition and functioning to critical processes linked to soil N and P dynamics and efficiency of use. In the longer-term the objectives are (iii) to elaborate, across contrasting agroecosystems, the relative sensitivity of the soil microbial community versus higher trophic levels (which may contribute weed and pest management services), to contrasting farming systems, and (iv) to determine the relative influence of field size, field margin management and landscape complexity on these observed changes. The research will directly address soil and fertility management issues constraining system sustainability for organic agriculture in Canada, while providing novel insights with respect to the relationship between contrasting farming systems and practices, soil heath and nutrient dynamics.