Agroecological impact of farming systems

认证有机生产是加拿大农业中一个迅速扩大的部门。我们已经记录了加拿大主要有机生产部门的低土壤磷（P）状况，这可能严重限制生产力。有机农业的一个核心前提是，这种低投入的耕作系统提高了土壤生物多样性或土壤健康，这反过来又被认为是改善养分循环，包括P.我们最近的研究，但是，使用分子和土壤生物化学技术，表明土壤微生物群落多样性的高度弹性耕作系统管理。菌根真菌（AMF）似乎是一个例外，我们已经表明，即使在多年生牧草系统有机管理的AMF社区的变化。豆科植物是有机种植系统的重要组成部分，似乎影响AMF和土壤P动态的这些变化，但机制知之甚少。 我们还展示了关键的功能特性，如有机磷的生物化学周转率的提高，是如何通过长期的有机耕作来提高的，但目前还不清楚这是否足以维持作物磷的可用性。与土壤微生物群落相比，我们发现热带水平较高的土壤生物（甲虫、蚯蚓）的丰度和多样性似乎对有机耕作系统和做法（包括新的绿色肥料少耕系统）更敏感。总体研究目标是提高我们对低投入和有机种植系统的农业生态影响的理解，以及与这种耕作系统或相关管理做法有关的与生产力的内在权衡。提出的是一个多规模（长期实验，配对农场）的研究计划，将应用新技术和跨学科合作的特点。短期目标是：（i）研究植被复杂性与土壤磷状况对土壤微生物丰度、多样性和活性的相对影响;（ii）将任何观察到的土壤生物群落组成和功能的变化与土壤氮磷动态和利用效率相关的关键过程联系起来。从长远来看，目标是（三）阐述，在对比农业生态系统，土壤微生物群落的相对敏感性与较高的营养水平（这可能有助于杂草和害虫管理服务），对比耕作制度，及（四）确定相对影响的领域大小，外地利润管理和景观复杂性对这些观察到的变化。该研究将直接解决限制加拿大有机农业系统可持续性的土壤和肥力管理问题，同时提供关于对比农业系统和实践，土壤健康和养分动态之间关系的新见解。

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.