Agroecological impact of farming systems

经过认证的有机生产是加拿大农业中一个迅速发展的部门。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，这可能会严重限制生产率。有机农业的一个核心前提是，这种低投入的耕作系统可以提高土壤生物多样性或土壤健康，进而促进包括磷在内的养分循环。然而，我们最近的研究表明，利用分子和土壤生物化学技术，土壤微生物群落多样性对耕作系统管理具有高度的弹性。菌根真菌(AMF)似乎是一个例外，我们已经显示出AMF群落的变化，即使在多年生饲料系统下，当有机管理时也是如此。豆类是有机种植系统中的重要组成部分，似乎会影响AMF和土壤P动态的这些变化，但其机制尚不清楚。我们还展示了长期有机耕作如何提高关键的功能特性，如提高有机磷的生化周转，但尚不清楚这是否足以维持作物的磷供应。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制度和做法更敏感，包括新型绿肥减耕制度。总体研究目标是提高我们对低投入和有机种植制度的农业生态影响的理解，以及与这种耕作制度或相关管理做法相关的内在生产力权衡。提出了一个多尺度(长期实验，配对农场)研究计划，该计划将应用新技术，并以跨学科合作为特色。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，以及(Ii)将观察到的土壤生物群落组成和功能的任何变化与与土壤氮磷动态和利用效率有关的关键过程联系起来。长期目标是(Iii)在不同的农业生态系统中阐述土壤微生物群落对较高营养水平(可能有助于杂草和病虫害管理服务)的相对敏感性，对不同的耕作制度的相对敏感性，以及(Iv)确定农田大小、农田边缘管理和景观复杂性对这些观察到的变化的相对影响。这项研究将直接解决制约加拿大有机农业系统可持续性的土壤和肥力管理问题，同时就不同耕作制度和做法、土壤健康和养分动态之间的关系提供新的见解。

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.