Soil phosphorus (P) cycling in agroecosystems is highly complex, with many chemical, physical, and biological processes affecting the availability of P to plants. Traditionally, P fertilizer recommendations have been made using an insurance‐based approach, which has resulted in the accumulation of P in many intensively managed agricultural soils worldwide and contributed to the widespread water quality issue of eutrophication. To mitigate further environmental degradation and because future P fertilizer supplies are threatened due to finite phosphate rock resources and associated geopolitical and quality issues, there is an immediate need to increase P use efficiency (PUE) in agroecosystems. Through cultivar selection and improved cropping system design, contemporary research suggests that sufficient crop yields could be maintained at reduced soil test P (STP) concentrations. In addition, more efficient P cycling at the field scale can be achieved through agroecosystem management that increases soil organic matter and organic P mineralization and optimizes arbuscular mycorrhizal fungi (AMF) symbioses. This review paper provides a perspective on how agriculture has the potential to utilize plant and microbial traits to improve PUE at the field scale and accordingly, maintain crop yields at lower STP concentrations. It also links with the need to tighten the P cycle at the regional scale, including a discussion of P recovery and recycling technologies, with a particular focus on the use of struvite as a recycled P fertilizer. Guidance on directions for future research is provided.Core Ideas: There is an urgent need to increase P use efficiency in agroecosystems. Crop yields could be maintained at lower than recommended soil test P concentrations. Both the quantity and quality of organic matter influence P availability. Further research on ability of organic P to supply P to crops is needed. Struvite has the potential to fill an important niche in P recycling.

Thiessen Martens, J. R., Entz, M. H. and Wonneck, M. D. 2015. Review: Redesigning Canadian prairie cropping systems for profitability, sustainability, and resilience. Can. J. Plant Sci. 95: 1049–1072. Redesign of agricultural systems according to ecological principles has been proposed for the development of sustainable systems. We review a wide variety of ecologically based crop production practices, including crop varieties and genetic diversity, crop selection and rotation, cover crops, annual polyculture, perennial forages, perennial grains, agroforestry systems, reducing tillage, use of animal manures and green manures, soil biological fertility, organic production systems, integrated crop–livestock systems, and purposeful design of farm landscapes (farmscaping), and discuss their potential role in enhancing the profitability, environmental sustainability, and resilience of Canadian prairie cropping systems. Farming systems that most closely mimic natural systems through appropriate integration of diverse components, within a context of supportive social and economic structures, appear to offer the greatest potential benefits, while creating a framework in which to place all other farming practices. Our understanding of ecological relationships within agricultural systems is currently lacking, and a major shift in research, education, and policy will be required to purposefully and proactively redesign Canadian prairie agricultural systems for long-term sustainability.

Thiessen Martens, J. R. and Entz, M. H. 2011. Integrating green manure and grazing systems: A review. Can. J. Plant Sci. 91: 811–824. Green manuring, also referred to as cover cropping, is an ancient practice that is gaining popularity, especially in ecologically integrated farming systems. Much green manure research in Canada has focused on legumes, where green manure plant material is incorporated into soil. This review focuses on the role of livestock in utilizing traditional and novel green manure crops adapted to the Canadian prairies. Legume and non-legume green manure plant species are discussed in terms of suitability to grazing management by different livestock species. Integrating grazing livestock into green manure systems affects nutrient cycling and potential nitrogen (N) loss pathways. However, losses may not be substantially different from other production systems, especially when loss mitigation practices are employed. Grazing green manures may also affect soil biological and physical properties. We conclude that grazing green manures may provide economic as well as biological advantages over the traditional approach of soil incorporation. For example, a green manure biomass yield of 5000 kg ha⁻¹is sufficient to produce 175 kg ha⁻¹of animal live weight gain, providing a gross revenue of $385 to $770 ha⁻¹at April 2011 prices, while returning at least 75% of N and other nutrients to the field. Barriers to farmer adoption of grazed green manure systems include a lack of livestock management knowledge and infrastructure.

Knowledge of rotational N benefits of grain legumes can assist in crop rotation planning and N fertilizer management. Four annual grain legumes were tested in Manitoba field trials over 3 yr. Field pea provided the largest and most consistent apparent N benefit to a succeeding wheat crop; soybean provided relatively little N benefit. The apparent N benefits of chickpea and dry bean were inconsistent, although chickpea shows greater potential in dry conditions. Key words: Wheat rotations, N credit, crop rotation

Struvite (NH₄MgPO₄·6H₂O) may be an appropriate fertilizer to address phosphorus (P) deficiencies in organic cropping systems, but field studies assessing crop response to struvite are lacking. Field experiments were conducted over 3 yr on a low‐P, alkaline soil in Manitoba to assess the effect of struvite application rate on the yield and P accumulation of organically managed grain and forage crops. Struvite was applied to spring wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) at 0, 20, 30, and 40 kg P ha^–1 in separate experiments each year and to alfalfa (Medicago sativa L.)–grass forage at 0, 30, 60, and 90 kg P ha^–1 in a single application in a 3‐yr experiment. Wheat grain yield, P concentration, and P accumulation increased linearly with increasing struvite rate, whereas flax showed little to no response. Forage yield, P concentration, and P accumulation also increased with struvite rate. Benefits to forage yield and P accumulation were greatest in the second year, demonstrating important residual effects of struvite application. Struvite application shifted forage composition to become dominated by alfalfa whereas the unfertilized treatment was dominated by grasses. Annual P recovery efficiency was 4–7% for wheat, 1–2% for flax, and 7–12% for forage and did not vary significantly with struvite application rate. Our findings demonstrate that struvite applied at a relatively high rate is an effective P source for wheat and alfalfa‐based forage under organic management, but not for flax.