Trade-offs in organic nutrient management strategies across mixed vegetable farms in Southwest British Columbia

• Published in: Frontiers in sustainable food systems Vol. 6
• Main Authors: Norgaard, Amy E., Lewis, DeLisa, Borden, Kira A., Krzic, Maja, Carrillo, Juli, Smukler, Sean M.
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 06.10.2022
• Subjects: compost; ecological nutrient cycling; manure; nitrogen; organic agriculture; phosphorus
• ISSN: 2571-581X; 2571-581X
• DOI: 10.3389/fsufs.2022.706271

Balancing economic and environmental objectives can present trade-offs for organic farmers maximizing crop yields while maintaining core principles of ecology and health. A primary challenge for achieving this balance is nitrogen (N) and phosphorus (P) management. Meeting crop N requirements with compost can build soil carbon (C) and soil health but often over-applies P and increases soil P and associated environmental risks. Alternatively, high-N organic fertilizers can provide N without surplus P but can be expensive and lack C inputs that composts supply. We evaluated these potential trade-offs in 2-year field trials on 20 mixed vegetable farms across three regions of Southwest British Columbia, Canada, capturing a range of climatic-edaphic conditions and organic amendments. Three nutrient management strategies were evaluated: High Compost : compost applied to meet crop N removal, Low Compost + N : compost applied to meet crop P removal plus an organic fertilizer to meet crop N removal, and Typical : varying combinations of composts and/or organic fertilizers (“typical” nutrient application on the farm). Nutrient strategies were evaluated in terms of yield, input costs, and soil properties [permanganate oxidizable C (labile C responsive to soil management), and post-season available N and P]. Soil P was 21% higher with High Compost than Low Compost + N . In one region characterized by inexpensive but nutrient-rich composts and soils high in P, input costs were lowest with Typical , but in the second year, High Compost outperformed Typical in crop yield. Principal component analysis showed a divergence in post-season NO 3 - between nutrient strategies in relation to compost and soil properties: High Compost using high-N composts increased post-season NO 3 - (0–30 cm), whereas relative yields in High Compost tended to be higher on farms with lower soil C and lower C:N composts, while yields with Typical were higher under opposite conditions but associated with higher post-season NO 3 - . Combining input types (e.g., Low Compost + N ) can meet environmental objectives in reducing surplus soil P without short-term yield or cost trade-offs compared to High Compost . However, maintaining soil C needs to be investigated to achieve effective ecological nutrient management in organic vegetable production with improved nutrient balances.