A soil test N (STN) is required to implement N fertilizer recommendations for vegetable crops in cultivated organic soils. A STN can be developed using the isometric log ratio (ILR) to balance soil C, N, and other soil components amalgamated into a filling value (Fv) and to derive a Mahalanobis distance () as STN. Our objective was to conduct a meta-analysis of multi-year and multi-site N trials on lettuce (Latuca sativa L.) response to added N along a gradient of values, and to develop an N recommendation model. Twenty-four N fertilization experiments were conducted from 2002 to 2006 in organic soils of southwestern Quebec. Each crop received four N rates from zero to 120-150 kg N ha-1 applied before seeding or in split applications. The relationship between N requirements by lettuce and STN was quadratic whether lettuce was seeded or planted. There were three STN fertility classes delineated by values of 1 and 5.5. The N recommendation model and its uncertainty were valuable for values up to 8.4. This approach provides a reliable test soil N to implement appropriate fertilizer recommendations for lettuce in organic soils.
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