Improved nitrogen (N) fertilizer management strategies are required to optimize yield and quality in processing carrots (Daucus carota L.) while minimizing risks of N loss. A 2-year field study was conducted in commercial carrot fields near Hesperia and Pentwater, MI, USA, to investigate the effects of N fertilizer rate (29, 67, 135, and 202 kg ha −1 N), topdress N frequency (single vs. three split applications), and timing of split N applications on carrot production and N utilization. In addition, the potential for remote sensing-based vegetation indices (VIs) to guide in-season N topdress decisions was evaluated relative to conventional methods including petiole sap nitrate testing. Both carrot root yield and shoot biomass increased with greater N rates but did not plateau. Split-applied topdress N and timing of topdress applications did not affect yield. However, greater N rates, single front-loaded applications, and both earlier and later than typical topdress timings exhibited potential to increase N loss depending on the year. While VIs explained at most 66% and 29% of the variation in yield in 2019 and 2020, respectively, the indices consistently explained greater variation compared to petiole sap nitrate (6%), shoot N concentration (8%), and carrot root (10%) and shoot (14%) weights. Hypothetical N topdress decisions made using VI-based sufficiency indices recommended N 26% less often than petiole sap nitrate, but more research is needed to evaluate reference and threshold selections. Despite labor and technological tradeoffs, remote sensing may increase accuracy, resolution, and scalability of N decision support in processing carrot production. INTRODUCTIONEffective nitrogen (N) management is integral to optimizing carrot (Daucus carota L.) yield and quality while minimiz-Abbreviations: AGL, above ground level; BGI, blue-green index; GLI, green leaf index; GNDVI, green normalized difference vegetation index; NDRE, normalized difference red-edge index; NDVI, normalized difference vegetation index; NPCI, normalized pigment chlorophyll index; RGB, red green blue; RS, remote sensing; SI, sufficiency index; VI, vegetation index.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Zonal management of cereal–legume cover crop mixtures may help address weed and nitrogen management challenges common in organic reduced tillage systems. During a field study conducted over 3 years in Michigan, we evaluated the effects of cover crop management, tillage, and supplemental mulch on organically produced acorn squash (Cucurbita pepo). During the fall season before squash production, rye (Secale cereale L.) and vetch (Vicia villosa Roth) cover crop mixtures were sown in two distinct spatial arrangements: a “mixed planting,” in which seeds were sown in the same rows, and a “zonal planting,” in which vetch was planted only in the in-row zone and rye was planted only in the between-row zone of the subsequent squash crop. During the following spring season, cover crops were mowed, and four tillage and cover crop management combinations were established: full-width tillage with the mixed planting of rye–vetch (full-till mixed); strip-till with the same mixed planting (strip-till mixed); strip-till with the rye–vetch zonal planting (strip-till zonal); and strip-till with the zonal planting and additional rye mulch added between crop rows immediately after crop establishment (strip-till zonal plus rye). The strip-till mixed treatment resulted in yields equivalent to those of the full-till mixed treatment despite lower available nitrogen and greater early weed competition in some cases. Within strip-till treatments, zonal planting of rye–vetch provided no benefits relative to full-width planting (treatment 2 vs 3) and resulted in lower total cover crop biomass, a higher density of escaped weeds, and lower squash yields during 1 of 3 years. Supplemental rye mulch improved weed suppression and yields in strip-till zonal treatments and resulted in yields equivalent to those of the full-till mixed treatment in all years, but it provided no benefits relative to strip-till mixed. Our results demonstrate that strip-till organic squash production can produce yields equivalent to full-till production in Northern climates, but that zonal planting and supplemental mulch have limited benefits for addressing ongoing weed and nitrogen management challenges. Growers must weigh costs associated with these challenges against potential benefits for soil and pest regulating ecosystem services before adopting these agricultural conservation practices.