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Using Cover Crops and Arbuscular Mycorrhizal (AM) Fungi to Enhance the Sustainability of Hardneck Garlic Production in the Northeast

Sustainable intensification has been proposed as a necessary means to ensure global food security by increasing agricultural production while protecting the environment. This dissertation evaluated an alternative garlic production system in which two major components of sustainable agriculture, cover crops and arbuscular mycorrhizal (AM) fungi, were integrated into production via a relay cropping system. Garlic was relay cropped into three species of annual, fall planted cover crops, planted in monoculture and as a mixture, and inoculated with a commercially available AM fungi inoculant at the time of planting. The three cover crop species chosen for evaluation in the alternative system were oat (Avena sativa), daikon radish (Raphanus sativus) and field pea (Pisum sativum). Rhizodeposition of fall cover crops provides soil organisms with a steady source of labile C until frost termination, after which nutrients are recycled via the decomposition of cover crop residues. Further, cover crops facilitate the development of AM fungi, which can improve crop nutrient uptake and soil structure via aggregate formation. Growers in the northeastern United States are confined by limited production acreage and a short growing season; thus, maximizing land use efficiency on farms is viii critical to maintaining economic viability. Due to the exceptionally long cultivation period associated with hardneck garlic, garlic producers miss an opportunity to plant fall cover crops. The proposed system was developed to enhance soil health and nitrogen use efficiency, support soil biology, and facilitate nutrient cycling without taking land out of production. Overall, the alternative system showed promise to improve the sustainability of garlic production by increasing soil food web structure and improving nitrogen use efficiency (NUE), particularly when garlic was relay cropped into oat cover crops. Additionally, AM fungi improved iron (Fe) uptake in garlic in Fe limited soils. However, garlic bulb yield was negatively impacted by the relay crop system when cover crop biomass was high, suggesting that the economic viability of this system is dependent on cover crop biomass accumulation in the fall and that further research is required to ensure the feasibility of farmer adoption.
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