Poultry litter and freeze–thaw cycles affect cover crop quality and organic kale production

Abstract Poultry litter is an affordable, widely available nutrient source in the Southeastern USA, but National Organic Program’s “90–120-Day Rule” complicates nutrient-crop synchronizationn, making application of raw manures to cover crops a suitable and compliant alternative. In this study, four rates of poultry litter (0, 1.8, 3.6, and 7.2 Mt ha −1 ) were applied to white oat ( Avena satvia L . ‘Rushmore’) cover crop in October 2022/2023 on certified organic land. Treatments were evaluated for impacts on cover crop biomass and quality (nitrogen, carbohydrates, cellulose, lignin, and carbon); soil chemical properties (inorganic nitrogen, pH, electrical conductivity), and subsequent kale crop ( Brassica oleracea ‘Winterbor’). Significant differences were determined between years for cover crop biomass but not treatment with 1920 kg ha −1 for Year 1 and 4308 kg ha −1 for Year 2, respectively. Cover crop quality differed significantly due to a mid-season freeze in Year 1 but not in Year 2. Soil inorganic nitrogen and kale biomass were unchanged in Year 1 but increased in Year 2 at the highest application. Kale yield was unimpacted in Year 1, but in Year 2, was significantly greater in all poultry litter applications compared to the control. Due to differences in the field study between years, a 21-day incubation was conducted to determine the effect of freezing and poultry litter applications on nitrogen cover crop/soil dynamics. Oats with poultry litter application and freeze treatments had significantly less inorganic N recovery compared to unfrozen oats with poultry litter application recovering, 1.7% and 9.2% of oat-derived total N, respectively.