Application of different amendments to optimize nitrogen management in sweet corn ( <i>Zea mays</i> L.) with winter cover crops in Hokkaido, Japan

In devising a suitable nitrogen (N) fertilisation method to reduce environmental impacts, the N supply must be optimized to meet the demand for crop production. Sweet corn (Zea mays L.) was grown using different fertilisation methods and winter cover crops from 2021 to 2023. Hairy vetch (HV; Vicia villosa Roth.) and rye (Secale cereale L.) were mixed-sown at the rate of HV:rye = 50:50 and 70:30 kg∙ha−1 in September 2021 and 2022, respectively. In addition, different fertiliser treatments – a mixture of poultry manure and bark manure (manure), polymer-coated urea fertiliser (slow-release fertiliser), and ammonium sulfate (fast-release fertiliser) – were applied before seeding sweet corn in May 2022 and 2023. Soil inorganic N, microbial biomass nitrogen (MBN), and N absorption of corn were measured during the corn growing seasons. In both years, inorganic N in the soil treated with fast-release fertiliser increased drastically and leached into the 30–60 cm soil layer at the corn seeding stage. The N supply from manure or slow-release fertiliser gradually increased inorganic N in the soil. MBN was highest in the soil surface layer where manure was applied. The N uptake rate was the highest just before the reproductive stage. The 100-grain weight was slightly lower when slow-release fertiliser was applied because of the delay in N supply. The combination of cover crops and manure was found to be preferable to the application of commonly used fast-release fertiliser to maximize corn yield while reducing environmental impacts.