Nitrogen services provided by interseeded cover crops in organic corn systems

Cover crops (CC) can be used to reduce soil inorganic N (SIN) losses from agricultural soils. However, challenges exist in establishing CCs after corn (Zea mays L.) harvest in regions with a limited window for fall CC growth. One solution to this constraint is to establish a CC by interseeding into a standing corn crop. This experiment aims to assess the effect of interseeding CCs on the N cycle. Within organically managed corn grain and silage systems, we implemented three CC treatments: interseeded annual ryegrass (Lolium multiflorum Lam.), postharvest seeded cereal rye (Secale cereale L.), and a no-CC fallow. We applied fertilizer at a standard level (336 kg N ha⁻¹) and at a high level (420 kg N ha⁻¹). Silage was harvested in October and grain in November. Corn yields were not affected by CC treatments. In the fall in the silage system, the interseeded treatment had reduced SIN compared with the postharvest seeded treatment. In the spring, both interseeded and postharvest seeded treatments had less deep SIN than fallow in grain and silage. Under high N conditions in the spring, interseeded treatments had greater microbial biomass than all other treatment combinations. Both CC treatments and applied N levels affected microbial taxonomic groups. In terms of N retention services, interseeded CCs do have potential to outperform a postharvest seeded CC with a longer window for unshaded fall growth (as in a silage system) and may perform just as well as a postharvest seeded CC in the spring.