Impact of Cover Crops and Nitrogen Management on Soil Bacterial Alpha Diversity

Corn (<i>Zea mays</i> L.) nitrogen (N) strategies that account for fertilizer timing and source may differentially affect soil bacterial communities and require further validation when preceded by cover crops (CC). Field studies were conducted (2014–2016) evaluating the effects of daikon radish [<i>Raphanus sativus</i> (L.)], forage oat [<i>Avena sativa</i> (L.)], and no CC combined with multiple N management strategies on soil bacterial alpha diversity metrics. Nitrogen strategies consisted of 179 kg N ha⁻¹ applied pre-plant incorporated (PPI), poultry litter (PL) (61 kg N ha⁻¹) applied PPI plus sidedress (SD) N at V11 (11 leaf collars), starter N (45 kg N ha⁻¹) applied 5 cm beside and below the furrow followed by SD at V4 (4 leaf collars), V11, or 50:50 (split) V4 and V11, and a zero N control. In 1 of 2 years, radish reduced diversity 47–53% during active growth compared to remaining treatments. Inverse relationships regarding diversity of in-row (IR) soils at R1 (silking) and grain yield indicated that increased bacterial diversity did not correspond to increased grain production. Relative to PL and the zero-N control, starter N strategies reduced R1 rhizosphere bacterial diversity, evenness, and richness. Combining organic with soluble N sources may stabilize changes to soil alpha diversity metrics at corn silking.