Winter cereal rye and selected brassica cover crops for forage prior to soybeans

Despite myriad benefits to incorporating winter cover crops into conventionally managed row crop systems farmer adoption remains low in Iowa. Commonly cited apprehensions include the costs associated with managing cover crops without any short term economic benefits and the complexities associated with management of cover crops. The management of cover crops as a forage could potentially help address both of these issues while at the same time enhancing the environmental sustainability of conventionally managed systems. The work provided in this thesis is an attempt to evaluate the potential for four selected species to be managed as dual-purpose winter cover crops and early spring forages in Iowa. Winter cereal rye (Secale cereale L.) ‘Spooner’ was included (as rye is the most commonly grown cover crop in Iowa) as were three brassica species [canola (Brassica napus L.) ‘Sitro’, camelina [Camelina sativa (L.) Crantz] ‘Bison’, and turnip (Brassica rapa L.), ‘Purple top turnip’] as potential alternatives. Two other issues critical to cover crop forage management were addressed in this work as well: the role played by spring termination timing and the benefits or detriments of removing cover crop biomass. Each of four cover crops in the study was shown to be well suited to a different cover crop niche. Turnips were suitable for significant fall soil protection when cover crop winterkill is desired. Canola provided significant fall growth but had the potential to overwinter. Rye had excellent winter survival and vigorous spring growth. Perhaps most significantly, camelina was intermediate between canola and rye, with excellent winter survival combined with more limited spring growth. Canola and camelina had high suitability as spring forages with limited impacts to subsequent soybean yields even when grown into late May. Cover crop biomass removal had potentially beneficial effects on yield and agronomics, particularly when there were high levels of biomass or incomplete chemical control of cover crops. Lastly, cover crops potentially had a net positive effect on system economics when managed as forages, even in cases where there were significant reductions to subsequent soybean grain yields