Winter annual alternative crops for enhanced sustainability in Iowa cropping systems
Cropping systems that consist of corn (Zea mays L.)-corn or alternate year corn-soybean [Glycine max (L.) Merr.] rotations can degrade environmental resources due to increased susceptibility to topsoil erosion and nitrate (NO3) leaching. Winter annual crops such as winter canola (Brassica napus L.) and winter wheat (Triticum aestivum L.) can provide a positive environmental and economic impact when included in crop rotations. However, winter canola has not been shown to overwinter consistently in Iowa, and agronomic and economic considerations need to be addressed when relay intercropping soybeans with winter wheat production. The work presented in this thesis is an effort to assess the suitability of these two alternative crops in the conventional Iowa crop rotation of corn and soybean. Based on observations from in-field experiments, it is determined that interseeding winter canola into standing soybeans in early September will provide greater environmental services including, nitrogen accumulation and canopy cover, when compared to later seeding dates. However, successful overwintering of winter canola may still be limited by Iowa winter conditions and the cold tolerance of winter canola varieties. Early September seeded winter canola has the ability to accrue sufficient heat units for proper fall plant development before the onset of winter to potentially survive winter and produce yield. Therefore, we recommend that winter canola should be used with caution in Iowa cropping systems until winter canola variety cold tolerance is suitable to Iowa winter conditions, or is seeded in early September and receives adequate rainfall for proper germination and establishment. Furthermore, a decision case study created for this thesis provides students in Higher Learning, the opportunity to determine the management decisions, economics, and challenges involved with relay intercropping winter wheat and soybean. Economic analyses determine that when proper precautions and agronomic considerations are taken, relay intercropping can lower input costs and increase profit.