Agronomic Performance of a Reduced-tillage Grain Crop Rotation During the Transition to Organic Production

Open Access
Keene, Clair Lynn
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
May 07, 2015
Committee Members:
  • William Curran, Dissertation Advisor
  • Mary Ellen Barbercheck, Committee Member
  • David A Mortensen, Committee Member
  • Sjoerd Willem Duiker, Committee Member
  • Steven Mirsky, Special Member
  • Organic agriculture
  • Rotational no-till
  • Cover crops
  • Weeds
  • High-residue cultivator
Cover crop-based organic rotational no-till is one strategy for reducing tillage in organic systems and relies on rolled cover crop mulches to substitute for spring tillage and mechanical weed control in summer annual crops. This experiment was conducted at three locations to test if delaying cover crop termination would increase biomass production, weed suppression, and corn and soybean yields during the three-year transition to certified organic production. Three cover crop termination timings/ cash crop planting date treatments were examined in corn and soybean (Early, Middle, and Late). Additional split- and split-split plots within the planting date treatments were the presence or absence of high-residue cultivation and cash crop variety selection, respectively. The crop rotation was hairy vetch plus triticale cover crop-corn-cereal rye cover crop-soybean-winter wheat and was implemented in a full-entry design with all cash crops present in each year. Hairy vetch-triticale biomass did not consistently increase with delayed termination, and Late termination corresponding to full flower and the onset of pod formation in hairy vetch was necessary to prevent hairy vetch from competing with corn and becoming a weed. Cereal rye biomass increased as termination was delayed, but the Middle termination date corresponding to 50% anthesis to early milk was optimal for minimizing cereal rye competition with soybean and seed production. Volunteer cover crops negatively impacted winter wheat at two sites: hairy vetch at Maryland and cereal rye at Pennsylvania. Delaying planting tended to reduce corn but not soybean yields across sites. Regression stability analysis identified the Middle planting date as minimizing the variability of corn and soybean yields. These findings suggest that a tradeoff between hairy vetch control and corn yield cannot be avoided in this system while a tradeoff is not likely in cereal rye-soybean. Pulse-chase additions of three summer annual weed species identified high-residue cultivation as an effective weed control tactic in cover crop-based organic rotational no-till. Delaying cover crop termination and cash crop planting date did not have a clear impact on the target weeds across sites. Later-emerging species giant foxtail and smooth pigweed appeared to more readily exploit low cash crop populations at later planting dates than the early-emerging common ragweed. Yellow nut-sedge, a perennial species not included in the pulse-chase experiment, increased during the experiment across sites. In a separate experiment examining the timing and frequency of high-residue cultivation in a conventional conservation tillage system, two high-residue cultivator passes plus banded herbicide at planting resulted in weed control and yields similar to weed-free check plots in corn and soybean. Cover crop residues increased cash crop yields in droughty years. However, higher yields were not typically enough to offset the cost of cover crop establishment. Nitrogen credit from a cover crop can improve the economics of cover crop establishment in corn.