ALTERNATIVES FOR REDUCING TILLAGE IN AN ORGANIC GRAIN/SILAGE PRODUCTION SYSTEM: IMPLICATIONS FOR WEED MANAGEMENT

Open Access
Author:
Champagne, Rebecca Joan
Graduate Program:
Agronomy
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 10, 2017
Committee Members:
  • William Curran, Thesis Advisor
  • David A Mortensen, Committee Member
  • John Wallace, Committee Member
  • Mary Ellen Barbercheck, Committee Member
  • Gregory Wayne Roth, Committee Member
Keywords:
  • Organic
  • reduced-tillage
  • weed management
  • organic soybean
  • organic corn
  • weed seedbank
  • cover crop-based organic rotational no-till
Abstract:
Many organic farmers would like to reduce tillage to aid with soil conservation and decrease labor and fuel costs. However, tillage is still necessary for weed control and incorporation of nutrient amendments. One strategy for reducing tillage revolves around cover crop-based, organic rotational no-till, which employs cover crop mulches and no-till cash crop planting. Primary tillage occurs in the fall at cover crop establishment, and in-season weed control relies on suppression by the cover crop mulch along with supplemental inter-row cultivation. We initiated a cropping systems experiment to study several strategies for reducing tillage frequency and intensity within an organic grain/silage rotation in the Mid-Atlantic. Four cropping systems (S1-S4) were examined before soybean and corn crops. For soybean, either a cover crop mixture interseeded into corn harvested for grain or fall sown cereal rye after corn silage and before soybean was terminated via tillage or roller-crimper, respectively. Soybean were either seeded into the tilled cover crop mixture (S2 and S4) or no-till planted into the cereal rye mulch (S1 and S3). Cover crops preceding corn included two systems of hairy vetch/triticale sown after spelt harvest (S1 and S2) and primary tillage, and two systems of red clover/timothy frost-seeded into spelt in late winter (S3 and S4). One hairy vetch system was terminated via roller-crimping (S1), while the other three systems relied on spring tillage to incorporate the cover crop and livestock manure. One hairy vetch and red clover system were grown for corn silage (S1 and S3), while the other two were harvested as grain corn. The results showed that for the soybean crop, while the interseeded mix generally produced around 2,000 kg ha-1 biomass, cereal rye typically produced about 5,000 kg ha-1, with upwards of 8,000 kg ha-1. Weed suppression varied from year to year based on environmental conditions which sometimes hindered in-season cultivation. Weed control was good and subsequent biomass production was as low as 95 kg ha-1 in 2015, but reached upwards of 2,000 kg ha-1 in 2016, when weather conditions prevented effective mechanical weed control. Despite differences in both soybean stand and weed biomass, yields were comparable between the no-till and tilled soybean systems, ranging from 1,800-3,000 kg ha-1 across years. For the corn crop, red clover/timothy produced 3,300-4,500 kg ha-1 cover crop biomass, while hairy vetch/triticale was more variable, producing 3,600-7,500 kg ha-1 biomass over the three years. Although weed biomass at the time of corn planting was below 78 kg ha-1, in-season weed control varied by both treatment and year depending on the effectiveness of in-season cultivation. Late-summer weed biomass levels ranged from 300 kg ha-1 up to 2,700 kg ha-1, with less effective weed control resulting when environmental conditions prevented timely blind tillage and inter-row cultivation. Corn grain yields were not different from year to year; however, corn silage yields were different between systems every year likely due to later planted corn and a reduced nutrient supply. Finally, the weed seedbanks were measured to the plow layer each March preceding the cash crop growing season. Our results show that poor in-season weed control greatly drives the density of the weed seedbank, with seeds m-2 increasing after a droughty 2016 which hindered in-season cultivation efforts. Foxtail species dominated the seedbank in all three cash crops (corn, soybean, spelt), comprising at least 40% of the germinable seedbank. Other prevalent species included purslane speedwell, yellow woodsorrel, Eastern black nightshade, common lambsquarters, and redroot pigweed, among others. Seedbank trends showed that seed density increased after the corn and soybean phases, but decreased after the spelt phase. No-till corn and soybean systems tended to have lower seed density relative to tilled systems, but this was dependent on successful in-season weed control. Our results also show that interseeding a cover crop in corn can help reduce returns to the seedbank, with seed density being lower than corn systems which did not employ interseeding.