Evaluating Strategies for Reducing Herbicide Use in a No-till Dairy Cropping System

Open Access
Snyder, Elina Miriam
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 07, 2013
Committee Members:
  • Heather D Karsten, Thesis Advisor
  • William Curran, Thesis Advisor
  • Sjoerd Willem Duiker, Thesis Advisor
  • Jeffrey Hyde, Thesis Advisor
  • no-till
  • herbicide banding
  • high-residue cultivation
  • corn
  • soybean
  • cover crops
  • cereal rye
  • red clover
  • hairy vetch
  • cropping systems
The Sustainable Dairy Cropping Systems Project is an interdisciplinary experiment being conducted in central Pennsylvania, USA. This no-till cropping system consists of two diverse six-year crop rotations designed to produce all of the feed, forage, and fuel needed to sustain a 65-cow dairy herd. This thesis project focused on managing weeds in these diverse, reduced-tillage rotations, with less herbicide. The first study compared using integrated weed management tactics to control weeds. Weed management comparisons include a “Standard Herbicide” (SH) and “Reduced Herbicide” (RH) approach to control weeds in no-till corn (Zea mays L.) and soybean (Glycine max L.) crop rotation. The SH treatment employs a standard herbicide-based program, while the RH treatment uses less total herbicide by incorporating rolling cover crops, banded herbicides over the crop row followed by high-residue inter-row cultivation, and planting companion crops. Weed density and biomass were often greater under RH management, but weed biomass never exceeded 19 g m-2 in corn and 21 g m-2 in soybean. Corn yield and population did not differ in any year, and experimental net financial returns to management were $90.42 ha-1 higher in RH corn due to lower herbicide costs and slightly not significantly higher average yield. Soybean yield was greater in SH in two of three years, but in both of these years, SH was replanted due to poor early establishment and RH was not replanted. In 2012, soybean population was lower in RH and population trends correlated with yield in both treatments. Greater rye cover crop biomass and delayed planting, failure of planting slits to close, slug pressure and wider row spacing may have all contributed to the lower yield in RH. RH management met NRCS national no-till standards for a 2% slope, but predicted soil loss was greater under RH than SH management due to two high-residue cultivation events that occur in RH only. Herbicide active ingredient use was reduced by 48% in corn in the RH vs. SH management and 12% in RH vs. SH soybean. While designed as a comparison between green manure crops, the second study compared planting red clover (Trifolium pretense L.) with hairy vetch (Vicia villosa Roth) between winter wheat and corn silage. Red clover was drilled in one half of the wheat plots in early spring of each year (RC treatment); hairy vetch was planted in the other half (HV treatment) 4 to 6 weeks following wheat harvest. Triticale (x Triticosecale) was added to HV beginning in 2011. Weeds were sampled: i) in wheat, ii) after wheat harvest, but before hairy vetch seeding, iii) before green manure termination, and iv) in corn. Herbicide active ingredient was reduced by 40% in the RC system as compared with HV. Weed control was often similar in wheat and corn between the green manure systems, but in 2012 wheat and corn yield were greater in RC. Corn yield was likely reduced in the HV due to population differences in 2012 that resulted from early season pest pressure. Because red clover can be harvested as forage, RC resulted in greater net financial returns to management by $1,399.67 ha-1, though harvesting forage requires some additional labor. A second study in 2012 evaluated weed control and yield of corn grown after the green manures compared to no cover crop. Weed biomass before corn planting was greater where there was no green manure, but weed biomass late summer was greater when hairy vetch-triticale residue was present as compared with having no residue. Population in corn after hairy vetch-triticale was lower than after no cover crop, most likely due to increased pest pressure where green manure residue was present. While the green manure residues did not always provide greater weed suppression during corn, and in fact may have stimulated weed seed germination later in the season, yields were still better following both cover crops, most likely because of soil moisture retained by cover crop residue and/or nitrogen from the residue.