Effects of Preplant and Postplant Rotary Hoe Use on Weed Control, Soybean Pod Position, and Soybean Yield

Demand for organic food products has consistently increased for more than 20 yr. The largest obstacle to organic soybean production in the southeastern United States is weed management. Current organic soybean production relies on mechanical weed control, including multiple postplant rotary hoe uses. Although postplant rotary hoe use is effective at the weed germination stage, its efficacy is severely compromised by delays due to weather. Preplant rotary hoeing is also a practice that has been utilized for weed control but the effectiveness of this practice to reduce the need for multiple postplant rotary hoeing for organic soybean production in the southeastern United States has not been investigated. Preplant rotary hoe treatments included a weekly rotary hoeing 4 wk before planting, 2 wk before planting, and none. Postplant rotary hoe treatments consisted of zero, one, two, three, and four postplant rotary hoe uses. Weed control was increased with preplant rotary hoeing at Plymouth in 2006 and 2007 but this effect disappeared with the first postplant rotary hoeing. Multiple postplant rotary hoe uses decreased soybean plant populations, decreased soybean canopy height, lowered soybean pod position, and decreased soybean yield. Plant mapping revealed that the percentage of total nodes and pods below 30 cm was increased by increased frequency of postplant rotary hoe use

Optimizing cover crop management for biomass production and potential of weed suppression

International audienceCover crops have been identified as an efficient tool in non-chemical weed management strategies. Cover crops suppress weeds mainly by competing with them for resources. High production of biomass limits the access of weeds to light and thus reduces their growth. However, cover crop biomass depends on seeding rate, date and termination timing. This study was conducted in seven location (five states) in the Northeastern United States and replicated 3 years. Hairy vetch (Vicia villosa Roth), an annual legume, which is one of the most commonly utilized species due to its cold hardiness, was planted at two dates in autumn and at rates of 6 to 50 kg ha-1. The cover crop was terminated in the next spring at the stages of early, intermediate vegetative, and 50% flowering. Cover crop biomass was mainly determined by the total growing degree days (GDD) between planting and termination and increased by 529 kg.ha-1 every 100 GDD. A nonlinear model (asymptotic regression through the origin) was used to fit the biomass data as a function of the seeding rate. The model included two parameters: asym was the asymptote (i.e., the maximum biomass when seeding rate approaches infinity); lrc was the natural log of the rate constant, representing how quickly the asymptote was reached. Only 3 out of 80 data sets (4%) could not be fitted to the model. Contour plots provided a visual demonstration of the interactions between seeding rate and seeding dates on hairy vetch biomass by termination timing. Thus, the study identified how much seeding rate needed to be increased when seeding date was delayed to maintain a given biomass production

Hairy vetch biomass across the Eastern United States : effects of latitude, seeding rate and date, and termination timing

EA GESTAD INRAInternational audienceHairy vetch (Vicia villosa Roth) is a legume grown for high biomass and N fixation. Climate, population density, establishment date, and termination timing affect biomass production; the combined effect of these factors has not been documented. We conducted an experiment in Massachusetts, New York, Pennsylvania, Maryland, and North Carolina across a range of hairy vetch seeding rates and dates and termination timings to define biomass production potential and determine minimum seeding rates. Hairy vetch was planted at two dates at rates of 6 to 50 kg ha–1. The cover crop was terminated at early and intermediate vegetative and 50% flowering stages. Across the factorial of planting and termination dates, biomass increased 529 kg ha–1 on average for every 100 growing degree days (GDD) accumulated. Maximum biomass across treatments was 460 to 2815 kg ha–1 in Massachusetts, 23 to 4523 kg ha–1 in New York, 72 to 6570 kg ha–1 in Pennsylvania, 1106 to 7117 kg ha–1 in Maryland, and 4314 to 7759 kg ha–1 in North Carolina. In Massachusetts, New York, and Pennsylvania, hairy vetch produced maximum biomass at seeding rates of 15 to 20 kg ha–1, at the low end of the currently recommended rate of 18 to 22 kg ha–1. In Maryland and North Carolina, hairy vetch produced maximum biomass when seeded at 5 to 10 kg ha–1. Our results show significant variation in optimal seeding rates across a latitudinal gradient, and illustrate the importance of site-specific management

Establishing the relationship of soil nitrogen immobilization to cereal rye residues in a mulched system

Background and aims: Soil nitrogen (N) immobilization from cover crop residues may help suppress weeds. We established a gradient of cereal rye shoot biomass to determine the extent that soil N can be immobilized and its effect on redroot pigweed (Amaranthus retroflexus L.). Methods: A microplot study was conducted in no-till cereal rye (Secale cereale L.)—soybean (Glycine max L. (Merr.)) systems at two sites in eastern USA. Microplots received 0, 2000, 5000, 8000, 12,000 or 15,000 kg ha of cereal rye shoot biomass, and were injected with two mg N kg soil 5 cm below the soil surface. Pigweeds were sown and allowed to germinate. Results: Maximum rates of cereal rye shoot decomposition were observed at ≥5000 kg ha. Although cereal rye shoot N declined, shoots became enriched with N, indicating fungal transfer of soil N to shoots. Soil inorganic N declined by an average of 5 kg N ha. Pigweed tissue N and biomass were reduced in the presence of cereal rye. The magnitude of pigweed N reduction was similar across all shoot application rates. Conclusions: We found weak evidence for a cereal rye shoot-based N immobilization mechanism of weed suppression. Our results indicate N immobilization may be primarily due to root residues