Janet L. Hedtcke

Weed Community Dynamics and Suppression in Tilled and No-Tillage Transitional Organic Winter Rye–Soybean Systems

Abstract Grower adoption of no-tillage (NT) approaches to organic soybean production has been limited, in part because of the perceived risks of ineffective cover crop management and lack of season-long weed suppression. We conducted research in 2008 and 2009 to assess those risks by quantifying the effects of winter rye cover-crop management (tilling, crimping, or mowing), soybean planting date (mid May or early June), and row width (19 or 76 cm) on weed recruitment, emergence patterns, season-long suppression, and late-season weed community composition in transitional organic production systems. The weed plant community consisted largely of summer annual species in each year, with velvetleaf or common lambsquarters as the most abundant species. Seedling recruitment from the soil seedbank varied between years, but velvetleaf recruitment was consistently greater in the tilled rye than in the NT rye treatments. Weed emergence tended to peak early in the season in the tilled rye treatment, but in the NT rye treatments, the peak occurred in mid or late season. More-diverse summer annual and perennial species were associated with the NT rye treatments. Even so, weed suppression (as measured by late-season weed shoot mass) was much greater in crimped or mowed rye NT treatments than it was in the tilled treatment. Weed suppression among NT rye treatments was greater in 19- than in 76-row spacing treatments in each year and was greater for mid May than it was for early June planted soybean in 2009. The NT planting of soybean into standing rye before termination (crimping or mowing) facilitated timely planting of soybean, as well as effective, season-long weed suppression, suggesting that those approaches to rye and weed management are of less risk than those typically perceived by growers. Our results suggest that NT systems in winter rye provide effective weed-management alternatives to the typical tillage-intensive approach for organic soybean production. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; velvetleaf, Abutilon theophrasti Medik. ABUTH; cereal rye, Secale cereale L.; soybean, Glycine max (L.) Merr.

Seasonal Nitrous Oxide and Methane Fluxes from Grain- and Forage-Based Production Systems in Wisconsin, USA

Agriculture in the midwestern United States is a major anthropogenic source of nitrous oxide (NO) and is both a source and sink for methane (CH), but the degree to which cropping systems differ in emissions of these gases is not well understood. Our objectives were to determine if fluxes of NO and CH varied among cropping systems and among crop phases within a cropping system. We compare NO and CH fluxes over the 2010 and 2011 growing seasons from the six cropping systems at the Wisconsin Integrated Cropping Systems Trial (WICST), a 20-yr-old cropping systems experiment. The study is composed of three grain and three forage cropping systems spanning a spectrum of crop diversity and perenniality that model a wide range of realistic cropping systems that differ in management, crop rotation, and fertilizer regimes. Among the grain systems, cumulative growing season NO emissions were greater for continuous corn ( L.) (3.7 kg NO-N ha) than corn-soybean [ (L.) Merr.] (2.0 kg NO-N ha) or organic corn-soybean-wheat ( L.) (1.7 kg NO-N ha). Among the forage systems, cumulative growing-season NO emissions were greater for organic corn-alfalfa ( L.)-alfalfa (2.9 kg NO-N ha) and conventional corn-alfalfa-alfalfa-alfalfa (2.5 kg NO-N ha), and lower for rotational pasture (1.9 kg NO-N ha). Application of mineral or organic N fertilizer was associated with elevated NO emissions. Yield-scaled emissions (kg NO-N Mg) did not differ by cropping system. Methane fluxes were highly variable and no effect of cropping system was observed. These results suggest that extended and diversified cropping systems could reduce area-scaled NO emissions from agriculture, but none of the systems studied significantly reduced yield-scaled NO emissions.

Browsing for conservation: springtime forage value of midstory shrubs of degraded oak savannas in southern Wisconsin.

Oak (Quercus spp.) savanna is a rare and dwindling ecosystem primarily due to the clearing of vast areas for agriculture and encroachment of woody midstory shrubs in the remnant areas. There is interest in introducing controlled grazing to re-open these ecologically sensitive semi-wooded areas. We report the forage quality and diet selection by Scottish Highland cattle (Bos taurus spp.), a breed recognized for their browsing behavior, of the most common shrubs in this ecosystem. Shrub species sampled included prickly ash (Xanthoxylem americana Mill), gooseberry (Ribes missouriense Nutt.), gray dogwood (Cornus racemesa L.), multiflora rose (Rosa multiflora Thunb. ex Murr.), black or red raspberry (Rubus spp.) and wild parsnip (Pastinaca sativa L). Leaf biomass was collected in June 2001 and 2002 and analyzed for forage quality. Animal observations showed that diet included a fairly even mixture of shrub leaves, grass and herbaceous forbs. Prickly ash and raspberry were most frequently browsed and had the highest crude protein (CP; 190 g kg - 1 ), while multiflora rose and gray dogwood, neither highly browsed upon, had the lowest levels of CP (120 g kg - 1 ). All shrubs had high in-vitro true digestibility, with prickly ash approaching 850 g kg - 1 (as compared to 688 g kg - 1 for mature alfalfa). The quality of the shrub layer in late spring is adequate to provide nutritional support for beef cattle as long as dry matter intake is not limited. Integrating shrubs into the rotation could expand the pasture base by providing feed at a time when cool-season pastures are typically quasi-dormant.