Integration of conservation tilage and cover crops in broccoli production systems of the Pacific Northwest

Abstract

Field and greenhouse experiments were conducted in 1996 and 1997 to evaluate the effects of integrating conservation tillage and cover cropping on broccoli production as well as agroecological parameters. A field experiment was conducted during 1996-97 at the Oregon State University Horticulture Research farm near Corvallis, OR. The specific objectives of the research project were: To evaluate the effects of the integration and management of cover crops and strip-tillage on: 1) broccoli yield, 2) weed populations, and 3) relative abundance of earthworms. The experimental design was a split-split-plot in randomized complete blocks with 3 replications. Two tillage types (strip and conventional) constituted the main effects; two cover crops comprised the sub-effects. Time of cover crop suppression (early or late glyphosate) constituted the second sub-effect within the cover crop treatments. Strip-till plots had significantly lower total weed density than conventional till plots. 'Dacold' rye and vetch plots in combination with early glyphosate and strip-tillage had the highest broccoli yield. An on-farm research experiment was conducted during the summer of 1996 at Crestview Farms, Inc. near Molalla, OR. to compare strip-till and conventional tillage on broccoli yield. After the fall sown (1995) cover crop mixture 'Steptoe' barley / common vetch was chemically suppressed in the spring, two tillage regimes consisting of: striptillage and disc/harrow tillage were evaluated for their impact on broccoli yield, relative earthworm abundance, and relative Carabidae and Staphylinidae beetle abundance. The experimental design was a randomized complete block with three replications. No significant differences were detected for broccoli yields between the two tillage regimes, nor were statistical differences detected for Carabidae beetle relative abundance under the different tillage regimes. The carabid sampling period was only two weeks thus not allowing for justifiable conclusions to be drawn. Significantly higher densities of earthworms were detected in the strip-till plots on the first sample date but no earthworms were found on the second sampling date. A field experiment was conducted during 1996-97 in a cherry (Prunus avium) orchard at the Botany and Plant Pathology Research Farm near Corvallis, OR. The objective of this research was: 1) To evaluate the effectiveness of formalin, xylene, and ground cooking mustard in estimating relative abundance of the earthworm, Lumbricus terrestris, and 2) To evaluate the effectiveness of the three expulsion materials at three different times of the year. The mustard treatment extracted statistically similar numbers of L. terrestris as the formalin treatment in the fall and winter experiments but fewer worms in the spring experiment. The xylene treatment extracted significanlty fewer L. terrestris than formalin and mustard in all three sample dates. Three greenhouse studies were conducted in 1996 and 1997 to evaluate the effects of two agricultural by-products (meadowfoam meal and hydrolyzed com gluten) and a cover crop 'Monida' oat (Avena sativa) on the biomass accumulation of broccoli (Brassica oleraceae var. italica (direct seeded and transplanted), sweet corn (Zea mais), barnyardgrass (Echinichloa crus-gali), and pigweed (Amaranthus retrqflexus). The addition of meadowfoam meal to sterile greenhouse potting mix significantly reduced broccoli biomass (direct seed by 34% and transplanted by 50%) when compared to controls. Hydrolyzed corn gluten significantly reduced sweet corn biomass by 46% when compared to controls..'Monica' oat reduced the biomass of both weeds as well as broccoli (direct seeded). Results suggest that hydrolyzed corn gluten and meadowfoam meal inhibit the biomass accumulation of barnyardgrass and pigweed.