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Cover crop effects on reducing manure volatilization, improving forage rape production and weed suppression in the northeast U.S.A

Cover crops can provide multiple soil, agricultural production, and environmental benefits. Cover crops improve recovery and recycling of nitrogen and impart weed suppression in crop production. Establishing best management practices is critical in a sustainable agricultural system. Planting of crops under no-till or reduced tillage and selecting of the best main crop, cover-crop species, and planting date for a given region or environment will aid in optimizing weed suppression and crop productivity and reducing costs of energy, labor, and machinery. Cover crops including hairy vetch (Vicia villosa L), winter rye (Secale cereale L.), oat (Avena sativa L), and forage radish (Raphanus sativus L.) have been grown commonly throughout the United States and evaluated for their weed-suppressive potential, nitrogen accumulation and retention, organic matter maintenance, and suppressed erosion. A two-year study with six weekly plantings of cover crops (Sep 9, Sep 16, Sep 23, Sep 30, Oct 9 and Oct 14) including non-winterkilled species (hairy vetch, winter rye) and winterkilled species (oat, forage radish,) were assessed for effects on growth of forage rape (Brassica napus L.) and weed suppression. Early planting of cover crops gave the highest biomass and highest nitrogen accumulation. Delaying planting from early-September to mid-October suppressed cover crop biomass by about 40%. Forage radish produced more biomass in the fall than other cover crops but was winterkilled. Spring biomass was highest with rye or vetch. All cover crops suppressed weeds, but suppression was greatest under rye or hairy vetch. Hairy vetch accumulated the largest nitrogen content. Forage rape plants yielded more biomass after a cover crop than after no cover crop. Rye (Secale cereale L.) is the most widely grown cover crop in the Northeast U.S.A., and its N scavenging capacity and adaptability to the soils and climates in the region have been well documented. However, it might not be an adequate source of nitrogen for the early planted cash crops in the spring because it is not given the opportunity to grow in the spring and accumulate substantial amount of biomass. Therefore, use of livestock manure as a source of nitrogen for crop production is a common practice used worldwide. Ammonia emissions from dairy and livestock operations are of significant environmental and human health concern in the United States. Conservation of ammonia from fall surface-applied manure could benefit farmers by retaining nitrogen for use by crops in the spring growing season. The primary goal of this research was to investigate a management strategy by planting rye cover crop for mitigating ammonia volatility from manure at the time of field application with no incorporation in the fall before snow fall. A two-year study investigated the time of planting of winter annual rye along with late fall application of manure when air temperature is low and can influence ammonia emission and preserve nitrogen to meet the nitrogen requirement of forage rape. Three planting dates (Sep 16, Sep 30, and Oct 14) of rye cover crop with two manure application treatments including late-fall application and no manure were assessed for mitigating ammonia volatilization, and also yield and recovery of nitrogen by forage rape. The highest rates of ammonia volatilization were detected in the first 24 hours after manure spreading regardless of the treatment. The result indicated that cover use of crops significantly limited volatilization compared with no cover crop. The earliest planting date produced higher dry matter than second and third dates of planting. Forage rape yielded more biomass if planted after all cover crop treatments with manure application. The results of this study suggest that if immediate incorporation of manure into soil is not feasible, establishing cover crop early and then applying manure in the late fall, is a practical management to limit nonpoint source pollution from ammonia loss.
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