John R. Teasdale

COVER CROPS IN SUSTAINABLE FOOD PRODUCTION

Cover crops are important components of sustainable agricultural systems. They increase surface residue and aid in the reduction of soil erosion. They improve the structure and water-holding capacity of the soil and thus increase the effectiveness of applied N fertilizer. Legume cover crops such as hairy vetch and crimson clover fix nitrogen and contribute to the nitrogen requirements of subsequent crops. Cover crops can also suppress weeds, provide suitable habitat for beneficial predator insects, and act as non-host crops for nematodes and other pests in crop rotations. This paper reviews the agronomic and economic literature on using cover crops in sustainable food production and reports on past and present research on cover crops and sustainable agriculture at the Beltsville Agricultural Research Center, Maryland. Previous studies suggested that the profitability of cover crops is primarily the result of enhanced crop yields rather than reduced input costs. The experiments at the Beltsville Agricultural Research Center on fresh-market tomato production showed that tomatoes grown with hairy vetch mulch were higher yielding and more profitable than those grown with black polyethylene and no mulch system. Previous studies of cover crops in grain production indicated that legume cover crops such as hairy vetch and crimson clover are more profitable than grass cover crops such as rye or wheat because of the ability of legumes to contribute N to the following crop. A comparative analysis of four reduced-tillage corn based cropping systems at the Sustainable Agricultural Demonstration site showed that the cover crop system with corn following hairy vetch produced the largest average gross margin, followed by the conventional no-tillage system, a manure-based system, and a crown vetch living mulch system. The EPIC model to simulate the long-term economic and environmental impacts of incorporating cover crops into grain production systems in mid-Atlantic states was used. Results based on 60 simulation years indicated that there are tradeoffs between the competing objectives of increased profitability, lower soil erosion, and reduced nutrient and pesticide hazards to surface and groundwater supplies. A corn/soybean two-year rotation was found to be the most profitable, while the cover crop system and the manure system were found to be the most environmentally sound.

Denitrification and N mineralization from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) cover crop monocultures and bicultures

N mineralization, N immobilization and denitrification were determined for vetch, rye and rye-vetch cover crops using large packed soil cores. Plants were grown to maturity from seed in cores. Cores were periodically leached, allowing for quantification of NO3− and NH4+ production, and denitrification incubations were conducted before and after cover crop kill. Gas permeable tubing was buried at two depths in cores allowing for quantification of N2O in the soil profile. Cover crops assimilated most soil N prior to kill. After kill, relative rates of N mineralization were vetch > rye-vetch mixture > fallow > rye. After correcting for N mineralization from fallow cores, net N mineralization was observed in vetch and rye-vetch cores, while net N immobilization was observed in rye cores. Denitrification incubations were conducted 5, 15 and 55 days after kill, with adjustment of cores to 75% water filled pore space (WFPS). The highest denitrification was observed in vetch cores 5 days after kill, when soil NO3− and respiration rates were high. Substantially lower denitrification was observed on subsequent measurement dates and in other treatments probably due to either limited NO3− or organic carbon in the soil. On day 5, 3%, 23%, 31% and 31% of the N2O was recovered in the headspace of fallow, vetch, rye and rye-vetch cores, respectively. The rest was stored in the soil profile. In a field study using intact soil cores, denitrification rates also peaked 1 week after cover crop kill and decreased significantly thereafter. Results suggest greater potential N losses from vetch than rye or rye-vetch cover crops due to rapid N-mineralization in conjunction with denitrification and potential leaching, prior to significant crop N-assimilation.

Corn-yield estimation through assimilation of remotely sensed data into the CSM-CERES-Maize model

One of the applications of crop simulation models is to estimate crop yield during the current growing season. Several studies have tried to integrate crop simulation models with remotely sensed data through data‐assimilation methods. This approach has the advantage of allowing reinitialization of model parameters with remotely sensed observations to improve model performance. In this study, the Cropping System Model‐CERES‐Maize was integrated with the Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) products for estimating corn yield in the state of Indiana, USA. This procedure, inversion of crop simulation model, facilitates several different user input modes and outputs a series of agronomic and biophysical parameters, including crop yield. The estimated corn yield in 2000 compared reasonably well with the US Department of Agriculture National Agricultural Statistics Service statistics for most counties. Using the seasonal LAI in the optimization procedure produced the best results compared with only the green‐up LAIs or the highest LAI values. Planting, emergence and maturation dates, and N fertilizer application rates were also estimated at a regional level. Further studies will include investigating model uncertainties and using other MODIS products, such as the enhanced vegetation index.

Conservation tillage issues: Cover crop-based organic rotational no-till grain production in the mid-Atlantic region, USA

Organic producers in the mid-Atlantic region of the USA are interested in reducing tillage, labor and time requirements for grain production. Cover crop-based, organic rotational no-till grain production is one approach to accomplish these goals. This approach is becoming more viable with advancements in a system for planting crops into cover crop residue flattened by a roller–crimper. However, inability to consistently control weeds, particularly perennial weeds, is a major constraint. Cover crop biomass can be increased by manipulating seeding rate, timing of planting and fertility to achieve levels(>8000kgha �1 ) necessary for suppressing summerannual weeds. However, while cover crops are multi-functional tools, when enhancing performance for a given function there are trade-off with other functions. While cover crop management is required for optimal system performance, integration into a crop rotation becomes a critical challenge to the overall success of the production system. Further, high levels of cover crop biomass can constrain crop establishment by reducing optimal seed placement, creating suitable habitat for seed- and seedling-feeding herbivores, and impeding placement of supplemental fertilizers. Multi-institutional and -disciplinary teams have been working in the mid-Atlantic region to address system constraints and management trade-off challenges. Here, we report on past and current research on cover crop-based organic rotational no-till grain production conducted in the mid-Atlantic region.

Overcoming weed management challenges in cover crop-based organic rotational no-till soybean production in the Eastern United States

Abstract Cover crop–based organic rotational no-till soybean production has attracted attention from farmers, researchers, and other agricultural professionals because of the ability of this new system to enhance soil conservation, reduce labor requirements, and decrease diesel fuel use compared to traditional organic production. This system is based on the use of cereal rye cover crops that are mechanically terminated with a roller-crimper to create in situ mulch that suppresses weeds and promotes soybean growth. In this paper, we report experiments that were conducted over the past decade in the eastern region of the United States on cover crop–based organic rotational no-till soybean production, and we outline current management strategies and future research needs. Our research has focused on maximizing cereal rye spring ground cover and biomass because of the crucial role this cover crop plays in weed suppression. Soil fertility and cereal rye sowing and termination timing affect biomass production, and these factors can be manipulated to achieve levels greater than 8,000 kg ha−1, a threshold identified for consistent suppression of annual weeds. Manipulating cereal rye seeding rate and seeding method also influences ground cover and weed suppression. In general, weed suppression is species-specific, with early emerging summer annual weeds (e.g., common ragweed), high weed seed bank densities (e.g. > 10,000 seeds m−2), and perennial weeds (e.g., yellow nutsedge) posing the greatest challenges. Due to the challenges with maximizing cereal rye weed suppression potential, we have also found high-residue cultivation to significantly improve weed control. In addition to cover crop and weed management, we have made progress with planting equipment and planting density for establishing soybean into a thick cover crop residue. Our current and future research will focus on integrated multitactic weed management, cultivar selection, insect pest suppression, and nitrogen management as part of a systems approach to advancing this new production system. Nomenclature: Common ragweed, Ambrosia artemisiifolia L.; yellow nutsedge, Cyperus esculentus L.; cereal rye, Secale cereale L.; corn, Zea mays L.; soybean, Glycine max (L). Merr.; wheat, Triticum aestivum L. Resumen La producción orgánica de soya en sistemas de rotación con cero labranza basados en cultivos de cobertura, ha atraído la atención de productores, investigadores y otros profesionales agrícolas por la habilidad de este nuevo sistema de mejorar la conservación del suelo, reducir los requerimientos de mano de obra y disminuir el uso de combustible diesel en comparación con la producción orgánica tradicional. Este sistema está basado en el uso de centeno como cultivo de cobertura el cual es terminado mecánicamente con un rodillo de cuchillas para crear una cobertura de residuos in situ que suprime malezas y promueve el crecimiento de la soya. En este artículo, reportamos experimentos que fueron realizados durante la década pasada en la región este de los Estados Unidos sobre la producción orgánica de soya en sistemas de rotación con cero labranza basados en cultivos de cobertura, y delineamos las estrategias actuales de manejo y las necesidades futuras de investigación. Nuestra investigación se ha enfocado en maximizar la cobertura y la biomasa del centeno de primavera debido al papel crucial que este cultivo de cobertura juega en la supresión de malezas. La fertilidad del suelo y el momento de siembra y término del centeno afectan la producción de biomasa, y estos factores pueden ser manipulados para alcanzar niveles mayores a 8,000 kg ha−1, el cual es el umbral identificado para la supresión consistente de malezas anuales. Manipular la densidad y métodos de siembra también influencia la cobertura del suelo y la supresión de malezas. En general, la supresión de malezas es específica a la especie, siendo las malezas anuales de verano que emergen temprano (e.g. Ambrosia artemisiifolia), los banco de semillas con altas densidades (e.g. >10,000 semillas m−2), y las malezas perennes (e.g. Cyperus esculentus) los mayores retos. Debido a los retos de maximizar el potencial de supresión de malezas del centeno, hemos encontrado que el cultivar con altos residuos también puede mejorar el control de malezas significativamente. Adicionalmente al cultivo de cobertura y el manejo de malezas, hemos progresado con el equipo y la densidad de siembra para el establecimiento de la soya en capas gruesas de residuos de cultivos de cobertura. Nuestra investigación actual y futura se centrará en el manejo integrado de malezas multitáctico, la selección de cultivares, la supresión de plagas insectiles, y el manejo del nitrógeno como parte de un enfoque de sistemas para el avance de este nuevo sistema de producción.

Sustained growth and increased tolerance to glyphosate observed in a C3 perennial weed, quackgrass (Elytrigia repens), grown at elevated carbon dioxide

Although the response of crop plants to rising atmospheric carbon dioxide concentration ([CO2]) has been well characterized, little is known concerning the long-term growth and/or photosynthetic response of peren-nial weeds. The growth and photosynthetic characteristics of three cohorts of a perennial C3 weedy species, quack-grass (Elytrigia repens (L.) Nevski) were examined at ~380 µmol mol−1 (ambient) and 720 µmol mol−1 (elevated) [CO2] in temperature-controlled greenhouses during 1998 and early 1999. Different cohorts were used to assess the sensitivity of growth, photosynthesis and glyphosate tolerance to elevated [CO2] for different stages in the life cycle of quackgrass. For the ‘old’ cohort, planted on Day of Year (DOY) 187, elevated [CO2] resulted in a consistent stim-ulation of single leaf photosynthesis, vegetative and whole plant biomass relative to the ambient [CO2] condition over a 231-d period. Data from the ‘intermediate’ (DOY 268) and ‘young’ cohorts (DOY 350) indicated that the stimula-tion of biomass at the elevated [CO2] was time-dependent. To determine if the observed stimulation of growth at ele-vated [CO2] altered tolerance to chemical weed control, glyphosate [(N-phosphonomethyl)glycine] was applied to each cohort and each [CO2] treatment at rates of 0 (control) and 2.24 kg ai ha−1 (sprayed). Tolerance was determined by following the growth and slope of each cohort at the growth [CO2] treatment for a 28-d period following glyphosate application. For the young cohort, [CO2] had no affect on glyphosate tolerance; however, an application rate of 2.24 kg ai ha−1, reduced but did not eliminate growth for the intermediate and old cohorts grown at elevated [CO2]. The basis for increased glyphosate tolerance at elevated [CO2] for these cohorts was unclear, but was not related to plant size at the time of glyphosate application. Data from this experiment indicate that sustained stimula-tion of photosynthesis and growth in perennial weeds could occur as atmospheric [CO2] increases, with a reduction in chemical control effectiveness and potential increases in weed/crop competition.

Hydroxamic acid content and toxicity of rye at selected growth stages

Rye (Secale cereale L.) is an important cover crop that provides many benefits to cropping systems including weed and pest suppression resulting from allelopathic substances. Hydroxamic acids have been identified as allelopathic compounds in rye. This research was conducted to improve the methodology for quantifying hydroxamic acids and to determine the relationship between hydroxamic acid content and phytotoxicity of extracts of rye root and shoot tissue harvested at selected growth stages. Detection limits for an LC/MS-MS method for analysis of hydroxamic acids from crude aqueous extracts were better than have been reported previously. (2R)-2-β-d-Glucopyranosyloxy-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-G), 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA), benzoxazolin-2(3H)-one (BOA), and the methoxy-substituted form of these compounds, (2R)-2-β-d-glucopyranosyloxy-4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA glucose), 2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 6-methoxy-benzoxazolin-2(3H)-one (MBOA), were all detected in rye tissue. DIBOA and BOA were prevalent in shoot tissue, whereas the methoxy-substituted compounds, DIMBOA glucose and MBOA, were prevalent in root tissue. Total hydroxamic acid concentration in rye tissue generally declined with age. Aqueous crude extracts of rye shoot tissue were more toxic than extracts of root tissue to lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) root length. Extracts of rye seedlings (Feekes growth stage 2) were most phytotoxic, but there was no pattern to the phytotoxicity of extracts of rye sampled at growth stages 4 to 10.5.4, and no correlation of hydroxamic acid content and phytotoxicity (I50 values). Analysis of dose–response model slope coefficients indicated a lack of parallelism among models for rye extracts from different growth stages, suggesting that phytotoxicity may be attributed to compounds with different modes of action at different stages. Hydroxamic acids may account for the phytoxicity of extracts derived from rye at early growth stages, but other compounds are probably responsible in later growth stages.

Long-term economic performance of organic and conventional field crops in the mid-Atlantic region

Interest in organic grain production is increasing in the United States but there is limited information regarding the economic performance of organic grain and forage production in the mid-Atlantic region. We present the results from enterprise budget analyses for individual crops and for complete rotations with and without organic price premiums for five cropping systems at the US Department of Agriculture–Agricultural Research Service (USDA–ARS) Beltsville Farming Systems Project (FSP) from 2000 to 2005. The FSP is a long-term cropping systems trial established in 1996 to evaluate the sustainability of organic and conventional grain crop production. The five FSP cropping systems include a conventional, three-year no-till corn ( Zea mays L.)–rye ( Secale cereale L.) cover crop/soybean ( Glycine max (L.) Merr)–wheat ( Triticum aestivum L.)/soybean rotation (no-till (NT)), a conventional, three-year chisel-till corn–rye/soybean–wheat/soybean rotation (chisel tillage (CT)), a two-year organic hairy vetch ( Vicia villosa Roth)/corn–rye/soybean rotation (Org2), a three-year organic vetch/corn–rye/soybean–wheat rotation (Org3) and a four- to six-year organic corn–rye/soybean–wheat–red clover ( Trifolium pratense L.)/orchard grass ( Dactylis glomerata L.) or alfalfa ( Medicago sativa L.) rotation (Org4+). Economic returns were calculated for rotations present from 2000 to 2005, which included some slight changes in crop rotation sequences due to weather conditions and management changes; additional analyses were conducted for 2000 to 2002 when all crops described above were present in all organic rotations. Production costs were, in general, greatest for CT, while those for the organic systems were lower than or similar to those for NT for all crops. Present value of net returns for individual crops and for full rotations were greater and risks were lower for NT than for CT. When price premiums for organic crops were included in the analysis, cumulative present value of net returns for organic systems (US

Potential Synergistic Effects of Cereal Rye Biomass and Soybean Planting Density on Weed Suppression

3933 to 5446 ha −1 , 2000 to 2005; US

Sweet corn production and efficiency of nitrogen use in high cover crop residue

2653 to 2869 ha −1 , 2000 to 2002) were always substantially greater than for the conventional systems (US