Management of Overwintering Cover Crops Influences Floral Resources and Visitation by Native Bees

Cover crop cultivation strategies in a Scandinavian context for climate change mitigation and biogas production - Insights from a life cycle perspective

Cover crop cultivation can be a vital strategy for mitigating climate change in agriculture, by increasing soil carbon stocks and resource efficiency within the cropping system. Another mitigation option is to harvest the cover crop and use the biomass to replace greenhouse gas-intensive products, such as fossil fuels. Harvesting cover crop biomass could also reduce the risk of elevated N2O emissions associated with cover crop cultivation under certain conditions, which would offset much of the mitigation potential. However, harvesting cover crops also reduces soil carbon sequestration potential, as biomass is removed from the field, and cultivation of cover crops requires additional field operations that generate greenhouse gas emissions. To explore these synergies and trade-offs, this study investigated the life cycle climate effect of cultivating an oilseed radish cover crop under different management strategies in southern Scandinavia. Three alternative scenarios (Incorporation of biomass into soil; Mowing and harvesting aboveground biomass; Uprooting and harvesting above- and belowground biomass) were compared with a reference scenario with no cover crop. Harvested biomass in the Mowing and Uprooting scenarios was assumed to be transported to a biogas plant for conversion to upgraded biogas, with the digestate returned to the field as an organic fertiliser for the subsequent crop. The climate change mitigation potential of cover crop cultivation was found to be 0.056, 0.58 and 0.93 Mg CO2-eq ha-1 in the Incorporation, Mowing and Uprooting scenario, respectively. The Incorporation scenario resulted in the highest soil carbon sequestration, but also the greatest soil N2O emissions. Substitution of fossil diesel showed considerable mitigation potential, especially in the Uprooting scenario, where biogas production was highest. Sensitivity analysis revealed a strong impact of time of cover crop establishment, with earlier establishment leading to greater biomass production and thus greater mitigation potential.

ABEJAS EN SISTEMAS AGRÍCOLAS: REVISIÓN DE LA DIVERSIDAD TAXONÓMICA Y FUNCIONAL, Y PERSPECTIVAS DE INVESTIGACIÓN

Las abejas son insectos de gran importancia ecológica ya que son responsables de procesos como la polinización en ambientes naturales y agrícolas, contribuyendo a la salud y resiliencia de los ecosistemas. Se hizo una revisión para abordar las dimensiones taxonómica y funcional de la diversidad de abejas en cultivos de palma, papa, café, granadilla, gulupa y maracuyá. Se realizó la búsqueda de información en bases de datos usando palabras claves y operadores boléanos. Se construyeron curvas análogas a las de acumulación de especies y se realizó un análisis de complementariedad, para evaluar la diversidad taxonómica. Se utilizó un análisis de conglomerados para identificar tipos funcionales y se evaluó la riqueza funcional de cada cultivo. Se encontraron 19 publicaciones de abejas asociadas a cultivos, con registros de 116 especies. El cultivo de palma presentó la mayor riqueza con 48 especies, seguido de papa (44) y café (41). Se identificaron 11 tipos funcionales, donde el más representativo fue el de abejas con corbícula, eusociales, que anidan en cualquier cavidad (ScEuCc). La riqueza funcional fue mayor en el café (3,33), seguido de papa (2,83) y gulupa (2,00). La alta diversidad de abejas en agroecosistemas parece estar relacionada con la cercanía de cada cultivo a fragmentos de bosque, de acuerdo a las publicaciones analizadas. Los agroecosistemas podrían ofrecer un recurso alternativo a las abejas al permitirles combatir la disminución de sus hábitats, por lo que sugerimos ampliar las investigaciones de los beneficios de los cultivos agrícolas sobre las abejas y viceversa.

Efficacy of Cover Crops for Pollinator Habitat Provision and Weed Suppression

Pollinator declines have been documented globally, but little information is available about native bee ecology in Midwestern U.S. agriculture. This project seeks to optimize pollinator support and weed suppression in a 3-yr crop rotation with a fallow growing season. During fallow, one of five cover crop treatments (T1: crimson, red, and ladino clover and Bob oats [Fabales: Fabaceae - Trifolium incarnatum L., Trifolium pratense L., Trifolium repens L., and Cyperales: Poaceae - Avena sativa]; T2: crimson clover and oats; T3: red clover and oats; T4: ladino clover and oats; T5: no cover crop; T6/control: winter wheat [Cyperales: Poaceae - Triticum aestivum] L.) was seeded in one-half of 25 agricultural fields, whereas wheat was left unharvested in the other half as a comparison. Treatments that provide season-long floral resources support the greatest bee diversity and abundance (T1), and treatments with red clover support declining (Hymenoptera: Apidae) Bombus species (T1 and T3). Late-season floral resources may be important, yet limited (T1 and T4), and some species of agricultural weeds provide floral resources. Floral diversity may be less important than flower abundance or timing for pollinator diversity (T1-T4). Weed diversity was greatest in the no cover crop treatment (T5), least in winter wheat (T6), and intermediate in cover crop treatments (T1-T4) with no differences in weeds of economic concern. Wheat suppresses weeds but does not provide floral resources for pollinators. These results may also be applicable to marginal lands taken out of cultivation or field margin pollinator plantings in a typical corn-soybean rotation. Floral resource availability across the landscape is critical to maintain pollinator diversity.

Wildflower Seed Sales as Incentive for Adopting Flower Strips for Native Bee Conservation: A Cost-Benefit Analysis

Improving pollinator habitat on farmlands is needed to further wild bee conservation and to sustain crop pollination in light of relationships between global declines in pollinators and reductions in floral resources. One management strategy gaining much attention is the use of wildflower strips planted alongside crops to provide supplemental floral resources for pollinators. However, farmer adoption of pollinator-friendly strategies has been minimal, likely due to uncertainty about costs and benefits of providing non-crop flowering plants for bees. Over 3 yr, on four diversified farms in Montana, United States, we estimated the potential economic profit of harvesting and selling wildflower seeds collected from flower strips implemented for wild bee conservation, as an incentive for farmers to adopt this management practice. We compared the potential profitability of selling small retail seed packets versus bulk wholesale seed. Our economic analyses indicated that potential revenue from retail seed sales exceeded the costs associated with establishing and maintaining wildflower strips after the second growing season. A wholesale approach, in contrast, resulted in considerable net economic losses. We provide proof-of-concept that, under retail scenarios, the sale of native wildflower seeds may provide an alternative economic benefit that, to our knowledge, remains unexplored. The retail seed-sales approach could encourage greater farmer adoption of wildflower strips as a pollinator-conservation strategy in agroecosystems. The approach could also fill a need for regionally produced, native wildflower seed for habitat restoration and landscaping aimed at conserving native plants and pollinators.

Documenting Potential Sunn Hemp (Crotalaria juncea L.) (Fabaceae) Pollinators in Florida

Sunn hemp, Crotalaria juncea L., is a warm-season legume that can be planted in rotation to cash crops to add nitrogen and organic matter to the soils, for weed growth prevention, and to suppress nematode populations. Sunn hemp flowers also provide nectar and pollen for pollinators and enhance biological control by furnishing habitat for natural enemies. Experiments were conducted in Northern and North Central Florida to evaluate bee populations that visited flowers within mixed plots of sunn hemp and sorghum-sudangrass and plots of two sunn hemp germplasm lines. Collections of bees that visited 'AU Golden' and Tillage Sunn flowers indicated that Xylocopa virginica (L.) (Hymenoptera: Apidae), Xylocopa micans Lepeletier (Hymenoptera: Apidae), Megachile sculpturalis Smith (Hymenoptera: Megachilidae), Megachile mendica (Cresson) (Hymenoptera: Megachilidae), and Megachile georgica Cresson (Hymenoptera: Megachilidae) were present in large numbers in May through July and then again in October. Although Tillage Sunn seeds planted in March flowered in May, percent bloom and number of bee visits were low. Compared with short day sunn hemp cultivars, 'AU Golden' plants produced flowers early in the season to provide food and habitat for pollinators and have the potential to produce an abundant seed crop in Northern and North Central Florida.