Red Clover Fields Research Articles

Improving pollen and nectar supply by identifying the red clover (Trifolium pratense) cultivars that attract most pollinators

Abstract Red clover (Trifolium pratense) is an important legume in agriculture for fodder and building soil fertility. Red clover flowers are also a valuable pollen and nectar source for pollinators during bloom. Farmers can choose among hundreds of commercially available red clover cultivars to plant, but the value of different cultivars for pollinators is not currently assessed or used as a recommendation criterion for farmers. Here, we compared the numbers of pollinators on 20 red clover accessions (12 cultivars and 8 breeding lines) grown under management typical for silage production in the UK in 2022 and 2023. Other potentially pollinator‐friendly traits (inflorescence density, florets per inflorescence, floret length and nectar sugar production) were also measured to help determine which would be desirable to integrate into red clover breeding programmes. Accessions varied greatly, 50‐fold, in numbers of pollinators attracted per plot and varied significantly in all other traits examined. Only inflorescence density was significantly positively related to insect abundance and species richness. These results suggest that breeding and using red clover cultivars that produce more inflorescences can increase the value of red clover to pollinators. We note that data on insect visitation can be gathered easily and could be provided to farmers to help improve the value of red clover fields to pollinators.

Mass-flowering red clover crops have positive effects on bumblebee richness and diversity after bloom

Floral resource quantity in agricultural landscapes plays a key role in the persistence of wild pollinators. An equally important, but less investigated factor is how variation in floral resource availability over time, e.g. floral resource pulses, affects pollinator abundances and diversity. Despite the potential importance of late-season resource pulses for bumblebee reproduction, few studies have evaluated the effects of late-season mass-flowering crops on bumblebee abundances and diversity during and after crop bloom. We assessed how bumblebee abundances, diversity and traits associated with species rarity were affected by cultivation of late-season mass-flowering red clover grown for seed production. Bumblebees were surveyed in red clover fields and flower-rich field borders across 20 landscapes with or without a red clover field during and after crop bloom in southern Sweden. Bumblebee worker abundances were higher in clover fields compared to flower-rich borders in the surrounding landscape. There was no relationship between presence of clover fields and the abundance of males of social bumblebees, but more male cuckoo bumblebees were found in flower-rich borders in landscapes with clover following crop bloom. Mass-flowering red clover also had a positive effect on bumblebee species richness and diversity after crop bloom. Overall, clover had positive and lasting effects on less common bumblebees thereby sustaining higher bumblebee species richness after bloom. Cultivation of red clover has the potential, in combination with the management of flower-rich habitats, to benefit less common bumblebee species in temperate agroecosystems.

Estimating cover crop biomass nitrogen credits with Sentinel‐2 imagery and sites covariates

AbstractCover crops can positively impact productivity and the environment. While improved estimates of cover crop N benefits could help promote their adoption, little information is currently available at the broad scale. We conducted a multi‐site study to determine whether use of satellite images and site factors could fill this gap. Six spectral indices were extracted from Sentinel‐2 satellite imagery and used with modeling covariates to estimate cover crop properties and biomass N credits (biomass × N contents). The partial least squares regression (PLSR) models were calibrated and validated with samples from 42 cover crop fields located in the midwestern and northeastern United States collected in 2017–2018. Remote sensing (RS)‐derived spectral indices strongly correlated (r > .7) with red clover (Trifolium pratense L.) but not with rye (Secale cereale L.) biomass. Growing degree days (GDDs), cover height, ground cover percentage, and temperature often had high importance (variable importance in projection >1) in PLSR models. Model predictive power was limited for estimates of biomass N credits when data from all validation sites and cover types were used (adjusted [adj] R2 = .52). However, models for both biomass (adj R2 = .81) and biomass N credits (adj R2 = .89) were successful for red clover fields. This suggests N benefits could be more effectively modeled for specific cover crop types. We also found RS‐based estimation of C/N ratios performed moderately well when applied to the complete dataset (adj R2 = .54), suggesting a way to differentiate grass and legume cover crops that can potentially inform biogeochemical models.

Assessing chemical control options and their effects on the lesser clover leaf weevil (Hypera nigrirostris) and red clover pollinators in Western Canada

Single-cut red clover (Trifolium pratense L.) is an important forage seed crop in Western Canada due to its winter hardiness and economical value. However, infestation of lesser clover leaf weevil (Hypera nigrirostris F.) can lead to drastic yield losses (over 50%). The aim of this research was to evaluate the effectiveness of insecticides deltamethrin (Decis) and cyantraniliprole (Exirel) in controlling H. nigrirostris in red clover in both field and laboratory conditions and their impacts on the pollinator community. Pest pressure data in red clover fields was tracked during the 2018 and 2019 growing season in six locations. Under the field conditions both deltamethrin and cyantraniliprole were effective at controlling H. nigrirostris numbers. However, only deltamethrin provided rapid pest suppression in 24 h after treatment application. Rearing H. nigrirostris larvae on treated plants in laboratory conditions showed similar results where both insecticides significantly reduced H. nigrirostris numbers in 10–12 days after treatment. The abundances of H. nigrirostris was always negatively related to seed yield regardless of treatment and initial weevil pressure. Seed yield was significantly lower in untreated controls whereas no differences were found between deltamethrin and cyantraniliprole. In contrast, no yield response was found when H. nigrirostris abundance was lower than 4 larvae per 10 shoots. Unexpectedly, densities of bees were not affected by either treatment and were not related to seed yield. Overall, results indicate that both insecticides can provide sufficient H. nigrirostris control, and that pollinator densities are not limiting seed yield, whereas lack of H. nigrirostris management can cause substantial yield losses.

Data on the bumblebee assemblages (Apidae: Bombus spp.) lives in lands under agri-environment commitment

The goal of agri-environmental schemes (AES) and greening programs are protecting and increasing biodiversity in agricultural lands. The evaluation of effectiveness of AES needs further investigations. For the purpose of investigations, species and species groups should be selected which can indicate the effects of changes in landscape use on biodiversity. Bumblebees are good indicators for this purpose.
 The role of bumblebees in pollination is well studied but in the case of different crops, much less detailed data are available. In 2018, bumblebee assemblages of 44 sites belonged to 8 different agricultural and semi-natural habitat types were studied in the surroundings of Sajószöged, Tiszaújváros and Derecske.
 This study provides new distribution data of 8 bumblebee species in three 10×10 km UTM cells covering the sampling area. According to our results, the alfalfa and red clover fields and semi-natural grasslands has more species rich and abundant bumblebee assemblages than different crop fields (sunflower, oilseed radish and vegetable morrow) and can help protect bumblebee assemblages of agricultural lands. Based on the collected distribution and abundance data, the role of the bumblebees in pollination of the studied crops should be re-evaluated.

Can Costs of Pesticide Exposure for Bumblebees Be Balanced by Benefits from a Mass-Flowering Crop?

Mass-flowering crops provide forage for bees but also contain pesticides. Such pesticide exposure can harm bees, but our understanding of how this cost is balanced by forage benefits is limited. To provide insights into benefits and costs, we placed bumblebee colonies in 18 landscapes with conventional red clover fields treated with the neonicotinoid thiacloprid (flowers + pesticide), untreated organic red clover fields (flowers), or landscapes lacking clover fields (controls). Colonies grew heavier near thiacloprid-treated clover compared to controls lacking clover, while colonies near untreated clover did not differ from colonies in neither of the other landscape types. Thiacloprid treatment effectively controlled pests and increased bumblebee crop visitation. However, colony production of queens and males did not differ among landscape types. In conclusion, thiacloprid application in clover appears to be of low risk for bumblebees. More generally, neonicotinoids may not be equally harmful when used in flowering crops and effective low-risk pest control in such crops could potentially benefit bumblebees and crop pollination.

Field Evaluation of Potato N Needs Following Forage Legumes

In an attempt to quantify the nitrogen (N) contribution from forage legumes to succeeding potatoes, trials were conducted on 28 Wisconsin alfalfa or red clover fields. Potato total yield and crop value were determined following in-season fertilizer N applications of 0 to 280 kg ha−1. Only 2 of the 12 alfalfa sites and 6 of the 16 red clover sites responded to applied fertilizer N when total yield was considered. However, using crop value, responses were seen at 5 alfalfa and 7 red clover sites. Apparent fertilizer replacement value ranged from 0 to 224 kg N ha−1 for both alfalfa and red clover, and averaged 129 or 102 kg N ha−1 for the respective forages. Due to the wide variation, consideration of criteria in addition to preceding crop is necessary to accurately estimate potato N needs following legume forages. Use of the petiole nitrate-N test did not improve the predictive capability.

Historical change and drivers of insect pest abundances in red clover seed production

Plant-feeding insects reduce yields substantially in all major crops despite considerable crop protection efforts. A lack of long-term monitoring data and insufficient ecological knowledge of pest insects limit our possibilities to characterize drivers of change in their abundances. We demonstrate how a suite of complementary methods and data sources can be used to analyse historical shifts in pest abundance and species composition when continuous monitoring data for pest insects and their natural enemies are lacking. We compared historic and current abundances of seed weevils (Protapion spp.) in red clover fields grown for seed in southernmost Sweden using data from 60 fields 1935–1937 and 53 fields 2008–2011 respectively. We found higher pest abundances in the current data, and parasitism rates provided by wasps appeared to be lower in recent times compared with the 1930s. A separate analysis of 1504 observations of the insect pest species made 1936–2012 and reported into a public database showed that a formerly subdominant seed weevil species, Protapion trifolii L. has now become the dominating pest species, whereas Protapion apricans Hbst. became relatively less common over time. This shift correlated with increased spring temperatures in the study area. Finally, we analysed if the proportion farmland in the surrounding landscape, temperature, precipitation and distance to nearest clover field in the previous year could explain pest abundances 2008–2011. We found that fields with less precipitation that were embedded in landscapes with a high proportion of farmland at the 5km radius had higher pest abundances. Our results combined suggest that landscape scale changes in agricultural land use and increased spring temperatures both have contributed to the increased pest abundances observed 2008–2011 compared to 1935–1937. This study illustrates that a combination of approaches can compensate for the common situation when continuous long-term monitoring data is lacking, and improve our understanding of historic versus current insect pest abundances and the potential drivers of change.

Towards Integrated Pest Management in Red Clover Seed Production

The development of integrated pest management is hampered by lack of information on how insect pest abundances relate to yield losses, and how pests are affected by control measures. In this study, we develop integrated pest management tactics for Apion spp. weevils (Coleoptera: Brentidae) in seed production of red clover, Trifolium pratense L. We tested a method to forecast pest damage, quantified the relationship between pest abundance and yield, and evaluated chemical and biological pest control in 29 Swedish red clover fields in 2008 and 2011. Pest inflorescence abundance, which had a highly negative effect on yield, could be predicted with pan trap catches of adult pests. In 2008, chemical control with typically one application of pyrethroids was ineffective both in decreasing pest abundances and in increasing yields. In 2011, when chemical control included applications of the neonicotinoid thiacloprid, pest abundances decreased and yields increased considerably in treated field zones. A post hoc analysis indicated that using pyrethroids in addition to thiacloprid was largely redundant. Infestation rates by parasitoids was higher and reached average levels of around 40% in insecticide treated field zones in 2011, which is a level of interest for biological pest control. Based on the data presented, an economic threshold for chemical control is developed, and guidelines are provided on minimum effective chemical pest control.

Small Broomrape (Orobanche minor) in Oregon and the 3 Rs: Regulation, Research, and Reality

Small broomrape is a federally listed noxious weed that was first identified in Oregon in 1923. Between 1923 and 1997, there were only six reports of the species in Oregon. Small broomrape is a holoparasitic weed that attaches to the root of its host and can lead to crop failure depending on the level of infestation. Small broomrape was identified in a red clover field in Oregon in 1998. In 2000 and 2001, the Oregon Department of Agriculture surveyed red and white clover fields in Oregon for the presence of small broomrape; 15 infested fields were identified in 2000 and 22 in 2001. The source of the small broomrape seed was not identified although there was speculation that small broomrape seed may have been contaminated clover seed stock. In 2000, a quarantine was established for small broomrape in red clover seed. Research identified effective, easy to implement management strategies for small broomrape including the use of false host crops and imazamox. In 2003, the ODA amended the quarantine to eliminate the mandatory seed sampling and testing and the requirement of reporting infested fields and seed lots. In 2011, there are still populations of small broomrape present in red clover fields in Oregon.

Quantitative Historical Change in Bumblebee (Bombus spp.) Assemblages of Red Clover Fields

BackgroundFlower visiting insects provide a vitally important pollination service for many crops and wild plants. Recent decline of pollinating insects due to anthropogenic modification of habitats and climate, in particular from 1950's onwards, is a major and widespread concern. However, few studies document the extent of declines in species diversity, and no studies have previously quantified local abundance declines. We here make a quantitative assessment of recent historical changes in bumblebee assemblages by comparing contemporary and historical survey data.Methodology/Principal FindingsWe take advantage of detailed, quantitative historical survey data from the 1930's on bumblebee (Bombus spp.) abundances and species composition in red clover (Trifolium pratense) fields, an important floral resource and an attractant of all bumblebee species. We used the historical survey data as a pre-industrialization baseline, and repeated the same sampling protocol at nearly the same localities at present, hence setting up a historical experiment. We detected historical changes in abundances (bees/m2) of both workers (the “pollinatory units”) and queens (effective population size), in addition to species composition. In particular, long-tongued bumblebee species showed consistent and dramatic declines in species richness and abundances throughout the flowering season of red clover, while short-tongued species were largely unaffected. Of 12 Bombus species observed in the 1930's, five species were not observed at present. The latter were all long-tongued, late-emerging species.Conclusions/SignificanceBecause bumblebees are important pollinators, historical changes in local bumblebee assemblages are expected to severely affect plant reproduction, in particular long-tubed species, which are pollinated by long-tongued bumblebees.

Drastic historic shifts in bumble-bee community composition in Sweden

The species richness of flower-visiting insects has declined in past decades, raising concerns that the ecosystem service they provide by pollinating crops and wild plants is threatened. The relative commonness of different species with shared ecological traits can play a pervasive role in determining ecosystem functioning, but information on changes in abundances of pollinators over time is lacking. We gathered data on relative abundances of bumble-bee species in Swedish red clover fields during three periods in the last 70 years (1940s, 1960s and present), and on clover seed yields since 1921. We found drastic decreases in bumble-bee community evenness, with potential consequences for level and stability of red clover seed yield. The relative abundances of two short-tongued bumble-bees have increased from 40 per cent in the 1940s to entirely dominate present communities with 89 per cent. Average seed yield declined in recent years and variation in yield doubled, suggesting that the current dependence on few species for pollination has been especially detrimental to stability in seed yield. Our results suggest a need to develop management schemes that promote not only species-rich but also more evenly composed communities of service-providing organisms.

Effects of field characteristics on abundance of bumblebees (Bombusspp.) and seed yield in red clover fields

Red clover is a key floral ressource for bumblebees (Bombus spp.). We here investigate variation within and among red clover fields in species richness and abundance of Bombus spp. in addition to Apis mellifera. Bumblebee individuals were grouped into the following functional groups, based on castes and tongue length: (1) all queens, (2) all workers, (3) short-tongued workers and (4) long-tongued workers. In 14 study fields, no spatial or diurnal within-field differences were found in abundances of bee groups. However, seasonal differences were detected. On average 6.3±0.6 Bombus spp. were observed in each field. In general, maximum observed bee abundances of a field were not associated with field size, weediness, or presence of commercial honeybee hives. However, long-tongued bumblebee abundance was significantly lower in fields with beehives. Seed yield was marginally higher in less weedy fields, but not significantly augmented by presence of bee hives.

Bumble Bee Pollinators in Red Clover Seed Production

ABSTRACTBumble bees pollinate red clover (Trifolium pratense L.) but impact on seed production depends on the species, abundance, and synchrony with bloom. The objectives of the current study were to examine pollination by a native bumble bee, Bombus vosnesenskii (Radoszkowski), determine the bumble bee fauna associated with red clover in Oregon, and assess if seed set is limiting. In a cage study, yields with B. vosnesenskii (average = 661 kg ha−1) and honey bees (Apis mellifera L.) (average = 640 kgha−1) were comparable. Yields were lower compared with open pollinated plots (average = 1127 kg ha−1), which was likely due to cage effect, as seed set (# seeds/# florets per seed head) was similar in all three treatments (excluding control). Examination of the diversity of endemic bumble bees through field counts and trapping in red clover fields indicated the presence of six species. Over 92% of these were B. vosnesenskii indicating that it is the key pollinator in Oregon. Seed set across four commercial fields was high (0.84–0.88) documenting that existing pollinators, including rented honey bees, and indigenous bumble bees and solitary bees, provide close to maximum pollination of red clover in Oregon. Higher yields will require improved production practices and new cultivars with more heads per plant. Sustainability of high yields in Oregon will depend on protection of indigenous bee pollinators through conservation of habitats that provide nesting sites, judicious pesticide use, and provision of floral resources before red clover bloom.

Prediction of Pollen-Mediated Gene Flow Between Fields of Red Clover (Trifolium pratense)

Pollen-mediated gene flow between red clover fields by bumblebees is predicted by estimating or simulating the parameters in a gene flow model for insect-pollinated crops. Generally, the predicted level of gene flow was found to depend on the visiting bee species and the spatial arrangement of the red clover fields. When the fields are close to each other, the gene flow depends mainly on the typical foraging distance of the visiting bee species, but when the fields are far apart, the gene flow between red clover fields is more sensitive to the distances between red clover fields than to the actual bumblebee species that pollinates the fields. Using the suggested methodology, the gene flow may be predicted in different agricultural scenarios. For example, if the gene flow between red clover fields is mediated by Bombus terrestris and the red clover fields that were assumed to be quadrates with sides of 100 m are separated by 200 m, then the median gene flow is predicted to be 0.17%.

Seasonal Variation of Red Clover (Trifolium pratense L., Fabaceae) Isoflavones and Estrogenic Activity

Red clover (Trifolium pratense L., Fabaceae) dietary supplements are currently used to treat menopausal symptoms because of their high content of the mildly estrogenic isoflavones daidzein, genistein, formononetin, and biochanin A. These compounds are estrogenic in vitro and in vivo, but little information exists on the best time to harvest red clover fields to maximize content of the isoflavones and thus make an optimal product. Samples of cultivated red clover above-ground parts and flower heads were collected in parallel over one growing season in northeastern Illinois. Generally, autohydrolytic extracts of above-ground parts contained more isoflavones and had more estrogenic activity in Ishikawa endometrial cells as compared with extracts of flower heads. Daidzein and genistein contents peaked around June to July, while formononetin and biochanin A contents peaked in early September. Flower head and total above-ground parts extracts exhibited differential estrogenic activity in an Ishikawa (endometrial) cell-based alkaline phosphatase induction assay, whereas nondifferential activity was observed for most extracts tested in an MCF-7 (breast) cell proliferation assay when tested at the same final concentrations. Ishikawa assay results could be mapped onto the extracts' content of individual isoflavones, but MCF-7 results did not show such a pattern. These results suggest that significant metabolism of isoflavones may occur in MCF-7 cells but not in Ishikawa cells; therefore, caution is advised in the choice of bioassay used for the biological standardization of botanical dietary supplements.

A predictive degree-days model for small broomrape (Orobanche minor) parasitism in red clover in Oregon

Abstract Weeds of the genus Orobanche parasitize many dicotyledonous species, causing severe damage to vegetable and field crops worldwide. In Oregon, the number of red clover fields contaminated with small broomrape has increased in recent years. Small broomrape parasitism in red clover is temperature related. In this study, the temperature-dependent relationship was developed into a predictive model based on growing degree-days (GDD) for small broomrape parasitism in red clover. The model was developed in greenhouse studies and validated in the field during three growing seasons. A strong relationship between GDD and parasite size allowed for the creation of a simple predictive model for tubercle number based on GDD. The proposed model is based on a temperature range realistic to western Oregon climatic conditions and predicts lag, log, and maximum phases for four parasitism sizes in relation to GDD. Small broomrape parasitism in red clover began at about 400 GDD, but red clover biomass accumulation was...

Small broomrape (Orobanche minor) germination and early development in response to plant species

Small broomrape, a holoparasitic weed, was recently introduced to the Pacific Northwest and contaminates a limited number of red clover fields in Oregon. Greenhouse and field studies were conducted to evaluate small broomrape response to common crop and weed species in the Pacific Northwest, and to evaluate a quick-screening method for plant species response to the parasite. In greenhouse studies, plants were grown in a hydroponic polyethylene bag system to allow for continuous visibility of their roots and monitoring of small broomrape seed germination and tubercle development. Results of the greenhouse study were validated in a field contaminated with small broomrape. In the greenhouse polyethylene bag study, small broomrape germinated and tubercles developed on alfalfa, arrowleaf clover, carrot, celery, crimson clover, lettuce, prickly lettuce, red clover, spotted catsear, subterranean clover, white clover, and wild carrot. Small broomrape germinated but did not develop tubercles when grown with barley, birdsfoot trefoil, common vetch, creeping bentgrass, cucumber, field corn, red fescue, flax, Italian ryegrass, nasturtium, oats, orchardgrass, perennial ryegrass, snap bean, sugar pea, sunflower, sweet corn, tall fescue, tomato, and wheat. In the field study, tubercles developed on alfalfa, arrowleaf clover, common vetch, crimson clover, red clover, subterranean clover, and white clover, but small broomrape flower stalks did not emerge in arrowleaf clover or crimson clover. Common vetch was a host for small broomrape in the field study but not in the hydroponic polyethylene bag system, thus, caution is warranted in using the quick screening method to elucidate potential small broomrape host species.

A Plant that Changed the World: The rise and fall of clover 1000-2000

Among the big crops in world agriculture, clover is a late-comer. From southern Spain, where it was domesticated around the year 1000, clover conquered Europe. In the 17th and 18th centuries, when European agriculture ran into a critical nitrogen deficit due to growing exports of cereals to ever-increasing numbers of populous cities, clover, which is an efficient nitrogen fixer, became essential for feeding the population. In the 19th century clover was the agricultural equivalent of coal. Just as coal-smoking chimneys changed the landscape, so did the vast, sweet-smelling white and red clover fields. The romantic 19th-century landscape was a clover landscape. And just as coal was phased out in the 20th century by other energy carriers, clover was made superfluous by the Haber-Bosch ammonia synthesis method (1909), which made possible the production of nitrogen for agriculture 'from the air' without intermediaries. The phasing out of clover contributed to the creation of the dull, post-Second World War monocultural landscape.

THE BIOLOGY OF THE LESSER CLOVER LEAF WEEVIL, HYPERA NIGRIROSTRIS (FABR.) (COLEOPTERA: CURCULIONIDAE), ON RED CLOVER, TRIFOLIUM PRATENSE L., IN SASKATCHEWAN

AbstractPopulations of the lesser clover leaf weevil, Hypera nigrirostris (Fabr.), on red clover, Trifolium pratense L., in northeastern Saskatchewan were sampled weekly from May to August 1986 and 1987. Adults overwintered in red clover fields, and began to feed, mate, and oviposit in late April and early May. Eggs were laid subepidermally in stipules, shoots, and leaves from early May to mid-July. Larvae were located on red clover stipules, buds, and fiowerheads and developed through four instars Larvae were collected from early June until mid-August. Spatial distributions of eggs and larvae were aggregated, though the degree of aggregation decreased with succeeding developmental stages. Pupae were collected on shoots and in debris from late June until August. New-season adults first occurred in mid-July; large increases in adult densities corresponded to the appearance of these adults.