Under-seeding potato with nurse crops in eastern Canada: challenges and opportunities

Soil erosion can be a serious issue in eastern Canada during the 3–5 wk that it takes for potato (Solanum tuberosum L.) to emerge under the cool, humid climatic conditions with frequent heavy rainfall events. Seeding a fast-growing nurse crop at the same time as the potato crop can hold the soil particles in place, reduce surface crusting, and increase water infiltration. The objective of this study, conducted in Prince Edward Island and in New Brunswick in 2017, was to evaluate the effects of under-seeding potato with barley (Hordeum vulgare L.) and winter rye (Secale cereale L.) on marketable potato yield, nitrate dynamics during the growing season, and soil moisture content. Nurse crop growth was terminated mechanically (hilling), with a selective herbicide, or with a nonselective herbicide. Yield increases ranging from 9% to 91% were observed when nurse crop growth was terminated using a nonselective herbicide at both sites. Inconsistent results were obtained when a mechanical method or a selective herbicide were used, with marketable yield reduced at one site and no effect on yield at another site. There was a trend toward higher soil nitrate contents under the control than under the nurse crop treatments, though it was not consistent across sampling times. Results demonstrated that there are circumstances under which nurse crops can be successfully integrated into a potato-based system and provided future hypotheses to test. Potential confounding factors that can impact the nurse crop efficiency are discussed.

Organic Establishment of Pollination Reservoirs in the Lowbush Blueberry (Ericales: Ericaceae) Agroecosystem

Pollination reservoirs are pollen and nectar rich wildflower plantings intended to enhance pollination services in pollinator-dependent crops. Despite government assistance, plantings often fail to establish. Our focal crop, wild blueberries, is a unique cropping-system native to the U.S.A. It is never planted or cultivated, and typically exists in isolated fields within a mostly coniferous forest matrix. Our study takes place in Maine, U.S.A., where growers could economically benefit by switching reliance from rented honey bees to native bee pollination. Lowbush blueberry growers support wild bee enhancement efforts, but the low pH (4.0-5.0) of this agro-ecosystem presents unique challenges to wildflower establishment. We sought to identify methods that Organic certified growers can use to successfully establish pollination reservoirs in this system. We tested the effects of nurse crops and mowing on the success of a custom wildflower mixture over four years. Success was considered in terms of longevity, sown species diversity, above-ground biomass, and the number and weight of inflorescences. The authors present an economic analysis of cost versus projected planting longevity. In the fourth year of establishment, sown plant diversity significantly decreased, Solidago spp. weeds became dominant, and treatments were not a strong determinant of planting success. The economic analysis suggests that the high cost of pollination reservoir establishment may be a barrier to grower adoption. This study provides evidence and economic justification that weeds must be controlled prior to planting and represents one of the first studies to empirically test organic strategies for wildflower establishment in an agricultural context.

Origin and Effect of Alpha 2.2 Acetobacteraceae in Honey Bee Larvae and Description of Parasaccharibacter apium gen. nov., sp. nov.

ABSTRACTThe honey bee hive environment contains a rich microbial community that differs according to niche.AcetobacteraceaeAlpha 2.2 (Alpha 2.2) bacteria are present in the food stores, the forager crop, and larvae but at negligible levels in the nurse and forager midgut and hindgut. We first sought to determine the source of Alpha 2.2 in young larvae by assaying the diversity of microbes in nurse crops, hypopharyngeal glands (HGs), and royal jelly (RJ). Amplicon-based pyrosequencing showed that Alpha 2.2 bacteria occupy each of these environments along with a variety of other bacteria, includingLactobacillus kunkeei. RJ and the crop contained fewer bacteria than the HGs, suggesting that these tissues are rather selective environments. Phylogenetic analyses showed that honey bee-derived Alpha 2.2 bacteria are specific to bees that “nurse” the hive's developing brood with HG secretions and are distinct from theSaccharibacter-type bacteria found in bees that provision their young differently, such as with a pollen ball coated in crop-derived contents.Acetobacteraceaecan form symbiotic relationships with insects, so we next tested whether Alpha 2.2 increased larval fitness. We cultured 44 Alpha 2.2 strains from young larvae that grouped into nine distinct clades. Three isolates from these nine clades flourished in royal jelly, and one isolate increased larval survivalin vitro. We conclude that Alpha 2.2 bacteria are not gut bacteria but are prolific in the crop-HG-RJ-larva niche, passed to the developing brood through nurse worker feeding behavior. We propose the nameParasaccharibacter apiumfor this bacterial symbiont of bees in the genusApis.

Evaluation of Nurse Crops for Weed Control and Plant Establishment in Prairie Restoration

Nurse crops are often recommended in prairie restoration planting. This work investigated several alternative nurse crops to determine their utility in prairie planting. Nurse crops were composed of increasing densities (900, 1800, or 2700 seeds/m2) of partridge pea, spring oats, spring barley, Canada wild rye, or equal mixtures of partridge pea and one of the grasses. The experimental design was a randomized complete-block set in two sites with three blocks per site and 48 treatments per block. Each 3 × 3-m plot contained 1 m2 planted in Dec. 1995 or Mar. 1996 with an equal mix of seven prairie species. The nurse crops were sown over each nine square meter area in April 1996. Plots lacking nurse crops served as controls. Evaluated data consisted of weed pressure rankings and weed and prairie plant dry weight. Nurse crop treatments had a significant effect on weed pressure in both sites. Barley (1800 and 2700 seeds/m2) as well as partridge pea + barley (2700 seeds/m2) were most effective at reducing weed pressure. When weed and prairie plant biomass values were compared, a significant difference was observed for site quality and planting season. Prairie plant establishment was significantly greater in the poorly drained, less-fertile site and spring-sown plots in both sites had significantly higher prairie biomass values. Overall, after two seasons, there was no advantage in using nurse crops over the control. Among nurse crop treatments, oats were most effective in reducing weed competition and enhancing prairie plant growth.

Comparison of Nodular Efficiencies Between Partridge Pea and Soybean Using Acetylene Reduction

Legumes are grown as nurse crops in agriculture because they increase soil microbial life and productivity. Native legumes have potential in ecological restoration to mimic the benefits found in agriculture plus they enhance the restored ecosystem. This study was initiated to compare the growth rates, nodulation characteristics, and nitrogen fixation rates of a native versus a non-native legume. The two legumes were partridge pea (Cassia fasciculata); a native, wild, annual legume and soybean (Glycine max `Century Yellow); a domesticated, agricultural, annual legume native to Asia. Plants were grown for 11 weeks in pots containing silica sand and received a nitrogen-free Hoagland's nutrient solution. Beginning at week 12, plants were harvested weekly for four consecutive weeks. Nodulated root systems were exposed to acetylene gas and the resulting ethylene amounts were measured. The two legumes exhibited significant differences in nodule size and shape and plant growth rate. In soybean, nodules were large, spherical, and clustered around the taproot while in partridge pea, nodules were small, irregularly shaped, and spread throughout the fibrous root system. Soybean plants had a significantly faster growth rate at the onset of the experiment but partridge pea maintained a constant growth rate and eventually exceeded soybean plant size. In spite of these observed differences, partridge pea and soybean plants were equally efficient at reducing acetylene to ethylene. These results indicate partridge pea has the potential to produce as much nitrogen in the field as soybean. Native legumes such as partridge pea deserve further research to explore their use as nurse crops in agricultural or restoration regimes.