Cover crops have the potential to be agricultural nitrogen (N) regulators that reduce leaching through soils and then deliver N to subsequent cash crops. Yet, regulating N in this way has proven ...difficult because the few cover crop species that are well-studied excel at either reducing N leaching or increasing N supply to cash crops, but they fail to excel at both simultaneously. We hypothesized that mixed species cover crop stands might balance the N fixing and N scavenging capabilities of individual species. We tested six cover crop monocultures and four mixtures for their effects on N cycling in an organically managed maize-soybean-wheat feed grain rotation in Pennsylvania, USA. For three years, we used a suite of integrated approaches to quantify N dynamics, including extractable soil inorganic N, buried anion exchange resins, bucket lysimeters, and plant N uptake. All cover crop species, including legume monocultures, reduced N leaching compared to fallow plots. Cereal rye monocultures reduced N leaching to buried resins by 90% relative to fallow; notably, mixtures with just a low seeding rate of rye did almost as well. Austrian winter pea monocultures increased N uptake in maize silage by 40 kg N ha-1 relative to fallow, and conversely rye monocultures decreased N uptake into maize silage by 40 kg N ha-1 relative to fallow. Importantly, cover crop mixtures had larger impacts on leaching reduction than on maize N uptake, when compared to fallow plots. For example, a three-species mixture of pea, red clover, and rye had similar maize N uptake to fallow plots, but leaching rates were 80% lower in this mixture than fallow plots. Our results show clearly that cover crop species selection and mixture design can substantially mitigate tradeoffs between N retention and N supply to cash crops, providing a powerful tool for managing N in temperate cropping systems.
Cover crop mixtures retain higher diversity when allowed sufficient growth in fall.
Cereal rye dominates mixtures in spring, particularly when fall planting is delayed.
Grasses overperform in cover ...crop mixtures compared to their growth in monoculture.
Brassicas underperform in cover crop mixtures compared to their growth in monoculture.
Legumes’ growth in cover crop mixtures varies depending on species and planting time.
Cover crop mixtures may provide greater diversity of benefits than monocultures. To develop management principles to establish diverse cover crop mixtures, we conducted a 3‐yr study in which monocultures and mixtures of six cover crop species (cereal rye Secale cereale L., oat Avena sativa L., common medium red clover Trifolium pratense L., Austrian winter pea Pisum sativum L., forage radish Raphanus sativus L., and winter canola Brassica napus L.) were planted in a wheat (Triticum aestivum L.)–maize (Zea mays L.)–soybean Glycine max (L.) Merr. rotation after wheat (AW) and after maize (AM). Post‐emergence stand counts and aboveground biomass in fall and spring were measured by species for all cover crop treatments. All species planted manifested in monocultures and mixtures in fall, though oat dominated and red clover, canola, and radish underperformed in mixtures. Cereal rye had the highest spring biomass in all mixtures, especially AM. Pea spring biomass was disproportionally greater in relation to seeding rate in the six‐species mixture (6 Spp.) than in monoculture when planted AW. A four‐species mixture (4 Spp.) planted AW retained the highest diversity after overwintering in two of the three planting years. Our study demonstrated that (i) cover crop mixtures retain higher diversity when allowed sufficient growth in fall; (ii) cereal rye dominates mixtures in spring, particularly when fall planting is delayed; (iii) grasses overperform in mixtures compared to their growth in monocultures; (iv) brassicas underperform in mixtures vs. monocultures; and (v) legume growth in mixtures depends on species and planting time.
Summary
Background
Markers of microbial exposure are thought to be associated with risk of allergic sensitization; however, the associations are inconsistent and may be related to gene‐environment ...interactions.
Objective
To examine the relationship between polymorphisms in the CD14 gene and allergic sensitization and whether sibling exposure, as a marker of microbial exposure, modified this relationship.
Methods
We used data from the Tasmanian Longitudinal Health Study and the Melbourne Atopy Cohort Study. Two CD14 polymorphisms were genotyped. Allergic sensitization was defined by a positive response to a skin prick test. Sibling exposure was measured as cumulative exposure to siblings before age 6 months, 2 and 4 years. Logistic regression and multi‐level mixed‐effects logistic regression were used to examine the associations. Effect estimates across the cohorts were pooled using random‐effects meta‐analysis.
Results
CD14 SNPs were not individually associated with allergic sensitization in either cohort. In TAHS, cumulative sibling exposure before age 6 months, 2 and 4 years was each associated with a reduced risk of allergic sensitization at age 45 years. A similar effect was observed in MACS. Meta‐analysis across the two cohorts showed consistent evidence of an interaction between cumulative sibling exposure before 6 months and the rs5744455‐SNP (P = 0.001) but not with the rs2569190‐SNP (P = 0.60). The pooled meta‐analysis showed that the odds of sensitization with increasing cumulative exposure to sibling before 6 months of age was 20.9% smaller in those with the rs5744455‐C‐allele than the T‐allele (OR = 0.83 vs 1.05, respectively).
Conclusion and Clinical Relevance
Cumulative sibling exposure reduced the risk of sensitization from childhood to middle age in genetically susceptible individuals.
Objectives
To investigate the patterns and frequency of multiple risk behaviours (alcohol, drugs, smoking, higher risk sexual activity) among men who have sex with men (MSM) living with HIV.
Methods
...Cross sectional study.
Results
147 out of 819 HIV‐positive MSM exhibited a high‐risk phenotype (defined as >3 of smoking, excess alcohol, sexually transmitted infection and recent recreational drug use). This phenotype was associated with younger age, depressive symptoms and <90% adherence in multivariable logistic regression.
Conclusion
In a cohort of MSM, a small, but significant proportion exhibited multiple concurrent risk behaviours.
PDF
