Elasto-thixotropic properties of bronchial mucus and polymer analogs. I. Experimental results

The non-newtonian viscous and elasto-thixotropic properties of native and lyophilized pathological bronchial mucus and of polymer solutions (3% and 6% PIB in decalin) used as mucus analogs were analyzed using a cone-plate Carri-Med rheometer and a Couette viscoelastometer that we have specifically developed for measuring the rheological properties of bronchial mucus in clinical practice. The master curves obtained for apparent viscosity under steady conditions as a function of shear rates (gamma: 2.6 X 10(-3) to 6.9 X 10(1) sec-1) were fairly similar, whatever the apparatus used. Under transient conditions, at low shear rate (gamma less than 1.4 sec-1), PIB and mucus exhibited a typical viscoelastic behavior: the shear stress increased slightly up to a steady-state value. At higher gamma, a transitory overshoot of sigma characteristic of the elastothixotropic systems appeared. Such a behavior can be interpreted as resulting from structural changes such as formation and rupture of the three-dimensional network present in bronchial mucus as in polymer solutions.     

Characteristic moisture curves and maximum water content of two crop residues

Limited data are available relating water potential () to crop residue water content (), although this relationship is important to study decomposition and moisture retention of the residue layer in no-till systems and other agricultural situations where residues are used. The objectives of this study were (i) to determine the characteristic moisture curves of rye (Secale cereale L.) and clover residues (Trifolium incarnatum L.), and (ii) to determine residue characteristics that can predict maximum water content of crop residues. Air-dried residues were separated into leaves and stems, cut into 0.5 cm length pieces and saturated with distilled water. Pieces of the drained residues were dried to various water contents in the laboratory and then transferred into thermocouple psychrometer chambers. Characteristic moisture functions of the type = a ^–b, where a and b are empirical constants, were fitted to the data. The characteristic moisture curves had a similar shape to that of a Cecil sandy loam soil used as an example; however, while plant residues were able to retain up to 4.3 g H₂O g^–1, the mineral soil retained only 0.22 g H₂O g^–1. Soluble carbohydrate concentration can be used as a practical index to estimate maximum water content of residues, given the good relationship between both variables (R ² = 0.92).     

Lessons learned from the introduction of genetically engineered crops: relevance to gene drive deployment in Africa

The application of gene drives to achieve public health goals, such as the suppression of Anopheles gambiae populations, or altering their ability to sustain Plasmodium spp. infections, has received much attention from researchers. If successful, this genetic tool can contribute greatly to the wellbeing of people in regions severely affected by malaria. However, engineered gene drives are a product of genetic engineering, and the experience to date, gained through the deployment of genetically engineered (GE) crops, is that GE technology has had difficulty receiving public acceptance in Africa, a key region for the deployment of gene drives. The history of GE crop deployment in this region provides good lessons for the deployment of gene drives as well. GE crops have been in commercial production for 24 years, since the planting of the first GE soybean crop in 1996. During this time, regulatory approvals and farmer adoption of these crops has grown rapidly in the Americas, and to a lesser extent in Asia. Their safety has been recognized by numerous scientific organizations. Economic and health benefits have been well documented in the countries that have grown them. However, only one transgenic crop event is being grown in Europe, and only in two countries in that region. Europe has been extremely opposed to GE crops, due in large part to the public view of agriculture that opposes “industrial” farming. This attitude is reflected in a highly precautionary regulatory and policy environment, which has highly influenced how African countries have dealt with GE technology and are likely to be applied to future genetic technologies, including gene drives. Furthermore, a mistrust of government regulatory agencies, the publication of scientific reports claiming adverse effects of GE crops, the involvement of corporations as the first GE crop developers, the lack of identifiable consumer benefit, and low public understanding of the technology further contributed to the lack of acceptance. Coupled with more emotionally impactful messaging to the public by opposition groups and the general tendency of negative messages to be more credible than positive ones, GE crops failed to gain a place in European agriculture, thus influencing African acceptance and government policy. From this experience, the following lessons have been learned that would apply to the deployment of gene drives, in Africa:

It will be important to establish trust in those who are developing the technology, as well as in those who are making regulatory decisions. Engagement of the community, where those who are involved are able to make genuine contributions to the decision-making process, are necessary to achieve that trust. The use of tools to facilitate participatory modeling could be considered in order to enhance current community engagement efforts.

Trusted, accurate information on gene drives should be made available to the general public, journalists, and scientists who are not connected with the field. Those sources of information should also be able to summarize and analyze important scientific results and emerging issues in the field in order to place those developments in the proper context. Engagement should involve more opportunities for participation of stakeholders in conceptualizing, planning, and decision-making.

Diversifying the source of funding for gene drive research and development, particularly by participation of countries and regional bodies, would show that country or regional interests are represented.

Efforts by developers and neutral groups to provide the public and decisionmakers with a more thorough understanding of the benefits and risks of this technology, especially to local communities, would help them reach more informed decisions.

A better understanding of gene drive technology can be fostered by governments, as part of established biosafety policy in several African countries. Developers and neutral groups could also be helpful in increasing public understanding of the technology of genetic engineering, including gene drives.

Effective messaging to balance the messaging of groups opposed to gene drives is needed. These messages should be not only factual but also have emotional and intuitive appeal.

     

Temperature and moisture effects on C and N mineralization from surface applied clover residue

A better understanding of the effect of temperature (T) and moisture on soil microbial activity should improve our ability to predict N mineralization from soil organic matter and crop residues. The objective of this study was to evaluate the effects of water potential () and T on C and N mineralization from unamended Cecil loamy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) and from crimson clover (Trifolium incarnatum L.) residues applied on the soil surface. Cecil soil was packed into acrylic plastic cylinders, adjusted to -5.0, -1.5, -0.03, or -0.003 MPa, treated with clover residues on the surface or left unamended, and incubated at 10, 20, 28, or 35°C for 21 d. Headspace gas samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped. Inorganic N in soil and residue extracts was analyzed after 21 d. When increased from -5.0 to -0.003 MPa, total CO2 evolved from unamended soil increased linearly with ln(-), whereas total CO2 evolved from clover residue increased exponentially with . In both cases the effect of was enhanced as T increased. Two-dimensional (T, ) equations were developed to describe these effects. Apparent net mineralized N from the clover residue increased with until it reached a maximum between -0.5 and -0.03 Mpa.     

Integrated management for sustainable cropping systems: Looking beyond the greenhouse balance at the field scale

Cover crops (CC) promote the accumulation of soil organic carbon (SOC), which provides multiple benefits to agro‐ecosystems. However, additional nitrogen (N) inputs into the soil could offset the CO₂ mitigation potential due to increasing N₂O emissions. Integrated management approaches use organic and synthetic fertilizers to maximize yields while minimizing impacts by crop sequencing adapted to local conditions. The goal of this work was to test whether integrated management, centered on CC adoption, has the potential to maximize SOC stocks without increasing the soil greenhouse gas (GHG) net flux and other agro‐environmental impacts such as nitrate leaching. To this purpose, we ran the DayCent bio‐geochemistry model on 8,554 soil sampling locations across the European Union. We found that soil N₂O emissions could be limited with simple crop sequencing rules, such as switching from leguminous to grass CC when the GHG flux was positive (source). Additional reductions of synthetic fertilizers applications are possible through better accounting for N available in green manures and from mineralization of soil reservoirs while maintaining cash crop yields. Therefore, our results suggest that a CC integrated management approach can maximize the agro‐environmental performance of cropping systems while reducing environmental trade‐offs.     

The Kill Date as a Management Tool for Cover Cropping Success

Integrating cover crops (CC) in rotations provides multiple ecological services, but it must be ensured that management does not increase pre-emptive competition with the subsequent crop. This experiment was conducted to study the effect of kill date on: (i) CC growth and N content; (ii) the chemical composition of residues; (iii) soil inorganic N and potentially mineralizable N; and (iv) soil water content. Treatments were fallow and a CC mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates in spring. Above-ground biomass and chemical composition of CC were determined at harvest, and ground cover was monitored based on digital image analysis. Soil mineral N was determined before sowing and after killing the CC, and potentially mineralizable N was measured by aerobic incubation at the end of the experiment. Soil water content was monitored daily to a depth of 1.1 m using capacitance sensors. Under the present conditions of high N availability, delaying kill date increased barley above-ground biomass and N uptake from deep soil layers; little differences were observed in vetch. Postponing kill date increased the C/N ratio and the fiber content of plant residues. Ground cover reached >80% by the first kill date (∼1250°C days). Kill date was a means to control soil inorganic N by balancing the N retained in the residue and soil, and showed promise for mitigating N losses. The early kill date decreased the risk of water and N pre-emptive competition by reducing soil depletion, preserving rain harvested between kill dates and allowing more time for N release in spring. The soil potentially mineralizable N was enhanced by the CC and kill date delay. Therefore kill date is a crucial management variable for maximizing the CC benefits in agricultural systems.