Summer Experiment Research Articles

Characterization of a commercial gas chromatography–flame ionization detection system for the in situ determination of C 5–C 10 hydrocarbons in ambient air

A commercial automated gas chromatograph with preconcentration on solid adsorbents (AirmoVoc HC1010) was coupled with a mass spectrometer in parallel with the flame ionization detection (FID) system and characterized for its suitability for quasi continuous measurements of atmospheric hydrocarbons (HCs) with a time resolution of 20 min. Of the 50 identified HCs in the range C 5–C 10, 15 elute in isolated peaks and 20 in groups of two or more HCs. The remaining 15 HCs suffer from coelution by oxygenated and halogenated compounds. Procedures to minimize and quantify the blanks and the memory from the adsorbents are described. Calibration was based on a custom-made diffusion source. The accuracy of this calibration (±10%, 2 σ) was verified by analysis of a certified 70-component standard (average deviation: −4.3±2%). During a field experiment in Summer 1998, the HC1010 system was compared with a custom-made GC system with cryogenic preconcentration and much better separation properties but lower time resolution. In ambient air, good agreement (2 σ deviation <14% or 10 ppt) was found for HCs and groups of HCs that are free from coelution with oxygenated compounds, whereas large discrepancies (in some cases more than a factor of three) were found for those HCs that coelute with oxygenated compounds, as identified by MS. Analysis of the mass spectra from those peaks via specific target ions showed much better agreement with the FID system of the reference GC within 25%.

Branchial Na+K+ATPase activity in brook charr (Salvelinus fontinalis): Effect of gonadal development in hypo- and hyperosmotic environments

Changes in gill Na(+)K(+)ATPase activity were examined following the transfer of brook charr (Salvelinus fontinalis) from fresh water (FW) to seawater (SW). Gonadal development was altered at the hatching stage using three doses of ionizing radiation (IR): 6.2, 7.8, and 11.4 Gray (Gy). A non-irradiated control group was also included in the experimental set-up. Following 15 and 19 months of growth in FW, assessment of gill activity in regard to gonadal status (sterile vs. mature) and level of IR exposure was realized by conducting two estuarine challenge tests. A first introduction was performed during June (period of highest osmoregulatory capacities for this species) (summer experiment). A second introduction was conducted during October (period of diminished osmoregulatory capacities) (fall experiment). Gill Na(+)K(+)ATPase activity and water content were measured at different times and two FW control samplings were added in October and January. In the summer experiment (June-December), normal gonadal development of female brook charr was related to reduced gill Na(+)K(+)ATPase activity during the spawning period as compared to sterile fish (4.0+/-1.5 and 7.2+/-1.9 micromole Pi. mg protein(-1). hr(-1)) (P<0.0002). Similar results were not observed in FW conditions, implying that a lack of gonadal growth does not initiate a significant advantage when the osmoregulatory system including the gills are not highly in demand, i.e. in a FW environment. Ionizing radiation exposure of < or =11.4 Gy at the hatching stage had no significant negative or positive effect on Na(+)K(+)ATPase activity either in FW or SW conditions.

Effect of fluctuating flow and temperature on cover type selection and behaviour by juvenile brown trout in artificial flumes

Brown troutSalmo truttain a flume used cover more often and were more aggregated at low water temperatures in winter compared with summer. Cover combinations providing the most cover (overhead, visual and velocity cover) were preferred in winter whereas velocity refuges were preferred in late summer; and brown trout rarely used any of these cover structures in early summer. Flow affected cover use especially in winter, when most of the trout moved to shelters during the first high flow period. Movements by brown trout were most frequent in early summer. The much higher aggression rate in summer compared with winter decreased during the first period of high flow in both summer experiments. The results indicate seasonal changes in cover habitat and cover type preferences suggesting that habitat complexity is important, and availability of cover is particularly important during different seasons and fluctuating flow.

Microcosm experiments on the effect of nutrient enrichment and a soil layer on the development of freshwater plankton

We investigated the response of phytoplankton and zooplankton to experimental alteration of nitrate and phosphate levels in outdoor enclosures. Experiments were conducted in summer and winter and in the absence and presence of a layer of soil. The tubs (12 in all) except the two plain water controls were manured initially with a mixture of fresh cowdung (50g 1 −1), mustard oil cake (25 g l −1) and poultry wastes (25 g l −1; mostly excreta), prior to enrichment. Water samples were collected from the experimental tubs twice a week to measure selected physico-chemical and biological variables. Water temperature in the summer experiments ranged from 20–30 °C and during the winter experiments from 11–15 °C. The pH values ranged from 8.0 to 9.5 and the dissolved oxygen levels from 8.2–10.0 mg l −1. The levels of soluble reactive phosphorus and nitrate nitrogen ranged from undetectable levels to 1800 μg l −1 and 6000 μg l −1, respectively. The increase in chlorophyll-a following enrichment was rapid (3–7 days) during summer, but slower in winter (7–14 days). The predominant phytoplankton species observed in the tubs belong to the genera Sphaerocystis, Chlorella, Scenedesmus, Cosmarium, Ulothrix, Zygnema, Gonium and Pandorina. The rotifer species observed were Brachionus calyciflorus, Rotaria neptunia, Lecane bulla, L. luna, L. unguitata, Euchlanis dilatata, Asplanchna intermedia, Pseudoharringia spp., Eosphora spp., Lepadella ovalis, Epiphanes brachionus, Hexarthra mira and Cephalodella gibba. The cladocerans observed were Macrothrix spp. and Alona spp.

Relationships between phenolics and soil microorganisms in spruce forests: significance for natural regeneration.

Plant-produced phenolic compounds inhibit soil microbial activity and are suspected to be involved in the failure of natural regeneration of French subalpine Norway spruce (Picea abies) forests. This work evaluated relationships between phenolic compounds and soil microorganisms in humus collected in spruce forest during winter and summer seasons. After having identified and quantified different phenolics from humus samples, we incubated another set of humus samples with 10 times the concentration of naturally occurring phenolics, and effects on the density of microorganisms were compared to humus with no addition of phenolic compounds. Furthermore, in order to follow the degradation of phenolic compounds by microbes, the concentration of phenolics in the incubated humus samples was determined by HPLC after three and six days of incubation. The results indicate that humus microorganisms use phenolics as a carbon source, since almost all phenolic compounds had disappeared after six days of incubation. Addition of phenolic compounds to the humus samples also affected the soil microbial populations so that bacteria were inhibited in the humus collected both in the winter and in the summer. However, there were differences between the experiments. Fungi and cellulose hydrolyzers were stimulated in the winter humus experiment, while fungi were unaffected and cellulose hydrolyzers were inhibited in the summer experiment. The addition of phenolic compounds stimulated ammonifiers in the summer experiment. We anticipate that the role of soil microorganisms in the problem of natural regeneration failure is probably more important than previously thought.

Towards more sustainable pastures: lessons learnt

The Temperate Pasture Sustainability Key Program (TPSKP) was established across south-eastern Australia to test the hypotheses that an improved perennial grass content in pastures would result in fewer weeds, better water use (and hence lesser impacts on soil salinity), and lower soil acidification rates. Grazing tactics were seen as a means to enhance or maintain the perennial grass content. Soil and water sustainability experiments in summer and winter dominant rainfall environments showed fewer weeds, improvements in water use and less acidity under perennial versus annual grass pastures. Further work is needed to determine if these gains are sufficient to make perennial grass pastures sustainable in the long-term as some nitrate leakage still occurred at the winter rainfall site. Indicators were developed to rate the sustainability of treatments within experiments. A subset of these indicators was common across experiments and could readily be used by farmers to provide an initial assessment of the soil and water sustainability of their pasture systems. These are: the mineral nitrogen at the bottom of the root zone (40–60 cm); soil pH at the surface and bottom of the root zone and perennial grass content by species. Managing pastures through droughts is a critical aspect of grazing management in Australia. Experiments within the TPSKP demonstrated that perennial grasses survived during drought when maintained above critical lower biomass values. These values ranged from 0.5 to 1.5 t DM/ha depending upon species. Over all experiments, there was general support for the view that maintaining a higher level of biomass in pastures resulted in more sustainable systems. Twenty-three grazing experiments using an open communal grazing design showed that most perennial grasses were sensitive to grazing at some stage in their seasonal growth cycles. The exceptions were inconclusive for several reasons e.g. the grazing pressure may not have been high enough at those sites to elucidate any effects; they occurred where the perennial grass content was less than 10% or exceeded 70%, of the sward; or were confounded by interactions between species where the species under study was not dominant. After taking these exceptions into account, it was then possible to determine where grazing tactics could be expected to work. Species differed in their response to grazing. Some perennial grasses were more sensitive to grazing during periods of stress (e.g. dry summers) than when actively growing (e.g. cocksfoot), while the reverse applied with others (e.g. phalaris). Of the grasses sensitive to grazing when actively growing, sensitivity of some was largely confined to the reproductive period (e.g. perennial ryegrass). Across most experiments, continuous grazing resulted in either a decline in or no net benefit to, the perennial grass content. Microlaena stipoides was the only species to respond to increased grazing pressure — this only applied in spring. The experiments clearly showed that tactical rests were an important tool for grassland management. The effects recorded were predominantly expressed through impacts on vegetative growth and survival of existing plants. Short-term experiments and dry seasons did not enable recruitment processes to be studied. Within pastures, grazing tactics can influence many species. The challenge is to use the TPSKP outcomes to develop strategies that optimise the composition of these swards. Due to the short-term nature of these experiments the results were evaluated within a conservative framework and often simply on the absolute level of parameters. Techniques need to be developed to more effectively monitor the process (i.e. rates of change), rather than the consequences (i.e. ends). The information gained in this program needs to be incorporated into practical strategies for better management of pastures and tested at a commercial scale. The TPSKP was one of the largest, coordinated pasture programs ever attempted. Some major outcomes were the experience gained by a large number of grassland scientists in running such programs, the development and acceptance of standardised measurement protocols and a much stronger network among grazing systems scientists committed to achieving improved management systems.

The Preferred Shower Temperatures with Post-shower Physiological and Subjective Responses for Young Females in Summer and Winter Experiments

The Preferred Shower Temperatures with Post-shower Physiological and Subjective Responses for Young Females in Summer and Winter Experiments

Nutrient uptake in experimental estuarine ecosystems:scaling and partitioning rates

Studies of nutrient cycling and enrichment in aquatic ecosystems are commonly con- ducted in enclosed experimental ecosystems. Although there is considerable information about how the dimensions of natural aquatic ecosystems influence nutrient cycling processes, little is known on how nutrient cycling studies might be affected by the physical scales of experimental enclosures. In the present study, replicate (n = 3) cylindrical containers of 5 dimensions with 3 volumes (0.1, 1.0, 10 m3), 3 depths (0.46, 1.0, 2.15 m), and 5 diameters (0.35, 0.52, 1.13, 2.44, 3.57 m) were established and subjected to pulsed additions of dissolved inorganic nutrients (DIN, Pod3-, Si) in summer and autumn experiments. Consistent with common experimental protocols, walls of these containers were not cleaned of periphytic growth during the 8 wk studies. Nutrient concentrations in experi- mental ecosystems were low prior to nutrient-pulse additions and exhibited exponential depletion following treatments. Overall, larger containers had lower net uptake rates and higher nutrient con- centrations than did smaller tanks. Relative contributions of planktonic, benthic and wall periphytic communities to total nutrient uptake varied in relation to dimensions of experimental systems. In general, net uptake rates by planktonic communities were inversely related to water depth, with higher rates associated with increased mean Light-energy in shallower systems. Indirect estimates of benthic uptake rates, which were relatively low in all but the shallowest systems, tended also to be inversely related to depth and directly proportional to light levels at the sediment surface. In contrast, nutrient uptake by wall communities (per water volume) was inversely related to the radius of exper- imental containers. Differences in the 2 container dimensions, depth and radius, accounted for more than 90 % of the variance in both net nutrient uptake by the whole ecosystem and the molar ratio of DIN/POd3- concentrations in the water column. Similarly, differences in net nutrient uptake rates among experimental ecosystems of different dimensions could be explained by the relative partition-, ing of rates among planktonic, periphytic, and benthic habitats. These results demonstrated that the physical dimensions of experimental ecosystems can have profound effects on measured nutrient dynamics. We also suggest that many of these experimental observations may be relevant also to more genera1 scaling relations for nutrient cycling in natural aquatic ecosystems.

Evaluation of a Lagrangian box model using field measurements from EASE (Eastern Atlantic Summer Experiment) 1996

The Cambridge Tropospheric Trajectory model of Chemistry and Transport (CiTTyCAT), a Lagrangian chemistry model, has been evaluated using atmospheric chemical measurements collected during the East Atlantic Summer Experiment 1996 (EASE '96). This field campaign was part of the UK Natural Environment Research Council's (NERC) Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) programme, conducted at Mace Head, Republic of Ireland, during July and August 1996. The model includes a description of gas-phase tropospheric chemistry, and simple parameterisations for surface deposition, mixing from the free troposphere and emissions. The model generally compares well with the measurements and is used to study the production and loss of O 3 under a variety of conditions. The mean difference between the hourly O 3 concentrations calculated by the model and those measured is 0.6 ppbv with a standard deviation of 8.7 ppbv. Three specific air-flow regimes were identified during the campaign – westerly, anticyclonic (easterly) and south westerly. The westerly flow is typical of background conditions for Mace Head. However, on some occasions there was evidence of long-range transport of pollutants from North America. In periods of anticyclonic flow, air parcels had collected emissions of NO x and VOCs immediately before arriving at Mace Head, leading to O 3 production. The level of calculated O 3 depends critically on the precise details of the trajectory, and hence on the emissions into the air parcel. In several periods of south westerly flow, low concentrations of O 3 were measured which were consistent with deposition and photochemical destruction inside the tropical marine boundary layer.

Changes in the plankton community following introduction of filter‐feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter‐feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.2. During a summer experiment, a bloom of Anabaena flos‐aquae developed (≈ 8000 cells mL−1) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L−1) after the bloom in this fish‐free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm‐water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.

Comparison of MkIV balloon and ER‐2 aircraft measurements of atmospheric trace gases

On May 8, 1997, vertical profiles of over 30 different gases were measured remotely in solar occultation by the Jet Propulsion Laboratory MkIV Interferometer during a balloon flight launched from Fairbanks, Alaska. These gases included H2O, N2O, CH4, CO, NOx, NOy, HCl, ClNO3, CCl2F2, CCl3F, CCl4, CHClF2, CClF2CCl2F, SF6, CH3Cl, and C2H6, all of which were also measured in situ by instruments on board the NASA ER‐2 aircraft, which was making flights from Fairbanks during this same early May time period as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) experiment. A comparison of the gas volume mixing ratios in the upper troposphere and lower stratosphere reveals agreement better than 5% for most gases. The three significant exceptions to this are SF6 and CCl4 for which the remote measurements exceed the in situ observations by 15–20% at all altitudes, and H2O for which the remote measurements are up to 30% smaller than the in situ observations near the hygropause.

Evolution of the aerosol composition in the BASYS network study and Lagrangian experiments in summer 1997 and winter 1998

Evolution of the aerosol composition in the BASYS network study and Lagrangian experiments in summer 1997 and winter 1998

Duration times of the immature stages of Cacopsylla pyri L. (Hom., Psyllidae), estimated under field conditions, and their relationship to ambient temperature

The duration of the immature stages of Cacopsylla pyri L. was studied under field conditions by artificially infesting pear branches on several dates during the year. The duration of the egg stage decreased from winter to summer, as the season progresses and temperature rises, and slightly increased in September. It ranged from 27.4 to 6.7 days. The same trend was observed in the duration of the first three larval stages (L1−3) which ranged from 18.8 to 10.3 days. For eggs deposited during the period February–August the duration of the last two larval stages (L4−5) ranged from 17.5 to 12.1 days. However, the duration of L4−5 developed from eggs deposited in September and which give rise to winter‐form adults were the longest observed. The rate of egg development was related to average ambient temperature with a highly significant linear relationship. This relationship indicates that the egg stage requires a constant number of 158.9 (SD = 5.0) of day‐degrees above an average temperature of 2.31°C to complete development. The rate of development both of L1−3 and L4−5 were related to average ambient temperature with curvilinear relationships. These relationships indicate a proportional increase in the developmental rate as temperature rises between 10–22°C. At the higher average temperatures that occurred in the summer experiments (24–27°C) the acceleration of development of L1−3 is reduced and the developmental rate of L4−5 decreases. The developmental rates of L4−5 developed from eggs deposited in September did not follow the established relationship with temperature and they were lower than those in the other periods of the year with the same average temperature.

Effects of medetomidine and atipamezole on serum glucose and cortisol levels in captive reindeer (Rangifer tarandus tarandus)

&lt;p&gt;Serum concentrations of glucose and Cortisol were measured in five adult captive reindeer (Rangifer tarandus tarandus) at 24 h and 10 min before, and at 0.5, 1,2,4, 8, 12 and 24 h after, treatment with 60 p.g/kg of medetomidine i.v. followed by 300 jig/kg of atipamezole i.v. 60 min later. The experiments were performed in January and repeated in July-August. The animals were used as their own controls and treated with saline in July-August. The wash-out period between experiments in summer was 2 weeks or more. No obvious seasonal differences were observed. Mederomidine induced a 2.5-fold increase in glucose (mean &amp;plusmn; standard error of the mean being 15.4 &amp;plusmn; 0.6 mmol/1 at 1 h) and a 3.5-fold increase Cortisol (349 &amp;plusmn; 28 nmol/1 at 0.5 h). Serum glucose reached control levels within 12 h, and Cortisol declined to baseline levels within 4 h after injection og medetomidine. The use of blood concentrations of glucose and Cortisol to assess nutritonal status, body condition and stress may be significantly biased in animals chemically immobilized with medetomidine or other alpha-2 adrenoceptor agonists.&lt;/p&gt;

Interactions between canopy forming algae in the eulittoral zone of sheltered rocky shores on the Isle of Man

The distribution and abundance of Ascophyllum nodosum, Fucus serratus and F. vesiculosus were described at four sheltered, rocky shores in the south of the Isle of Man. Canopy removal experiments were performed at mid tide level of one sheltered, canopy dominated shore to investigate the interactions between the dominant canopy alga, Ascophyllum nodosum and the competitively inferior canopy species of Fucus serratus and F. vesiculosus. Ascophyllum was removed from replicated plots, 2×2 m in size, in both winter and summer; the early growth and survival of fucoids in the presence and absence of the Ascophyllum canopy were monitored and the eventual development of a new canopy described. Juveniles of F. serratus originally present beneath the undisturbed canopy of Ascophyllum died following canopy removal but new recruitment resulted in some canopy development, principally in the winter experiment. Fucus vesiculosus, despite being completely excluded from the Ascophyllum zone of all four shores described, dominated the canopy removal plots of both winter and summer experiments. The Ascophyllum canopy did not recover over a five year period of observation, although a considerable increase in the abundance of Ascophyllum juveniles occurred.

Newly characterized products and composition of secondary aerosols from the reaction of α-pinene with ozone

Secondary aerosols from the reaction of α-pinene with ozone were generated in a 190 m 3 outdoor Teflon chamber, and products of these aerosols were characterized. Products were separated by gas chromatography and detected with electron-impact mass spectrometry, chemical-impact mass spectrometry, and Fourier transform infrared spectrometry. Because products from the reaction of α-pinene with ozone contain oxidized functional groups such as carboxylic acids and carbonyls, these products are poorly resolved by standard gas chromatography. To use standard chromatographic techniques, derivatization of oxidized functional groups was necessary. Carbonyl products were derivatized with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride and carboxylic acids with pentafluorobenzyl bromide. The major identified products were nor-pinonic acid, pinonic acid, 2,2-dimethylcyclobutane-1,3-dicarboxylic acid, pinic acid, and pinonaldehyde. Dicarboxylic acids have lower vapor pressures than either their corresponding di-aldehydes or mono-acids, and have only recently been identified in α-pinene–ozone aerosols. Given their comparatively low vapor pressures, diacids contribute significantly to the aerosol formation process from the reaction of α-pinene with ozone. The composition of these secondary aerosols is strongly influenced by temperature. During the summer experiments, the aerosol composition is dominated by diacids. During the cooler winter experiments, the di-carbonyl and carbonyl-acid products also contributed to the aerosol composition.

Effects of dietary roxarsone supplementation, lighting program, and season on the incidence of leg abnormalities in broiler chickens

Two 4 x 2 factorial experiments were designed to test the effects of four diets, differing in anticoccidial programs and roxarsone (3-nitro-4-hydroxyphenylarsonic acid) content, and two lighting programs on the incidence of leg abnormalities in 56-d-old male and female broiler chickens. The four diets were: A) basal diet + salinomycin (60.0 g/ton); B) basal diet + salinomycin (60.0 g/ton) + roxarsone (45.4 g/ton); C) basal diet + roxarsone (45.4 g/ton) + live coccidial vaccine; and D) basal diet + live coccidial vaccine. The light treatments were: 1) restricted (R) [18 h light (L): 6 h dark (D)] and 2) standard (S) [23L:1D]. The respective experiments were conducted during winter (Experiment 1, November to January) and summer (Experiment 2, June to August) growing conditions in the southeastern U.S. Light treatment had no significant (P > 0.10) effect on the incidence of leg abnormalities in either experiment. However, in Experiment 1, there was a light treatment by sex interaction; leg abnormalities were greater for males on Treatment R than Treatment S. In Experiment 2, females had a higher incidence of leg abnormalities than males (8.29 vs 4.73%). There was a diet by sex interaction for the incidence of leg abnormalities in Experiment 2; females had a greater incidence of leg abnormalities than males on Treatment A. In both experiments, the incidence was greater with dietary treatments containing roxarsone (P < 0.10). The percentage of leg abnormalities was greater in Experiment 2 than Experiment 1. Leg abnormalities were primarily due to fibrosis of the gastrocnemius tendons and tendon sheaths.

Tropospheric box-modelling and analytical studies of the hydroxyl (OH) radical and related species : Comparison with observations

Calculated and observed hydroxyl (OH) fields are presented. Calculated OH was obtained in three ways using (1) a photochemical box-model (2) a simple OH steady state approach and (3) a variant on (2) – the ‘multiple equation steady state’ approach which assumes steady state for OH, HO2 and RO2 and hence obtains three simultaneous, non linear, equations. All three methods used data collected in June 1995 during the Weybourne Atmospheric Observatory Summer Experiment (WAOSE'95). Julian Days 169, 178, 179 and 180 displayed especially good data capture and were consequently chosen for study. The two steady state methods are essentially driven purely by observations and derive OH from the ratio of the relevant source and sink terms. The box-model was constrained where possible to observations; remaining unmeasured volatile organic compounds (VOCs) were initialised to an arbitrary low value of 10 ppt. Agreement between theory and experiment was usually around 50% and often better than this value, especially on J169, though discrepancies of up to a factor of 3 were occasionally apparent. Despite the inherent scatter, neither the box-model nor the simple steady state method were found to consistently over-estimate OH (a common feature of many numerical approaches) although this did occur to a certain extent using the multiple equation steady state approach, probably due to breakdowns in the steady state approximation. More data spread was evident in the box-model approach compared with the other methods. An analysis of the major sources and sinks of OH is presented for the three methods of calculation. Calculated and observed peroxy radicals are also presented. Calculated peroxy radicals were generally lower than that observed at night yet higher, sometimes by up to a factor of 7, during the day. Possible explanations for this result are explored.

Effect of season and dietary energy concentration on composition and strength of skin in naked neck fowl

1. Two experiments, in spring and summer, were conducted to evaluate the effect of dietary energy concentration on the composition and strength of the skin of naked neck fowl. The heterozygous naked neck birds were also compared with their normally feathered sibs under summer temperatures. 2. The average temperatures were 21.2°C and 27.1°C in spring and summer experiments, respectively. Three concentrations of dietary energy were fed to the birds. The diets used were: a low energy diet of 12.12 MJ ME/kg; a medium energy diet of 12.96 MJ ME/kg; and a high energy diet of 13.79 MJ ME/kg. Two protein concentration per energy treatment, 230 and 200 g/kg, respectively were used from 0 to 3 and 3 to 7 weeks of age. 3. A significant season sex interaction showed that the skin of males had higher protein and collagen and lower dry matter and fat content than that of females, when grown under summer conditions. No sex differences were present under spring conditions. 4. The differences between sexes was not significant in spring but males had stronger skin than females in summer. Neither ambient temperature nor dietary energy concentration significantly affected skin displacement of naked neck birds. 5. In comparing the naked neck and their normally feathered sibs in the summer experiment, it was found that naked neck birds had lower skin fat content and higher skin protein content than normally feathered birds.

Integration of rice crop residue into sustainable rice production system

Rice is the staple food for nearly 40% of the world's population. In Malawi, rice is ranked second only to maize as a cereal food crop. In rainfed areas of Malawi, grain yields typically average 1.0–1:5 t ha‐1 while potential yield is 4–5 t ha1. To bridge the gap between current and potential yields, several novel nutrient management systems were studied. Many research reports indicate that rice responds to silicon (Si) application as well as to nitrogen (N), phosphorus (P), and potassium (K) which are commonly applied. Rice crop residues (straws and hulls) are rich in Si and K, but are not utilized currently in rice production. The effect of rice‐hull ash, rice straw, and method of N application (prilled or briquetted urea) on a transplanted rice crop was studied through field experiments in Malawi during 1995 and 1996. Application of urea in briquette form increased rice grain yield by 1056 and 122 kg ha‐1 compared to prilled urea in the 1995 winter and 1996 summer experiments, respectively. However in the 1996 winter experiment, prilled urea was superior to urea briquette and increased the rice grain yield by 307 kg ha1. Incorporation of rice straw significantly increased rice grain yields over the control in three consecutive experiments. Rice‐hull ash alone increased the rice grain yields in all three experiments up to 12%; however, the increase was not statistically significant. The combination of rice straw and rice‐hull ash along with optimum N rates (60 kg ha‐1) increased the rice grain yields significantly in 1996 winter season but the increase was not significant in the other two experiments.