Mid Season Research Articles

The role of a dambo in the hydrology of a catchment and the river network downstream

Abstract. Dambos are shallow, seasonally inundated wetlands and are a widespread landform in Central and Southern Africa. Owing to their importance in local agriculture and as a water resource, the hydrology of dambos is of considerable interest: varied, and sometimes contradictory, hydrological characteristics have been described in the literature. The issues in contention focus on the role of the dambo in (i) the catchment evapotranspiration (ET) budget, (ii) flood flow retardation and attenuation, and (iii) sustaining dry season flow to the river down-stream. In addition, both rainfall and groundwater have been identified as the dominant source of water to the dambo and various hydrogeological models have been proposed to describe the hydrological functions of the landform. In this paper, hydrological and geochemical data collected over a full hydrological year are used to investigate and describe the hydrological functions of a dambo in north-western Zambia. The Penman estimate of wetland ET was less than the ET from the miombo-wooded interfluve and the wetland has been shown to have little effect on flood flow retardation or attenuation. Discharge of water stored within the wetland contributed little to the dry season flow from the dambo, which was sustained primarily by groundwater discharge. Flow in a perched aquifer within the catchment soils contributed a large portion of baseflow during the rains and early dry season. This source ceased by the mid dry season, implying that the sustained middle to late dry season streamflow from the wetland is through discharge of a deeper aquifer within the underlying regolith or bedrock. This hypothesis is tested through an analysis of groundwater and wetland geochemistry. Various physical parameters, PHREEQC model results and end member mixing analysis (EMMA) suggest strongly that the deep Upper Roan dolomite aquifer is the source of sustained discharge from the wetland. Keywords: dambo, hydrology, hydrogeology, stormflow, evapotranspiration, baseflow, sponge effect, Zambia

Electricity Demand and Price Analysis in California Using Possibility Regression Model

In this paper, the authors analyze the prices of electricity spot market in California. Firstly, we discuss the relation between annual demand of electricity and the temperature in California. We identify the electricity demand is related to temperature using possibility regression analysis. Then we show the fluctuation of electricity price is influenced by the demand. In the early summer season of 1998, the relationship between temperature and electricity price in California was simple. However, in the mid summer season in 1998, the price volatility of the electricity goes on increasing. Secondly we show that the expectation (speculative buying) of the market participant which is formed by temperature fluctuation induced the price volatility. We show that the price volatility is affected by temperature fluctuation for a previous few days.

INFLUENCE OF SUBMAXIMAL VO2 AT VENTILATORY THRESHOLD ON SELF-SELECTED WORK RATE DURING WILDLAND FIREFIGHTING

Wildland firefighters (WLFF) are often asked to perform extended and arduous workshifts to suppress fire quickly and efficiently. In order to perform for extended periods, crew members are required to maintain a sustainable work rate both for productivity and to ensure safety. PURPOSE To investigate the relationship between sustainable fitness as measured by VO2 at ventilatory threshold (VO2vt) and self-selected work rate over individual days and an extended 9-day period of arduous wildfire suppression. METHODS Ten (9 males and 1 female) elite WLFF from a Montana hotshot crew volunteered to wear CSA activity monitors in their pockets (Heil, Ergonomics 33:405–413, 2002) to determine work rate during the 9-day Kelly Creek fire (Salmon River, ID). Prior to the fire, subjects performed a midseason labVO2vt test using a Parvo Medics metabolic system. Daily and total CSA counts over the 9-day fire were correlated with midseason VO2vt (ml·kg-1·min-1) to evaluate the relationship between sustainable fitness and self-selected work rate during extended arduous fire suppression. RESULTS The total CSA activity count over the 9-day period (6,100,000 ± 720,000) was strongly related (r = 0.94) to the mid season VO2vt. Daily correlations between CSA counts and VO2vt values ranged from r=0.36 to r=0.80. Discussion: Over a 9-day period of arduous duty, the self-selected work rate of the WLFF is highly related to VO2vt. Daily work rate to VO2vt relationships are lower probably as a result of differing individual work assignments on a daily basis. CONCLUSION Sustainable aerobic fitness levels (VO2vt (ml·kg-1·min-1)) of wildland firefighters are strongly related to long-term self-selected work rate during wildland firefighting and may suggest the need for higher fitness and training standards than are currently in place for elite WLFF crews. Supported by the USFS and the Missoula Technology and Development Center

Seasonal abundance and spatial distribution of the predatorMacrolophus costalis and its preyMyzus persicae on tobacco

Field studies were conducted to assess the population and the spatial dynamics of the predatory bugMacrolophus costalis Fieber (Hemiptera: Miridae) and of its prey, the aphidMyzus persicae (Sulzer) (Hemiptera: Aphidoidea), on tobacco. From an untreated tobacco field in Tithorea (central Greece), tobacco leaves were collected from the upper and the lower half of the plants from June until September, in 1999 and 2000. The numbers ofM. costalis andM. persicae individuals per leaf were counted. Most aphids were observed during July and August (early and mid season), with densities dropping markedly in September. In contrast,M. costalis population densities increased late in the season (September). Significantly higher numbers of aphids were found on the upper half of the plants than on the lower half. In contrast, significantly moreM. costalis individuals were observed on the lower half. Iwao’s Regression Analysis was used in order to characterize the spatial pattern of the two species. According to this model, in both sampling seasons, aphids andM. costalis nymphs displayed an aggregated spatial pattern, whileM. costalis adults were found to be randomly distributed among sampling units. Although moreM. costalis individuals were recorded on leaves with relatively high aphid densities, this species did not react numerically to changes in prey density. In addition, a significant number of bugs were found on leaves with low aphid densities or no aphids at all.

Distribution of Monilinia fructicola Isolates Resistant to Dicarboximide or to both Procymidone and Carbendazim in Korea

To evaluate the sensitivity of Monilinia fructicola to dicarboximides used in controlling brown rot of peach, the fungus was isolated from commercial peach orchards in Chochiwon (CH), Chongdo (CD), Gyeongsan (GY), and Youngduk (YO) in Korea. The population shift of dicarboximide-resistant isolates of M. fructicola was investigated for 3 years starting 1998. The frequency of procymidone-resistant isolates (PRI) was higher in CD and GY than in CH and YO. The frequency of PRI was higher in the mid season (July-August) than in the rest of the year. Cross-resistance rate of PRI to iprodione was over 87.8% during the investigation, and double-resistance to both procymidone and carbendazim was less than 10%. However, the rate of cross-resistant isolates to vinclozolin was low. In the orchards in GY and CH without any fungicide spray, the PRI population was persistent and did not vary for 3 years. The results suggest that dicarboximide resistance of M. fructicola could be a problem in controlling brown rot and blossom blight on peach trees because it may take a long time to recover the population with sensitive isolates even in the absence of these fungicides.

Consumo, composição botânica e valor nutritivo da dieta de bovinos em pastos tropicais consorciados sob três taxas de lotação

Foram avaliados o consumo, a composição botânica e o valor nutritivo da dieta de bovinos em pastagens de Brachiaria decumbens e Stylosanthes guianensis cv. Mineirão e de Brachiaria brizantha cv. Marandu e Stylosanthes guianensis cv. Mineirão, submetidas a três taxas de lotação. Adotou-se o delineamento experimental em blocos completos casualizados com os tratamentos no esquema de parcelas subdivididas, com duas repetições. Os tratamentos das parcelas constituíram um fatorial 2x3, sendo duas gramíneas (B. decumbens e B. brizantha cv. Marandu) em consorciação com S. guianensis cv. Mineirão e três taxas de lotação (0,8; 1,2 e 1,6 UA/ha), e as subparcelas, os meses de amostragem (julho e outubro de 1998, correspondendo à época seca; janeiro e abril de 1999, correspondendo à época das águas). Foram utilizados bezerros Nelore, desmamados, com peso vivo médio de 138 kg, no início do experimento. Não foi observado efeito da taxa de lotação sobre as variáveis estudadas. O consumo diário de MS foi maior em pastagens com B. brizantha, em outubro (no final da seca) e em abril (no final das águas), entretanto, dietas de melhor valor nutritivo foram obtidas em pastagens com B. decumbens. As dietas foram constituídas por mais de 80% de folhas de gramínea, enquanto a participação da leguminosa nas dietas foi de apenas 2,1%, com um índice de seleção de 0,08, indicando pouca aceitação deste componente da MS disponível pelos animais em pastejo.

A Study of a Mixed Mode Environment in 25 Cellular Offices at the University of Sydney

Twenty five cellular offices in the Wilkinson Building at the University of Sydney, Australia are ventilated through operable windows and doors and have been retrofitted with a supplementary reverse cycle cooling/heating system with an occupant controlled fancoil unit in each room. Energy consumption and occupancy and temperature status of rooms have been monitored since the system was commissioned at the end of 1997. Occupant surveys have shown that perceptions of air quality and thermal comfort have improved considerably since the system was commissioned and are now significantly above whole population averages. Regression analysis suggests significant relationships between perceived air quality, thermal comfort and overall comfort with a very strong relationship between overall comfort and perceived effect on performance of work. Estimation by dynamic simulation indicates that measured energy consumption by the supplementary system is less than a quarter of what would be expected if the same spaces were air-conditioned. Mean temperatures in occupied rooms are found to have a linear association with outdoor temperatures until the outdoor daily minimum reaches about 17°C corresponding to a mean indoor temperature of about 25°C. As outdoor temperature continues to rise mean indoor temperature remains constant indicating mechanical intervention by a considerable proportion of occupants. As would be expected, the number of rooms using the equipment displays a strong binomial relationship with outdoor daily temperatures with a minimum in mild mid season weather. Monthly energy consumption displays a similar relationship with outdoor conditions.

Biologia floral e polinização de Aechmea beeriana (Bromeliaceae) em vegetação de baixio na Amazônia Central.

O presente estudo trata a biologia floral, a polinização e o sistema reprodutivo de Aechmea beeriana Smith & Spencer, acrescidas de algumas informações fenológicas. A espécie foi estudada nos arredores de Manaus-AM. A. beeriana ocorre principalmente como epífita a várias alturas, com preferência por locais mais sombreados. Apresenta-se adaptada a síndrome de ornitofilia, com antese diurna e inflorescências vistosas. A antese possui duração de um dia e as flores são homogâmicas. Os indivíduos são auto-incompatíveis. Três espécies de beija-flores, Phaethornis superciliosus, P. bourcieri e Thalurania furcata (Trochilinae), são considerados os principais polinizadores. A espécie apresenta padrão de floração sub-anual, com 98,4% dos indivíduos apresentando flores ao longo do período, florescendo principalmente entre os meses de agosto e dezembro,ou seja, da metade da época de estiagem até o início da estação chuvosa. Brotos e folhas novas foram observados desenvolvendo-se ao longo do ano.

Rice Response to Phosphorus Fertilizer Application Rate and Timing on Alkaline Soils in Arkansas

Phosphorus deficiency of rice (Oryza sativa L.) in Arkansas occurs almost exclusively on alkaline silt loam soils. Phosphorus‐deficient rice has been observed where P fertilizer was applied near the time of seeding, which suggests that fertilizer P is rapidly converted to a form not available to flooded rice on alkaline soils. The primary objective of this study was to evaluate rice response to P fertilizer applied at different times. Field studies were established in six commercial rice fields. Three rates of P (9.8, 19.6, and 39.1 kg P ha−1) were applied at four different times during the growing season including preemergence (PRE), preflood (PF), 5 to 10 d postflood (POF), or at midseason (MS) and compared with an untreated control. Significant grain yield increases were measured at two of the six locations. Grain yields were maximized by application of 19.6 kg P ha−1 at the two highly responsive sites with yield increases of 24 to 41%. Application of P fertilizer PRE, PF, and POF were superior to MS applications, which were not different from the control. Phosphorus concentration in harvested grain was not affected by time or rate of P fertilizer application. The average grain P content represented 56 to 75% of the total P in the aboveground portion of rice at physiological maturity. Broadcast applications of P fertilizer to the soil surface between seeding and active tillering were equally effective at increasing rice yields and optimizing P uptake on the P deficient soils.

Actual evapotranspiration and crop coefficients of wheat ( Triticum aestivum) under varying moisture levels of humid tropical canal command area

Wheat ( Triticum aestivum L.) is the most important cereal crop after rice in India. Optimum schedule of irrigation for wheat and its response to irrigation based on the ratio of irrigation water and cumulative pan evaporation (irrigation depth (IW):CPE at 1.2, 0.9 and 0.6) was studied in a field experiment during the winter seasons of 1989–1990 and 1990–1991. The site had a sandy loam (Typic Fluvaquent) soil and shallow water table, located in the humid tropical canal command area at the University Experimental Farm, Memari (23°1′N, 88°5′E and 21.34 m above mean sea level) in West Bengal, India. The yield of wheat, weekly and seasonal actual evapotranspiration (ETa) from water balance equation, crop coefficients ( K c), soil water stress coefficients ( K s), water extraction patterns, water use efficiency (WUE) and water application efficiency ( A e) were determined. Maximum profile water depletion and ETa of wheat occurred in the wetter moisture regime (1.2 IW:CPE). The average daily ETa varied from <1 mm per day in the early growing period to a maximum value of 2.72 mm per day at 9–14 weeks after sowing (WAS) under 1.2 IW:CPE when leaf area index (LAI) was >3. During crop development to mid season (4–14 WAS), 1.2 IW:CPE showed 9–15% increased ETa than 0.9 and 0.6 IW:CPE. The seasonal ETa of wheat with IW:CPE of 1.2 was 238.2 and 261.95 mm during 1989–1990 and 1990–1991, respectively. Maximum roots were concentrated in the top 150 mm layer (57% of root length density) and maximum root water extraction efficiency ( U z) was observed at 600–750 mm depth under the drier soil moisture regimes of 0.9 and 0.6 IW:CPE, respectively. The yield increased significantly with increasing levels of irrigation. IW:CPE ratio of 1.2 produced 13 and 21% more yield, and 8 and 14% improved WUE than 0.9 and 0.6 IW:CPE, respectively. Water application efficiency ( A e) was noticed higher (79.85%) under 0.6 IW:CPE irrigation regime. Precise information of K c, which is required for regional scale irrigation planning is lacking in developing countries. The estimated values of K c for wheat at four crop growth stages (initial, crop development, mid season and maturity) were 0.33, 0.82, 1.08 and 0.64, respectively which were identical to those suggested by the FAO indicating need for generating these values at the local/regional level. The K s values of 0.6 IW:CPE decreased steeply and experienced more stress condition than 0.9 IW:CPE.

VOMITING IN A DIVISION I COLLEGE FOOTBALL PLAYER

HISTORY: A 21 year-old senior football player had the onset of vomiting prior to every game for at least 10 years. In mid season he then developed vomiting episodes prior to or during each practice session with an associated weight loss of 6–7 pounds. Upon presentation this had been occuring for 1–2 weeks. He denied any associated nausea, abdominal pain, symptoms not associated with practice, history of performance anxiety, personal or family history of psychiatric illness, suicidal or homicidal ideation, history of or current symptoms of heartburn or reflux, fevers, chills, change in bowel habits or sick contacts. He felt from his initial presentation that it was “all in his head.” He also described tactile stimuli for the vomiting, which included having dry heaves or vomiting from the sensation of his chin strap or shoulder pads hitting his neck area and progressing to trouble with touching his neck at all. PHYSICAL EXAMINATION: Initial exam revealed a well-developed, well-nourished young black male who had occasional diminished eye contact, but full affect, was neat and well groomed and in no distress. MMSE was 30/30. There was no scleral or sublingual icterus, mucus membranes were moist; heart had normal rate and rhythm and no audible murmur, rub or gallop; lungs were clear to auscultation; abdomen had normoactive bowel sounds with no tenderness, rebound, guarding or organomegaly. Brief neurologic exam was within normal limits. DIFFERENTIAL DIAGNOSIS: Generalized anxiety disorder with panic attacks GERD 41.08 Gastroenteritis TEST AND RESULTS: TSH 0.50 Free T CBC: WBC7.0, Hgb14.9, Hct43.8, Plt341, Differentialnormal Comprehensivechempanelwithinnormallimits FINAL/WORKINGDIAGNOSIS: Generalizedanxietydisorder with panicattacksmani festingasvomitingwithexposuretostres TREATMENT ANDOUTCOMES: Trial of Prevacidf or GERD withnobene fitandcontinuedweightloss. Initiation oftherapywithiniPaxilwithinitialpartialresponse. Cognitive Behavioral Therapywithstaf fpsychologist. Maintenanceo factivestatusthroughoutandcessationofweightloss.

Phenological patterns in a southern Amazonian tropical forest: implications for sustainable management

Phenological transects were employed to assess monthly leaf, flower, unripe fruit and ripe fruit abundance for a total of 1732 individual plants within five tropical forest habitats at the ‘Lago Caiman Research Camp’, Noel Kempff Mercado National Park, northeastern Santa Cruz Department, Bolivia. Fruit surveys along trails were conducted concomitantly to assess fruit availability for the resident terrestrial frugivore community. The results of the two methodologies are compared and discussed with respect to wildlife and forest management in the region. Phenological transects revealed that Cerrado forest, tall forest, low vine forest, Sartenejal (swamp) forest, and pied mont (premontane) forest, showed seasonal variations in flower, unripe fruit and ripe fruit abundance, however, the broad temporal patterns were significantly different across habitats. Seasonal variation in overall foliage abundance was only marked for Cerrado forest. Ripe fruit production within the study site was not significantly different across months, with different habitats peaking asynchronously in abundance. From a frugivory perspective, overall ripe fleshy fruit abundance also varied considerably between habitats, and again showed asynchronous peaks in habitat production. However, both methodologies revealed the early dry season (June–July) as a period of ripe fleshy fruit scarcity throughout the study area. This period represents a resource ‘bottleneck’ for the resident frugivore community and phenological results allowed the identification of a number of keystone fruit resources for the region. Furthermore, fruit resources which are super-abundant in the early–mid wet season (November–February) might also be considered keystone resources for the region, given that they are available in an otherwise fruit scarce forest. The dynamic spatial patterning of fruit availability at Lago Caiman suggests that certain habitats might be considered keystone habitats, since they provide the majority of fruit resources on a seasonal basis. Finally, the potential of phenological information in tropical forest management plans is discussed and underlined by the observation that rainfall in itself fails to predict fruit availability in the dominant habitats at Lago Caiman.

RIPENING CURVE OF EARLY, MIDSEASON AND LATE MATURING HIGHBUSH BLUEBERRY CULTIVARS

To investigate the evolution of quality parameters during ripening, berries of three highbush blueberry cultivars (early, mid season and late maturing) have been harvested at regular intervals of 4 days, at 6 picking stages, each of them corresponding to a ripening stage, identified by the color of the skin, according to an evaluation scale. For each phase, the most significant physico-chemical parameters have been measured. Quality traits evolve quickly from the green-blue to the blue phase. A crucial moment of ripening is the red-blue stage when there is a quick improvement in quality properties. If the picking date coincides with that stage or if it is done earlier, quality does not evolve during postharvest and remains poor. Significant modifications in quality from the blue stage have not been recorded. This allows to reduce the number of berry picking without compromising the quality of the berries.

Climate change and caribou: effects of summer weather on forage

In 1989, the Chisana caribou (Rangifer tarandus) herd in the northern Wrangell Mountains, Alaska, U.S.A., declined substantially in population size and productivity. Grasses, sedges, forbs, and willows (Salix spp.) are critical components of the diet of caribou in spring and summer, and the abundance and quality of forage are influenced by climate. To evaluate effects of climatic variation on caribou forage we conducted a field experiment in subarctic tundra where light, air temperature, and precipitation were manipulated. We used a plastic tarpaulin to increase air temperature and decrease precipitation. We also decreased light intensity with a shade cloth and increased precipitation by adding water to determine climatic effects on nutrient content and biomass of forage for caribou during the summers of 1994 and 1995. The most notable treatment effect on aboveground biomass was that shading resulted in higher nitrogen concentrations in all plant growth forms. In addition, shading consistently reduced biomass in forbs during mid and late season. Water treatment increased total plant biomass in the greenhouse plots during midseason in 1994 and in late spring in 1995. Water treatment also increased late-season biomass in control plots during 1994 but had no effect on biomass in shaded plots in either 1994 or 1995. A decline in nitrogen concentration in plants occurred throughout summer, a pattern that was not evident in in vitro dry matter digestibility. Climate variation and subsequent effects on forage plants have the potential to influence the population dynamics of caribou through effects on their food supply.

Effect of herbage allowance on pasture utilization, regrowth and milk yield of dairy cows in early, mid and late season

The effect of herbage allowance (HA) on milk yield of dairy cows, pasture utilization and pasture regrowth was studied in a field trial conducted at the North Savo Research Station, Maaninka, Finland in 1998. The experiment was conducted with 24 lactating Holstein-Friesian cows that were strip-grazed on Phleum pratense L.– Festuca pratensis Huds. pastures. The pastures received 220 kg ha −1 N divided into three allocations and adequate amounts of P and K. The experiment was conducted as a replicated 3×3 Latin square design with three HA levels and three periods. The three HA levels were 19, 23 and 27 kg dry matter (DM) per cow per day (cut over 3 cm stubble height). The cows did not receive any supplements except minerals. Data were collected during three 10 days periods: mid-June, mid-July and beginning of August. Increasing HA decreased pasture utilization from 77.7 to 61.0%. Increasing HA increased post-grazing leaf area index (LAI) in each period, but the regrowth rate was similar for each treatment. The calculated energy-corrected milk (ECM) yield per hectare during the 15 days collection periods increased with decreasing HA from 2116 to 2406 and to 2808 kg ECM ha −1, respectively. The reduction in individual animal performance of 6% led to a 33% increase in animal production per area (i.e. HA 27 versus HA 19). A post-grazing sward height (SH) of 9–10 cm indicated an effective utilization of P. pratense L.– Festuca pratensis Huds. pastures. Increasing HA from 19 to 27 kg DM increased the milk yield by 0.16 kg ECM kg −1 ( P<0.01). HA had no effect on the milk composition. Milk yield decreased from 25.6 to 18.8 kg ECM ( P<0.01) when the grazing season advanced. HA had no effect on the rumen DM content ( P=0.58), instead, the rumen DM content increased from June to August ( P<0.01).

The breeding status and colony dynamics of Cape Vulture Gyps coprotheres in Botswana

Cape Vulture Gyps coprotheres is endemic to southern Africa and is globally threatened. Colonies in Botswana comprise part of one of the two core breeding areas in the species's range, and very little has previously been published about them. Ground censusing of 11 Cape Vulture sites in Botswana was undertaken from 1992 to 1999, continuing a monitoring programme initiated by the authors in 1984. Survey methods and census procedures are documented. The potential Cape Vulture breeding population in Botswana is estimated to be about 600 pairs, comprising at least 100 pairs at Mannyelanong in the south-east and about 500 pairs in eastern Botswana. This represents an increase from previous estimates, and reflects improved census techniques rather than an increase in population size. The mean turnover rate of nest site usage from one year to the next averaged 21% at Mannyelanong, and was about 26% at Manong Yeng in eastern Botswana. Annual productivity of nest sites increased with the number of years the site had been occupied. Over the eight years of study eggs were laid in at least 436 of 477 nests (91.4%) at Mannyelanong; chicks survived to mid season (60–80 days old) in 327 nests (75% of eggs laid), and fledged (best estimate) in 248 nests (56.9% of eggs laid and 52% of pairs attempting to breed). In eastern Botswana eggs were laid in at least 1,825 of 2,101 nests (86.9%); chicks survived to mid season in 1,272 nests (69.7% of eggs laid). Two seasons have been excluded for eastern Botswana (1994 and 1995) due to incomplete data, and breeding success can be estimated only from 1997 to 1999: of 990 eggs laid out of 1,108 nests, chicks fledged in 384 nests (38.8% of eggs laid and 34.6% of pairs attempting to breed). The eastern Botswana breeding population remains in a state of flux following the collapse of a primary colony that was the country's Cape Vulture stronghold. Conservation concerns and the vulnerability of Cape Vulture sites are discussed.

Tritrophic interactions between cabbage cultivars with different resistance and fertilizer levels, cruciferous aphids and parasitoids under field conditions.

Tritrophic interactions involving cabbage Brassica oleracea var. capitata cultivars +/- fertilizer, Brevicoryne brassicae (Linnaeus) and Myzus persicae (Sulzer), and the parasitoids Diaeretiella rapae (M'cIntosh) and Aphidius sp. were conducted in 1998 and 1999. Brevicorne brassicae was the dominant aphid species on all cultivars +/- fertilizer, except for some treatments in late season 1998. Ruby Ball (red-leaved with antixenosis factors for B. brassicae alates) +/- fertilizer was consistently less colonized by aphids in early stages of plant growth, although only significantly so compared with Derby Day (green-leaved, susceptible to aphids) without fertilizer for B. brassicae and Minicole (green-leaved with antibiosis factors for B. brassicae) with fertilizer for M. persicae. In early 1999, only B. brassicae was present and no significant differences between cultivars were seen. In the mid to late season 1998, the highest aphid infestations were usually found on Derby Day, although only significantly so for B. brassicae, in some treatments. In 1999, higher aphid infestations were observed on Derby Day in mid to late season and some significant differences were found for M. persicae as well as for B. brassicae. In both years, Ruby Ball had the greatest mummy:aphid ratios early season, with no consistent difference between the other cultivars. Later in the season, mummy:aphid ratios were generally highest on Minicole. Parasitism differed in seasonal occurrence and relative abundance. Diaeretiella rapae mummies were found earlier than Aphidius sp. There was evidence of a beneficial interaction between the degree of plant resistance and biological control in early to mid season.

Impact of nitrogen and environmental conditions on corn as detected by hyperspectral reflectance

Indices derived from hyperspectral reflectance spectra have the potential to be used as indicators of environmental stress in crops. This study uses canopy-scale, ground-based measurements of hyperspectral reflectance to demonstrate the temporal patterns in corn development under imposed fertility (N rate) and environmental (water availability) stresses. In 1998, two large areas in a 30-ha corn ( Zea mays, L.) field near Ottawa, Canada (45°18′N, 75°44′W) were supplied with 99 and 17 kg N ha −1, while the balance of the field received the recommended rate of 155 kg N ha −1. Reflectance measurements were taken nine times using a portable spectroradiometer at georeferenced locations within these areas. Individual reflectance-based indices demonstrated the relative differences between application rates and identified both nitrogen and water stresses at various times in the growing season. No single index was able to describe the status of the corn crop throughout the season. Canonical discriminant analysis provided accurate classification of samples by N rate during early, mid, and late season conditions with overall success rates of 70%, 88%, and 93%, respectively. A shift in importance from green-based derivatives to red-based derivatives was noted from mid to late season and attributed to the natural reduction in green pigments as the crop entered senescence. Canopy-scale photochemical reflectance index (PRI) was shown to be correlated with canopy radiation use efficiency (RUE). Mid-season water stress affected the relationship. Multiple years of data are required to demonstrate robust relationships between hyperspectral indices and corn ecophysiological status because of the interaction between environmental and nutrient stresses. Identifying areas of fields sensitive to weather-induced stresses will allow better management of N application. Timing the collection of hyperspectral image data at early and late vegetative phase could enhance precision agriculture by allowing supplemental nutrient application, identifying stress patterns and aid in yield forecasting.

Characterization of protein components of natural and heat-treated milk fat globule membranes

The proteins associated with the milk fat globule membrane (MFGM), isolated from early, mid and late season whole milks, were characterized using one- and two-dimensional SDS-PAGE under reducing and non-reducing conditions. In some experiments, MFGM separated from fresh whole milk was suspended in simulated milk ultrafiltrate (SMUF) and heated at various temperatures and times. SDS-PAGE under reducing conditions followed by staining with Coomassie blue showed the presence of about 37 protein bands, ranging in molecular weight from 15 to 200 kDa. SDS-PAGE under non-reducing conditions showed only about 25 distinct bands and the intensity of xanthine oxidase and butyrophilin bands was much less, while the intensity of PAS 6/7 band was similar compared with the reduced SDS-PAGE. Two-dimensional SDS-PAGE showed that the protein complexes that remained at the top of non-reducing gel were resolved into mostly xanthine oxidase and butyrophilin with a small proportion of PAS 6. These results indicate that xanthine oxidase and butyrophilin may be complexed via intermolecular disulfide bonds in the natural MFGM, although it is not possible to differentiate the individual protein distributions within these aggregates. It was found that the total protein content (mg/g fat) of MFGM and the percentage of xanthine oxidase and butyrophilin in early and late season MFGM were higher than that of mid season MFGM. In heated samples (above 60°C), xanthine oxidase and butyrophilin interacted further to form higher molecular weight protein complexes, while PAS 6/7 was relatively heat stable.

Influence of Bed Cover Types on Production Time and Quality of Sweetpotato Slips

Sweetpotato (Ipomoea batatas) cultivars, Carver, Potojam, Jewel and Centennial were evaluated for slip production, using topsoil, sawdust, sand and a general-purpose peat-based commercial growing media as bed covers. Temperature measured 2 inches (5.1 cm) below the surface of the hot bed varied with covers and date measured. Sand maintained the highest bed temperature, 77 °F (25.0 °C) at 0800 hr and 79 °F (26.1 °C) at 1400 hr, throughout the growing season. Peat-covered roots produced the maximum number of slips/plot (111), while roots covered with topsoil and sawdust produced comparable yields, 55 and 45 slips/plot, respectively. Slip production varied according to harvest date, with the third harvest producing the most slips/plot (83 and 153, in year 1 and year 2, respectively), which, was likely related to increased temperatures. Cultivar significantly influenced number of slips, length of slips, and number of roots per slip. `Potojam' was the most prolific slip producer for both early and mid season production under all bed covers.