Effect of pH and Ca2+-induced associations of soybean proteins

An experimental procedure was developed to characterize the solubility of the soybean protein fractions close to the isoelectric point. The results show that the 7S fraction is precipitated in a much narrower range of pH values than the 11S fraction. Surprisingly, the addition of salt to the solutions leads to increased solubility of proteins, unlike the common "salting out" effect generally expected for proteins in solution in this range of salt concentrations. The precipitation equilibria of both soybean fractions in the presence of calcium ions and electrolyte were characterized. The amount of calcium ions required to precipitate a mole of the 7S fraction is much larger than that required for the 11S fractions. The precipitation pattern can be correlated to the charge density per surface area of the proteins.     

Use of chemistry and stable sulfur isotopes to determine sources of trends in sulfate of Colorado lakes

The chemistry of lakes in the Mt. Zirkel Wilderness Area (MZWA) and the Weminuche Wilderness Area (WWA) of Colorado has been monitored since 1985. The initial results indicate that changes have occurred in the chemistry of some lakes in both areas. Increased concentration of sulfate in lakes may be related to increased atmospheric depositon of sulfate or to changes of sulfate released by weathering and to changing dilution of sulfate by snowmelt. Stable S isotopes seem to be capable of separating the fraction of change in sulfate that is related to atmospheric and watershed sources. Because of the short period of record, it is not possible to determine whether the changes are part of a long-term trend or are merely natural fluctuations about some baseline.     

Conservation tillage for maize production in the U.S. southeastern coastal plain

Eight conservation tillage methods were evaluated for maize (Zea mays L.) production and were related to water conserved, soil strength, plant stand, plant nutrient status, and methods of managing crop residues on Norfolk loamy sands (Typic Paleudults) in the U.S. southeastern coastal plain. This study summarizes 10 site-years of data collected from 1978 through 1982.

Seasonal soil-water balance and crop residue management largely determined the success of maize production under conservation tillage. Autumn subsoiling increased winter forage and maize production under both conventional and conservation tillage. When early-season rainfall was limited, water extraction by a winter cover crop or winter weeds often reduced early-season growth and yield of maize under conservation tillage. For adequate stands, increased seeding rates and effective weed-, rodent-, bird- and insect-control were all necessary.

Under adequate water regimes, conventional tillage resulted in greater yields at low levels of nitrogen, but maximum yields occurred regardless of tillage system, when 200 kg ha⁻¹ were applied. Conventionally-tilled maize generally resulted in higher yields than conservation tillage production. The only significant increase for conservation tillage occurred under non-irrigated conditions in 1981 during severe drought. The interactive soil and climatic factors which have impact on conservation tillage in this physiographic region were identified.     

Patch-occupancy models indicate human activity as major determinant of forest elephant Loxodonta cyclotis seasonal distribution in an industrial corridor in Gabon

The importance of human activity and ecological features in influencing African forest elephant ranging behaviour was investigated in the Rabi-Ndogo corridor of the Gamba Complex of Protected Areas in southwest Gabon. Locations in a wide geographical area with a range of environmental variables were selected for patch-occupancy surveys using elephant dung to assess seasonal presence and absence of elephants. Patch-occupancy procedures allowed for covariate modelling evaluating hypotheses for both occupancy in relation to human activity and ecological features, and detection probability in relation to vegetation density. The best fitting models for old and fresh dung data sets indicate that (1) detection probability for elephant dung is negatively related to the relative density of the vegetation, and (2) human activity, such as presence and infrastructure, are more closely associated with elephant distribution patterns than are ecological features, such as the presence of wetlands and preferred fresh fruit. Our findings emphasize the sensitivity of elephants to human disturbance, in this case infrastructure development associated with gas and oil production. Patch-occupancy methodology offers a viable alternative to current transect protocols for monitoring programs with multiple covariates.     

The influence of neighbouring grassland plants on each others'' endomycorrhizas and root-surface microorganisms

In three glasshouse experiments the grassland plants Anthoxanthum odorattum. Lolium perenne, Plantayo lanceolata and Trifolium repens were grown in pots of grassland soil, in monocultures and various two-species mixtures. Mixed-species and single-species swards were also sown in a garden bed; and in a permanent pasture P. lanceolata individuals whose surrounding vegetation had been removed were compared with control plants. Abundance of root-surface bacteria and fungi, and of internal mycorrhizal infection were measured by direct observation of randomly-selected root segments.

The abundance of all three microbial groups on a given “host” species was often significantly altered by the presence of other plant species. Bacteria usually changed in the same direction as fungi, but proportionately less. Mycorrhizas usually changed less than the other two groups and not always in the same direction. In the pot experiments, when growth in a mixture resulted in a plant being larger and having higher nutrient concentration than in monoculture, the abundance of fungi on its roots also increased; bacteria and mycorrhizas showed this correlation less clearly. Superimposed on this relationship was a general tendency for fungi, and to a lesser extent bacteria, to be more abundant in mixture than monoculture even when the plants did not change in size. Possible mechanisms involved in these responses are discussed.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Development of direct-drilling systems for sandy loam soils in the cool humid climate of Atlantic Canada

This study provides an overview of the adaptation of direct-drilling systems on sandy loam soils under the cool boreal, humid to perhumid soil climate of Prince Edward Island in Atlantic Canada, where the growing season is relatively short (May–October). Direct drilling can overcome the constraints of limited field workdays for seeding of spring cereals, owing to wet soil conditions in early May, or the integration of planting date with optimum soil temperatures for silage corn (Zea mays L.). However, the advantage of timeliness may be offset under sequential direct drilling for these crops, owing to a combination of reduced macroporosity at the soil surface and increased percentage of water-filled pore space, especially in soils with levels of organic carbon below 2% (w/w). In contrast, the presence of standing-crop residue, in pasture-renovation studies, allowed sequential or regular direct drilling of various forage species to occur with no adverse effect on soil structure. Use of direct drilling for spring cereals and silage corn on a rotational basis allowed intermittent soil loosening to prevent increasing surface soil compaction. Overall, direct drilling on perhumid, sandy loam soils proved successful when soil surface compaction was alleviated or circumvented.     

Hydroponic Study of Aluminum Accumulation by Aquatic Plants: Effects of Fluoride and pH

The potential of five common aquatic plant species (Typha latifolia, Myriophyllum exalbescens, Potamogeton epihydrus, Sparganium angustifolium and Sparganium multipedunculatum)to be used for Al phytoremediation was tested. The plants were exposed, for 14 days under hydroponic conditions, to synthetic effluents representing extreme conditions that could occur accidentally at an aluminum refinery site. Tested Al concentrationsranged between 0 and 400 μM, fluoride concentrations between 0 and 900 μM, and the pH varied from 4.5 to 7.5. The results indicate that all the plants tested accumulated aluminum, and as a result induced a decrease of Al in the ambient water. For individual species Al uptake (in mol g^-1 dw d^-1) decreased in the following order: Myriophyllum exalbescens > Sparganium sp. ≌Typha latifolia > Potamogeton epihydrus. M. exalbescens accumulated Al more rapidly in its leaves than in other tissues, whereas T. latifolia and Sparganium sp. accumulated Al essentially in their roots. For P. epihydrus the relative importance of the leaves and roots varied with exposure conditions. For all species, fluoro-Al complexes contributed to Al uptake, contrary to the predictions of the Free-Ion Model, according to which the bioavailability of aluminum should be best predicted by the concentration of the free ion, Al³⁺. The influence of pH on Al uptake varied among the different species and among the parts of the plant: competition between Al and the H⁺-ion was evident for the roots of T. latifolia and the leaves and stem of M. exalbescensand P. epihydrus, whereas the roots of M. exalbescens, P. epihydrus and Sparganium sp. showed an inverse trend (Al uptake increased at low pH). For the leaves of T. latifolia and Sparganium sp., no pH influence could be demonstrated. Overall, the results of this study indicate that aquatic plants have a potential for Al phytoremediation.     

High pressure liquid chromatographic determination of aflatoxins in peanut butter using a silica gel-packed flowcell for fluorescence detection

A high pressure liquid chromatographic method has been developed for determining aflatoxins B1, B2, G1, and G2 in peanut butter. The method is based on extraction with acidified aqueous methanol, partition of the aflatoxin into methylene chloride, and purification of the extract on a 2 g silica gel column. The extracted aflatoxins are resolved on a microparticulate (10 micrometer) porous silica gel column in ca 10 min with a water-washed chloroform-cyclohexane-acetonitrile solvent that contains 2% isopropanol. The fluorescence detection system determines aflatoxins B1, B2, G1, and G2 at low levels, i.e., 0.25 ppb B1, 0.5 ppb G1, and 0.2 ppb B2 and G2. Multiple assays of 5 samples of naturally contaminated peanut butters containing total aflatoxins (B1 + B2 + G1 + G2) at levels of 1, 2, 3, 9, and 17 ppb gave intralaboratory coefficients of variation of 7, 4, 4, 11, and 3%, respectively. Samples spiked at levels of 5, 9, and 17 ppb total aflatoxins showed recoveries of 79, 81, and 81%, respectively.     

On the relationship between incoming solar radiation and daily maximum and minimum temperature

A relationship between atmospheric transmittance and the daily range of air temperature is developed. The relationship is T_t = A[1—exp(—BΔT^c)] where T_t is the daily total atmospheric transmittance, ΔT is the daily range of air temperature, and A, B, and C are empirical coefficients, determined for a particular location from measured solar radiation data. Tests on three data sets indicate that 70–90% of the variation in daily solar radiation can be accounted for by this simple model.