Mass-accumulation rates for the non-authigenic, inorganic, crystalline, eolian component of sediments recovered at DSDP Sites 62-464 to 62-466

The mass-accumulation rate (MAR) of the non-authigenic, inorganic, crystalline component of deep-sea sediments from the Pacific aseismic rises apparently reflects influx of eolian sediment. The eolian sediment usually is dominated by volcanic material, except during glacial times. Sediments from Hess Rise provide a discontinuous record of eolian MARs. During Albian to Cenomanian time, the influx of volcanic material was fairly high (0.35-0.6 g/cm**2/10**3 yr), recording the latest stages of the Albian volcanism that formed Hess Rise. From the Campanian through the Paleocene, influx of eolian sediment was low, averaging 0.03 g/cm**2/10**3 yr. None of the four Hess Rise drill sites show evidence of the Late Cretaceous volcanic episode recorded at many sites now in the equatorial to subtropical Pacific. Pliocene to Pleistocene samples record a peak in volcanic influx about 4 to 5 m.y. ago, which has been well documented elsewhere. The several-fold increase in eolian accumulation rates elsewhere which are correlated with the onset of severe northernhemisphere glaciation 2.5 m.y. ago is not obvious in the Hess Rise data.

Physical properties, sedimentation rates, and accumulation rates of bottom sediments from the Laptev Sea collected during SPASIBA-91 Russian-French Program

Humidity and wet and dry bulk densities were determined for bottom sediments of the Lena River marginal filter within a 700 km section from the outer boundary of the river delta. Earlier determinations of suspended matter concentration in water, material and grain-size composition and age of sediments were made along the same section. Sediment matter fluxes (accumulation rates), their changes in space and time (about 14 ka) were inferred from measurements of physical parameters. A correlation was found between the physical parameters of bottom sediments and changes in the Lena river marginal filter including those caused by sea-level fluctuations.

Radiocarbon datings of mollusk shells, sedimentation rates and accumulation rates of sediment matter in core PS2718-6

A bottom sediment core about 8 m long sampled in the eastern Kara Sea near the entrance to the Vil'kitsky Strait was studied. An age model was constructed based on four 14C datings obtained from by thy accelerating mass spectrometry method. Results of grain size, chemical, mineralogical, and foraminiferal analyses were adjusted to the model. A paleoceanological interpretation of these data together with paleoclimatic data on the Bol'shevik Island located in the neighborhood was performed.

Accumulation rates and composition of organic matter in sediments off Peru

Deep-sea sediment samples from three Ocean Drilling Program (ODP) Leg 112 sites on the Peru continental margin were investigated, using a number of organic geochemical and organic petrographic techniques, for amounts and compositions of the organic matter preserved. Preliminary results include mass accumulation rates of organic carbon at Site 679 and characteristics of the organic facies for sediments from Sites 679, 681, and 684. Organic-carbon contents are high, with few exceptions. Particularly high values were determined in the Pliocene interval at Site 684 (4%-7.5%) and in the early Pliocene to Quaternary section of Hole 679D (2%-9%). Older sediments at this site have distinctively lower organic-carbon contents (0.2%-2.5%). Mass accumulation rates of organic matter at Site 679 are 0.02 to 0.07 g carbon/cm**2/k.y. for late Miocene to early Pliocene sediments and higher by a factor of 5 to 10 in the Quaternary sediments. The organic matter in all samples has a predominantly marine planktonic and bacterial origin, with minor terrigenous contribution. Organic particle sizes are strikingly small, so that only a minor portion is covered by visual maceral analysis. Molecular organic-geochemical data were obtained for nonaromatic hydrocarbons, aromatic hydrocarbons (including sulfur compounds), alcohols, ketones, esters, and carboxylic acids. Among the total extractable lipids, long-chain unsaturated ketones from Prymnesiophyte algae strongly predominate among the gas chromatography (GC) amenable components. Steroids are major constituents of the ketone and free- and bound-alcohol fractions. Perylene is the most abundant aromatic hydrocarbon, whereas in the nonaromatic hydrocarbon fractions, long-chain n-alkanes from higher land plants predominate, although the total terrigenous organic matter proportion in the sediments is small.

Estimation of weed dry biomass and grain yield as a function of growth and yield traits under allelopathic weed management in maize

Growing concerns about toxicity and development of resistance against synthetic herbicides have demanded looking for alternative weed management approaches. Allelopathy has gained sufficient support and potential for sustainable weed management. Aqueous extracts of six plant species (sunflower, rice, mulberry, maize, brassica and sorghum) in different combinations alone or in mixture with 75% reduced dose of herbicides were evaluated for two consecutive years under field conditions. A weedy check and S-metolachlor with atrazine (pre emergence) and atrazine alone (post emergence) at recommended rates was included for comparison. Weed dynamics, maize growth indices and yield estimation were done by following standard procedures. All aqueous plant extract combinations suppressed weed growth and biomass. Moreover, the suppressive effect was more pronounced when aqueous plant extracts were supplemented with reduced doses of herbicides. Brassica-sunflower-sorghum combination suppressed weeds by 74-80, 78-70, 65-68% during both years of study that was similar with S-metolachlor along half dose of atrazine and full dose of atrazine alone. Crop growth rate and dry matter accumulation attained peak values of 32.68 and 1,502 g m-2 d-1 for brassica-sunflower-sorghum combination at 60 and 75 days after sowing. Curve fitting regression for growth and yield traits predicted strong positive correlation to grain yield and negative correlation to weed dry biomass under allelopathic weed management in maize crop.

Dry matter production of shoots and root density of two cultivars of Lablab purpureus (L.) Sweet

This experiment was conducted in green house conditions to evaluate the DM accumulation in the shoots and in the roots of two cultivars of Lablab purpureus (L.) Sweet. A 2x3 factorial (two cultivars and three evaluation dates) was conducted according to a randomized complete block design with four replications, being the cultivars Highworth and Rongai evaluated at 42, 56, and 70 days after seedling emergence (DASE). The results indicated that the cvs. Highworth and Rongai have the same pattern of DM accumulation in the shoots. In the upper layer of the soil (0-0.20 in) it was found 38.83% and 43.64% of the DM accumulated in the roots down to 2.00 in depth, in the cvs. Highworth and Rongai, respectively. In the deepest layer (1.80-2.00 in) it was found 3.02% and 1.5% of the DM accumulated in the roots of the cvs. Highworth and Rongai, respectively. The root density showed a striking decrease upper layer from the soil (0-0.2 m) down to the depth of 0.60 0.80 in (from 10.83 to 1.75 cm.cm(-3) in the cv. Highworth and from 10.76 to 1.28 cm.cm(-3) in the cv. Rongai). At the bottom layer (1.80-2.00 in) the root density values were 0.98 cm.cm(-3) and 0.59 cm.cm(-3), respectively for the cvs. Highworth and Rongai. The root/shoot ratios were similar in both cvs. and decreased from 42 to 70 DASE showing that the cvs. evaluated had the same dynamics of DM accumulation.