Sulphur mineralization kinetics of cattle manure and green waste compost in soils.

Sulphur mineralization of cattle manure (CM) and green waste compost (GWC) added to six agricultural soils with different chemical properties was monitored over 10 weeks in a laboratory incubation experiment. Although the amount of sulphur was higher in CM than in GWC, the cumulative SO4(2-)-S values in GWC-treated soils were higher than in soil amended with CM. The percentages of mineralized S were always higher in GWC-treated soil (in the range 1.3-8.5%) than in CM-treated soil (in the range 0.9-3.8%). In three of the six soils, particularly for CM, an immobilization of sulphur was observed. Three kinetic models were evaluated for their suitability to describe the mineralization process. The first-order model best described S mineralization for both amended and control soils. The GWC substantially increased the amount of potentially mineralizable S (S0) relative to the controls. In GWC-treated soils, the rates of S mineralization (k) were higher than rates in the controls. The k of CM-amended soils was often lower than the k of control soils. Parameters derived from the model were tested as indices for assessing the relationships between S mineralization and soil characteristics. The S0 was positively correlated to the amount of cumulative SO4(2-)-S and also to the content of organic C, N and S in soil.     

Effects of hand weeding strip and nitrogen fertilizer on corn plants

The objective of the present research was to evaluate effects of different strip weed control associated with nitrogen fertilizer on corn applied after planting. The experiment was set and conducted in Botucatu, S?o Paulo State, Brazil, and the hybrid planted was Dekalb 333-B. A completely randomized block design with four replications was used. Experimental plots were disposed as a factorial scheme 2 x 2 x 4, constituted by two types of weeding on row (with or without manual hoeing), two types of weeding on inter-row (with or without manual hoeing), and four nitrogen levels applied after planting (00, 60, 90, and 120 kg ha(-1)). Plots were composed by six rows with 5 m length. Nitrogen fertilizer was applied at 35 days after emergence (d.a.e). For weed community it was evaluated: weed density, dominancy, frequency, and relative importance. The main weed species were: Brachiaria plantiginea, Amaranthus retroflexus, Bidens pilosa, Cyperus rotunds, Brachiaria decumbens, Euphorbia heterofila, Oxalis latifolia, Acanthospermum hispidum, Commelina benghalensis. It was evaluated corn height at 40 and 100 d.a.e., first ear insertion height at 100 d.a.e., and final grain yield at harvesting. Plants and first ear insertion height were affected when nitrogen fertilizer was not applied. Treatments without weed control showed that weed interfered negatively with plants height. There were no correlation between weeds and nitrogen fertilizer for all parameters evaluated. Parcels without weed showed the highest ear weights and final grain production. Treatments that received nitrogen fertilizer, independently of studied arrangement, provided higher yields.     

Contrasting structure and composition of the understory in species-rich tropical rain forests

In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.     

The combined use of chemical and biochemical markers to assess water quality along the Ebro River

Carp (Cyprinus carpio) and barbel (Barbus graellsii) were collected from five sites along the Ebro River. The study was designed to assess levels of persistent organic pollutants and metals bioaccumulated by fish, and some biochemical responses (cytochrome P450 system, phase II activities, and metallothioneins) against those pollutants. The highest levels of PCBs and DDTs were detected in carp from industrialised areas, which also showed high levels of mercury and cadmium in the liver, and high levels of nonylphenol in bile. Significant alterations in some biochemical markers were observed and associated to combined exposure to pollutants. The activity 7-ethoxyresorufin O-deethylase ranged from 69 pmol/min/mg protein in carp from the reference site to 415 pmol/min/mg protein in those from polluted sites. Carp from the Ebro Delta, an agricultural area, had depressed acetylcholinesterase in muscle tissue. Metallothionein concentrations were positively correlated with copper residues, but no significant differences among sampling points were observed.     

234U and 230Th determination by FIA-ICP-MS and application to uranium-series disequilibrium in marine samples

A 234U and 230Th determination method based on an extraction chromatographic separation on a flow injection system coupled to a quadruple ICP-MS was developed. Two-milliliter UTEVA (Eichrom Co.) cartridges were applied as separation tool and 236U and 229Th as spikes. Loading and washing steps were carried out in 3 M HNO3 solution and 0.05 M ammonium oxalate applied to elute both uranium and thorium. The method was applied initially to the IAEA-327 soil reference sample and NIST SRM 4357 ocean sediment reference material, with the obtained 234U and 230Th concentrations in agreement with the reference levels. Samples from a deep-sea sediment core (2450 m water depth) were analyzed and based on 230Th/234U dating, a mean sedimentation rate of 3.3 cm ky(-1) was calculated. Samples from two sediment layers were also dated by 14C-AMS and the observed ages agree with the 230Th/234U results.     

Scale-invariant movements of fishermen: the same foraging strategy as natural predators.

We analyzed the movement of fishing vessels during fishing trips in order to understand how fishermen behave in space while searching for fish. For that purpose we used hourly geo-referenced positions of vessels, provided by a satellite vessel monitoring system, for the entire industrial fleet (809 vessels) of the world's largest single species fishery (Peruvian anchovy, Engraulis ringens) from December 1999 to March 2003. Observed trajectories of fishing vessels are well modeled by Lévy random walks, suggesting that fishermen use a stochastic search strategy which conforms to the same search statistics as non-human predators. We show that human skills (technology, communication, or others) do not result in the fishermen's spatial behavior being fundamentally different from that of animal predators. With respect to probability of prey encounter, our results suggest that fishermen, on average, evolved an optimal movement pattern (mu = 2.00) among the family of Lévy random walks. This Lagrangian approach opens several perspectives in terms of operational management of the pelagic fish stock.     

Reef coral reproduction in the eastern Pacific: Costa Rica,Panamá, and Galápagos Islands (Ecuador). II. Poritidae

A comparative study of the reproductive ecology of the zooxanthellate, scleractinian corals Porites lobata Dana and P. panamensis Verrill was conducted from 1985 to 1991 in eastern Pacific reef environments that were severly impacted by the 1982–1983 El Niño warming events. P. lobata, a presumed broadcast spawner of large colony size, is widely distributed in the equatorial eastern Pacific, whereas P. panamensis, a brooder of small colony size, is abundant only on some reefs in Panamá. Both species were gonochoric with nearly 1:1 sex ratios in large study populations except for P. lobata at Caño Island that had 14% hermaphroditic colonies. Mature, unfertilized oocytes contained numerous zooxanthellae in both Porites species, and all planula developmental stages contained zooxanthellae in P. panamensis. Year-round sampling revealed high proportions of colonies with gonads, ranging from 30 to 68% in P. lobata and from 60 to 68% in P. panamensis. No clear relationship between numbers of reproductive colonies and the thermal stability of the habitat was evident in P. lobata: percent colonies with gonads at non-upwelling sites was 48 to 68% at Caño Island (Costa Rica) and Uva Island (Panamá), and at upwelling sites 30 to 50% at Saboga Island and Taboga Island (Panamá), and the Galápagos Islands (Ecuador). Similarly, 90% of all P. panamensis colonies were reproductive at Uva Island (a non-upwelling site), and 86% were reproductive at Taboga Island (an upwelling site). Upwelling at Taboga Island is seasonal, nevertheless P. panamensis produced mature gonads or planulae over most of the year (11 mo), whereas P. lobata exhibited reproductive activity during only 2 mo (May and June). No clear lunar periodicity was observed in P. panamensis (Taboga Island), but a high proportion of P. lobata showed increased gonadal development around full and new moon, especially at Caño and Uva Islands. Estimated fecundities were relatively high for P. lobata at Caño (4000 eggs cm^-2 yr^-1) and Uva (5200 eggs cm^-2 yr^-1) Islands, and notably low (70 to 110 eggs cm^-2 yr^-1) in the Galápagos Islands. P. panamensis mean fecundity at Taboga Island was 720 planulae cm^-2 yr^-1 or 4.0 mm³ cm^-2 yr^-1, which was lower than the egg volume production of P. lobata at Caño and Uva Islands (7.0 to 10.0 mm³ cm^-2 yr^-1). The capacity of P. lobata and P. panamensis to reproduce sexually supports the notion that eastern Pacific coral reef recovery may not be dependent on long-distance dispersal from central Pacific areas. However, sexual recruits of P. lobata are absent or uncommon at all eastern Pacific study sites while recruits of P. panamensis were common to abundant only at the Uva Island study site. Asexual fragmentation in P. lobata augments recruitment locally, but plays no role in P. panamensis recruitment.