Soil and sediment properties affecting the accumulation of mercury in a flood control reservoir

Mercury accumulations in some fish species from Grenada Lake in north Mississippi exceed the Food and Drug Administration standards for human consumption. This large flood control reservoir serves as a sink for the Skuna and Yalobusha River watersheds whose highly erodible soils contribute to excessively high sediment yields and impaired water quality. This study was conducted to characterize the distribution of total Hg in watershed soils and determine the relationship between the easily transportable clay, organic C (OC), and Fe oxide fractions and the movement of Hg from upland sources to reservoir sinks. Cores were collected from soils, of different land-use, representative of the three soil orders (Alfisols, Entisols, and Vertisols) found in the watersheds. Sediment cores were collected from the Yalobusha River and Grenada Lake. In the laboratory, soil cores were sampled by horizon while sediment cores were sampled in 10 cm increments. These samples were characterized for total Hg, particle size distribution, OC, Fe oxide contents, and pH. Mercury concentrations ranged from 10 to 112 µg kg^− 1 in the soil profiles, with average regression coefficient (r²) values of 0.104, 0.362, and 0.06 for Hg versus clay, OC, and Fe oxides, respectively. River sediment cores had Hg concentrations ranging from 0 to 38 µg kg^− 1, and significant (1% level) r² values of 0.611, 0.447, and 0.632 versus clay, OC, and Fe oxides, respectively. Mercury concentrations in the lake sediment ranged from 0 to 125 µg kg^− 1. The r² values for Hg versus clay, OC, and Fe oxides in the lake sediment were 0.813, 0.499, and 0.805, respectively, all significant at the 1% level. These results indicate that total Hg is poorly correlated with the clay, OC, and Fe oxide fractions at depth in the soil profiles because maximum Hg concentrations occur in the surface horizons due to atmospheric in-fall. The statistically significant r² values for Hg versus these components in the sediment cores are the result of particulate clay, Fe oxides, and finely divided OC sorption of Hg from solution during the runoff and sediment transport process. The higher correlations for the lake sediment reflect an enrichment of the Hg-laden clay fraction relative to stream sediment through flocculation and sedimentation processes in the slack-water environment of the reservoir.     

Deforestation and loss of bushland and grassland primarily due to expansion of cultivation in mainland Tanzania (1995–2010)

Information on land use and cover changes (LUCC) is important for planning of conservation and development and thus ensure forest sustainability. The current paper assesses LUCC for the whole of the mainland Tanzania. The analyses were done using land use and cover maps covering the whole of mainland Tanzania for 1995 and 2010. For 1995, forest, bushland, grassland, cultivation and other land use and cover (built up areas, bare land, etc.) covered 43.5%, 19.8%, 23.5%, 11.2%, and 2.0% of the study area, respectively. For 2010, the same land use and cover classes covered 38.0%, 14.5%, 6.9%, 36.5%, and 4.1% of the study area, respectively. The annual rate of deforestation was 320,067 ha, which is equivalent to 0.9%. Bushland and grassland were lost at 313,745 and 969,982 ha/year, respectively. Most forest was converted to cultivation and least to other land use and cover. In conclusion, the net changes were deforestation and loss of bushland and grassland primarily due to expansion of cultivation. Further research on how to reduce or halt expansion of cultivation may shed light on improving sustainability of forest, bushland, and grassland in mainland Tanzania.     

Interactive influence of livestock grazing and manipulated rainfall on soil properties in a humid tropical savanna

Purpose

The effect of uncontrolled grazing and unpredictable rainfall pattern on future changes in soil properties and processes of savanna ecosystems is poorly understood. This study investigated how rainfall amount at a gradient of 50%, 100%, and 150% would influence soil bulk density (ρ), volumetric water content (θ_v), carbon (C), and nitrogen (N) contents in grazed (G) and ungrazed (U) areas.

Materials and methods

Rainfall was manipulated by 50% reduction (simulating drought—50%) and 50% increase (simulating abundance—150%) from the ambient (100%) in both G and U areas. Plots were named by combining the first letter of the area followed by rainfall amount, i.e., G150%. Samples for soil ρ, C, and N analysis were extracted using soil corer (8 cm diameter and 10 cm height). Real-time θ_v was measured using 5TE soil probes (20 cm depth). The EA2400CHNS/O and EA2410 analyzers were used to estimate soil C and N contents respectively.

Results and discussion

The interaction between grazing and rainfall manipulation increased θ_v and C but decreased N with no effect on ρ and C:N ratio. Rainfall reduction (50%) strongly affected most soil properties compared to an increase (150%). The highest (1.241?±?0.10 g cm^?3) and lowest (1.099?±?0.05 g cm^?3) ρ were in the G50% and U150% plots respectively. Soil θ_v decreased by 34.0% (grazed) and 25.8% (ungrazed) due to drought after rainfall cessation. Soil ρ increased with grazing due to trampling effect, therefore reducing infiltration of rainwater and soil moisture availability. Consequently, soil C content (11.45%) and C:N ratio (24.68%) decreased, whereas N increased (7.8%) in the grazed plots due to reduced C input and decomposition rate.

Conclusions

The combined effect of grazing and rainfall variability will likely increase soil θ_v, thereby enhancing C and N input. Grazing during drought will induce water stress that will destabilize soil C and N contents therefore affecting other soil properties. Such changes are important in predicting the response of soil properties to extreme rainfall pattern and uncontrolled livestock grazing that currently characterize most savanna ecosystems.

     

The metal silo: An effective grain storage technology for reducing post-harvest insect and pathogen losses in maize while improving smallholder farmers’ food security in developing countries

Traditional storage practices in developing countries cannot guarantee protection against major storage pests of staple food crops like maize, leading to 20-30% grain losses, particularly due to post-harvest insect pests and grain pathogens. As a result, smallholder farmers end up selling their grain soon after harvest, only to buy it back at an expensive price just a few months after harvest, falling in a poverty trap. The potential impact on poverty reduction and greater livelihood security will not be realized, however, if farmers are unable to store grains and sell surplus production at attractive prices. Apart from causing quantitative losses, pests in stored grain are also linked to aflatoxin contamination and poisoning. To address this problem, a metal silo was developed as a valid option and proven effective in protecting stored grains from attack by storage insect pests. A metal silo is a cylindrical structure, constructed from a galvanized iron sheet and hermetically sealed, killing any insect pests that may be present. The impact of metal silo technology in Africa, Asia and Latin America includes, improving food security, empowering smallholder farmers, enhancing income opportunities and job creation, and safeguarding the agro-ecosystems. The metal silo can be fabricated in different sizes, 100 kg-3000 kg holding capacity by trained local artisans, with the corresponding prices of $35 to $375. The use of metal silo, therefore, should be encouraged in order to prevent storage losses and enhance food security in developing countries.     

The potential of a herbicide resistant maize technology for Striga control in Africa

Striga is an obligate parasitic weed that attacks cereal crops in sub-Saharan Africa. In Western Kenya, it has been identified by farmers as their major pest problem in maize. A new technology, consisting of coating seed of imidazolinone resistant (IR) maize varieties with the imidazolinone herbicide, imazapyr, has proven to be very effective in controlling Striga on farmer fields. To bring this technology to the farmer, a sustainable delivery system needs to be developed, preferably with substantial participation of the private sector. To help extension agents and seed companies to develop appropriate strategies, the potential for this technology was analyzed by combining different data sources into a Geographic Information System (GIS). Superimposing secondary data, field surveys, agricultural statistics and farmer surveys made it possible to clearly identify the Striga-prone areas in western Kenya. Results found that Striga affected a maize area of 246,000 ha annually, with a population of 6.4 million people and maize production of 580,000 tons, or 81 kg/person. Population density in this area is high at 359 people/km². A survey of 123 farmers revealed that 70% of them have Striga in their fields. A contingent valuation (CV) survey indicated that farmers would, on average, be willing to buy 3.67 kg of the IR-maize seed each at current seed prices, sufficient to sow 44% of their maize area. By extrapolation over the maize area in the zone, total potential demand for IR-maize seed is estimated at 2000–2700 tons annually. Similar calculations, but based on much less precise data and expert opinion rather than farmer surveys or trials, gives an estimate of the potential demand for IR-maize seed in Africa of 153,000 tons.     

Genetic variability in duration of pre-heading phases and relationships with leaf appearance and tillering dynamics in a barley population

The stem elongation phase seems critical in yield potential determination in barley (Hordeum vulgare L.). Extending its duration, without modifying total time to anthesis, has been proposed as a promising breeding tool. A prerequisite for its use is that the duration of phases before and after jointing (that including leaf and spikelet initiation, LS, and that of stem elongation, SE) should be under different genetic control. In addition, little is known about the implications of changes in the duration of LS and SE upon other developmental traits which could affect other aspects of yield generation, such as phyllochron and tillering. Thus, the objectives of the present work were to study the genetic variability in LS and SE, in traits related to leaf appearance and tillering, as well as their relationships, in a double-haploid (DH) population derived from the cross Henni × Meltan. DH lines and both parents were studied in four field trials. Despite the similarity in development between parents, there was significant genetic variability in duration of both LS and SE (i.e. considerable transgressive segregation was observed), with no major genetic correlations found between them. Although some significant genetic correlations were found between duration of phases and leaf appearance and tillering traits, it has been shown that modifying the duration of LS does not necessarily imply concomitant changes in traits that could be important for an early expansion of the crop canopy (i.e. phyllochron, onset and rate of tillering).     

Needs for and effectiveness of slow release herbicide seed treatment Striga control formulations for protection against early season crop phytotoxicity

Imidazolinone resistant maize seed dressed with imazapyr has been successfully used to control the parasitic weed Striga in many locations, and has begun to be commercially successful in Africa. Despite this, occasionally poor effectiveness of control had been documented in some sites that required explanation. Analysis of the data against rainfall patterns suggested that: 1. poor maize emergence occurred when there was limited rainfall at germination, possibly due to inhibition by a very high herbicide concentration too near the maize seed; 2. there was poor Striga control in seasons of very high rainfall, possibly due to herbicide washout away from the maize root zone where Striga germinates and attaches. These field assessments were matched by experiments suggesting that slow release formulations might alleviate the problems. A series of slow release formulations were synthesized based on binding imazapyr to high capacity anion exchangers and using them to coat maize seed. The best seems to be a polyethyleneimine gel. Epidemiological field data from a multitude of sites support the conclusion that the slow release formulations increased stand establishment across sites and seasons compared to the control where there was low rainfall.     

Modeling seasonal dynamics of small fish cohorts in fluctuating freshwater marsh landscapes

Small-bodied fishes constitute an important assemblage in many wetlands. In wetlands that dry periodically except for small permanent waterbodies, these fishes are quick to respond to change and can undergo large fluctuations in numbers and biomasses. An important aspect of landscapes that are mixtures of marsh and permanent waterbodies is that high rates of biomass production occur in the marshes during flooding phases, while the permanent waterbodies serve as refuges for many biotic components during the dry phases. The temporal and spatial dynamics of the small fishes are ecologically important, as these fishes provide a crucial food base for higher trophic levels, such as wading birds. We develop a simple model that is analytically tractable, describing the main processes of the spatio-temporal dynamics of a population of small-bodied fish in a seasonal wetland environment, consisting of marsh and permanent waterbodies. The population expands into newly flooded areas during the wet season and contracts during declining water levels in the dry season. If the marsh dries completely during these times (a drydown), the fish need refuge in permanent waterbodies. At least three new and general conclusions arise from the model: (1) there is an optimal rate at which fish should expand into a newly flooding area to maximize population production; (2) there is also a fluctuation amplitude of water level that maximizes fish production, and (3) there is an upper limit on the number of fish that can reach a permanent waterbody during a drydown, no matter how large the marsh surface area is that drains into the waterbody. Because water levels can be manipulated in many wetlands, it is useful to have an understanding of the role of these fluctuations.     

Identification of markers associated with genes for rust resistance in <Emphasis Type="Italic">Lens culinaris</Emphasis> Medik.

Lentil rust caused by Uromyces vicia-fabae (Pers.) Schroet is one of the most important diseases of lentil in South Asia, North Africa and East Africa. This disease is usually observed during late flowering and early podding stages. Early infection accompanied by favorable environmental conditions can result in complete crop failure and huge economic losses. Therefore, breeding for resistance against this pathogen is one of the major challenges for the breeders in those regions. It is important to identify resistance sources and to determine the location of the genes for resistance in the lentil genome. Since field screening is often difficult due to the unpredictable nature of the disease, selectable molecular markers can be useful tools to assist lentil breeding and complement field screening and selection for resistance. To map the genes for resistance, a recombinant inbred line (RILs) population composed of 220 RILs was developed from a cross between a rust resistant line, ILL-4605, and a susceptible line from Bangladesh, ILL-5888. Phenotyping of the RIL population was carried out during 2006–2007 and 2008–2009 cropping seasons at the Pulse Research Center, Ishurdi, Bangladesh. There was a lack of uniformity of disease pressure in the 2006–2007 cropping year causing inconsistencies between replicates. Nevertheless, we were able to choose clearly resistant and clearly susceptible RILs for selective genotyping using markers previously placed on our lentil genetic map. One of the 62 markers used for selective genotyping proved to be linked to the gene for resistance. The identified sequence related amplified polymorphism (SRAP) marker, F7XEM4a, was estimated to be 7.9 cM from the gene for resistance. The F7XEM4a marker could be used for marker assisted selection for resistance; however, additional markers closer to the resistance gene are needed.     

Influence of Boron on Sunflower Yield and Nutritional Status

Sunflower has been mentioned in the literature as a plant that requires large amounts of boron (B) to achieve a successful crop. This study aimed at evaluating the influence of sunflower fertilization with boron on the soil nutrient concentration, index leaf, seed yield, fatty acids’ composition of sunflower oil, and oil content. Cultivar M734 was selected for boron fertilization at 0, 3, 6, 9, and 12 kg ha^?1 rates. The maximum economic return was obtained with 3.13 kg ha^?1. Neither oil content nor fatty acid composition was affected by boron. With proper irrigation, the M734 cultivar was able to absorb boron in the 0 ? 40-cm layer, ultimately producing about 3000 kg ha^?1 of seeds in soils with only 0.30 mg kg^?1 of boron. Based on these results, it is suggested that the boron fertilization program be expanded to include the soil strata at 0?20 cm and 20?40 cm.