Studies on the Persistence of a Commercial Formulation of Chlorpyrifos on an Agricultural Soil from Provincia de Buenos Aires,República Argentina

Mercury and cadmium are priority hazardous substances. Some titanosilicates have been tested for the removal of Cd²⁺ and Hg²⁺ from single solutions by ion exchange. In this work, the competition between both contaminants for the exchanger binding sites of titanosilicate Engelhard titanosilicate material number 4 (ETS-4) was studied by performing batch experiments with aqueous solutions containing the two counter ions. The results evidenced the large capacity of ETS-4 and shown that the cadmium(II) diffusivity through the sorbent is higher than that of mercury(II). Furthermore, the ETS-4 exhibited higher kinetic and equilibrium selectivities for Cd²⁺, which attained values in the ranges 8.9–12.5 and 7.9–12.8, respectively. With respect to modelling, the pseudo-second-order equation described successfully the competitive removal of Cd²⁺ and Hg²⁺.     

Effect of continuous grazing in the dohne sourveld on species composition and basal cover

Abstract

In a grazing trial conducted at the Dohne Agricultural Research Station, natural grassland was grazed continuously for 36 years with cattle. In a second investigation conducted on similar grassland, paddocks were grazed or rested, in all combinations of the four seasons of the year, over a ten year period. Changes in botanical composition and cover of the sward were monitored at regular intervals. The results of these investigations indicate that under a regime of non‐selective grazing the composition of Dohne Sourveld is remarkably stable. After 36 years of continuous grazing the species composition of the sward was largely maintained. Floristically Dohne Sourveld is dominated by a small number of grass species of which Andropogon appendiculatus, Elionurus muticus, Heteropogon contortus, Sporobolus africanus, Themeda triandra and Tristachya leucothrix are the most important. These species react differently to under‐utilization or increasingly severe defoliation, enabling them to be classified into decreaser or increaser categories. Severe defoliation resulted in a marked decrease in basal cover but only small changes in relative species composition. As the intensity of defoliation increases, decrease in grass cover is associated with an increase of forbs, such as Senecio retrorsus.     

Dietary patterns of two herbivorous rodents: Otomys unisulcatus and Parotomys brantsii in the Karoo

Differences and overlap in the diets of two sympatric, herbivorous rodents Otomys unisulcatus and Parotomys brantsii were investigated. Frequency of occurrence of plant species in the diets were compared with availability of the plants in the rodents' habitats. Both rodents are generalist herbivores, eating plants species in proportion to the availability in their habitats. Dietary patterns, diversity of diet and degree of overlap between rodent's diets are a function of food availability in the different habitats. It is suggested that these rodents separate niches on a spatial rather than trophic basis. Differences in dietary patterns are therefore not critical for niche separation but are the result of habitat segregation.     

Bioaccumulation of chromium and nickel in the tissues of Barbus marequensis A. Smith, 1841 from the Lower Olifants River,Mpumalanga

Bioaccumulation of chromium and nickel in selected tissues and organs of the freshwater fish Barbus marequensis was investigated. According to the monthly data, the blood accumulated the highest amount of chromium, followed by the bile and vertebrae, while the skin accumulated the lowest amount. Nickel mainly accumulated in the blood, followed by the vertebrae and gills, while the lowest nickel concentrations occurred in the fat tissue. Although significant differences (p ≤ 0,05) between localities were detected, no definite trend as to where the highest bioaccumulation had occurred could be established. The levels in the tissues and organs of B. marequensis suggested no serious chromium or nickel pollution in the study area.     

Effect of dietary n-3 series fatty acids on sperm production in the freshwater crayfish, Astacus leptodactylus (Eschscholtz) (Astacidae)

The objective of the present work was to evaluate the effects of three different rates of long chain n-3 polyunsaturated fatty acid (LC n-3 PUFA) on the sperm number of Astacus leptodactylus. The experiment was carried out with the four following treatments: control group (not supplemented LC n-3 PUFA), D1 (1 %), D2 (2 %) and D3 (3 %). The sperm number of A. leptodactylus was counted; the reproductive system was weighted; and the macroscopical analysis of the testes and vasa deferentia (DVD) were conducted. In addition, gonado-somatic index (GI) and testes index (TI) were also calculated. The results showed that there was a significant difference between the crayfish fed LC n-3 PUFA supplemented diets (D1, D2, D3) and control in mean sperm number (P < 0.05). The highest sperm number was found for the crayfish fed D3 (6.27 ± 0.14 × 10⁸ sperm/distal vas deferens section). The results also showed that the reproductive system of the crayfish fed D3 and D2 was significantly heavier than that of the crayfish fed the control and D1 (P < 0.05). On the other hand, there was not a significant difference in the testes weight and vasa deferentia weight between the crayfish fed the control and D1, and between the crayfish fed D2 and D3 (P < 0.05). GI of the crayfish fed D3 and D2 was significantly higher than that of the crayfish fed control and D1 (P > 0.05), but there was not a significant difference in the TI of the crayfish fed control, D1, D2 and D3 (P > 0.05). In conclusion, diets containing different levels of LC n-3 PUFA significantly increase the sperm number of A. leptodactylus, and they are crucial for the production of higher number of sperm in this species.     

ＥＭ 菌对海参养殖水体理化因子的影响

摘要：利用室内试验与池塘试验相结合的方法,研究了不同浓度的EM菌原液对海参养殖水体理化因子的影响效果。结果表明,EM菌对水体的溶解性固体（TDS）、电导率（cond）无显著影响（p>0.05）;能显著增加水体氧化还原电位（ORP）、DO、透明度（SD）（p<0.05）：其中以Ⅳ组（4*109cfu/m3）效果最好,分别平均增加3.39%（试验箱）和8.38%（试验池）、26.20%（试验箱）和18.58%（试验池）、54.69%（试验池）;pH各试验箱间缓慢下降,但差别不显著（p>0.05）,试验池比对照池平均下降3.94%,均值为7.79,仍在适宜范围内。 关键词：EM菌; 海参养殖; 水体理化因子     

天津农业高校毕业生通向农村的机制探究

天津正在社会主义新农村建设的过程中朝着沿海都市型农业的方向发展,这期间必然需要大量高等农业人才的支撑。但当前农业院校的毕业生却对农业和农村采取漠视态度。那么,如何引导天津农业高校毕业生到农村就业,成为当前亟待解决的问题。本文正是对如何引导天津农业高校毕业生通向农村就业的机制进行了探索。     

Early recognition of graft compatibility in <Emphasis Type="Italic">Uapaca kirkiana</Emphasis> Müell Arg. clones,provenances and species

Examination of callus micro-grafts in Uapaca kirkiana Müell Arg. was carried out with the objective of determining early signs of graft compatibility. Leaves from U. kirkiana, U. nitida and Jatropha curcas trees were used for callus induction. Two pieces of callus were co-cultured on Murashige and Skoog (MS) medium with different supplements. Co-cultured calli were embedded in paraffin wax and dissected. The specimens were stained in safranin and fast green before viewing under a light microscope. Results showed that MS medium with 0.1 mg l⁻¹ thidiazuron (TDZ) and 0.5 mg l⁻¹ naphthaleneacetic acid (NAA) or 1.0 mg l⁻¹ dichlorophenoxyacetic acid (2,4-D) and 0.5 mg l⁻¹ NAA was effective for callus induction. There were no necrotic layers at the unions within U. kirkiana clones and provenances, but a differential growth (irregularity) between U. kirkiana and U. nitida co-cultured calli. Phenol deposits were observed at the union interfaces of U. kirkiana combinations and were high on calli derived from mature trees. Phenol deposits were absent at the union of J. curcas heterografts. Necrotic layers developed at the unions of U. kirkiana and J. curcas micro-grafts and indicating an outright graft incompatibility. Accumulation of phenol deposits at the union interfaces inhibited graft compatibility in many U. kirkiana combinations. Callus fusion technique can be used to identify partners with an outright graft incompatibility, especially for distant related plant species.     

The response of Phragmites australis to harvesting pressure in the Muzi Swamp of the Tembe Elephant Park,South Africa

Phragmites australis (Cav.) Trin. ex Steud. has been harvested in the Muzi Swamp in Maputaland, South Africa for generations. Over the last ten years, however, a flourishing trade in this reed has developed. Concern has now been expressed that at the current levels of utilization the ecological integrity of the Muzi Swamp is being compromised, and that the current harvesting rates are not sustainable in the long term. The hypothesis was put forward that a degradation gradient exists with the most severe degradation occurring the closest to where community members enter the park, and the least degradation the furthest from this point. The results of this study, however, show no distinct degradation gradient. Yet the overall condition of the reeds in the harvesting area is poorer than in the non‐utilized area. Expansion of the current harvesting area, coupled with adaptive harvesting systems and yearly monitoring will improve the quality of the reeds within the harvesting area without affecting the harvesting quotas. Copyright © 2004 John Wiley & Sons, Ltd.