Long-Term Transformation and Redistribution of Potentially Toxic Heavy Metals in Arid-Zone Soils: II. Incubation at the Field Capacity Moisture Content

Solid-phase transformation of added Cd, Cu, Cr, Ni, Pb and Zn, in two arid-zone soils incubated in the field capacity moisture regime for one year, were studied. The heavy metals were fractionated into six empirically defined fractions using a selective sequential dissolution (SSD) protocol optimized for arid-zone soils. Each of these fractions was named based on the major soil component targeted for dissolution during the specific SSD step, but it is not assumed that they are mineralogically and chemically totally specific. The transformations of the metals in the two soils incubated at the field capacity regime were compared with those at the moisture saturation regime (Han and Banin, 1997). An initial fast stage of transformation of the soluble metals from the exchangeable (EXC) fraction to the less labile fractions (the carbonate (CARB) fraction for Cd, Pb, Zn, Ni and Cu, and the organic matter (OM) fraction for Cr, and to some extent Cu and Ni) occurred during the fractionation and within one hour after addition. This was followed by a second stage, involving long-term transformation processes of all metals: added Cd was transferred from the EXC into the CARB fraction; added Cr was transferred from the CARB to the OM fraction and Pb was transferred very slowly to the easily reducible oxide (ERO) fraction. Added Cu, Ni and Zn were transferred from the EXC and CARB fractions into the ERO fraction and to some extent OM and RO fractions. In Part I of this series, we reported that during incubation in the saturated moisture regime, Zn and Ni were transferred mainly into the RO and OM fractions. Cadmium, Cr and Pb underwent the same transformation pathways during the slow long-term process, with slightly different rates, in both water regimes. At low levels of addition, the incubated soils moved over one year towards a distribution similar to that of the native soil. At higher levels, the soils still remained removed from the quasi-equilibrium which characterized the native soil, even at the end of one year of incubation.     

Influence of rate of soil fertilization on alternaria leaf blight (Alternaria dauci) in carrots

The possibility of suppressingAlternaria dauci (Kühn) Groves & Skolko, the causal agent of Alternaria leaf blight in carrot, by excess application of fertilizer was examined in greenhouse and field experiments. Reducing the rate of fertilization by one half from the optimal rate (100 ppm N, 19 ppm P and 74 ppm K) resulted in a 23–30% increase in the severity of Alternaria leaf blight. However, doubling the rate of fertilization resulted in only a 10–15% decrease in disease severity. Inoculating with different concentrations ofA. dauci spores (10³ or 10⁴ spores/ml) did not alter the response of the plants to the fertilization rate, although significantly higher disease severity was observed in plants inoculated with the higher spore concentration. These results were corroborated in the field, where neither disease severity nor harvested yield was significantly affected by tripling the amount of soil fertilization. Application of foliar fungicides, on the other hand, had substantial effects on both disease and yield. Therefore, it was concluded that carrot crops should be fertilized and maintained for optimum yield, and thatA. dauci should be managed by properly timed applications of fungicides during the growing season. Contribution no. 533/99 from the Inst. of Plant Protection, Agricultural Research Organization.     

Biological control of weeds using plant pathogens: accomplishments and limitations

The science and technology of weed control by using plant pathogens gained attention and momentum in the 1970s when some century-old concepts in weed biocontrol and plant disease epidemiology were successfully put to test and a few economically important weeds were controlled by two different strategies. Since then, researchers in different parts of the world have critically examined and tried to apply these strategies with the hope of solving some of the most intractable weed problems. Depending on one"s point of view, this biological control approach has been quite successful or wrought with limitations. In this paper, we describe some of the accomplishments as well as the limitations in this field.     

Adsorption of systemic pesticides on ground stems and in the apoplastic pathway of stems,as related to lignification and lipophilicity of the pesticides

The adsorption of five systemic fungicides (carbendazim, triadimefon, nuarimol, triarimol, and fenarimol) and one herbicide (fluometuron) on ground stems and in the apoplastic pathway of excised pepper, cotton, and bean stems was studied. Adsorption on ground and water extracted stems, as well as retention in the apoplast of excised stems, increased with the 1-octanol/water partition coefficients of the pesticides. Methylation of ground stems increased their adsorption capacity (carbendazim excluded), while extraction with organic solvents did not affect it. Woody stems adsorbed more of the pesticides than herbaceous ones. Binding of pesticides in the apoplastic pathway of stems seems to be related to their degree of lignification and to the lipophilicity of the pesticides.     

Marine Aquaculture in Israel with Special Emphasis on Larval Rearing

The goal of mariculture research in Israel is the development of an industry, based on available sea and brackish water, in the Arava Desert, the Gulf of Eilat and along the Mediterranean coast. Urgent progress is needed due to the shortage of fresh water for agriculture. High priced euryhaline fish like Sparus aurata and Dicentrarchus labrax are the obvious choice for development along with the more common grey mullet Mugil cephalus. The aim of this paper is to present the research and zootechnical state of the art in Sparus aurata and Dicentrarchus labrax larval rearing at the National Center for Mariculture (NCM). Fertilized eggs are stocked in 600 L tanks and hatching success estimated from aliquot counts. Rearing continued for 32 d after which larvae are removed from these tanks with minimum mortality. Under normal rearing conditions these tanks produce 15-35 32 d old (10 mg, ww) Sparus aurata larvae/L (20-40% survival). Average seabass survival to 80 mg (40 d) is 35%. Tanks were continuously supplied with filtered (10 μm), temperature and salinity controlled seawater and freshly enriched food organisms through a special delivery system. This system was recently upscaled to 1,700 L tanks with equally good results for seabream larval rearing. Live food enrichment regimes for the two species were developed to maximize their growth and survival. A microdiet is presently being used from the age of 20 d. The problems involved with using dry diets with larvae were found to be associated with both their digestibility and attractivity. As a result of a salinity reduction from the ambient 40 to 25 ppt, swim bladders developed in 90% of seabream and 75% of seabass. In addition, growth rate of larvae improved by 15%. Finally, seabream tend to show strong aggressive behavior once size differences in the population of 32 d larvae is greater than 300%. Therefore, once seabream ended their 32 d hatchery period they are graded to three size groups of 5, 10.3 and 23 mg (ww). The graded fish are counted with a locally developed Computer Aided Fish Counter (CAFIC) and stocked separately in 5 m³ nursery tanks.     

Influence of foliar application of nitrogen and potassium onalternaria diseases in potato,tomato and cotton

The hypothesis that enrichment of the foliage with nitrogen and potassium may enhance host resistance toAlternaria and thus reduce disease severity, was examined for potato and tomato (A.solani) and for cotton (A.macrospora). First, the activity of urea (CO(NH₂)₂) and the salts NH₄NO₃, (NH₄)₂S0₄, KNO₃, KCl, K₂SO₄ and KH₂P0₄ againstA. solani andA. macrospora was determinedin vitro; each of the compounds tested had a weak inhibitory effect on spore germination of A.solani (ED50 > 1000 μg/l) and on mycelial growth of both A.macrospora andA. solani (ED50 > 10,000 μg/l). Next, the effect of foliar application of selected nutrients onA. solani andA. macrospora was evaluatedin vivo on detached leaves of tomato and cotton. The diameter of A.solani lesions on leaves sampled from tomato plants treated with KNO₃ was significantly smaller (by 56.5%) than that recorded on leaves sampled from untreated plants.A. macrospora severity on leaves sampled from cotton plants treated with urea was significantly lower than that observed on untreated leaves (70.8% reduction) but KNO₃ did not affect disease severity significantly. The following step was to examine the effects of foliar application of urea and KNO3 onAlternaria development in field experiments, two with potato and one with cotton. Foliar application of both nutrients (8-10 sprays in total) did not affectAlternaria severity as compared with the untreated control in any of the experiments. The fungicides chlorothalonil and tebuconazole, on the other hand, significantly suppressed the disease throughout most of the growing season. A mixture of urea or KNO₃ with the fungicides did not further improve the effects of the latter when applied alone. Based on these results, it was concluded that foliar application of urea or KNO₃ does not affect host response toAlternaria.     

Compensation for seasonal changes in eggshell conductance and hatchability of goose eggs by dynamic control of egg water loss

1. The water loss for optimal hatchability of goose eggs was 12% of initial egg mass.

2. Mass specific eggshell water vapour conductance, G_sp, increased by approximately 50% over about 13 weeks during the winter breeding cycle. A similar increase occurred over 8 weeks during summer.

3. Constant setting of humidity in goose incubators and changes in mean G_sp may cause sub‐optimal egg water loss which increases late mortality.

4. Mean G_sp was measured for every batch from each flock. Humidity was changed accordingly in order to reach optimal water loss. A significant improvement of 6% in hatchability and of 8% in Class‐A goslings was noted during 14 successive weeks compared with the previous 11 weeks.

5. Dynamic humidity control for optimising water loss according to mean batch G_sp thus increases hatchability.     

Rearing the Maize Weevil, Sitophilus zeamais, on an Artificial Maize-Cassava Diet

Abstract Dry artificial diet pellets prepared with maize, cassava chips, and amino acid supplements (lysine and methionine) were evaluated for mass culture of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), a highly polyphagous pest of many stored grains. Evaluation was done in the laboratory at temperature 26 ± 2 °C, 60-70% RH, 12:12 L:D photoperiod. The artificial diet was compounded from different proportions of maize (M) variety TZPB-SW-R, cassava (C) variety TMS-2110, and amino acid supplements, and was pelletized into 6 mm diameter pellets on which five pairs of one-day-old S. zeamais were bioassayed. The diet M(9)C(1) (90% M and 10% C) was the most suitable diet with comparatively shorter developmental period (34.8 days) and the highest F(1) emergence of progeny (145.4) compared to the control, M(10)C(0) (100% M and 0% C).