Subsoiling in some heavy clay soils of Egypt

Four soil profiles were selected to represent the heavy clay soils of alluvial and lacustrine origin. The locations studied had been subsoiled at least once during the year before the investigation. Field observations and laboratory analyses were carried out to ascertain the subsoiling effect on the soil profile properties. For further confirmation, soil penetration tests were performed on material from all the sites studied. The data revealed that subsoiling is not to be recommended in the Vertisols or the heavy clay soils adjacent to the northern Delta lakes of Egypt because these soils develop abundant natural cracks of 3–5 cm in width and 50–70 cm in depth. There are no impervious layers in the top 60 cm of the soils in the study area, and there is no evidence of soil compaction throughout the top 70 cm in all the sites studied.     

Isolation and characterization of iron-reducing nitrogen-fixing saccharolytic clostridia from gley soils

Thirty strains of saccharolytic, N₂-fixing clostridia isolated from gleyed soils, capable of reducing Fe₂O₃-powder, were characterized physiologically and classified by conventional and numerical methods. After redefining the distinguishing features of saccharolytic Clostridium-species, 23 of the 30 isolates were assigned to the newly proposed species C. butyricum (12), C. saccharobutyricum (8), C. acetobutylicum (1). C. beijerinckii (1), and C. tyrobutyricum (1). Seven strains could not be classified and were regarded as intermediate forms. Numerical analysis confirmed the close relationship between 27 of the 30 isolates as well as to the type cultures used in comparison.     

Clay minerals of some soils of the Nile Valley in Egypt

The mineralogical composition of clay fractions of thirteen profiles, representing the soils of four transects across the Nile Valley, were studied. The soils represent Torrerts and Torrifluvents. The dominant mineral in the fractions is montmorillonite. Kaolinite is present in small amounts. Illite and chlorite are found in trace amounts. Traces of calcite, feldspar and goethite were also indicated in most of the samples. The mineralogical composition of the clay fractions is nearly the same. There is no significant difference in the clay mineral composition between Torrerts and Torrifluvents. The mineral composition of the clay fractions in soils across the transects from west to east and from south to north does not differ significantly.     

Zinc and copper in some soils of Egypt as related to other soil properties

Total Zn in alluvial and calcareous soils (average 138 and 70 ppm respectively) was significantly related to their contents of CaCO₃ (negatively), O.M. and clay (positively). Extracting Zn by Na₂EDTA gave the highest values for both soil types. Total Cu contents varied widely from 26 to 111 ppm in alluvial and from 15 to 30 ppm in calcareous soils. They were negatively correlated with the CaCO₃ contents. The pot experiments showed that EDTA(NH₄)₂CO₃, Na₂EDTA and DTPA are reasonable extractants for available Zn from both soil types. DTPA was efficient for all soils investigated, while Na₂ EDTA and EDTA-citrate were specific for extracting Cu from calcareous soils.     

Isolation and characterization of potassium solubilizing bacteria in some Iranian soils

The ability of a few soil bacteria to transform unavailable forms of potassium (K) to an available form is an important feature in plant growth-promoting bacteria for increasing plant yields of high-K-demand crops. In this research, isolation, screening, and characterization of six isolates of K solubilizing bacteria (KSB) from some Iranian soils were carried out. The ability of all isolates were tested in three treatments including acid-leached soil, biotite, and muscovite by analyzing the soluble K content after 5 days of incubation at 28 ± 2°C. Identification and phylogenetic analyses were also carried out by morphological, biochemical, and 16S rDNA analyses. Among the six efficient isolates, five isolates belonged to Bacillus megaterium (JK3, JK4, JK5, JK6, and JK7), while isolate JK2 belonged to Arthrobacter sp. The soluble K contents in all isolated-treatments were significantly (p < 0.01) higher than the contents in nonbacteria treatment. Herein, isolate JK2 had lower potential for K solubilization (910 mg kg^?1) compared with other isolates in acid-leached soils. The six bacterial strains showed higher solubilized K in biotite treatment than other two treatments. Overall, it can be concluded that the isolates belong to B. megaterium are the most efficient KSB under in vitro condition.     

Occurrence and infectivity of arbuscular mycorrhizal fungi in some norwegian soils influenced by heavy metals and soil properties

Mycorrhizae are ubiquitous symbiosis which can mediate uptake of some plant nutrients. In polluted soils they could be of great importance in heavy metal availability and toxicity to plants. Mycorrhizae have also been reported to protect plants against toxic metals. We investigated the occurrence and infectivity of arbuscular mycorrhizal (AM) spores as affected by heavy metal levels and other soil properties in Norwegian soils collected from heavy metal polluted, high natural background and non-polluted areas. Spore numbers, mycorrhizal infectivity and spore germination of indigenous mycorrhizal fungi and of a reference strain (Glomus mosseae) in soils showed lower values in two soils with high metal concentrations and in one soil with a low pH. Mycorrhizal infectivity was negatively correlated with extractable metals. Spore number and mycorrhizal infectivity in a soil with naturally high heavy metal content were not different to in non-polluted soils, and indigenous AM fungi appeared more tolerant to metals than those in non-polluted soils. Mycorrhizal infectivity, expressed as MSI₅₀ values, was significantly correlated (r′=0.89, P< 0.05) with the percentage of germinating G. mosseae spores in the soils. However, the number of spores per volume of soil was not significantly correlated with infectivity or spore germination of the reference strain. The spore germination method is discussed as a bioassay of heavy metal toxicity in soil.     

Occurrence and distribution of chemical pollutants in Lake Mariut,Egypt

Occurrence and distribution of organochlorine pesticides in the water of Lake Mariut, a brackish coastal Egyptian lake suffering from pollution, and their accumulation in the common fish Tilapia were studied. The major pesticides detected in the lake water were lindane, p,p′-DDE, o,p′-DDT, and p,p′-DDT. These compounds, except o,p′-DDT, were detected in the fish samples in exceedingly higher concentrations compared with those found in the lake water.     

Occurrence and genesis of secondary magnesium-bearing calcites in soils

The presence of magnesium-bearing calcites is indicated in soil carbonate accumulation layers and concretions. A differential solubility method permitted estimation of the mol percent magnesium-carbonate content of calcites in the presence of dolomite. The relationship between diffraction spacings and mol percent MgCO₃, of selected samples is in good agreement with that depicted by other workers for biogenic magnesium-bearing calcites.Magnesium-containing calcites are concentrated in clay (< 2 μ) and fine silt (2–10 μ) sizes of Cca horizons. Their presence in the clay fraction of Ck horizons is an indication that carbonate mineralogy may change at profile depths often considered to be unaffected by pedogenic processes.The dissolution of existing carbonates within solum horizons, the translocation of ions in solution and the reprecipitation of calcite in Cca and underlying horizons are the main processes applicable to a variety of different natural situations. The Mg level of the secondary calcites is likely regulated by the partitioning effect during their precipitation. Periodic moisture movement to greater depths and lateral movement of soil solutions serve as a regulating factor in maintaining soluble Mg at levels favorable to the precipitation of low-magnesium calcites in upland chernozemic soils of central Saskatchewan; higher magnesium contents occur in calcites occurring in subsoils underlying solonetzic and depressional chernozemic soils of the same area. Formation of magnesium-bearing calcites within concretions in soils of the Rusizi basin in Africa were likely influenced by Mg-rich ground waters; associated dolomite may also have been of a secondary nature.     

Growth of accidental vegetation on desert soils in SW Egypt

In SW Egypt accidental vegetation is the only type of precipitation dependent vegetation in the area with (1−) 5 (−10) mm/yr rainfall, whereas permanent (contracted) vegetation needs at least ca. 10 mm/yr, and the area with 1 mm/yr shows only groundwater dependent vegetation. Since no correct data exist, calculations were made on the possible water consumption based (a) on phytomass estimation, (b) on experiments with artificial rainstorms (BLUME et al. 1985) with the result of a local minimum requirement of ca. 100 mm. The role of the accidental vegetation as the typical vegetation of extreme desert is discussed, which grows below the extrapolated zero-yield intercept of ca. 20 mm/yr.     

Placement effects of organic sources on nitrogenase activity and nitrogen-fixing bacteria in flooded rice soils

The placement effects of organic sources (cellulose and rice straw) at different depths on nitrogenase activity (acetylene reduction assay, ARA) associated with four tropical rice soils were investigated. Results showed that placement of organic sources in the top profile (1–2 cm) produced a higher nitrogenase activity; while placement in the 2–4 cm and 4–6cm profiles significantly decreased the activity irrespective of soil type. The effect of organic sources on nitrogenase varied depending on the soil type. Cellulose and rice straw caused differential stimulation in response to the placement. Evidence was provided for the creation of favourable redox potential supporting higher nitrogenase activity in series receiving organic amendments in the top profile. Higher nitrogenase activity in the top profile was associated with greater populations of nitrogen-fixing Azospirillum sp., anaerobic nitrogen fixers and Azotobacter sp. Moreover, the lower amounts of reducing sugars and higher carbon dioxide evolution gave evidence of higher microbial activity in the top profile. These results clearly indicate the positive relationship between nitrogenase activity, nitrogen-fixing populations and redox status in the top layers of flooded tropical rice soils. Received: 5 June 1996     

Daily dynamics of the number and activity of nitrogen-fixing bacteria in fallow and intensely cultivated soils

The daily dynamics (during 33 days) of the number (colony-forming units (CFU)) of nitrogen-fixing bacteria and of the nitrogen-fixing activity (the acetylene method) were determined in a gray forest soil under a fallow land and under an intensely cultivated field. The daily dynamics of the CFUs determined on the nitrogen-free medium in the samples from both plots had wavelike patterns. The daily values of the actual and potential activities of nitrogen fixation in the samples from the fallow land plot and of the actual activity of nitrogen fixation in the samples from the intensely cultivated soil were low and close to the detection limit. The potential activity of nitrogen fixation in the intensely cultivated soil was significant and also had a wavelike pattern. The harmonic analysis of the daily dynamics of the CFUs and nitrogen fixation showed the statistically significant harmonics of these biological characteristics pointing to the objective and regular character of the wavelike dynamics. The revealed dynamics of the biological characteristics of the soils and the methods of their analysis are important in terms of the comparative study of the biological properties of different soils.     

Imogolite in some ando soils

It was reported in a preceding paper⁷⁾ that the Ando soils from Uemura, Choyo, and Kawanishi contained an unknown mineral colloid which was distinctly different in some respects from coexisting allophane. In the Uemura soil, this clay fraction made up more than 20 per cent of the total clay and more than 6 per cent of the soil⁷⁾.     

Anaerobic nitrogen-fixing bacteria in U.S.S.R. soils

An account is given of a study of the size and diversity of populations of Clostridium pasteurianum and C. acetobutylicum in representative soils sampled at various latitudes and altitudes within the U.S.S.R. Evidence is presented to show that the two species are well adapted to soil and climatic factors in terms of the relative dominance of the two species and in terms of differences in their growth-temperature characteristics, carbohydrate utilization and fermentation products, nitrogen fixation and the comparative chemistry of their cells. In all of these characteristics, C. pasteurianum was more variable than C. acetobutylicum.     

Urea transformation in some tropical soils

The effects of incubation at 20°, 30° and 40°C and urea concentrations of 0, 50, 100 and 200 μg N/g soil on urea hydrolysis and nitrification were investigated in three Nigerian soils. At constant temperature urea hydrolysis and rate of NO₃^? accumulation increased with increasing rate of urea addition. Urea was rapidly hydrolyzed within 1 week of incubation. Nitrification in Apomu soil increased with increasing incubation temperature. Nitrification was slow in acid Nkpologu soil (pH 4.7). Texture, cation exchange capacity and C:N ratios of the soils were not related to urea hydrolysis or nitrification. Nitrite accumulation in these soils was insignificant. Soil pH was decreased by nitrification of hydrolyzed urea-N.     

Saccharides in some Japanese paddy soils

Monosaccharides released by acid hydrolysis from paddy field soil, from the light and the heavy fraction of soil, front some plant fragment were determined using automated anio-exchange chromatography.

Between 5 and 12 per cent of the organic carbon was present as saccharides.

The monosaccharide composition of the different soils was very similar, in spite of differences in the absolute amount of saccharides present. The amount of the various monosaccharide in the whole soil was found to be in the order glucose»xylose galactose, mannose, arabinose rhamnose ribose.

The monoccharide composition of the soils showed a marked contrast to that of the rice ra8ment, and partially decomposed plant remains taken from the soil. Glucose, xylose, arabi-the predominant saccharides in the rice fragments and the plant remains, while the amounts of galactose, mannose, rhamnose were negligibly small.

It was found that the proportion of galactose, mannose, rhamnose and ribose in the heavy fraction Of soil was greater than that of glucose, xylose, and arabinose

The present observation was in agreement with the view that soil sauharides comprised Pentoses originates in plant materials.

The molar ratio of xylose to mannose was calculated to show the characteristics of the mono-saccharide composition of soils and some plant muerials.     

Fixed ammonium in some Bangladesh soils

Nitrogen is the most deficient element and the most limiting factor for crop production in Bangladesh. The total N content in Bangladesh soils ranges between 0.02 and 0.12% (Ahsan and Karim 1988). The low N content indicates the presence of a small organic N pool and suggests that inorganic N plays an important role as a N source for crops. Contribution of “fixed” or “nonexchangeable” NH₄ ⁺ to the N economy of soil has been reported for many tropical soils (Rodrigues 1954; Moore and Ayeke 1965; Dalal 1977; Sahrawat 1995). However, there are few reports on fixed NH₄ ⁺ status in Bangladesh. In the present study, therefore, attempts were made to collect data on fixed NH₄ ⁺ of some major soil series from the important physiographic units of Bangladesh.     

Phosphate fractions in some tanzania soils

Inorganic-P fractions were determined in 17 soil profiles from eight soil orders widely occurring in Tanzania. Most of the inorganic-P fractions decreased with depth. Where soils were young, or calcareous, or the parent material rich in phosphorus-bearing minerals, Ca-P was the dominant inorganic-phosphorus fraction. Where the soils were highly weathered, Al-P and Fe-P were the dominant fractions.     

Elevated enzyme activities in soils under the invasive nitrogen-fixing tree Falcataria moluccana

Like other N-fixing invasive species in Hawaii, Falcataria moluccana dramatically alters forest structure, litterfall quality and quantity, and nutrient dynamics. We hypothesized that these biogeochemical changes would also affect the soil microbial community and the extracellular enzymes responsible for carbon and nutrient mineralization. Across three sites differing in substrate texture and age (50-300 years old), we measured soil enzyme activities and microbial community parameters in native-dominated and Falcataria-invaded plots. Falcataria invasion increased acid phosphatase (AP) activities to >90 μmol g⁻¹ soil h⁻¹ compared to 30-60 μmol g⁻¹ soil h⁻¹ in native-dominated stands. Extracellular enzymes that mineralize carbon and nitrogen also increased significantly under Falcataria on the younger substrates. By contrast, total microbial biomass and mycorrhizal abundance changed little with invasion or substrate. However, fungal:bacterial ratios declined dramatically with invasion, from 2.69 and 1.35 to <0.89 on the 50- and 200-year-old substrates, respectively. These results suggest that Falcataria invasion alters the composition and function of belowground soil communities in addition to forest structure and biogeochemistry. The increased activities of AP and other enzymes that we observed are consistent with a shift toward phosphorus limitation and rapid microbial processing of litterfall C and N following Falcataria invasion.     

Urease activity in some Trinidad soils

The effects of urea concentration, soil moisture content, period of storage of soil samples, temperature and toluene on the urease activity of fifteen Trinidad soils were investigated. From the multiple regression analysis of clay content, organic carbon, CEC and amorphous Fe and Al and the urease activity of the soils, it was found that the urease activity in the presence of toluene was largely associated with the clay-organic matter complex whereas in the absence of toluene it was associated with the organic matter of the soils.