Nitrogen balance and accumulation pattern in three contrasting prairie soils receiving repeated applications of liquid swine and solid cattle manure

The expansion of intensive livestock operations in western Canada has increased concerns about overloading of nutrients in manured lands. The magnitude of nutrient accumulation and its distribution in the soil profile varies with soil-climatic conditions. The objective of this study was to determine loading and distribution of manure-derived nitrogen (N) in the soil profile as influenced by repeated manure applications. Four field experiments were conducted at three sites (Dixon, Melfort and Plenty) in Saskatchewan under longer-term manure management. The four field experiments provide contrasts in soil type, climatic conditions, manure type, application and cropping history to enable the effect of these factors to be evaluated. Liquid hog manure (LHM—Experiment 1) and solid cattle manure (SCM—Experiment 2) treatments were applied annually over 8 years at Dixon (Black Chernozemic loam soil—Udic Boroll in sub-humid climate), while only LHM was applied at Plenty (Dark Brown Chernozemic heavy clay soil—Typic Boroll in semi-arid climate) over 6 years (Experiment 3), and at Melfort (Dark Gray Luvisol silty clay loam soil—Mollic Cryoboralf in humid climate) over 5 years (Experiment 4). Soil samples were collected in the spring and autumn of 2003 and 2004, and were analyzed for organic N, ammonium-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) concentrations. Plant samples were collected to determine the impact of manure application rate on plant N uptake and crop N removal. The annual application of LHM (37,000 L ha⁻¹ yr⁻¹) and SCM (7.6 Mg ha⁻¹ yr⁻¹) at agronomic rates at Dixon (added N balances crop demand for that year), or larger rates of LHM (111,000 L ha⁻¹) applied once every 3 years (Melfort) did not significantly elevate NO₃⁻-N in soil compared to the unfertilized control. Lower crop removal and reduced leaching of NO₃⁻-N due to drier conditions as occurred at the Plenty site contributed to greater accumulation of nitrate in the top 60 cm at equivalent rates compared to the other two sites. At large manure rates, excess N from the balance estimates could not be accounted for in soil organic N and was assumed to be lost from the soil-plant system. At the Dixon LHM site, deep leaching of NO₃⁻-N was observed at the excessive rate (148,000 L ha⁻¹ yr⁻¹) up to the 150 cm depth, compared to the control. At Dixon, the large annual application rate of SCM (30.4 Mg ha⁻¹ yr⁻¹) did not significantly increase NO₃⁻-N in the 0–60 cm soil compared to the control, which was attributed to lower mineralization of organic N from the SCM. Over the short and medium term, LHM application at large rates every year poses a greater risk for loading and deep migration of NO₃⁻-N in soil than large rates of SCM. Larger single applications made once every 3 years were not associated with accumulation or deep leaching. To prevent loading, rates of applied manure nitrogen should be reduced when crop N removal potential is diminished by high frequency of drought.     

Synthesis of β-bromoethoxylates and β-chloroethoxylates from olefinic fatty methyl esters

Olefinic fatty methyl esters [undec-10-enoate (1), octadec-Z-9-enoate (2), methyl-12 hydroxy octadec-Z-9-enoate (3)], on reaction with an N-halosuccinimide (4–5)—i.e., N-bromosuccinimide (NBS; 4) or N-chlorosuccinimide (NCS; 5)—in the presence of diols such as mono-, di-, tri-, and tetraethylene glycols (6–9), gave the respective β-bromo- or β-chloroethoxylates (11–34).     

Analysis and calculation of the electric drive for the extruder in a controllable electrical complex for production of synthetic yarns

The conditions that function W_e(z), which ensures the minimum acceptable time of the switching process, must satisfy can be formulated as follows: — function W_e(z) should have nulls equal to the poles of W_n(z) positioned in the unit circle or outside of plane z; — function W(z) or 1 — W_e(z) should have all nulls of W_n(z) located in the unit circle or outside of plane z as nulls; — function W(z) or 1 — W_e(z) should contain z⁻¹ as cofactor z⁻¹. If W_n(z) is an unstable unit impulse response, then F(z) should contain all poles of W_n(z) lying in the unit circle or outside of plane z as nulls (with the exception of the poles for z = 1). If W_n(z) has nulls located in or outside of the unit circle, these nulls must be nulls of W(z) = 1 − (1 − z⁻¹). In these two cases, the briefest time of the switching process will exceed the value which can be obtained for a system with a stable unit impulse response W_n(z) which has no nulls in or outside of the unit circle of plane z. __________ Translated from Khimicheskie Volokna, No. 56–59, March–April, 2008.     

Chemical bonds in carbon fibres

In reporting the results of an examination of the mechanism of formation of chemical bonds in carbon fibres, the following conclusions can be drawn: — the existing concepts concerning curved hybrid bonds and σ-, π-bonds do not explain their compatibility with the high thermal stability of carbon fibres; — the concept of formation of chemical bonds in carbon fibres because of the gravitational effect of atoms with energy corresponding to the energy of chemical bond formation due to the high value of the gravitational constant of 1.6·10⁻²⁸ cm³/g·sec²) caused by the high density of the substance in the atom of 10¹²–10¹³g/cm³, is substantiated; — the gravitational constant is calculated with the equation of the dynamics of orbital motion for the potential energy; the values obtained are in satisfactory agreement with the results of the calculation based on tensiometric and spectroscopic data. __________ Translated from Khimicheskie Volokna, No. 6, pp. 41–44, November–December, 2006.     

Soft magnetic properties of Ni–Cr and Co–Cr alloy thin films electrodeposited from aqueous solutions containing trivalent chromium ions and glycine

Ferromagnetic Ni–Cr and Co–Cr alloy thin films were electrodeposited from aqueous solution containing trivalent chromium (Cr³⁺) ions and glycine. According to the Tafel slopes obtained from the cathode polarization curves for Ni–Cr and Co–Cr alloy deposition, it was estimated that Cr³⁺ ions inhibited Ni²⁺ and Co²⁺ ions from electrodepositing. Ni and Co preferentially electrodeposited rather than Cr and the electrodeposition process of Ni–Cr and Co–Cr was categorized to “normal co-deposition type.” At the cathode potential of −1.8 V versus Ag/AgCl/KCl sat., Ni—9.5 %Cr and Co—8.4 %Cr alloy deposits were obtained. X-ray diffraction patterns of the electrodeposits revealed that pure Ni and pure Co consist of large crystal grains, while Ni—9.5 %Cr and Co—8.4 %Cr alloys were composed of a solid solution phase with fine crystal grains. Magnetization of Ni—9.5 %Cr and Co—8.4 %Cr alloy thin films with fine crystalline phase reached to saturation at ca. 2.5 kOe in perpendicular direction to the film plane, while pure Ni and pure Co thin film with large crystal grains were hardly magnetized in the perpendicular direction. Soft magnetic properties were improved with increasing Cr content in the deposits.     

Soil organic carbon fractions after 16-years of applications of fertilizers and organic manure in a Typic Rhodalfs in semi-arid tropics

Agricultural soils can act as a potential sink of the increased carbon dioxide in the atmosphere if managed properly by application of organic manures and balanced fertilizers. However, the rate of carbon (C) sequestration in soils is low in warm climates and thus the short term changes in soil organic carbon (SOC) contents are almost negligible. Therefore, the knowledge about other C fractions that are more sensitive or responsive and indicative of the early changes in SOC can help to determine the effect of the management practices on soil C sequestration. The objective of this study was to determine the soil C sequestration after 16-years of applications of chemical fertilizers and farmyard manure (FYM) to rice (Oryza sativa)—cowpea (Vigna unguiculata) rotation system in a sandy loam soil (Typic Rhodalfs). The treatments were—(1) one control (no fertilizer or FYM); (2) three chemical fertilizer treatments [100 kg N ha⁻¹ (N), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ (NP), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ + 50 kg K₂O ha⁻¹ (NPK)]; (3) one integrated treatment [(50 kg N ha⁻¹ + 25 kg P₂O₅ ha⁻¹ + 25 K₂O ha⁻¹) + (50 kg N ha⁻¹ from FYM)]; and (4) one organic treatment at10 Mg ha⁻¹ FYM. Compared to the control treatment, the increase in SOC was 36, 33, and 19% greater in organic, integrated, and NPK treatments. The 16-years application of fertilizers and/or FYM resulted in much greater changes in water soluble C (WSC), microbial biomass C (MBC), light fraction of C (LFC), and particulate organic matter (POM) than SOC. Of the SOC, the proportion of POM was highest (24–35%), which was followed by LFC (12–14%), MBC (4.6–6.6%), and WSC (0.6–0.8%). The application of fertilizers and/or FYM increased the mean weight diameter of soil aggregates; thus provided physical protection to SOC from decomposition. Our results suggests that the application of fertilizers and/or FYM helps to sequester C in the soil and that the labile fractions of C can be used as indicators to determine the amount of C sequestered as a result of different management practices.     

Kinetic Study of the Prooxidant Effect of α-Tocopherol. Hydrogen Abstraction from Lipids by α-Tocopheroxyl Radical

A kinetic study of the prooxidant effect of α-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by α-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k _p) obtained are <1 × 10⁻² M⁻¹ s⁻¹ for 1, 1.90 × 10⁻² M⁻¹ s⁻¹ for 2, 8.33 × 10⁻² M⁻¹ s⁻¹ for 3, 1.92 × 10⁻¹ M⁻¹ s⁻¹ for 4, and 2.43 × 10⁻¹ M⁻¹ s⁻¹ for 5 at 25.0 °C. Fatty acid esters 3, 4, and 5 contain two, four, and six –CH₂– hydrogen atoms activated by two π-electron systems (–C=C–CH₂–C=C–). On the other hand, fatty acid ester 2 has four –CH₂– hydrogen atoms activated by a single π-electron system (–CH₂–C=C–CH₂–). Thus, the rate constants, k _abstr/H, given on an available hydrogen basis are k _p/4 = 4.75 × 10⁻³ M⁻¹ s⁻¹ for 2, k _p/2 = 4.16 × 10⁻² M⁻¹ s⁻¹ for 3, k _p/4 = 4.79 × 10⁻² M⁻¹ s⁻¹ for 4, and k _p/6 = 4.05 × 10⁻² M⁻¹ s⁻¹ for 5. The k _abstr/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction.     

Electrocombustion of humic acid and removal of algae from aqueous solutions

This paper reports experiments involving the electrochemical combustion of humic acid (HA) and removal of algae from pond water. An electrochemical flow reactor with a boron-doped diamond film anode was used and constant current experiments were conducted in batch recirculation mode. The mass transfer characteristics of the electrochemical device were determined by voltammetric experiments in the potential region of water stability, followed by a controlled current experiment in the potential region of oxygen evolution. The average mass transfer coefficient was 5.2 × 10⁻⁵ m s⁻¹. The pond water was then processed to remove HA and algae in the conditions in which the reaction combustion occurred under mass transfer control. To this end, the mass transfer coefficient was used to estimate the initial limiting current density applied in the electrolytic experiments. As expected, all the parameters analyzed here—solution absorbance at 270 nm, total phenol concentration and total organic carbon concentration—decayed according to first-order kinetics. Since the diamond film anode successfully incinerated organic matter, the electrochemical system proved to be predictable and programmable.     

Soil nitrogen conservation with continuous no-till management

Tillage management is an important regulator of organic matter decomposition and N mineralization in agroecosystems. Tillage has resulted in the loss of considerable organic N from surface soils. There is potential to rebuild and conserve substantial amounts of soil N where no-till management is implemented in crop production systems. The objectives of our research were to measure N conservation rate with continuous no-till management of grain cropping systems and evaluate its impact on mineralizable and inorganic soil N. Samples were collected from 63 sites in production fields using a rotation of corn (Zea mays L.)—wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.)—double-crop soybean (Glysine max L.) across three soil series [Bojac (Coarse-loamy, mixed, semiactive, thermic Typic Hapludults), Altavista (Fine-loamy, mixed semiactive, thermic Aquic Hapludults), and Kempsville (Fine-loamy, siliceous, subactive, thermic Typic Hapludults)] with a history of continuous no-till that ranged from 0 to 14 yrs. Thirty-two of the sites had a history of biosolids application. Soil cores were collected at each site from 0–2.5, 2.5–7.5 and 7.5–15 cm and analyzed for total N, Illinois soil N test-N (ISNT-N), and [NH₄ + NO₃]-N. A history of biosolids application increased the concentration of total soil N by 154 ± 66.8 mg N kg⁻¹ (310 ± 140 kg N ha⁻¹) but did not increase ISNT-N in the surface 0 – 15 cm. Continuous no-till increased the concentration of total soil N by 9.98 mg N kg⁻¹ year⁻¹ (22.2 ± 21.2 kg N ha⁻¹ year⁻¹) and ISNT-N by 1.68 mg N kg⁻¹ year⁻¹ in the surface 0–15 cm. The implementation of continuous no-till management in this cropping system has resulted in conservation of soil N.

Synthesis and characterization of poly(aryl ether ketone)s with fluorinated phenyl in the side chain

New bisphenol monomers, (4-fluorophenyl)hydroquinone (3b) and (3,4-difluoro phenyl)hydroquinone (3c), were synthesized in a two-step synthesis. Poly(aryl ether ketone)s (PAEKs) (4a–c) were derived from these fluorinated bisphenols and nonfluorinated bisphenol—phenylhydroquinone (3a) with 4,4′-diflourobenzophenone via a nucleophilic aromatic substitution polycondensation. The obtained polymers had inherent viscosities of 0.50–0.92 dL/g. Thermal analysis showed that the obtained PAEKs had excellent thermal properties, the glass transition temperatures ranged from 148 to 160 °C, and the temperatures at 5% weight loss (Td₅) were above 527 °C and the temperatures at 10% weight loss (Td₁₀) were above 544 °C in nitrogen. All the polymers showed excellent solubility and could dissolve in common organic solvents, such as DMSO, NMP, DMF, etc. So the films of them were easily cast from their solutions, which possessed good mechanical properties, with tensile strengths of 95.2–104.0 MPa, Young’s moduli of 2.68–3.06 GPa, and elongation at break of 15–32%. Furthermore, the prepared PAEKs displayed low dielectric constants (2.75–2.95 at 1 MHz) and hydrophobic character (contact angles for water: 83.9^o–98.4^o).     

β-Oxidation of 18∶3n−3 in atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) hepatocytes treated with different fatty acids

To study whether Atlantic salmon β-oxidation was affected by dietary FA composition, an in vitro study with primary hepatocytes was undertaken. Isolated hepatocyte cultures were stimulated with either 16∶0, 18∶1n−9, 18∶2n−6, 18∶3n−3, 20∶5n−3, or 22∶6n−3 in triplicate for 24 h. In addition, a control was included where no FA stimulation was performed, also in triplicate. After stimulation, radiolabeled [1-¹⁴C]18∶3n−3 was added and the cells were incubated for 2 h at 20°C. The cells were then harvested, and radioactivity was determined in the acid-soluble part of the cells and medium, i.e., the end products of the β-oxidation pathway. Specific β-oxidation activity was significantly higher in hepatocytes stimulated with 18∶3n−3. Further, when taking into account the amount of radiolabeled [1-¹⁴C]18∶3n−3 taken up by the cells—the relative amount of β-oxidized [1-¹⁴C]18∶3n−3 of the total FA taken up by the hepatocytes—no significant differences were found. Thus, the regulation of β-oxidation activity in the primary Atlantic salmon hepatocytes seems to be at the level of FA uptake and transport into the cell. This in vitro study shows that the catabolism processes in salmon hepatocytes are affected by the FA available and probably already regulated at the level of FA uptake.     

Active coating

Preventing the corrosion of metal substrates by applying an active coating was studied. The active coating was prepared by addition of metal powder and polyaniline in xylene solution. Trials were conducted by coating a blast-cleaned, mild steel round bar with a brush. The coating was dried in the air and the steel samples were immersed in water collected from the open sea. Open circuit potential of steel was measured with silver/silver chloride reference electrode. The potential in seawater was in the range of — 740mV to — 956mV, indicating complete protection of steel against corrosion. This potential meets the criteria for protection as per clause 5.4.1 of Det Norsk Veritas Recommended Practice RPB 401 (1993), page 8.¹ The active coating system can be used for protecting the steel against corrosion in marine and any other highly corrosive environment. Accelerated tests in accordance with ASTM D5894 — 96² with freeze cycle developed by U.S. Federal Highway Administration are planned.     

Segmented thin-gap flow cells for process intensification in electrosynthesis

Design calculations are presented for a single-pass high-conversion electrochemical reactor suitable for process intensification in electroorganic synthesis. The key feature of the design is the use of a segmented working electrode, combined with a small anode—cathode gap. Each working electrode segment is operated at an optimal local current density, defined with respect to the local diffusion—limited current density of the reacting species. Two reactor configurations are considered:(i) an adiabatic reactor, and (ii) an isothermal reactor with integrated heat exchange. Calculated results for the devices in a classical electroorganic synthesis system, the methoxylation of 4-methoxy-toluene, are presented and the general features and performance characteristics of the cell are compared with those of a more conventional capillary-gap cell, currently used industrially. For an electrode gap of 0.1 mm, the average current density attainable in the novel design is of the order of 2700 A m⁻² in the adiabatic reactor and of the order of 7100 A m⁻² in the isothermal reactor, respectively, 5 and 14 times higher than the current densities applied in the current industrial process. In addition to process intensification, other advantages of the proposed technology are the absence of reactant recycle, short residence times and plug flow of the reagents, all of which contribute to improved process selectivity.     

Sodium Lauryl Ether Sulfate Micellization and Water Solubility Enhancement Towards Naphthalene and Pyrene: Effect of the Degree of Ethoxylation

The effect of ethoxylation on self-aggregation behavior in aqueous media of sodium lauryl ether sulfate (SLES), C₁₂H₂₅ (OCH₂CH₂)_xOSO₃Na, where x = 1 (SLE1S), x = 2 (SLE2S), and x = (SLE3S) was investigated. CMCs were determined from the effect of surfactant concentration on (2,2′-bipyridine dichloro-ruthenium(II) hexahydrate (Ru(bipy)₃²⁺,2Cl⁻) fluorescence emission. Aggregation numbers and micelle concentrations were estimated from the fluorescent quenching of (Ru(bipy)₃²⁺,2Cl⁻) by 9-methylanthracene. Interestingly, critical micelle concentrations (0.80 mM), average aggregation numbers (N = 43), and micelle concentrations ([M] = 40 μM) were found to be independent of the degree of ethoxylation. Water solubilization enhancement of naphthalene and pyrene by SLES was also investigated. Water solubility enhancement for naphthalene and pyrene was observed with increasing degrees of ethoxylation and follow the order SLE3S > SLE2S > SLE1S. The higher impact of oxyethylene (OE) groups on solubilization enhancement of naphthalene over pyrene was taken as an indication for a preferential distribution of the relatively polar organic naphthalene molecule at the outer layer of the micelle in close contact with the hydrated oxyethylene units, thereby allowing for a strong polycyclic aromatic hydrocarbon (PAH)—micelle interaction. On the other hand, pyrene molecule is preferentially distributed in the core of the micelle, relatively far away from the OE units located at the micelle-water interface for PAH-micelle interaction to occur. Water solubility enhancement for both PAHs was also was associated with an increase in SLES micelle size with the degree of ethoxylation as well as to the accessibility of the locus solubilization for the solute.     

Rice yield,potassium uptake and apparent balance under long-term fertilization in rice-based cropping systems in southern China

Potassium (K) imbalances are of growing concern in southern China, where rice (Oryza sativa L.) is the primary food resource for a growing population. This study examined rice yield, K uptake and apparent balance under long-term fertilization in rice-based systems at four experimental sites, including both rice-rice as well as rice–wheat rotations. The experiments consist of four treatments: control (no fertilizer), nitrogen and phosphorus (NP), nitrogen, phosphorus and potassium (NPK), and NPK plus manure (NPKM). Across all sites, rice yields increased by 3–20% due to K fertilization (NPK vs. NP) and 4–20% due to manure application (NPKM vs. NPK). The mean internal K use efficiency (IE) was lower (32–56 kg kg⁻¹) in treatments receiving K (NPK and NPKM) than in those without K application (36–91 kg kg⁻¹—control and NP). Estimated from the logarithmic model, a total K uptake of 38–212 kg ha⁻¹ was needed to produce 3–7 Mg ha⁻¹ of rice grain. The annual apparent K balances were negative (17–245 kg ha⁻¹ year⁻¹), irrespective of mineral K application and site. But the negative K balance reduced by 27–88 kg ha⁻¹ year⁻¹ through application of mineral K in combination with manure. The higher negative apparent K balances under rice–wheat cropping system were related to the lower K application rate and the soils rich in K-bearing minerals, while the lower negative apparent K balances under rice–rice cropping system were related to the higher K application rate and the soils low in K-bearing minerals. We conclude that a re-adjustment of the current K application rate is needed to improve the long-term rice production in southern China.     

Anodic oxidation of organic pollutants on a Ti/SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> anode

A Ti/SnO₂–Sb₂O₄ electrode was prepared by alternate Sn and Sb electrodepositions using the thermo-electrochemical method. The chemical, electrochemical, and structural characterization of the electrode was performed and it was tested in the anodic oxidation of several pollutants, phenol, ibuprofen, acid orange 7 (AO7), and diclofenac, all in aqueous 0.035 M Na₂SO₄ solutions at current densities of 10 and 20 mA cm⁻². After the 24 h assay, removal of chemical oxygen demand, total organic carbon (TOC) and absorbance were very high, especially at the higher current density. TOC removals presented the lowest value. However, after 24 h at 20 mA cm⁻², TOC removals were: phenol—94%; ibuprofen—83%; AO7—88%; and diclofenac—73%. Combustion efficiency and instantaneous and mineralization current efficiencies were also determined.     

Design and performance evaluation of vacuum cleaners using cyclone technology

A cyclone technology for a vacuum cleaner—axial inlet flow cyclone and the tangential inlet flow cyclone — to collect dusts efficiently and reduce pressure drop has been studied experimentally. The optimal design factors such as dust collection efficiency, pressure drop, and cut-size being the particle size corresponding to the fractional collection efficiency of 50% were investigated. The particle cut-size decreases with reduced inlet area, body diameter, and vortex finder diameter of the cyclone. The tangential inlet twin-flow cyclone has good performance taking into account the low pressure drop of 350 mmAq and the cut-size of 1.5 μm in mass median diameter at the flow rate of 1 m³/min. A vacuum cleaner using tangential inlet twin-flow cyclone shows the potential to be an effective method for collecting dusts generated in the household.     

Crop response of aerobic rice and winter wheat to nitrogen,phosphorus and potassium in a double cropping system

In the aerobic rice system, adapted rice cultivars are grown in non-flooded moist soil. Aerobic rice may be suitable for double cropping with winter wheat in the Huai River Basin, northern China plain. Field experiments in 2005 and 2006 were conducted to study the response of aerobic rice and winter wheat to sequential rates of nitrogen (N), phosphorus (P) and potassium (K) in aerobic rice—winter wheat (AR-WW) and winter wheat—aerobic rice (WW-AR) cropping sequences. Fertilizer treatments consisted of a complete NPK dose, a PK dose (N omission), a NK dose (P omission), a NP dose (K omission), and a control with no fertilizer input. Grain yields of crops with a complete NPK dose ranged from 3.7 to 3.8 t ha⁻¹ and from 6.6 to 7.1 for aerobic rice’ and ‘winter wheat’, respectively. N omissions caused yield reductions ranging from 0.5 to 0.8 t ha⁻¹ and from 1.6 to 4.3 t ha⁻¹ for rice and wheat, respectively. A single omission of P or K did not reduce rice and wheat yields, but a cumulative omission of P or K in a double cropping system significantly reduced wheat yields by 1.2–1.6 t ha⁻¹. N, P and K uptake of both crops were significantly influenced by fertilizer applications and indigenous soil nutrient supply. Nutrient omissions in a preceding crop reduced plant N and K contents and uptake additionally to direct effects of the fertilizer treatments in wheat, but not in rice. Apparent nutrient recoveries (ANR) differed strongly between ‘aerobic rice’ and ‘winter wheat’; in rice: for N it ranged from 0.30 to 0.32, for P from 0.01 to 0.06, and for K from 0.03 to 0.19 and in wheat: for N from 0.49 to 0.71, for P from 0.09 to 0.15, and for K from 0.26 to 0.31. Further improvements of crop productivity as well as nutrient-use efficiencies, should be brought about by developing cropping systems, by an appropriate choice of adapted cultivars, by a site- and time-specific fertilizer management and by eliminating other yield-limiting factors. It is concluded that nutrient recommendations should not be based on the yield response of single crops only, but also on the after-effects on nutrient availability for succeeding crops. A whole cropping system approach is needed.     

Changes in Lipid Class and Fatty Acid Composition of Cultures of <Emphasis Type="Italic">Pavlova lutheri</Emphasis>, in Response to Light Intensity

Aquaculture is a growing commercial activity worldwide, which resorts more and more often to microalgae as feed; the lipid composition of such microalgae is a critical factor with regard to the fish growth rate upon ingestion. The aim of this work was thus to study the influence of light intensity on the lipid profile of a known microalga, Pavlova lutheri. Several semi-continuous cultures were carried out, and biochemical parameters such as lipid, protein, carbohydrate, and chlorophyll contents were quantified. Lipids were specifically fractionated into classes by TLC, and those in each class were subjected to GC afterwards in an attempt to ascertain their fatty acid profile. Evidence was consequently provided which showed that cultures grown under low light intensity (9 W m⁻²) possess a higher fraction of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids esterified in polar classes—which are those with a more favorable role in aquaculture. It was also demonstrated that intermediate levels of light intensity (19 W m⁻²) may be misleading in terms of favorable effects upon EPA and DHA contents—because there is an increase in their total yields and productivities, but they appear mostly esterified into triacylglycerols; this may be a favorable deed for production and purification, but is metabolically not so effective in aquaculture. The highest EPA and DHA productivities attained were 1.29 and 0.69 mg L⁻¹ day⁻¹, respectively, at intermediate levels of light intensity (19 W m⁻²).     

Fumigant and Contact Toxicities of Monoterpenes to <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> (L.) and <Emphasis Type="Italic">Tribolium castaneum</Emphasis> (Herbst) and their Inhibitory Effects on Acetylcholinesterase Activity

A comparative study was conducted to assess the contact and fumigant toxicities of eleven monoterpenes on two important stored products insects—, Sitophilus oryzae, the rice weevil, and Tribolium castaneum, the rust red flour beetle. The monoterpenes included: camphene, (+)-camphor, (−)-carvone, 1-8-cineole, cuminaldehyde, (l)-fenchone, geraniol, (−)-limonene, (−)-linalool, (−)-menthol, and myrcene. The inhibitory effect of these compounds on acetylcholinesterase (AChE) activity also was examined to explore their possible mode(s) of toxic action. Although most of the compounds were toxic to S. oryzae and T. castaneum, their toxicity varied with insect species and with the bioassay test. In contact toxicity assays, (−)-carvone, geraniol, and cuminaldehyde showed the highest toxicity against S. oryzae with LC₅₀ values of 28.17, 28.76, and 42.08 μg/cm², respectively. (−)-Carvone (LC₅₀ = 19.80 μg/cm²) was the most effective compound against T. castaneum, followed by cuminaldehyde (LC₅₀ = 32.59 μg/cm²). In contrast, camphene, (+)-camphor, 1-8-cineole, and myrcene had weak activity against both insects (i.e., LC₅₀ values above 500 μg/cm²). In fumigant toxicity assays, 1-8-cineole was the most effective against S. oryzae and T. castaneum (LC₅₀ = 14.19 and 17.16 mg/l, respectively). Structure-toxicity investigations revealed that (−)-carvone—, a ketone—, had the highest contact toxicity against the both insects. 1-8-Cineole—, an ether—, was the most potent fumigant against both insects. In vitro inhibition studies of AChE from adults of S. oryzae showed that cuminaldehyde most effectively inhibited enzyme activity at the two tested concentrations (0.01 and 0.05 M) followed by 1-8-cineole, (−)-limonene, and (l)-fenchone. 1-8-Cineole was the most potent inhibitor of AChE activity from T. castaneum larvae followed by (−)-carvone and (−)-limonene. The results of the present study indicate that (−)-carvone, 1,8-cineole, cuminaldehyde, (l)-fenchone, and (−)-limonene could be effective biocontrol agents against S. oryzae and T. castaneum.