U.S. market basket study to determine residues of the insecticide chlorpyrifos.

A market basket study was conducted to measure residues of the insecticide chlorpyrifos in samples of apples, applesauce, apple juice, fresh orange juice, tomatoes, peanut butter, whole milk, ground beef, and pork sausage collected during a 12-month period from 200 grocery stores across the United States. Approximately 90% of the samples contained no detectable levels of chlorpyrifos, and all residues detected were below tolerances, the legal limits for the United States. No values greater than the limit of quantitation (LOQ) were found in applesauce (LOQ = 0.008 ppm), apple juice (LOQ = 0.003 ppm), whole milk (LOQ = 0.006 ppm), ground beef (LOQ = 0.005 ppm), or pork sausage (LOQ = 0.007 ppm) samples. Only one fresh orange juice sample contained residues greater than the LOQ at 0.015 ppm. Only about 20% of the apples (maximum = 0.052 ppm), 20% of the tomato samples (maximum = 0.058 ppm), and 50% of the peanut butter samples (maximum = 0.021 ppm) contained quantifiable residues.     

A comparison of nutrient losses following grassland improvement using two different techniques in an upland area of mid-Wales

Abstract. Water samples from ditches draining small upland areas in mid-Wales were collected before, during and after the improvement of the pasture using two different cultivation techniques. The samples were analysed for nitrogen, phosphorus, potassium and pH. The greatest release was associated with disc harrowing where nitrogen, in its nitrate form, exceeded European Economic Community maximum recommended concentrations for potable water supply for two weeks. Smaller losses of nitrogen, in the ammonium form, and of ortho-phosphate were observed following a minimum cultivation technique. It is concluded that, on a scale normally associated with upland Britain, pasture improvement is not likely to deteriorate significantly the quality of runoff within water supply catchments. This is confirmed by the results obtained from monitoring streamflow from catchments in which some degree of pasture improvement had been undertaken in the past.     

南亚热带丘陵土壤水分循环及其有效性研究

根据对丘陵缓坡地和低丘梯地的系统观测资料 ,阐明了赤红壤贮水库容、有效贮水库容较小 ,而通透库容较大 ;降雨集中 ,地表径流明显 ;赤红壤贮水量季节性变化明显 ,有效贮水量低等特征 ;同时对SPAC连续体系中的水分势能和水流阻力的分布规律进行了分析 .     

Effects of heavy metals on the structure and functioning of detritivore communities in a contaminated floodplain area

The aim of this study was to determine the effects of heavy metal pollution on the structure and functioning of detritivore soil communities that consist of isopods, millipedes and earthworms, in 15 heavily polluted flood plain soils, located in the delta area of the rivers Rhine and Meuse, in the Netherlands. The 15 study sites represent a gradient in Zn, Cu and Cd concentrations. The structural attributes of the detritivore community, which were assessed, were the species richness and densities in the field sites. The functioning of the detritivore community was studied by determining organic matter decomposition using litter bags and feeding activity with the bait-lamina method. Concentrations of Cd, Cu and Zn were measured in soil, pore water and 0.01 M CaCl₂ extracts of the soil, in adult earthworms and plant leaves. Results show that metal pollution is not a dominating factor determining the species richness and densities of the selected detritivore groups, although the biomass of the earthworm Lumbricus rubellus was positively and significantly correlated to Zn concentrations in pore water and 0.01 M CaCl₂ extracts. Litter decomposition was significantly and positively correlated to detritivore biomass and 0.01 M CaCl₂ extractable Cd concentrations in soil and negatively to pH-CaCl₂, although the range of pH values was very small. It can be concluded that in spite of high metal levels in the soil, bioavailable concentrations are too low to result in clear negative effects on the structure and functioning of detritivores in the Biesbosch, the Netherlands.     

A comparison of birds inhabiting pine plantation and indigenous forest patches in a tropical mountain area

Extensive changes in land use of afromontane woodlands are currently taking place, where indigenous forests are cleared for plantations of exotic conifers. The consequent impact on the avifauna was assessed in a mountain forest area in Kenya. The native bird fauna was severely depauperated where changes in forestry had taken place in terms of both number of species and densities. Forest specialist species fared worse than forest generalist species. Species with special habitat requirements were unaffected, probably because their habitat had not been changed. The results also suggest that pine plantations in Africa may extend the wintering range for some Palearctic migrant species.     

Nitrogen,a major limitation in the productivity of natural communities,crops and pastures in the pacific area

Various aspects of the nitrogen cycle are reviewed as a background for discussion of nitrogen balance and economy in plant communities. Even though fixation of atmospheric nitrogen generally exceeds losses of nitrogen from the biosphere it is pointed out that plants extract nitrogen from the soil faster than it can be mineralized from organic forms. This difference in rates leads to a nitrogen deficiency in plants, particularly in high yielding crop plants, and subsequently a protein deficiency in animals.Some facets of legume bacteriology are discussed also. In particular the introduction of legumes to new areas and the need for inoculation of seed with specific Rhizobium strains, importance of strain selection, testing and supply, legume inoculant quality and seed inoculation and pelleting.     

固、液态磷源在石灰性土壤中的移动性及其对土壤有效磷含量影响的研究

采用同心圆扩散法对固体和酸性液体磷肥在石灰性土壤中的移动性与有效性进行研究。结果表明,土壤Olsen-P含量随施肥点圈层由内向外层而递减,液肥处理的Olsen-P量在施肥点以外的3个土壤圈层中均高于固肥处理。固体肥料大部分停留在距施肥点0~7.5 mm圈层,占施磷总量的55%~70%;液体肥料虽在0~7.5 mm层的含量低于固体肥料(约占15%~40%),但在远离施肥点的后3个圈层(7.5~43 mm)中均高于固体肥料处理,其中7.5~13.5 mm最为明显(液肥占35%,固肥占20%)。3种施磷量在砂土、壤土及粘土上均表现出一致的变化规律。肥料对土壤pH值的影响仅限制在距施肥点最近的0~7.5 mm范围,该层的pH值显著低于后层。本研究说明在石灰性土壤中液体磷的移动性、有效性明显高于固体磷,但对土壤pH值无显著影响。     

Bacterial and archaeal communities in saline soils from a Los Negritos geothermal area in Mexico

In recent years, there has been a growing need to understand how salinity affects microbial communities in agricultural soils. Archaeal and bacterial community diversities and structures were investigated by high-throughput sequencing analysis of their 16S rRNA in two arable soils with low electrical conductivity(EC)(2.3 and 2.6 dS m^-1) and a saline soil(EC = 17.6 dS m^-1). The dominant bacterial phyla in the soils were Proteobacteria(relative abundance(RA) = 46.2%), followe...     

Increased N availability in grassland soils modifies their microbial communities and decreases the abundance of arbuscular mycorrhizal fungi

Two complementary studies were performed to examine (1) the effect of 18 years of nitrogen (N) fertilization, and (2) the effects of N fertilization during one growing season on soil microbial community composition and soil resource availability in a grassland ecosystem. N was added at three different rates: 0, 5.44, and 27.2 g N m⁻² y⁻¹. In both studies, Schizachyrium scoparium was the dominant plant species before N treatments were applied. Soil microbial communities from each experiment were characterized using fatty acid methyl ester (FAME) analysis. Discriminant analysis of the FAMEs separated the three N fertilizer treatments in both experiments, indicating shifts in the composition of the microbial communities. In general, plots that received N fertilizer at low or high application rates for 18 years showed increased proportions of bacterial FAMEs and decreased fungal FAMEs. In particular, control plots contained a significantly higher proportion of fungal FAMEs C18:1(cis9) and C18:2(cis9,12) and of the arbuscular mycorrhizal fungal (AMF) FAME, C16:1(cis11), than both of the N addition treatment plots. A significant negative effect of N fertilization on the AMF FAME, C16:1(cis11), was measured in the short-term experiment. Our results indicate that high rates of anthropogenic N deposition can lead to significant changes in the composition of soil microbial communities over short periods and can even disrupt the relationship between AMF and plants.     

Response of rhizosphere microbial communities to plant succession along a grassland chronosequence in a semiarid area

Journal of Soils and Sediments - Changes in microbial communities during natural succession in semiarid areas have been widely studied but their association with plant and soil properties remains...     

Belowground carbon allocation patterns in a dry Mediterranean ecosystem: A comparison of two models

Total belowground C allocation (TBCA) accounts for a large fraction of gross primary production, it may overtake aboveground net primary production, and contributes to the primary source of detrital C in the mineral soil. Here, we measure soil respiration, water erosion, litterfall and estimate annual changes in C stored in mineral soil, litter and roots, in three representative land uses in a Mediterranean ecosystem (late-successional forest, abandoned agricultural field, rain-fed olive grove), and use two C balance approaches (steady-state and non-steady-state) to estimate TBCA. Both TBCA approaches are compared to assess how different C fluxes (outputs and inputs) affect our estimates of TBCA within each land use. In addition, annual net primary productivity is determined and C allocation patterns are examined for each land use. We hypothesized that changes in C stored in mineral soil, litter and roots will be slight compared to soil respiration, but will still have a significant effect on the estimates of TBCA. Annual net primary productivity was 648 ± 31.5, 541 ± 42.3 and 324 ± 22.3 g C m⁻² yr⁻¹ for forest, abandoned agricultural field and olive grove, respectively. Across land uses, more than 60% of the C was allocated belowground. Soil respiration (F_S) was the largest component in the TBCA approaches across all land uses. Annual C losses through water erosion were negligible compared to F_S (less than 1%) and had little effect on the estimates of TBCA. Annual changes in C stored in the soil, litter layer and roots were low compared to F_S (16, 24 and 10% for forest, abandoned agricultural field and olive grove, respectively), but had a significant effect on the estimates of TBCA. In our sites, an assumption that Δ[C_S + C_R + C_L]/Δt = 0 will underestimate TBCA, particularly in the abandoned agricultural field, where soil C storage may be increasing more rapidly. Therefore, the steady-state model is unsuited to these Mediterranean ecosystems and the full model is recommended.     

Negative and positive effects of topsoil biological crusts on water availability along a rainfall gradient in a sandy arid area

Drylands are regarded as highly sensitive to climatic changes. A positive relationship between rainfall and environmental factors (water availability for plants, productivity, species diversity, etc.) is often assumed for areas with an annual rainfall of 100–300 mm. This assumption disregards the fact that a climatic change in arid and semi-arid areas is not limited to climatic factors. This change is often accompanied by a parallel change in surface properties. The alteration of surface properties may have opposite effects on the water regime and ecosystem characteristics. Data on rainfall, runoff, soil moisture regime, and vegetation cover were collected at five monitoring sites in a sandy area along the Israeli–Egyptian border, where average annual rainfall varies from 86 to 160 mm. Data obtained show a decrease in water availability for perennial plants with increasing annual rainfall, clearly expressed by a lower survival of perennial plants in the wetter area. Results obtained cast doubt of the prevailing idea regarding the positive relationship between average annual rainfall and ecosystem characteristics. The findings are attributed to the decisive role played by the non-uniform properties of the topsoil biological crusts along the rainfall gradient considered. Under wetter conditions a thick topsoil biological crust develops. This crust is able to absorb large rain amounts, limiting thus the depth of rainwater infiltration and water availability for the perennial vegetation. A better water regime was found in the drier area, where a thin crust allows deeper water infiltration and water concentration by surface runoff. The process described may be regarded as a desertification process with increasing annual rainfall.     

Effects of modified Pb-, Zn-, and Cd- availability on the microbial communities and on the degradation of isoproturon in a heavy metal contaminated soil

The effects of modified heavy metal (HM) availability on the microbial community structure and on the microbe-mediated degradation of herbicide isoproturon (IPU) were evaluated in soil with a long-term HM contamination. The fate of ¹⁴C-ring labelled IPU was investigated for over 60 days under controlled microcosm conditions. Phosphate mineral apatite and a water solution of Pb, Zn, and Cd salts were previously homogeneously mixed into the soil material to reduce and to increase the proportion of bioavailable HM, respectively. The availability of Pb, Zn, and Cd was determined by HM fractionation and plant uptake 110 days after the addition of amendments, shortly before IPU addition. Apatite treatment reduced the availability of HM, but did not affect the microbial biomass and the microbial community structure on the genotype level (total soil DNA-RAPD). However, it changed the microbial community structure on the phenotype level, based on the composition of phospholipid fatty acids (PLFA) at the end of the degradation experiment. The degradation of IPU did not change. In contrast to apatite treatment, HM supplementation increased the bioavailability of Pb, Zn and Cd, which resulted in biomass reduction and changes of microbial community structure on the genotypic (total soil DNA-RAPD) and phenotypic (PLFA) level. Increased bioavailability of HM also significantly reduced the rate of IPU degradation and mineralisation. The total mineralisation over a period of 60 days decreased from 12 to 5% of initial ¹⁴C. Increased HM bioavailability did not influence the degradation pathways and kinetics of IPU.     

A comparison of two methods for the estimation of mycelial biomass in leaf litter

The agar-film technique (AF) and hexosamine assay (HA) were compared as methods for measuring the biomass of fungal mycelium in plant litter by application to the growth of Mycena galopus in sterilised leaves of Fraxinus and Betula. The data were statistically analysed and the precision, sources of variation, efficiency (man-hr), sensitivity and potential accuracy compared. Satisfactory precision (coefficient of variation < 10%) was obtainable by both methods, when the experimental design was optimum for minimum variance with an acceptable amount of labour. With procedures as described, HA was slower (× 2) and less sensitive, the minimum measurable biomass difference being 0.29 v. 0.14 mg g^?1 oven-dry weight, but the efficiency of both methods could be improved. The major sources of variation were the primary litter samples (flasks), the sampling error of AF (microscope fields) and the experimental error of HA (hydrolyses and cation-exchange columns). The biomass values were broadly realistic in terms of the yield efficiency of the fungus and nutrient immobilization (C, N, P, K), but were 2–3 times larger by HA than AF. The AF technique is recommended for mixed mycelia in plant litter, although it is likely to underestimate biomass; HA is probably more accurate, but is limited to monocultures. The accuracy of AF could be greatly increased by optimizing the maceration of litter. Particular importance is placed on the necessity of obtaining more accurate factors for converting the experimental data to biomass, i.e. moisture content (AF), relative density (AF) and hexosamine content (HA) of mycelium of varying age.     

Plant availability of two phosphate rock materials in acid Malaysian soils

Abstract

The amount of phosphorus (P) dissolved in a closed‐incubation system, in soils receiving Christmas Island grade‐A phosphate rock (CIPR), Gafsa phosphate rock (GPR), and triple superphosphate (TSP), as measured by extraction with 0.5M NaHCO₃ (APb) or 0.5M NaOH (AP) and expressed as ?Pb/?P*100 (PDP) was compared to P uptake (?Ps) by Setaria in a glasshouse experiment. There was no direct relationship between APs and PDP for CIPR, GPR, and TSP added at 50 and 150 mgP/kg soil to three Malaysian soils (Bungor, Kundor, and Segamat) during a 10‐month period. Averaged across soils, rate of addition, and P sources, ?Ps was 17% higher than PDP. Overestimation of PDP by ?Ps could be due to the ability of the roots of Setaria to use more of the P which is dissolved from the three P sources and then chemisorbed, than can be extracted by the NaHCO₃ reagent. The chemisorbed P pool is extractable using 0.5M NaOH. There was a close relationship between ?Ps and ?P, with a correlation coefficient of 0.85**. Residual P, determined by Pb method after each harvest, successfully predicted Ps by Setaria in the subsequent harvest with correlation coefficients varying between 0.74* and 0.99** for CIPR, GPR, and TSP in five soils (Bungor, Durian, Kundor, Segamat, and Tok Yong). The critical Pb values ranged from 5 for Durian to 10 mgP/kg soil for Kundor.     

Sulfuric acid effects on iron and phosphorus availability in two calcareous soils

An attempt was made to study the effects of sulfuric acid additions to iron (Fe)‐ and phosphorus (P)‐deficient calcareous soils. Several greenhouse experiments were conducted with sorghum (Sorghum bicolor L.) grown in two calcareous soils. Addition of sulfuric acid to soils increased soil acidity, salinity, DTPA‐extractable Fe, available P (NaHCO₃‐extractable), and crop yield. The change in soil pH is the primary cause of increased nutrient availability and thus crop yield. Leaching after acid application is highly beneficial in decreasing salinity during germination and seedling stages and therefore has a direct impact on the yield. The beneficial effects of acid carried over for at least two greenhouse cropping seasons (approximately 4.5 months).