Impact of soil fumigation practices on soil nematodes and microbial biomass

This study was designed to understand the impact of methyl bromide (MB) (CHaBr) and its alternatives on both free-living and root-knot nematodes in the soil. A randomized complete block experiment with six treatments and 4 replicates (each replicate in a separate greenhouse) was established in Qingzhou, Shandong Province, China. In addition to MB and untreated control (CK) treatments there were four alternative soil fumigation practices including MB virtually impermeable films (VIF), metam sodium (MS), MS VIF and soil solarization combined with selected biological control agents (SS BCA). Two tomato (Lycopersicum esculentum Mill.) cultivars, cv. Maofen-802 from the Xian Institute of Vegetable Science, China, and cv. AF179 Brillante from the Israeli Hazera Quality Seeds, were selected as test crops. The results indicated that Rhabditidae was the most dominant population with percentage abundance as high as 85% of the total number of identified free-living nematodes, followed by that of Cephalobidae. Methyl bromide and its alternatives except for the non-chemical SS BCA treatment controlled the target pest, root-knot nematodes. Also, the impact of the three chemical alternatives on free-living nematode number and functional group abundance was similar to the impact associated with a typical methyl bromide application. Chemical fumigation practices, especially that with MB, significantly reduced the number of nematodes in the soil and simultaneously significantly reduced the number of nematode genera thereby reducing nematode diversity. All the four soil chemical fumigation activities decreased soil microbial biomass and had an obvious initial impact on microorganism biomass. Furthermore, both plant-parasitic and fungivore nematodes were positively correlated with soil microbial biomass.     

Ecotoxicological assessment of nickel pollution of soil and water environments adjacent to soddy–podzolic soil

The indicators of functioning of soil microorganisms in soddy–podzolic soil contaminated with Ni compounds show different ranges of soil ecotoxicity. A halving of soil microorganisms' nitrogen-fixing activity has been shown in slightly acidic soddy–podzolic cultivated soil with a Ni concentration of 150 mg/kg and for noncultivated acidic soils with a Ni concentration 100 mg/kg. The reduction of denitrification activity in cultivated soil has been observed with a Ni concentration of 500 mg/kg, and in uncultivated soil it has been observed at a Ni dose of 100 mg/kg. The inhibition of soil respiration in slightly acidic soil occurred only at the highest dose of Ni, 1000 mg/kg, while in the acidic soil it took place at 300 mg/kg. Biotesting based on bacterial luminescence can be used for determination of soil pollution with heavy metals such as Ni, as well as for the assessment of the toxicity of aqueous environments in contact with contaminated soils.     

Effects of concentrated application of soil conditioners on soil–air permeability and absorption of nitrogen by young peach trees

ABSTRACT

To study the effects of concentrated application of two soil conditioners, two-year-old peach trees (Prunus persica L.‘Chunmei’) were selected to test the soil air permeability, ¹⁵N absorption and the growth of trees. The experiment comprised three treatments involved concentrated applying either polyacrylamide (treatment I) or Agri-SC (a proprietary soil conditioner, treatment II) at the bottom of each pit or neither of the two (treatment III). And then the whole pit was back-filled with soil. Neither digging a hole nor use of soil conditioners as the control (CK). The results showed that volumetric oxygen content in gases in 5–10 cm soil layer upon concentrated application layer was significantly higher in treatments I and II than that in CK. Soil volumetric water content upon concentrated application layer was higher in treatments I and II than that in CK. Compared with CK, no matter root activity, leaf area, leaf chlorophyll content, or leaf net photosynthesis rate in treatments I and II increased in August and October, which promoted the growth of new shoots and the stem. Compared with CK, the leaf superoxide dismutase activity increased 31.24%, 22.66% and 4.74%, Guaiacol peroxidase increased 21.88%, 13.25% and 3.39%, Catalase increased 11.80%, 7.92% and 1.24% respectively in treatments I, II and III in October. As a result, values of the total roots surface area, total root volume, number of root tips, dry matter accumulation, and organ nitrogen content were markedly higher in treatments I and II than that in CK. And the ¹⁵N utilization rate significantly increased 24.22% and 10.40% respectively in treatments I and II. The result suggested that concentrated application of soil conditioners formed a rhizosphere water storage and breathable layer that not only stores moisture but is also permeable to air. That, in turn, promotes plant growth, increases the nitrogen use efficiency.     

Have you checked for charcoal? Assessment of soil condition using soil organic carbon

Soil condition is commonly assessed by using soil organic carbon (SOC) as an indicator; however, a large proportion of the world's soils can contain charcoal, a biologically‐inert form of organic carbon. We investigated whether the presence of charcoal in soil could lead to an inaccurate assessment of soil condition when using SOC as an indicator. We sampled topsoil in a south‐east Australian catchment affected by severe fires in 2003. Samples (n = 100) were analysed for two SOC fractions: (i) total SOC (t‐SOC, loss on ignition), which included charcoal, and (ii) biologically‐active SOC (a‐SOC, persulphate‐oxidation), which did not contain charcoal. Using novel (boosted regression trees) and traditional (linear regression) modelling methods we compared the relative importance of abiotic (slope, aspect, elevation and soil texture) and biotic (land use and vegetation structure) factors as predictors of t‐SOC and a‐SOC concentration. A major difference between the two response variables was less relative importance of land use as a predictor when using t‐SOC as a response variable. Therefore, ignoring the presence of charcoal would have led to an under‐estimation of the effect of land‐use conversion on the biologically‐available SOC fraction. The presence of charcoal has important ramifications for routine assessments of soil condition given that (i) SOC is a commonly used indicator and charcoal and biologically‐active SOC differ in their effects on soil properties, (ii) fires historically occur on a large area of land, (iii) charcoal is a long‐lasting consequence of fires and (iv) charcoal can account for a large proportion of SOC and yet be unnoticed during sample preparation.     

Extraction of humic-β-glucosidase fractions from soil

Humic compounds with -glucosidase activity were extracted from soil using tetrasodium pyrophosphate as extracting solution. Mixture of soil samples with 0.01 M pyrophosphate in a ratio of 1:5 (w/v), adjustment to pH 7.0–7.3, extraction for 18 h with reciprocating agitation, and bacteriological filtration after centrifugation were the optimum conditions for extraction of the -glucosidase complexes. Otherwise, experimental conditions for extraction indicated that the concentration and pH of pyrophosphate were the factors with the most influence on enzymatic extraction yields. The results indicated that the -glucosidase was extracellular and associated with soil humates.     

Effects of multiple soil conditioners on a mine site acid sulfate soil for vetiver growth

A pot experiment was conducted to investigate the effects of various soil treatments on the growth of vetiver grass ( Vetiveria zizanioides (L.) Nash) with the objective of formulating appropriate soil media for use in sulfide-bearing mined areas. An acidic mine site acid sulfate soil (pH 2.8) was treated with different soil conditioner formula including hydrated lime, red mud (bauxite residues), zeolitic rock powder, biosolids and a compound fertilizer. Soils treated with red mud and hydrated lime corrected soil acidity and reduced or eliminated metal toxicity enabling the establishment of vetiver grass.Although over-liming affected growth, some seedlings of vetiver survived the initial strong alkaline conditions. Addition of appropriate amounts of zeolitic rock powder also enhanced growth, but over-application caused detrimental effects. In this experiment, soil medium with the best growth performance of vetiver was 50 g of red mud, 10 g of lime, 30 g of zeolitic rock powder and 30 g of biosolids with 2 000 g of mine soils (100% survival rate with the greatest biomass and number of new shoots), but adding a chemical fertilizer to this media adversely impacted plant growth. In addition, a high application rate of biosolids resulted in poorer growth of vetiver, compared to a moderate application rate.     

Simulation of soil–blade interaction for sandy soil using advanced 3D finite element analysis

In this paper a finite element investigation of the tillage of dry sandy soil, using the hypoplastic constitutive material model, is described. In most earth moving machinery, such as bulldozers or tillage tools, the working tool is a blade. Hence for tillage systems, accurately predicting the forces acting on the blade is of prime importance in helping to enhance productivity. The initial conditions, such as blade geometry or soil type, and operating conditions, such as cutting speed and cutting depth, have been shown experimentally to have a great effect on machine productivity. Experimental studies give valuable insights but can be expensive and may be limited to certain cutting speeds and depths. Results are also highly dependent on the accuracy of the measuring devices. However with increasing computational power and the development of more sophisticated material models, finite element analysis shows more promise in analyzing the factors affecting soil–blade interaction. Most of the available finite element studies in the literature are two-dimensional or if three-dimensional (3D), are limited to a certain blade displacement depending on the element distortion limit before the solution has convergence problems. In this study, a 3D finite element analysis of soil–blade interaction was carried out based on predefined horizontal and vertical failure surfaces, to investigate the behavior of the soil–blade interface and study the effect of blade-cutting width and lateral boundary width on predicted forces. Sandy soil was considered in this study and modeled using the hypoplastic constitutive model implemented in a commercial finite code, ‘ABAQUS’. Results reveal the validity of the concept of predefined failure surfaces in simulating soil–blade interaction and the significant effect of blade-cutting width, lateral boundary width and soil swelling on cutting forces.     

Snow cover and soil moisture controls of freeze–thaw-related soil gas fluxes from a typical semi-arid grassland soil: a laboratory experiment

In situ field measurements as well as targeted laboratory studies have shown that freeze–thaw cycles (FTCs) affect soil trace gas fluxes. However, most of past laboratory studies adjusted soil moisture before soil freezing, thereby neglecting that snow cover or water from melting snow may modify effects of FTCs on soil trace gas fluxes. In the present laboratory study with a typical semi-arid grassland soil, three different soil moisture levels (32 %, 41 %, and 50 % WFPS) were established (a) prior to soil freezing or (b) by adding fresh snow to the soil surface after freezing to simulate field conditions and the effect of the melting snow on CO₂, CH₄, and N₂O fluxes during FTCs more realistically. Our results showed that adjusting soil moisture by watering before soil freezing resulted in significantly different cumulative fluxes of CH₄, CO₂, and N₂O throughout three FTCs as compared to the snow cover treatment, especially at a relatively high soil moisture level of 50 % WFPS. An increase of N₂O emissions was observed during thawing for both treatments. However, in the watering treatment, this increase was highest in the first thawing cycle and decreased in successive cycles, while in the snow cover treatment, a repetition of the FTCs resulted in a further increase of N₂O emissions. These differences might be partly due to the different soil water dynamics during FTCs in the two treatments. CO₂ emissions were a function of soil moisture, with emissions being largest at 50 % WFPS and smallest at 32 % WFPS. The largest N₂O emissions were observed at WFPS values around 50 %, whereas there were only small or negligible N₂O emissions from soil with relatively low soil water content, which indicates that a threshold value of soil moisture might exist that triggers N₂O peaks during thawing.     

Acid soil tolerances of two wheat cultivars related to soil Ph,KCl‐extractable aluminum and degree of aluminum saturation

Aluminum toxicity, associated with soil acidity, is a major growth‐limiting factor for plants in many parts of the world. More precise criteria are needed for the identification of potential Al toxicity in acid soils. The objective of the current study was to relate the acid soil tolerances of two wheat cultivars to three characteristics of an acid Tatum subsoil (clayey, mixed, thermic, typic Hapludult): pH in a 1:1 soil to water suspension; KCl‐extractable Al; and degree of Al saturation. Aluminum‐tolerant ‘BH 1146’ (Brazil) and Al‐sensitive ‘Sonora 63’ (Mexico) wheat cultivars were grown in greenhouse pots of soil treated with CaCO₃ to establish final soil pH levels of 4.1, 4.6, 4.7, 4.9, 5.2 and 7.3. Soil Al, Ca and Mg were extracted with 1 N KCl, and Al saturation was calculated as KCl‐Al/KCl Al + Ca + Mg%.

Within the soil pH range of 4.1 to 4.9, BH 1146 tops and roots produced significantly more dry matter than did those of Sonora 63; however, at pH 5.2 and 7.3, the top and root yields of the two cultivars were not significantly different. Significant cultivar differences in yield occurred over a range of 36 to 82% saturation of the Tatum soil. Graphs of relative top or root yields against soil pH, KCl‐extractable Al and Al saturation indicated that the two cultivars could be separated for tolerance to Tatum soil under the following conditions: pH less than 5.2 (1:1 soil‐water); KCl‐Al levels greater than 2 c mole kg^‐1 and Al saturations greater than 20%. Results demonstrated that any soil test used to predict Al toxicity in acid soils must take into account the Al tolerances of the plant cultivars involved.     

Do elevated soil concentrations of metals affect the diversity and activity of soil invertebrates in the long‐term?

This study aimed to elucidate the response of diversity and activity of soil invertebrates to elevated soil metal concentrations that were a result of sewage sludge application. Field sampling of soil invertebrates was carried out from 2002 to 2004 at an experimental site established in 1982 to test the effects on crop production of metal contamination from sewage sludge applications with elevated concentrations of zinc (Zn), copper (Cu) and nickel (Ni) with certain treatments exceeding the current UK statutory limits for the safe use of sludge on land. At metal concentrations within the limits, none of the invertebrates sampled showed adverse effects on their abundance or overall community diversity (from Shannon–Weiner index). At concentrations above the limits, individual taxa showed sensitivity to different metals, but overall diversity was not affected. Earthworm abundance was significantly reduced at total Cu concentrations at and above 176 mg kg^?1, while nematode and enchytraeid abundances were sensitive to Cu and high Zn concentrations. Correspondingly, litter decomposition was lower in Zn and Cu treatments although there was no direct relationship between decomposition and soil invertebrate abundance or diversity. Such enduring changes in both soil biodiversity and biological activity around the current UK regulatory limits warrant further investigation to determine whether they indicate detrimental damage to soil functioning over the long‐term.     

Use of diffusion for automated nttrogen‐15 analysis of soil extracts

Abstract

Studies to evaluate the use of diffusion for automated ¹⁵N analysis of inorganic N in soil extracts showed that serious error can arise from use of the Devarda's alloy recommended for steam distillations and that the error can be avoided by using a commercial product of higher purity. These studies showed that serious error can also arise when NO₃ ^‐‐N is diffused following NH₄ ⁺‐N and that separate diffusions should be performed for NH₄ ⁺‐N and (NH₄ ⁺ + NO₃‐)‐N. Other work demonstrated that the plastic specimen containers employed for diffusion can be reused if acid‐washed, that diffusions can be performed using either light or heavy MgO without ignition to decompose carbonate, and that labeled NO₂‐is completely removed from soil extracts by treatment with sulfamic acid before diffusion. A comparison of ¹⁵N analyses by steam distillation and diffusion using extracts from two soils revealed better agreement for the soil having a lower content of organic matter. Substantial differences in analyses by the two techniques for the soil having a higher organic‐matter content were attributed to enzymatic conversions of inorganic N during the 6‐d diffusion period.     

Critical soil phosphorus of a low‐P loess‐derived soil as affected by storage temperature

Abstract

Overwintering soil temperature may influence crop response to phosphorus (P) and indices of P availability in the humid, temperate, transitional climate of Tennessee. The effects of P fertilization and soil incubation temperature on sorghumsudangrass (Sorghum bicolor x S. Sudanese) grown on a Typic Hapludalf was investigated in a greenhouse study. In order to determine the effect of temperature on P availability, soils were incubated prior to cropping, at a constant temperature of 6°C or an average diurnal temperature of 24 and 36°C. Reagent grade Ca(H₂PO₄)₂.H₂O was used as the fertilizer source and applied at rates of 0, 10, 20, and 30 mg P kg^‐1 for the first test and 0, 20, 40, 60, and 80 mg P kg_‐ ¹ for the second test. Critical P concentration in the shoots for optimum yield was found to be 1.3 mg g‐¹, corresponding to soil solution and labile P concentrations of 5.5 μmol L^‐1 and 167 μg g^‐1, respectively. Optimum yield occurred for applications of >65 mg P kg^‐1 and was unaffected by soil incubation temperature. Applied P rates affected extractable P by five chemical extractants (Bray I, Bray II, Mehlich I, Mehlich III, and Mississippi), but soil incubation temperature had no affect. The extractants, however, were poorly correlated to plant P uptake and no one extractant appeared preferable to the others as an indicator of P availability.     

Effects of soil compaction and water‐filled pore space on soil microbial activity and N losses

Abstract

Soil compaction is a significant production problem for agriculture because of its negative impact on plant growth, which in many cases has been attributed to changes in soil N transformations. A laboratory experiment was conducted to study the effect of soil compaction and water‐filled pore space on soil microbial activity and N losses. A hydraulic soil compaction device was used to evenly compress a Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudults) soil into 50 mm diameter by 127 mm long cores. A factorial arrangement of three bulk density levels (1.4, 1.6, and 1.8 Mg/m³) and four water‐filled pore space levels (60, 65, 70, 75%) was used. Fertilizer application of 168 kg N/ha was made as 1.0 atom % ¹⁵N as NH₄NO₃. Soil cores were incubated at 25°C for 21 d. Microbial activity decreased with both increasing water‐filled pore space and soil bulk density as measured by CO₂‐C entrapment. Nitrogen loss increased with increasing bulk density from 92.8 to 334.4 g N/m³ soil at 60% water‐filled pore space, for 1.4 and 1.8 Mg/m³, respectively. These data indicate that N loss and soil microbial activity depends not only on the pore space occupied by water, but also on structure and size of soil pores which are altered by compaction.     

Genetic diversity of bacterial β-glucosidase-encoding genes as a function of soil management

This study is the first approach to evaluate the diversity of bacterial β-glucosidase-encoding gene sequences, aiming to identify the main environmental factors structuring bacterial β-glucosidase genetic diversity in semiarid soils. Two agricultural management systems, soils under spontaneous cover vegetation vs. noncovered herbicide-treated soils, were tested. The weed biomass generated in the former was estimated around 2,600 kg?ha^?1?year^?1, whereas leaves and root exudates from olive trees were the only input of C biomass in the latter. Dendrograms generated from polymerase chain reaction–denaturing gradient gel electrophoresis profiles of bacterial β-glucosidase-encoding genes revealed two clusters determined by soil treatment and sharing <20 % similarity. The sequences of a total of 59 DNA fragments, representing 39 operational taxonomic units, were successfully determined. The Proteobacteria phylum clearly dominated all the soil samples, but representatives of Chloroflexi, Deinococci, Actinobacteria, Thermotogae, and Firmicutes class were also detected. Management strategies favoring the presence of spontaneous vegetation determined a higher genetic diversity of β-glucosidase-encoding genes of soil bacteria. However, since there is little information of β-glucosidase gene sequences available in databases, it is difficult to establish particular relationships between bacterial networks for C degradation and land use. Results from canonical correspondence analysis indicated that bacterial metabolic networks for oligomeric C substrates utilization were affected by the physicochemical properties of the soil; the uppermost 10 cm of covered soil clustered together and were positively correlated with some chemical properties related to soil fertility, whereas less influence of soil texture was observed for the deeper layers of bare soils.     

Soil‐grinder type effects on grams of soil scooped

Abstract

Soil preparation can affect soil test results. This study was conducted to compare soil‐grinder effects on grams of soil scooped. Soil samples (n=15,000) were ground by two types of soil grinders, a roller and hammer mill, and then the soil was sieved (10‐mesh), and scooped with a one‐gram scoop (0.85 cm³). The contents of the soil scoop were weighed. Grams of soil scooped ranged from 0.4 to 1.8 g for both soil grinders. The bell‐shaped distribution was centered around 0.8 and 1.0 g for the roller‐ and hammer mill‐type grinder, respectively. When the soil was ground by the roller‐type grinder, 85% of the ground soil was retained on a 50‐mesh sieve. In contrast, with the hammer mill grinder, 45% of the soil was retained on a 50‐mesh, 13% retained on a 100‐mesh, and 42% passed a 100‐mesh sieves. The “heavier” soil scoops with the hammer mill grinder could be explained by the fact that the finer soil particles could pack into the voids that the coarse soil particles created. Bray extractable P and ammonium actetate extractable K, Mg, and Ca were increased 11 to 15% by the “heavier” scooping weight. Grams of soil scooped and soil test levels were affected by the type of soil grinder and soil type.     

Estimation of turnover and equilibrium of soil organic matter using a mathematical approach

The methods based on N uptake of aerial-plants, soil organic matter （SOM） dynamics, Jenny＇s equation, and actual measurement of long-term field experiments in Jiaxing, Quzhou, Huangyan and Hangzhou of Zhejiang Province, China were used to determine the organic mineralization rate being helpful in estimating the organic requirement for SOM equilibrium. The results showed that the estimated mineralization ratios of SOM for Jiaxing and Quzhou were, respectively, 0.0404 and 0.0508 based on N uptake of aerial-plants in non-fertilized plots; 0.0405 and 0.012 using SOM dynamics in non-fertilized plots; and 0.0413 and 0.0513 using the actual investigated data and Jenny＇s equation. With Jenny＇s equation, soil organic C balance in manure ＋ N-P-K plots was estimated at nearly 28.8 g kg^-1 for Jiaxing and 32.4 g kg^-1 for Quzhou with predicted SOM linearly related to the actual investigated values （r^2 = 0.9640 for Jiaxing and 0.8541 for Quzhou）. To maintain the SOM balance in the non-fertilized plots the recommended rate of organic materials was 3 000-6 600 kg ha^-1, and the relevant rates of farm yard manure （FYM） in the manure and N-P-K plots were estimated at 3 375 （dry） and 17670 kg ha^-1 （wet） for Jiaxing, 1845 （dry） and 6090 kg ha^-1 （wet） for Quzhou.     

Integrated effect of potassium humate and α-tocopherol applications on soil characteristics and performance of Phaseolus vulgaris plants grown on a saline soil

Soil salinity is one of the major problems of agriculture that limits plant performance, particularly in arid and semiarid regions. Therefore, the effect of potassium humate (KH) and α-tocopherol (TOC), used singly or in integration, on soil characteristics, and on plant performance, physio-biochemical attributes and antioxidative defense system of Phaseolus vulgaris L. plants grown under salt stress (EC = 6.35–6.42 dS m^?1) was investigated. Half g KH kg^?1 soil was used as soil amendment before sowing and 1.0 mM TOC was used as foliar spray twice; at 25 and 40 days after sowing. Results showed that, KH significantly improved soil physical and chemical properties, which positively reflected on plant growth and productivity, physio-biochemical attributes, mineral nutrients (N, P, K and Ca), osmoprotectants (soluble sugars and proline), non-enzymatic (ascorbic acid, glutathione and TOC) and enzymatic (superoxide dismutase, catalase and guaiacol peroxidase (GPOX)) antioxidants compared to untreated controls. The single TOC foliar application recorded the same positive results of KH. Integrated KH + TOC treatment was most effective compared to the single treatments. The above results recommended benefits of this integrated KH + TOC for the possibility of sustainable agronomic performance of common beans grown on saline soils.     

Fluorescence microscopy for visualization of soil microorganisms—a review

Direct microscopic observation of microorganisms is an important tool in many microbial studies. Such observations have been reported for Protozoa, fungi, inoculated bacteria, and rhizosphere microorganisms but few studies have focused on indigenous bacteria and their spatial relationship within various microhabitats. Principles and applications of epifluorescence microscopy and confocal laser scanning microscopy for visualization of soil microorganisms in situ are reviewed. Both cationic and anionic dyes (also commonly referred to as fluorochromes if they are fluorescent) have been used based on their ability to bind to specific cellular components of microbial cells. Common fluorochromes used for imaging of microbial cells include acridine orange, ethidium bromide, fluorescein isothiocyanate, 5-(4,6-dichlorotriazinyl) aminofluorescein, 4,6-diamidino-2-phenylindole, europium chelate, magnesium salt of 8-anilino-1-naphthalene sulfonic acid, and calcofluor white M2R. Combining fluorescence staining techniques with soil thin section technology allows one to obtain images of microorganisms in situ. Soil texture and the procedures used for resin embedding are important factors affecting the quality of stained soil thin sections. Indeed, general limitations of applying fluorescence microscopy to soil ecological studies are the non-specific binding of dyes to the soil matrix and the autofluorescence of some soil components. The development of fluorescent in situ hybridization and confocal laser scanning microscopy techniques provides new potential for microbial distribution studies.