Comparison of two different methods to measure nitric oxide turnover in soils

 The NO turnover in soils was measured in two different experimental set-ups, a flow-through system, which is very time-consuming and needs rather sophisticated equipment, and a closed system using serum bottles. We compared the NO turnover parameters (NO consumption rate constant, NO production rate, NO compensation concentration) that were measured with both systems in different soils, under different conditions and in the presence of 10 Pa acetylene to inhibit nitrification. The values of the NO turnover parameters that were measured with the two systems under oxic conditions were usually comparable. The addition of acetylene did not affect the NO consumption rate constants of the soils with the exception of soil G1. However, the NO production rates and the NO compensation concentrations decreased significantly in the presence of acetylene, indicating that nitrification was the main source of NO in these soils. Only one soil (Bol) showed no nitrifying activity. Increasing soil moisture content resulted in decreasing NO consumption rate constants and NO production rates. Even at a high soil moisture content of 80% water holding capacity, nitrification was the main source of NO. The values of the NO turnover parameters that were measured with the two systems were not comparable under anoxic conditions. The NO consumption rate constants and the NO production rates were much lower in the closed than in the flow-through system, indicating that the NO consumption activity became saturated by the high NO concentrations accumulating in the closed system. Under oxic conditions, however, closed serum bottles were a cheap, easy and reliable tool with which to determine NO turnover parameters and to distinguish between nitrification and denitrification as sources of NO. Received: 21 April 1998     

Improvements to two routine methods for calcium carbonate determination in soils

Abstract

In the course of routine analytical work, wide discrepancies were noted between results from alternative, established procedures for measuring calcium carbonate (CaCO₃) in soils. In one procedure (Method I), the CaCO₃ content is calculated from the weight of CO₂ lost after treating a sample with excess hydrochloric acid. Results of an investigation using this procedure in our laboratory tended to be inaccurate and poorly reproducible. The method was therefore modified by using as the reaction vessel a plastic vial with pin‐holes in its lid, instead of a glass Erlenmeyer flask with a stopper removed at intervals, to let CO₂ escape. Further, the weighed soil sample was placed in a disposable cup inside the vial of acid, instead of being weighed and transferred. These modifications greatly improved accuracy and reproducibility of results obtained by Method I. In another procedure, the CaCO₃ content was calculated from the pH of a suspension of the soil in dilute acetic acid (Method II). This method tends to give results appreciably greater than zero for acidic soils containing no free lime. This undesirable tendency was reduced after Method II was modified by calibrating it against soils spiked with known amounts of CaCO₃, instead of against CaCO₃ alone. As a result of the modifications, agreement between results for soils analyzed by both methods was greatly improved. Method I is considered more suitable for soils with appreciable free lime, or for liming materials, and Method II for soils with low CaCO₃ content (.5% or less).     

Time-dependent sorption of imidacloprid in two different soils

Time-dependent sorption of imidacloprid [1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine] was investigated with two German soils (sandy loam and silt loam). Soil batches containing the active ingredient (0.33 mg/kg) were incubated for 100 days. After selected aging periods, imidacloprid desorbed by 0.01 M CaCl(2) (soluble phase) and by organic solvents (methanol and acetonitrile) and reflux extraction with acidified methanol (sorbed phase) was determined. Calculated sorption coefficients K(d) and K(oc) increased by a factor of 3.2-3.8 during 100 days of aging. Additionally, the time-dependent sorption was verified by a column leaching experiment with the aged soil. The amount of imidacloprid in column eluates (0.01 M CaCl(2)) decreased compared to total recovered by a factor of approximately 2. Sorption of imidacloprid thus increased with residence time in soil, making it more resistant to leaching. These results are further information to explain the low leaching potential of imidacloprid in the field, despite its high water solubility.     

Comparison of different measuring and calculating methods to quantify the hydraulic conductivity of unsaturated soil

The double-plate method and the evaporation method provide comparable results on the hydraulic conductivity of soil (K(h_s)). Adaptation of the water retention curve according to the method of Vachaud and Vauclin proved to be very reliable. The course of the K(h_s) function is well shown by all indirect identification methods included in the comparison. In some cases, the absolute deviations of the measured from the calculated values are, however, considerable and primarily determined by the initial value of the hydraulic conductivity. In quantifying the capillary water rise, best approximation to the measured values was reached in 11 of 13 cases with the van Genuchten method.     

Response of nitrogen transformation to glucose additions in soils at two subtropical forest types subjected to simulated nitrogen deposition

Journal of Soils and Sediments - Soil nitrogen (N) transformation is an important phenomenon in forest ecosystems and it is regulated by carbon (C) input. This study aimed to evaluate the impacts...     

Fractionation and colorimetric determination of boron in soils

We attempted to modify and evaluate existing sequential fractionation schemes for B involving the use of chemicals, which subsequently do not interfere with the measurement of B by colorimetry. Also evaluated was the contribution of various soil B fractions to the amount of B extracted by hot CaCl₂, CaCl₂‐mannitol, salicylic acid, ammonium acetate, HCl, and tartaric acid. For this purpose, 17 soils with diverse properties were used. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl₂, 0.05 M KH₂PO₄, 0.175 M NH4‐oxalate (pH 3.25), 0.5 M NaOH, and HF + H₂SO₄ + HClO₄. The procedure of elimination of color from extracts of oxide bound, organically bound, and residual B fractions was also evolved. Relationships of individual B fractions with physicochemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme. The relationships of different B fractions with extractable B in soils suggest that hot CaCl₂ and salicylic acid may be better extractants for available B in soils.     

Long-term changes in microbial community structure in soils subjected to different fertilizing practices revealed by quinone profile analysis

Quinone profile analysis of stored air-dried soils gave an approximation of the long-term changes in the microbial community structure in four soils subjected to different types of fertilizer application from 1987 to 1997: unfertilized soil (NF-soil), soil amended with chemical fertilizers (CF-soil), soil amended with chemical fertilizers and 40 t ha^-1 y^-1 of farmyard manure (CF+ FYM-soil), and soil amended with 400 t ha^-1 y^-1 of farmyard manure (FYM-soil). The carbon content increased, and the soil pH remained higher in the soils receiving farmyard manure. Principal component analysis of the quinone profiles of the soils indicated that the microbial community structure showed a high similarity among the four soils before the onset of cultivation and changed to a different community structure specific to the respective fertilizing practices except for the NF-soil. The specific quinone profile became stable after two cropping seasons in the FYM-soil, after 10 cropping seasons in the CF+ FYM-soil and after 15 cropping seasons in the CF-soil, respectively. The quinone profile of the NF-soil did not become stable, and no specific profile was developed. The specific quinone profiles in the FYM- and CF+ FYM-soils were both characterized by large mole fractions of menaquinone with seven isoprenoid units (MK-7). Farmyard manure itself contained a large mole fraction of MK-7. It was suggested that the amount of MK-7 increased due to the application of farmyard manure. MK-7 indicates the presence of Gram-positive bacteria with low guanine plus cytosine contents such as Bacillus and Gram-negative bacteria of the Cytophaga-Flavobacterium complex. The specific quinone profile in the CF-soil was characterized by the presence of menaquinone with seven isoprenoid units dihydrated (MK-7(H₂)and MK-7(H₄). Although Brevibacterium and Kocuria contain MK-7(H₂), no microorganisms are known to have MK- 7(H.) as major quinone. The common major quinones were MK-8, MK-10(H₄) and a mixture of MK-8(H₄) and MK-9, suggesting the predominance of Grampositive bacteria in all the soils. Mole fractions of Ubiquinone with 8 isoprenoid units (Q-8) and Q-10 increased at various times in all the soils, indicating the sporadic growth of Gram-negative bacteria.     

Temporal denitrification patterns in different horizons of two riparian soils

The dynamics of biological denitrification in riparian soil is still poorly understood. We studied the spring‐time pattern of denitrifying enzyme activity (DEA) and the rate of denitrification (DNT) in two hydromorphic riparian soils, one a mollic Gleysol and the other a terric Histosol. The average DEA ranged from 73 to 1232 ng N g^?1 hour^?1, and DNT ranged from 4 to 36 ng N g^?1 hour^?1. Both DEA and DNT diminished with increasing depth in both soil types. This decrease corresponded to a decrease in total and K₂SO₄‐extractable organic carbon and K₂SO₄‐extractable mineral nitrogen. The DEA and DNT differed in their dynamics. The former had no evident pattern in subsurface horizons but increased with temperature at the end of spring in surface and structural horizons. The DNT diminished as the soil dried in the mollic Gleysol when the water table fell. In the terric Histosol, the water table was still too high at the end of spring to affect the DNT. The results suggest that the vertical pattern of denitrification is related to that of organic carbon content. This organic carbon content determines biological activity and the supply of carbon and nitrous oxides. In biologically active horizons temperature drives the dynamics of DEA, whereas soil moisture drives the dynamics of DNT. Our results show the importance of the dynamic soil–water relationship in controlling denitrification within the riparian zone.     

Comparison of extraction methods for recovery of extracellular β-glucosidase in two different forest soils

A study was made of the efficiency of three different extractants, 0.1 M sodium pyrophosphate (pH 7), 67 mM phosphate buffer (pH 6) and 0.5 M potassium sulphate (pH 6.6), in recovering the protein quantity and the β-glucosidase enzyme activity from two natural forest soils: (1) an Inceptisoil located in Tuscany (Italy) in a mild Mediterranean climate, and (2) a Lithic Calcixeroll soil located in Murcia (south-east of Spain) in a dry-semiarid climate. The pyrophosphate was used to determine the activity of extracellular-humic-bound proteins, while the phosphate buffer and potassium sulphate were used to extract dissolved extracellular proteins. The latter extractant, after chloroform fumigation, was also used to measure total proteins in soil. A preliminary screening, using SDS-PAGE in one dimension, was also carried out in order to optimize the separation condition of soil proteins extracted with different buffers. To remove the interfering co-extracted substances (humic acid) a purification step using a column packed with insoluble polyvinylpyrrolidone was performed. The highest β-glucosidase activity was recovered in the pyrophosphate extract, thus confirming its capability of extracting humic-bound β-glucosidase enzyme in a stable and active form. The extractants performed differently with the two soil types and band patterns obtained with SDS-PAGE were extractant-specific, demonstrating that each was selective for a particular class of proteins. Surprisingly, protein bands were also obtained using pyrophosphate, in spite of the very dark extract colour due to the presence of humic substances.     

不同氮肥管理措施在华北平原冬小麦上的应用效果

在河北省衡水和辛集试验点,采用田间试验研究了氮肥不同用量和不同基追比对冬小麦生长、产量和土壤氮素变化的影响。结果表明,衡水试验点的土壤本底供氮量能满足小麦返青前的正常生长,施氮肥对小麦增产无效,但与施基肥处理相比,不施基肥、仅在拔节和孕穗期2:1分次追肥显著提高了氮肥利用率。在辛集,不施基肥显著影响小麦返青前的生长,施N 60 kg /hm2能满足小麦拔节前的正常生长,不施基肥、仅在拔节后追肥不能消除前期氮缺乏对小麦生长和高产的影响;N 240 kg /hm2以基追比1:3施用时能获得较高的产量和氮肥利用率。冬小麦生育期田间氮肥表观损失主要来源于基肥,但中后期追肥比例过大也增加了收获后土壤的无机氮残留。由于土壤肥力和质地不同,相同氮肥管理方法下两试验点小麦的生长、产量和氮肥利用率的差异较大,因此,为达到作物高产和氮肥高效,对氮肥的同步调控应结合作物养分阶段需求、土壤养分供应特征和土壤肥力、质地的区域分异特征分区进行。     

Water-stable aggregates, glomalin-related soil protein, and carbohydrates in a chronosequence of sandy hydromorphic soils

The conversion of pasture to cropland leads to a decline of aggregation in topsoils and to a decrease of aggregate-binding agents such as carbohydrates and glomalin-related soil protein (GRSP). Till now, studies on soil aggregation focused either on carbohydrates or on GRSP as a binding agent in aggregates. In this study we analyse the development of the relationship between carbohydrates, GRSP, TOC and aggregate-stability following land-use change. Furthermore, we discuss the contents of carbohydrates, GRSP and TOC in each of the aggregate fractions. For these purposes, a chronosequence of sites, which were converted from pasture to cropland at different periods in history, was established. To get further insight into the impact of different types of land-use, also soils under forest, either afforested or permanent, were studied. The mean-weight diameter (MWD) of water-stable aggregates, the carbohydrate, and the GRSP content were determined in 49 soils. It was found that the MWD of the water-stable aggregates decreased monoexponentially (R² = 0.66) by 66% during the first 46 years after conversion of the soils from pasture to cropland. During the same period, the carbohydrate content decreased very rapidly after the land use change by 64% and the GRSP content decreased more slowly by 57%. The MWD of the forest soils were in the same range as those of the permanent pasture soils although they exhibit significantly higher TOC contents, which indicate that other stabilization mechanisms are dominant in forest soils, less important in the chronosequence soils. TOC, carbohydrates and the GRSP contents were sigmoidally correlated with the MWD. Among the four water-stable aggregate fractions TOC and carbohydrates exhibited high contents in the macroaggregates and were less present in the microaggregates. GRSP, in contrast, was more equally distributed among the four water-stable aggregate fractions.     

Nitrification in two coniferous forest soils after different fertilization treatments

The effects of seven different fertilization treatments on nitrification in the organic horizons of a Myrtillus-type (MT) and a Calluna-type pine forest in southern Finland were studied. No (NO^?₃ + NO^?₂)-N accumulated in unfertilized soils during 6 weeks at 14 or 20°C in the laboratory. Net nitrification was stimulated by urea in both soils (but more in the MT pine forest soil) and to a lesser degree by wood ash but not by ammonium nitrate or nitroform (ureaformaldehyde). Nitrification was not detected in nitroform fertilized soils although ammonium accumulation was high during incubation. In the MT pine forest soil, net nitrification appeared to be stimulated by apatite, biotite and micronutrients. Nitrapyrin inhibited nitrification indicating that it was carried out by autotrophic nitrifiers. In the urea-fertilized MT pine forest soil, nitrification took place at an incubation temperature of 0°C. Accumulation of (N0^?₃ + NO^?₂)-N was highest in soil sampled at < 10°C.     

ATP content of soils estimated by two contrasting extraction methods

The ATP content of a series of soils was investigated in relation to various soil properties. Special attention was paid to the discrepancy in ATP, as estimated after extracting with TEA/NRB and TCA. It appears that the first procedure particularly relates to active microbial cells but extracts rather poorly certain types of older microbial biomass. Nevertheless, the TEA/NRB ATP values correlate very significantly with total soil microbial biomass as determined by the CHCl₃ fumigation method. In soils with active growing microbial biomass, the TEA/NRB and the TCA ATP values are about equal. In normal equilibrated soils the TEA/NRB ATP levels average about 40% of the total soil ATP levels. Finally, in densely rooted soils, the TCA ATP levels surpass largely the TEA/NRB levels, but they appear to a major extent to be due to plant cells.     

Fungal community composition in sodic soils subjected to long-term rice cultivation

ABSTRACT

Rice cultivation is widely used to improve saline-sodic soils in Northeast China. However, the chronological effect of rice cultivation on soil fungal communities has not been studied. Therefore, this study investigated the variation of soil fungal communities in different rice cultivation years. Compared with the blank area, the rice cultivation for 20 years significantly decreased the pH and electrical conductivity by 16.6% and 70.1%, while significantly increased the soil organic carbon and available phosphorus by 90.6% and 17.4 times, respectively. Meanwhile, the relative abundance of Ascomycota and Basidiomycota significantly decreased and increased after rice cultivation, respectively. Moreover, some genera of arbuscular mycorrhizal fungi (AMF), e.g. Corymbiglomus, Glomus, and Rhizophagus, and pathogenic fungi (Thanatephorus cucumeris) disappeared, while Dentiscutata (one genus of AMF) appeared after rice cultivation. In addition, the fungal richness significantly increased when the rice cultivation less than 15 years and the fungal communities were similar between 15 and 20 years. Our findings showed that rice cultivation improved the nutrient availability and reduced salinity-alkalinity stress of sodic soils. After the rice cultivation for 15 years, the soil fungal community tended to be stable.     

Acidification and nutrient imbalance in forest soils subjected to nitrogen deposition

Emission of nitrogen oxides (NO_x) and ammonia (NH₃) from a fertilizer factory and the resulting input of nitrates (NO₃ ^?) and ammonium (NH₄ ⁺) into the soil were the main reasons of nitrogen (N) cycle disturbance in forest ecosystems near Novgorod, North-Western Russia (50°31′ North, 31°17′ East). Total N atmospheric input was about 100 kg/ha annually. NH₃ was a dominant pollutant, causing the increase of atmospheric precipitation pH within the polluted region compared to background territories (6.0–6.5 and 4.5–5.0, respectively). Soil acidification through NH₄ ⁺ nitrification was observed. N-NO₃ ^? concentrations in soil solution reached 20–30 mg/l, and proton (H) production was equal to 4.1 keq/ha per warm season (from April to October). Compared with soil status in 1983, pH decrease by 0.2 pH units was found in A horizon. The content of exchangeable calcium (Ca) and magnesium (Mg) decreased by the factor of 2–3 and 1.5–2 in A and B horizons, respectively. Triple increase of exchangeable aluminium (Al) content was detected in A horizon. Through recent decrease of pollutant emission, the polluted territory is now a suitable subject for recovery studies.     

Distribution of the particle-size fractions in soddy-podzolic soils subjected to sheet erosion

Tendencies in the formation of organomineral profiles of arable agrosoddy-podzolic soils on slopes in different denudation and accumulation zones were characterized on the basis of an integrated study of the humus status of the soils (using the granulodensimetric fractionation method), the content of clay, and the composition of clay minerals. It was shown that the organomineral and mineralogical parameters of the surface-horizon transformation could be used for improving the diagnostic accuracy of soils on the slopes basing on their conventional characteristics.     

硅钼蓝比色法测定石灰性土壤的有效硅含量

This paper deals with the determination of available Si content in calcareous soils with Mo blue colorimetric analysis method. The experimental results showed that two acid reagents of sodium acetate buffering solution (pH 4) and 0.025 mol/L citric acid generally had a strong ability of extracting soil available Si, and their soil filtrates were colorless. On the contrary, two alkaline extractants of 20 mg/mL sodium carbonate and 0.5 mol/L sodium bicarbonate only got a relevantly lower soil available Si and their extracts appeared deep color of organic and other pigments, which could be decolorized by adding certain amounts of P-free activated charcoal (about 0.1 g/g soil). In the procedure of Mo blue colorimetry, adding proper amount of oxalic acid and K(SbO)C₄H₄O₆ could eliminate the interference of P to Si and Si to P, respectively. The concentration of acids was not the major factor suppressing the interferences between P and Si in the colorimetric analysis. In the medium of 0.2-0.8 mole H⁺/L sulfuric acid, the intensity of the silicomolybdate blue color did not vary with acidity, no matter whether (NH₄)₂Fe(SO₄)₂ or ascorbic acid was used as reductive reagent. About 10 minutes was needed to form a fully blue complex at 20-25℃. After 30 minutes, the blue color would slowly change into light one, and hence, the colorimetric process should be finished within a short time.