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。     

No UV enhancement of litter decomposition observed on dry samples under controlled laboratory conditions

In field studies, various workers have observed a stimulation of organic matter breakdown by visible light and UV radiation. We aimed to confirm the involvement of UV radiation under controlled laboratory conditions and quantify the magnitude of any stimulation. Grass and pine foliage samples were oven-dried and continuously exposed to UV radiation at room temperature for up to 60 days. A range of UV flux densities was established using shading to different levels. After UV exposure under air-dry conditions, samples were rewetted and incubated in the dark with microbial inoculums to investigate whether UV exposure had rendered samples more susceptible to subsequent microbial decomposition.However, we found no weight loss associated with different UV flux densities. The same finding held true for grass and pine litter samples. Similarly, microbial decomposition of either grass or pine litter was not enhanced by prior UV exposure. These findings suggest that UV-induced photooxidation of dry materials cannot be responsible for the observed apparent enhancement of weight loss of litter samples under UV exposure in the field.     

Comparison of the persistence of atrazine and metolachlor under field and laboratory conditions

A study was carried out in a loamy soil to evaluate the degradation of atrazine and metolachlor under laboratory-controlled and field-variable conditions as a function of temperature and soil moisture content. In laboratory trials, metolachlor showed fast degradation, with half-lives from 100 to 5.7 days in a temperature range from 5 to 35 degrees C at 100% of field capacity, whereas in the same conditions the degradation rate of atrazine was relatively slow, with half-lives from 407 to 23 days. Modeling of laboratory degradation data to predict field persistence was carried out. Field persistence of atrazine and metolachlor was measured in the same soil during the corn growing seasons in 1993, 1994, and 1996. In the three years the mean half-dissipation times for atrazine and metolachlor were 36 and 21 days, respectively. Calculations from model equations gave acceptable prediction of field dissipation of both herbicides. Limitations and perspectives of employed modelization procedure are discussed.     

Microsensor analysis of oxygen and pH in the rice rhizosphere under field and laboratory conditions

 O₂ and pH microsensors were used to analyse the microdistribution of O₂ and pH inside and outside roots of lowland rice (Oryza sativa L.). The roots of 3-week-old transplants had O₂ concentrations of about 20% air saturation at the surface, but due to a high rate of O₂ consumption in the rhizosphere, the oxic region only extended about 0.4 mm into the surrounding soil. Also the fine lateral roots created an oxic zone extending about 0.15 mm into the soil. The O₂ concentration within the roots approached air saturation close to the base, but only about 40–60% of air saturation in a region about 8 cm below the base where lateral rootlets were present. A shift from air to N₂ around the leaves led to a drop of 50% in the O₂ concentration after 12 min at a distance of 8.5 cm from the base. Flowering plants did not export O₂ to the soil from the majority of their roots, but high microbial activity was present in a very thin biofilm covering the root surface. A brown colour around the thin lateral roots indicated some O₂ export from these also during flowering. No oxidized zone was present around the roots at later stages of crop growth. The roots caused only minor minima in pH (<0.2 pH units) in the rhizosphere as compared to the bulk soil. Illumination of the plants had no effect on rhizosphere pH. Received: 28 April 1998     

Impact of alum on crust prevention and aggregation of calcareous soil: laboratory studies

Alum was applied at rates of 0.01, 0.02, 0.05, 0.1 and 0.2% by weight to a calcareous silty clay soil in an attempt to reduce soil crusting and improve soil aggregation. Results indicated that the modulus of rupture (MR) was reduced from 176 to 60 kPa with the addition of 0.2% alum. The mean weight diameter (MWD) was doubled when the application rate of alum increased from 0 to 0.2%. Alum apparently modified the soil physical environment by making the soil fluffy which in turn reduces its MR. Gypsum was formed by the reaction of alum with calcium carbonate in proportion to the amount of alum applied, increasing from 0.2% in the control soil to 1.1% with the highest rate of alum applied. This increase may have lead to the reduction in the MR and an increase in the MWD. This research showed that alum was effective in improving soil aggregate stability and decreasing aggregate rupture stress.     

Emission of nitric oxide and nitrous oxide from soil under field and laboratory conditions

A detailed short-term (12 d) laboratory study was carried out to investigate the effects of applying animal urine, fertilizer (ammonium nitrate) and fertilizer+urine on emission of NO and N₂O from soil. A complementary 24 d field study measured the effect of fertilizer or fertilizer+sheep grazing on NO and N₂O emissions from pasture. The data generated were used to interpret the transformations responsible for the release of these gases. Application of urine to the soil (at a rate equivalent to 930 kg N ha⁻¹) increased the amount of mineral and microbial N in the soil. This was followed by increases in emissions of NO (from 0.02 to 1.76 mg NO-N m⁻² d⁻¹) and N₂O (from 15 to 330 mg N₂O-N m⁻² d⁻¹). Molar ratios of NO-N-to-N₂O-N were very low (<0.001 to 0.011) indicating that denitrification was the main process during the first 12 d after application. In the laboratory, nitrification was inhibited during the first 7 d due to an inhibitory effect of the urine, but even though nitrification was clearly underway 7–12 d after application, denitrification was still the dominant process. The fertilizer was applied at a lower rate (120 kg N ha⁻¹) than the urine. Consequently, the effect on soil mineral N was smaller. Nevertheless the fertilizer still increased NO and N₂O emission with denitrification the dominant process. The effects of fertilizer and grazing on NO and N₂O emissions was less obvious in the field compared with the laboratory and fluxes returned to background rates within 4 d. This was attributed to the rapid decline in soil mineral N in the field trial due to plant uptake and leaching, processes that did not occur in the laboratory.     

Mineralization of low molecular weight carbon substrates in soil solution under laboratory and field conditions

A more detailed mechanistic understanding of how low molecular weight (MW) carbon (C) substrates are mineralized within the rhizosphere by soil microbial communities is crucial to accurately model terrestrial C fluxes. Currently, most experiments regarding soil C dynamics are conducted ex-situ (laboratory) and can fail to account for key variables (e.g. temperature and soil water content) which vary in-situ. In addition, ex-situ experiments are often highly invasive, e.g. severing root and mycorrhizal networks, changing the input and concentrations of low MW exudates within soil. The aim of this study was to directly compare the mineralization rates of 31 common low MW C substrates under ex- and in-situ conditions. In addition, we also assessed the inter-annual field variability of substrate mineralization rates. We added trace concentrations of 31 individual ¹⁴C-labelled common low MW C substrates into the top soil of an agricultural grassland and monitored the mineralization rates by capturing ¹⁴CO₂ evolved from the soil over 7 d. Our results showed that the contribution of low MW C components to soil respiration was highly reproducible between parallel studies performed either in-situ or ex-situ. We also found that differences in the mineralization of individual compounds were more variable inter-annually in the field than between the laboratory and the field. Our results suggest that laboratory-based C mineralization data can be used to reliably parameterize C models but that multiple experimental measurements should be made over time to reduce uncertainty in model parameter estimation.     

Effect of earthworm on growth of late succession plant species in postmining sites under laboratory and field conditions

Earlier studies of postmining heaps near Sokolov, Czech Republic (0–46 years old) showed that massive changes in plant community composition occur around 23 year of succession when the heaps are colonized by the earthworms Lumbricus rubellus (Hoffm.) and Aporrectodea caliginosa (Savigny). The aim of the current study was to test the hypothesis that the introduction of earthworms into a postmining soil enhances growth of late succession plant species. In a laboratory experiment, earthworms significantly increased biomass of Festuca rubra and Trifolium hybridum grown in soil from a 17-year-old site. The biomass increase corresponded to a significant decrease in pH and an increase in oxidable C, total N, and exchangeable P, K, and Ca content. A second laboratory experiment showed higher biomass production of late successional plant community (Arrhenatherum elatius, Agrostis capillaris, Centaurea jacea, Plantago lanceolata, Lotus corniculatus, and Trifolium medium) in soil from late successional stage (46 years old); the introduction of earthworms into soil from an early successional stage (17 years old) increased biomass production. In a field experiment, introduction of L. rubellus to enclosures containing a 17-year-old soil not colonized by earthworms significantly increased the biomass of grasses after 1 year. The results support the hypothesis that colonization of postmining areas by earthworms can substantially modify soil properties and plant growth.     

Effect of simulated acid rain on nitrogenase activity in the lichen genus peltigera under field and laboratory conditions

Lichens of the genus Peltigera were exposed to simulated acid rain in the laboratory and at a field site in Southwestern Alaska. Exposure to simulated rainfall of pH 4.4 had no effect upon acetylene reduction in P. rufescens after experiments of 28 and 60 days duration, although in the former experiment there was some evidence of a transient effect after 14 days. Simulated acid rain of pH 3.4 or 4.4 also had no effect upon nitrogenase activity in P. aphthosa during a 21-day field study, indicating that nitrogenase activity in Peltigera is not sensitive to precipitation in this range of acidity.     

Iron chlorosis of rice seedlings in calcareous soil under upland conditions

The farm of All India Coordinated Rice Improvement Project is located in Rajendranagar, Hyderabad, which lies in the Deccan Peninsula of India. Hyderabad is in latitude 17°N with about 500 m above sea level. The average annual rainfall of this area is about 750 mm. So it is called a semi-dry area.     

Estimation of the total gaseous nitrogen losses from clay soils under laboratory and field conditions

Acetylene blockage was evaluated as a method for measuring losses of N₂O + N₂ from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha^?1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha^?1 per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N₂O was reduced to N₂ in the presence of C₂H₂. In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha^?1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N₂O-N ha^?1 per day for 8 days. In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha^?1 per day respectively before and after fertilizer application (70 kg N ha^?1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.     

Microbial immobilisation and turnover of C labelled substrates in two arable soils under field and laboratory conditions

Microbial biomass C immobilisation and turnover were studied under field and laboratory conditions in soils of high yield (HY) and low yield (LY) areas within an agricultural field. We compared the size and activity of soil microbial biomass (SMB) in the soils of the different yield areas under field and laboratory conditions. Soils were amended with ¹³C labelled mustard (Sinapis alba) residues (both experiments) and labelled glucose (laboratory only) at 500 μg C g⁻¹ dry soil. SMB-C, dissolved organic carbon (DOC) and total C content were monitored in the field and the laboratory. CO₂-efflux was also measured in laboratory treatments. Isotope ratios were determined for SMB in both experiments, but other variables only in the laboratory treatments. A positive priming effect was measured in three of four laboratory treatments. Priming was induced after a significant increase of soil derived C in the microbial biomass. Thereafter, the total C loss through priming was always smaller than or equal to the decline in microbial biomass C. In field and laboratory experiments SMB in the HY soil immobilised less of the added substrate C than LY soil SMB. Calculated turnover times in the laboratory glucose amendment were 0.24 (HY) and 0.31 y (LY), in the laboratory mustard treatment 0.58 (HY) and 0.44 y (LY) and in the field mustard amendments 1.09 (HY) and 1.25 y (LY). In both the field mustard and laboratory glucose treatments turnover in the HY soil tended to exceed that in the LY soil. These turnover times as well as the reaction of SMB-C to drying-rewetting and substrate addition, indicated that the HY soil possessed a more active microbial community with a more rapid C turnover than the LY soil. As C turnover is considered to be closely linked to nutrient cycles, faster turnover in the HY soil may involve a better nutrient supply for crops resulting in higher agricultural yield.     

Microbial immobilisation and turnover of N labelled substrates in two arable soils under field and laboratory conditions

Microbial biomass N dynamics were studied under field and laboratory conditions in soils of high yield (HY) and low yield (LY) areas in an agricultural field. The objective of the study was to determine the size and activity of soil microbial biomass in the soils of the different yield areas and to compare these data obtained under field and laboratory conditions. Soils were amended with ¹⁵N labelled mustard (Sinapis alba) residues (both experiments) and labelled nitrate (laboratory only) at 30 μg N g⁻¹ dry soil. Soil microbial biomass (SMB) N, mineral N (N_min) and total N content was monitored both in the field and in the laboratory. N₂O efflux was additionally measured in laboratory treatments. Isotope ratios were determined for SMB in both experiments, for all other parameters only in the laboratory treatments. In the laboratory less amounts of added substrate N were immobilised by the SMB in HY soils compared to LY soils, whereas in the field immobilisation of added N by SMB was higher in HY soils initially and slightly lower after 40 days of incubation. Calculated turnover times in the laboratory nitrate, laboratory mustard and field mustard amendments were 0.18, 0.27 and 0.74 years (HY) and 0.22, 0.61 and 1.01 years (LY), respectively. The turnover times of added substrate N always showed the trend to be faster in HY soils compared to LY soils. A faster turnover of nutrients in the HY soils may involve a better nutrient supply of the plants, which coincides with the higher agricultural yield observed in these areas.     

田间旱育条件下不同化感潜力水稻根际土壤酚酸类和萜类物质分析

酚酸类和萜类是水稻化感作用研究中研究较多、争议较大的2大类化感物质,但目前有关水稻根系分泌物的研究多在实验室条件下进行。本文以国际公认的强化感水稻‘PI312777’和弱化感水稻‘Lemont’为材料,以未种植水稻的土壤为对照,研究了其在田间旱育条件下,不同土壤水分状态(旱地和湿地)时,根际土壤酚酸类和萜类物质的差异。结果表明,不同水分条件下不同化感潜力水稻品种和对照根际土壤中酚酸类物质和萜类物质的组成较为相似,但各物质含量存在一定差异。适度旱胁迫下,各处理根际土壤中所检测到的咖啡酸、对羟基苯甲酸、香草酸、阿魏酸和肉桂酸5种酚酸类物质及总量均有提高,其中强化感水稻‘PI312777’根际土壤中5种酚酸类物质提高最显著,比CK湿地处理提高2.84倍;在各处理根际土壤共检测到的27种萜类物质中,17种是含氧单萜;干旱胁迫导致各处理根际土壤单萜烯、含氧单萜、含氧倍半萜和总萜变化程度和变化趋势不同,单萜烯相对含量在强化感水稻‘PI312777’根际土壤中明显提高,而在弱化感水稻‘Lemont’和对照根际土壤中则降低。本文在此基础上讨论了由此导致2种水稻田间化感抑草效果差异的原因与机制。     

Decomposition of crop residues under laboratory conditions

Abstract. A laboratory study was designed to provide data on the decomposition of rape, sunflower and soyabean residues put in bags buried in soil. The residue bags were removed at intervals during 1 year, analysed for remaining total mass, organic and water-soluble C, water-soluble sugars, as well as for volatile acids and phenolic compounds. The decomposition dynamics of total mass, total organic and water-soluble organic C, and water-soluble sugars were reproduced satisfactorily by a double-exponential model of the first-order type. Generally, no large differences in the rate and magnitude of decomposition among the residues were observed; the greatest losses of both total mass and chemical components occurred in the first month of the study, during which the volatile acids and phenolic compounds disappeared almost completely. Of the three residues, soyabean showed the lowest loss of organic carbon, losing 66% of the original content over the course of the year compared with 73 and 75% for sunflower and rape, respectively.     

实验室条件下不同盐度水体去分层试验

水产养殖中水体分层在水中形成屏障,阻碍质量和能量交换,进而导致水质恶化,影响水体中生物的生长。针对此问题,该研究在实验室条件下对玻璃水槽中2种不同盐度水体（淡水和4% NaCl溶液）染色,仅依靠浮力作用,观测水体去分层过程的准备、起动、混合和均匀4个阶段;在压力差的驱动下,形成“上升流”式的上涌对流,发现流体上浮至分层界面发生混合并使跃层增厚,最终引起分层水体失稳破坏。依据试验结果总结出水体分层破坏过程分为准备、起动、混合和均匀4个阶段,在给定工况下,100 L/h输水流量混合作用最强且完全混合的时间最短,25 L/h输水流量混合作用最弱且完全混合的时间最长。该文发现在一定盐度差异下,水体去分层起动时间和完全混合时间的变化规律对水产养殖产业有促进作用。     

Decomposition of beech litter cutin under laboratory conditions

A pot experiment was performed in order to obtain informations on the decomposition pattern of beech litter cutin under laboratory conditions. Results show that cutin is little resistant to biodegradation at 20°C and 70% WHC. An increasing ratio of the cutin- and suberin-derived monomeric compounds (THOA + EHOA)/DHHA is indicative of the input of root litter material into the organic matter pool of forest soils.     

Influence of cattle trampling on soil porosity under alternate dry and ponded conditions

Abstract. The impact of cattle trampling on the porosity of a representative soil (Typic Natraquoll) of the flooding Pampa of Argentina was studied from 1984 to 1987. Water content, total porosity (TP), macroporosity (> 30 μm) and mean weight diameter of water-stable aggregates (MWD) were determined in undisturbed topsoil samples taken from adjacent continuously grazed (1.0 animal unit/ha/yr) and ungrazed (since 1976) areas. It was expected that trampling would decrease macroporosity when the soil was ponded, and that the damaged macropores would regenerate during the subsequent soil drying. This was only partly verified. The soil varied in TP from 58 to 64% in the ungrazed area, and from 53 to 78% in the grazed area. This variation resulted mainly from shrink-swell processes. Trampling decreased soil macroporosity (mainly >60 μm) from 8 to 5% and decreased MWD from 5.35 to 4.58 mm under dry soil conditions. The damaged soil pores regenerated and aggregate stability recovered during the subsequent period of surface water ponding, when soil swelling increased macropores in the grazed area but not in the ungrazed area. There was no evidence of poaching damage in this soil.     

Effects of nanoscale pores in soils on carbon evolution under extremely dry conditions

Abstract

Soil carbon evolution under the lowest moisture conditions varies considerably among experimental systems/techniques, leading to discrepancies in the estimations from carbon dynamics models under low moisture conditions. We focused our study on clarifying the regulating factors of soil carbon evolution under the lowest moisture conditions by conducting laboratory experiments under precisely controlled conditions. Nanoscale porosity and surface properties of these soils were determined to analyze the role of residual water in the carbon evolution processes in dry soils. Laboratory incubation showed that the carbon evolution from a microporous (D < 2 n m) volcanic soil proceeded even at -100 U kg^-1 water potential (INT) in contrast to the carbon evolution from a phyllosilicate alluvial soil. Pore-size estimation and ¹H-NMR spectroscopy showed that the carbon evolution at -100 U kg^-1 WP proceeded through the utilization of nanopore-water in soils. Batch sorption experiment suggested that the surface affinity of the soils to dissolved organic matter (DOM) had enhanced carbon evolution by attracting DOM into hydrophilic spheres of the soil at -100 U kg^-1 MT. Solid-state IIGNMR of organic matter samples (incubated in the absence of soils) suggested that the chemical alteration of the samples was significant for aliphatic components, while the alteration was not observed in the samples incubated at -100 U kg^-1 WP. This fact also indicated the contribution of nanoscale pores in the volcanic components to carbon evolution. Application of the experimental results to several biogeochemical models revealed that both volumetric water content and MT are required to estimate carbon evolution under low moisture conditions. A micro habitat model showed that the carbon evolution at -100 U kg^-1 WP could be attributed to extracellular enzymatic processes or other abiotic processes rather than to the activities of living microorganisms.