Nitrogen transformations in cold and frozen agricultural soils following organic amendments

Though microbial activity is known to occur in frozen soils, little is known about the fate of animal manure N applied in the fall to agricultural soils located in areas with prolonged winter periods. Our objective was to examine transformations of soil and pig slurry N at low temperatures. Loamy and clay soils were either unamended (Control), amended with ¹⁵NH₄-labeled pig slurry, or amended with the pig slurry and wheat straw. Soils were incubated at −6, −2, 2, 6, and 10 °C. The amounts of NH₄, NO₃ and microbial biomass N (MBN), and the presence of ¹⁵N in these pools were monitored. Total mineral N, NO₃ and ¹⁵NO₃ increased at temperature down to −2 °C in the loam soil and −6 °C in the clay soil, indicating that nitrification and mineralization proceeded in frozen soils. Nitrification and mineralization rates were 1.8-4.9 times higher in the clay than in the loamy soil, especially below freezing point (3.2-4.9), possibly because more unfrozen water remained in the clay than in the loamy soil. Slurry addition increased nitrification rates by 3-14 times at all temperatures, indicating that this process was N-limited even in frozen soils. Straw incorporation caused significant net N immobilization only at temperatures ≥2 °C in both soils; the rates were 1.4-3.4 higher in the loam than in the clay soil. Nevertheless, up to 30% of the applied ¹⁵N was present in MBN at all temperatures. These findings indicate that microbial N immobilization occurred in frozen soils, but was not strong enough to induce net immobilization below the freezing point, even in the presence of straw. The Q₁₀ values for estimated mineralization and nitrification rates were one to two orders-of-magnitude larger below 2 °C than above this temperature (13-208 versus 1.5-6.9, respectively), indicating that these processes are highly sensitive to a small increase in soil temperature around the freezing point of water. This study confirms that net mineralization and nitrification can occur at potentially significant rates in frozen agricultural soils, especially in the presence of organic amendments. In contrast, net N immobilization could be detected essentially above the freezing point. Our results imply that fall-applied N could be at risk of overwinter losses, particularly in fine-textured soils.     

Influence of drying vs. freezing of archived soil samples on soil organic matter fractions

Archived soil samples are a valuable tool for any long‐term soil research. We analysed total carbon (C) and nitrogen (N) content and soil organic matter fractions in 38 archived soil samples that were stored for up to 21 years and compared air‐dried storage to frozen storage conditions. Samples include top‐ and upper subsoils, different soil texture and land use with C contents between 4.3 and 174 mg g^?1. The results from this study reveal no changes in total C and N contents with storage time up to 21 years or type of storage (freezing vs. air drying). The analyses of soil physical fractions also revealed no significant differences between air‐dried stored and frozen stored samples for most samples. However, we found indications, that freezing of soil material might lead to changes in the mineral fractions for soils containing high amounts of water. Therefore, and as archiving soils in a frozen state is more expensive than storing air‐dried samples, we recommend the use of air‐dried samples for C quality analyses of archived soil samples.     

影响冻融土壤水分入渗特性主要因素的试验研究

以冻融期间大田自然冻融土壤入渗试验为依据,分析讨论了影响冻融土壤水分入渗特性的主要因素。试验结果表明,冻融条件下,土壤水分入渗特性不仅受非冻结土壤基本理化特性（土壤结构、土壤质地、、土壤含水量等）的影响,还受冻融土壤的冻层厚度、冻层层位、冻层层数等特有因素的影响;在给定土壤质地条件下,土壤结构、土壤含水量、冻层厚度和冻层层位是其主导影响因素,冻层层数对土壤入渗能力也有一定影响。研究结果可为冻融土壤入渗特性的进一步研究奠定基础;可供季节性冻土区冬春灌溉参考。     

Effects of soil storage on the microbial community and degradation of metsulfuron-methyl

The effect storage had on the microbial biomass in two soils (Trevino and Fargo) was compared to the effect storage had on each soil's capacity to degrade metsulfuron-methyl. Soils were collected from the field and used fresh (<3 weeks old) or stored at 20 and 4 degrees C for 3 or 6 months. The phospholipid fatty acid content of the soils was used to monitor changes in the microbial biomass during storage and incubation in a flow-through apparatus. In both soils, [phenyl-U-14C]metsulfuron-methyl was used to monitor changes in the route and rate of degradation along with 14CO2 evolution (mineralization). Total microbial biomasses in both soils were significantly reduced for soils incubated in the flow-through apparatus, whereas only the Trevino soil's microbial biomass was significantly reduced as a result of storage. The microbial communities of both soils were significantly different as a result of storage as shown by discriminant analysis. In both soils, degradation rate, pathway of degradation, and mineralization of metsulfuron-methyl were significantly affected by storage compared to fresh soil. The half-life of metsulfuron-methyl increased significantly (P < 0.05) in the Trevino soil from 45 days (fresh) to 63 days (stored soil), whereas in the Fargo soil half-lives increased significantly (P < 0.05) from 23 days (fresh) to 29 days (soils stored for 6 months). In both soils, mineralization of [14C]metsulfuron-methyl was significantly (P < 0.05) higher in fresh soils compared to stored soils. The degradation pathways of metsulfuron-methyl changed with storage as evidenced by the loss of formation of one biologically derived metabolite (degradate) in stored soils compared to fresh soils.     

The influence of two agricultural biostimulants on nitrogen transformations, microbial activity, and plant growth in soil microcosms

The influence of two experimental soil treatments, Z93 and W91, on nitrogen transformations, microbial activity and plant growth was investigated in soil microcosms. These compounds are commercially marketed fermentation products (Agspectrum) that are sold to be added to field soils in small amounts to promote nitrogen and other nutrient uptake by crops in USA. In laboratory microcosm experiments, soils were amended with finely ground alfalfa-leaves or wheat straw, or left unamended, in an attempt to alter patterns of soil nitrogen mineralization and immobilization. Soils were treated in the microcosms with Z93 and W91 at rates equivalent to the recommended field application rates, that range from 0.2 to 1.1 l ha⁻¹, (0.005-0.03 μl g⁻¹ soil). We measured their effects on soil microbial activity (substrate-induced respiration (SIR), dehydrogenase activity (DHA) and acid phosphatase activity (PHOS)), soil nitrogen pools (microbial biomass N, mineral N, dissolved organic N), and transformations (net N mineralization and nitrification, ¹⁵N dilution of the mineral N pool, and accumulation of mineral N on ion-exchange resins), and on wheat plant germination and growth (shoot and root biomass, shoot length, N uptake and ¹⁵N enrichment of shoot tissues), for up to 56 days after treatment. To follow the movement of nitrogen from inorganic fertilizer into plant biomass we used a ¹⁵N isotopic tracer. Most of the soil and plant responses to treatment with Z93 or W91 differed according to the type of organic amendment that was used. Soil treatment with either Z93 or W91 influenced phosphatase activity strongly but did not have much effect on SIR or DHA. Both chemicals altered the rates of decomposition and mineralization of organic materials in the soil, which was evidenced by significant increases in the rates of the decomposition of buried wheat straw, and by the acceleration of net, rates of N mineralization, relative to those of the controls. Soil nitrate availability increased at the end of the experiment in response to both chemical treatments. In alfalfa-amended soils, the final plant biomass was decreased significantly by treatment with W91. Increased plant growth and N-use efficiency in straw-amended soil, resulting from treatments with Z93 or W91, was linked to increased rates of N mineralization from indigenous soil organic materials. This supports the marketing of these compounds as promoters of N uptake at these low dosage inputs.     

不同浸提剂以及保存方法对土壤矿质氮测定的影响

为探明影响土壤矿质氮测定的因素,从棕壤、潮土和黄棕壤3种类型土壤中各采集10个经不同施肥处理的土样,用连续流动注射分析仪测定经不同浸提剂以及不同保存方法处理后土样的NO3-N和NH4-N含量。结果表明:不论是棕壤、潮土还是黄棕壤,2 mol.L?1 KCl提取硝态氮的数量与0.01 mol.L?1 CaCl2提取的数量相关性均达到P<0.01水平;3种土壤各个土样硝态氮含量的测定值多表现为新鲜土<冷冻土<风干土;将鲜样浸提后作短时间的冷冻处理,其效果与鲜样24 h内的测定结果较接近;土样不同保存方式以及浸提液的保存时间对3种土壤NH4-N测定结果的影响规律不及NO3-N明显。     

Spatial variability of the functional stability of microbial respiration process: a microcosm study using tropical forest soil

Purpose

Understanding the ability of ecosystem processes to resist to and to recover from disturbances is critical to sustainable land use. However, the spatial variability of the stability has rarely been addressed. Here, we investigated the functional stability of a soil microbial process for 24 soils collected from adjacent locations from a 0.3?ha tropical rainforest plot in Paracou, French Guiana.

Materials and methods

The 24 locations were characterized regarding soil chemical and biological (microbial diversity) parameters and forest structure. The corresponding soils were submitted to an experimental transient heat disturbance during a microcosm experiment. The response of the respiration process was followed using substrate-induced respiration (SIR).

Results and discussion

The response of soil SIR to heat disturbance varied widely between samples. The variability of the SIR response increased just after the disturbance, and a global rather homogeneous decrease in SIR rates was observed 15 and 30?days after. The stability of SIR in response to heat disturbance could not be related to either the genetic or the metabolic diversity of the microbial community. The initial level of SIR before the disturbance was the soil variable that best correlated with the impact of the disturbance: the soil locations with the highest initial SIR rates were the most affected 15 and 30?days after the heat disturbance.

Conclusions

Such a heterogeneous response suggests that the response of soil processes to a disturbance will be difficult to assess from only local-scale analyses and highlights the need for spatial explicitness in understanding biogeochemical processes.     

Impact of tillage on microbial activity and the fate of pesticides in the upper soil

The impact of two tillage systems, plow tillage (PT) and no-tillage (NT), on microbial activity and the fate of pesticides in the 0–5 cm soil layer were studied. The insecticides carbofuran and diazinon, and the herbicides atrazine and metolachlor were used in the study, which included the incubation and leaching of pesticides from untreated soils and soils in which microorganisms had been inhibited. The mineralization of ring¹⁴C labeled pesticides was studied. The study differentiated between biotic and abiotic processes that determine the fate of pesticides in the soil. Higher leaching rates of pesticides from PT soils are explaned by the relative importance of each of these processes. In NT soils, higher microbial populations and activity were associated with higher mineralization rates of atrazine, diazinon and carbofuran. Enhanced transformation rates played an important role in minimizing the leaching of metolachlor and carbofuran from NT soils. The role of abiotic adsorption/retention was important in minimizing the leaching of metolachlor, carbofuran and atrazine from NT soils. The role of fungi and bacteria in the biodegradation process was studied by selective inhibition techniques. Synergistic effects between fungi and bacteria in the degradation of atrazine and diazinon were observed. Carbofuran was also degraded in the soils where fungi were selectively inhibited. Possible mechanisms for enhanced biodegradation and decreased mobility of these pesticides in the upper layer of NT soils are discussed.     

Experimental analysis of the effect of exotic and native plant species on the structure and function of soil microbial communities

Invasions of exotic plant species are among the most pervasive and important threats to natural ecosystems, however, the effects of plant invasions on soil processes and the soil biota have rarely been investigated. We grew two exotic and a native under-story plant species in the same mineral soil from a non-invaded forest stand in order to test whether observed differences in the field could be experimentally produced in the greenhouse. We characterized changes in the soil microbial community structure (as indexed by PLFAs) and function (as indexed by enzyme activities and SIR), as well as changes in potential nitrogen mineralization rates. We found that the invasion of two very dissimilar exotic species into the under-story of deciduous forests in eastern North America can rapidly cause changes in most of the studied soil properties. At the end of the three-month incubation, soils under the exotic species had significantly different PLFA, enzyme and SIR profiles than both initial soils and soils where native shrubs had been grown. We also observed a significant increase in pH and nitrification rates under one of the exotic plants. Such changes in the soil are potentially long-term (e.g. changes in soil pH) and are therefore likely to promote the re-invasion of these and other exotics. Both management of exotic plant invasions and the restoration of native communities must take into account exotic species effects on the soil.     

季节性冻融土壤的冻融特点和减渗特性的

本文基于季节性冻土地区冻融期间自然冻融土的大田入渗试验,分析了田间耕作土壤的冻融特点,讨论了冻融土壤的减渗特性;探讨了冻融土壤的减渗机理。研究结果表明：在不同的冻融阶段,土壤冻层的形态,厚度、层数和层位不同,对入渗水流的控制和影响不同;冻结土壤的减渗特性随冻融阶段的变化面变化;而结条件下,土壤导水率的减小是其入渗能力减小的根本原因,而土壤液态水的相变是土壤导水率减小的要源所在。研究结果对于季节性冻     

冻融交替对水稻土水溶性有机碳含量及有机碳矿化的影响

冻融交替影响土壤水分的有效性及土壤团聚体稳定性,进而影响土壤中微生物的活性及土壤有机碳的矿化。通过室内冻融模拟(即分别在-7℃和28℃下处理土壤)及培养实验,研究了不同冻融交替循环处理下土壤水溶性有机碳(WSOC)、微生物生物量及土壤有机碳矿化的变化规律。结果表明,1到3次冻融交替处理会增加土壤中水溶性有机碳的含量,其中经过1次冻融交替处理的2种土壤其WSOC含量分别增加了25%,20%;但在本实验条件下如果继续增加冻融交替次数则会使土壤水溶性有机碳含量减少。冻融交替处理降低土壤微生物生物量,因此也会影响土壤有机碳的矿化。冻融交替处理对培养第1天的土壤有机碳矿化具有激发效应,激发能力:1次冻融交替>3次冻融交替>6次冻融交替,经过1次冻融交替处理后的土壤其呼吸速率与对照相比增加了17%～40%;其后,冻融交替处理土壤呼吸速率迅速下降,在培养后期甚至低于对照处理。     

CO2 and N2O emissions from gleyic soils in the Russian tundra and a German forest during freeze-thaw periods—a microcosm study

Knowledge is scarce on mineralization of soil organic carbon (SOC) in and N₂O emissions from tundra soils in periods of alternate freezing and thawing. Our objectives were to study the CO₂ and N₂O emissions from two silty gleyic soils formed in different climate zones (a gleyic Cryosol located in the Russian tundra, and a stagnic Gleysol located in an oak stand in central Germany) during freeze-thaw events. Soils were adjusted to a matric potential of −0.2 kPa and emissions were measured in 3-h intervals during an incubation period of 50 days including three freeze-thaw cycles. CO₂ emissions from the German oak forest soil were twofold higher than those of the tundra soil. The ratios of the mean CO₂ production rate before the freezing to the mean CO₂ production rate after thawing ranged from 0.63 to 0.73 for the forest soil and from 0.85 to 0.89 for the tundra soil. The specific CO₂-C production rate (CO₂-C/SOC) was 0.16 for the tundra soil and 0.57 for the forest soil. The results indicate that bioavailability of SOC was markedly smaller in the tundra soil than in the forest soil. Large N₂O emissions were found for the German forest soil, but no N₂O emissions were observed for the tundra soil. The main reason for the absence of N₂O emissions was most likely the negligible availability of nitrate for denitrification. There was some indication that the initial increase in mineralization of SOC induced by freezing and thawing differs between soils from various climatic regions, probably mainly due to a differing bioavailability of the SOC and differing releases of nutrients after thawing.     

大同市季节性冻土的分布与变化特征

利用大同市1961-2008年8个站点地面气象观测记录中的冻土资料,对大同市地面冻结日期、解冻日期、冻结日数及最大冻土深度的时空分布进行分析。结果表明:40多年来土壤开始冻结期呈推迟的趋势,土壤完全解冻期呈提前的趋势,地面冻结日数相应呈减少趋势,累年最大冻土深度自西北向东南逐渐减小,全市历年平均最大冻土深度变化总体上呈减少趋势,但2000年以后较20世纪60-80年代有增加的趋势。     

土壤含水率对季节性冻土入渗特性影响的试验研究

基于季节性冻融期不同土壤含水率条件下的冬小麦田单点入渗试验,讨论了土壤含水率对冻融土壤水分入渗能力和入渗率的影响以及不同冻融阶段土壤入渗特性的变化。结果表明季节性冻融期土壤含水率对冻融土壤入渗特性的影响显著。土壤入渗能力随土壤含水率的升高而减小;冻融土壤累积入渗量随土壤含水率的变化符合幂函数规律;高土壤含水率导致的水力传导度减小是冻土入渗能力降低的主要原因。研究结果对于季节性冻土分布区农田冬春灌溉、确定合理灌水技术参数及水资源合理利用提供了参考。     

液氮冻结软壳青蟹在冻藏期间的营养物质变化

为探讨液氮(LN)冻结拟穴青蟹软壳蟹在冻藏期间的营养物质变化,本研究采用基于核磁共振(NMR)的代谢组学技术分析了LN冻结软壳蟹可食组织代谢谱在短期(7 d)和长期(8个月)冻藏期间的变化。结果表明,-20℃冻藏和LN冻结均对短期冻藏的软壳蟹代谢谱无显著影响(P>0.05),但 -20℃ 冻藏导致软壳蟹肌肉的二甲胺和肝胰腺的肌苷水平倍增,而LN冻结能抑制这两种物质的增加。长期冻藏可导致LN冻结软壳蟹肌肉的肌苷、麦芽糖和葡萄糖以及肝胰腺的肌苷、谷氨酰胺和尿苷水平显著升高(P<0.05)。表明LN冻结可有效缓解长期冻藏软壳蟹的质量下降。本研究结果为揭示软壳蟹冻藏过程中的品质变化提供了理论参考。     

一个冻土水盐热运动的数学模型

本文建立了一个冻土水盐热运动的数学模型。为了考虑土壤冻结和化冻时冰—液相变的影响,在传统土壤热传导方程中加入了溶化潜热运动项和存传统土壤水分运动方程中加入了相变项,从而推导出了三个相互关联的冻土水盐热运动方程,并提出了描述冻土未冻水含量随土壤冻结温度而变化的土壤冻结特征曲线及其实验测定方法。这个模型既可适应于冻土,也可适应于未冻土。     

冻融交替对砒砂岩与沙复配土壤氮素的影响

[目的]探讨冻融作用对毛乌素沙地陕北榆林地区砒砂岩与沙复配土壤氮素的影响,对于提升毛乌素沙地土壤肥力具有重要作用。[方法]通过室内培养试验,探讨不同比例砒砂岩与沙复配土壤氮矿化过程对冻融的响应特征。[结果]冻融交替作用对土壤氮的矿化有显著影响,在冻融1周期时,3种比例复配土壤中硝态氮、铵态氮含量增加较快。在冻融2周期后,复配土壤中硝态氮、铵态氮含量均出现下降趋势。冻融5周期,复配土壤中硝态氮、铵态氮含量均开始呈现稳定增加趋势。冻融10周期后,1∶1,1∶2及1∶5复配土壤铵态氮含量分别增加了10%,49%与11%,硝态氮含量分别增加了14%,39%与34%,其中1∶2复配土硝态氮、铵态氮含量较1∶1,1∶5增加显著,对氮素的保持性能较好。[结论]冻融循环促进了土壤有机氮的矿化,有利于土壤中硝态氮、铵态氮的累积,为早春农作物的生长提供足够的氮素。     

Cold storage and laboratory incubation of intact soil cores do not reflect in-situ nitrogen cycling rates of tropical forest soils

Measurements of N transformation rates in tropical forest soils are commonly conducted in the laboratory from disturbed or intact soil cores. On four sites with Andisol soils under old-growth forests of Panama and Ecuador, we compared N transformation rates measured from laboratory incubation (at soil temperatures of the sites) of intact soil cores after a period of cold storage (at 5 °C) with measurements conducted in situ. Laboratory measurements from stored soil cores showed lower gross N mineralization and NH₄⁺ consumption rates and higher gross nitrification and NO₃⁻ immobilization rates than the in-situ measurements. We conclude that cold storage and laboratory incubation change the soils to such an extent that N cycling rates do not reflect field conditions. The only reliable way to measure N transformation rates of tropical forest soils is in-situ incubation and mineral N extraction in the field.     

Nitrogen mineralization and microbial activity in permanent pastures amended with nitrogen fertilizer or dung

 Gross rates of soil processes and microbial activity were measured in two grazed permanent pasture soils which had recently been amended with N fertilizer or dung. ¹⁵N studies of rates of soil organic matter turnover showed gross N mineralization was higher, and gross N immobilization was lower, in a long-term fertilized soil than in a soil which had never received fertilizer N. Net mineralization was also found to be higher in the fertilized soil: a consequence of the difference between the opposing N turnover processes of N mineralization and immobilization. In both soils without amendments the soil microbial biomass contents were similar, but biomass activity (specific respiration) was higher in the fertilized soil. Short-term manipulation of fertilizer N input, i.e. adding N to unfertilized soil, or witholding N from previously fertilized soil, for one growing season, did not affect gross mineralization, immobilization or biomass size and activity. Amendments of dung had little effect on gross mineralization, but there was an increase in immobilization in both soils. Total biomass also increased under dung in the unfertilized soil, but specific respiration was reduced, suggesting changes in the composition of the biomass. Dung had a direct effect on the microbial biomass by temporarily increasing available soil C. Prolonged input of fertilizer N increases soil C indirectly as a result of enhanced plant growth, the effect of which may not become evident within one seasonal cycle. Received: 18 December 1998     

Effects of soil moisture on gross N transformations and N2O emission in acid subtropical forest soils

Soil moisture changes, arising from seasonal variation or from global climate changes, could influence soil nitrogen (N) transformation rates and N availability in unfertilized subtropical forests. A ¹⁵?N dilution study was carried out to investigate the effects of soil moisture change (30–90 % water-holding capacity (WHC)) on potential gross N transformation rates and N₂O and NO emissions in two contrasting (broad-leaved vs. coniferous) subtropical forest soils. Gross N mineralization rates were more sensitive to soil moisture change than gross NH₄ ⁺ immobilization rates for both forest soils. Gross nitrification rates gradually increased with increasing soil moisture in both forest soils. Thus, enhanced N availability at higher soil moisture values was attributed to increasing gross N mineralization and nitrification rates over the immobilization rate. The natural N enrichment in humid subtropical forest soils may partially be due to fast N mineralization and nitrification under relatively higher soil moisture. In broad-leaved forest soil, the high N₂O and NO emissions occurred at 30 % WHC, while the reverse was true in coniferous forest soil. Therefore, we propose that there are different mechanisms regulating N₂O and NO emissions between broad-leaved and coniferous forest soils. In coniferous forest soil, nitrification may be the primary process responsible for N₂O and NO emissions, while in broad-leaved forest soil, N₂O and NO emissions may originate from the denitrification process.