铝模块消解仪加热法测定土壤中有机质含量

铝模块消解仪加热法替代油浴加热消解土壤样品,测定土壤中有机质含量。通过优化消解仪的消解温度、加热时间等实验,确定消解仪温度220℃(沸腾时消化管内溶液温度约为170℃),沸腾时间12 min (消解时间约为22 min)为铝模块消解仪的最佳有机质测定条件。使用该方法测定的土壤标准样品的有机质含量均在误差允许范围以内,消解样品有机质回收率达99.98％,校正系数为1.00。同时用我国长期定位试验典型土壤进行该方法准确度和精密度测试,样品有机质测定结果标准偏差为0.06~0.78,变异系数为0.30％~4.11％,符合测定要求。与经典油浴加热方法相比,该方法温度易控制、操作简单、安全,可降低环境污染;结果的准确度和精密度满足要求,值得推广。     

电位滴定法测定土壤有机质

本文提出用电位滴定法测定土壤有机质。应用自动电位滴定装置,预置终点电位,可自动地滴定成批量的土样待测液。省时、省力、又方便,测定再现性好,准确度也不低于常用的И.В.丘林容量法。     

土壤碱溶有机质的测定研究与应用

研究了一种土壤供氮能力快速测定方法-土壤碱溶有机质的测定,以及碱溶有机质与常规土壤有机质的相关性、碱溶有机质与植株氮素吸收的相关性及其在测土推荐施肥中的初步应用。选择我国有代表性的潮土、黑土、红壤土样各50个,研究土壤碱溶有机质与常规方法-丘林法测定的土壤有机质的相关性,结果显示二者呈极显著相关(p>0.01),相关系数r=0.9345,相关直线回归方程为:土壤有机质(g kg-1)=3.3265μ碱溶有机质(g kg-1)+6.9389。选择代表我国主要土壤类型的28个土样进行盆栽试验,研究土壤供氮能力测定方法与植株氮素吸收的相关性,结果表明,土壤碱溶有机质与不施氮处理植株吸氮量相关性极显著(相关系数为0.628,p>0.01),且其相关系数高于土壤有机质和土壤全氮与植株吸氮量的相关系数。虽然土壤碱溶有机质与植株氮素吸收的相关性低于生物培养方法即好气培养2周后土壤矿质氮(硝态氮+铵态氮)与植株氮素吸收的相关性,但土壤碱溶有机质更适合测土推荐施肥实验室高效快速测定的需要,可见碱溶有机质是可浸提的土壤腐殖质,可用比色法快速测定并能较好估测土壤的供氮能力,值得推荐在测土配方施肥实验室应用。     

测定土壤有机质氧化条件的研究

丘林法测定土壤有机质因加热介质和氧化条件的不同,其氧化程度也不一样。应用ＧＢＷ０７４０１￣０７４０６国家标准物质筛选出土壤有机质测定的加热介质和氧化条件－甘油浴８ｍｉｎ。快速方便,结果准确可靠。     

土壤碱溶有机质的测定研究与应用

本文研究了一种土壤供氮能力快速测定方法-土壤碱溶有机质的测定,以及碱溶有机质与常规土壤有机质的相关性、碱溶有机质与植株氮素吸收的相关性及其在测土推荐施肥中的初步应用。选择我国有代表性的潮土、黑土、红壤土样各50个,研究土壤碱溶有机质与常规方法-丘林法测定的土壤有机质的相关性,结果显示二者呈极显著相关（p>0.01）,相关系数R = 0.9345,相关直线回归方程为：土壤有机质（gkg-1） = 3.3265碱溶有机质（gkg-1）+ 6.9389。选择代表我国主要土壤类型的28个土样进行盆栽试验,研究土壤供氮能力测定方法与植株氮素吸收的相关性,结果表明,土壤碱溶有机质与不施氮处理植株吸氮量相关性极显著（相关系数为0.628,p>0.01）,且其相关系数高于土壤有机质和土壤全氮与植株吸氮量的相关系数。虽然土壤碱溶有机质与植株氮素吸收的相关性低于生物培养方法即好气培养2周后土壤矿质氮（硝态氮+铵态氮）与植株氮素吸收的相关性,但土壤碱溶有机质更适合测土推荐施肥实验室高效快速测定的需要,可见碱溶有机质是可浸提的土壤腐殖质,可用比色法快速测定并能较好估测土壤的供氮能力,值得推荐在测土配方施肥实验室应用。     

土壤有机质含量测定方法的改进研究

通过研究改进了土壤有机质含量的测定方法。首先称取适量土壤置于长管消解系统中进行消解,然后采用全自动电位滴定仪进行滴定,直接获得土壤的有机质含量。使用该方法测定的土壤标准样品的有机质含量均在保证值以内,同时对实际样品进行精密度测试,得到相对标准偏差为1.03%。该方法降低了土壤有机质含量检测的实验成本,减少了环境污染,同时提高了实验数据的准确度与精密度,值得推广。     

土壤有机质消煮方法的改进

本文是在原电热板加热法的基础上作了一些改进,将电热板四周加上保温墙,电热板上铺以细小玻璃珠和简易导轨,三角瓶在电热板上易于滑动,使其在各不同位置上进行消煮。同时,还做了温度试验和水分蒸发试验,并用国家一级标准物质做了检验。     

测定土壤有机质氧化条件的研究

丘林法测定土壤有机质因加热介质和氧化条件的不同,其氧化程度也不一样.应用GBW07401～07406国家标准物质筛选出土壤有机质测定的加热介质和氧化条件--甘油浴8min.快速方便,结果准确可靠.     

利用烧失量方法精确测定土壤有机质

Wet oxidation procedure,i.e.,Walkley-Black (WB) method,is a routine,relatively accurate,and popular method for the determination of soil organic matter (SOM) but it is time-consuming,costly and also has a high potential to cause environmental pollution because of disposal of chromium and strong acids used in this analysis.Therefore,loss-on-ignition (LOI) procedure,a simple and cheap method for SOM estimation,which also avoids chromic acid wastes,deserves more attention.The aims of this research were to study the statistical relationships between SOM determined with the LOI (SOMLOI) and WB (SOMWB) methods to compare the spatial variability of SOM in two major plains,Shahrekord and Koohrang plains,of Chaharmahal-va-Bakhtiari Province,Iran.Fifty surface soil samples (0-25 cm) were randomly collected in each plain to determine SOM using the WB method and the LOI procedure at 300,360,400,500 and 550 ℃ for 2 h.The samples covered wide ranges of soil texture and calcium carbonate equivalent (CCE).The general linear form of the regression equation was calculated to estimate SOM LOI from SOM obtained by the WB method for both overall samples and individual plains.Forty soil samples were also randomly selected to compare the SOM and CCE before and after ignition at each temperature.Overall accuracy of the continuous maps generated for the LOI and WB methods was considered to determine the accordance of two procedures.Results showed a significant positive linear relationship between SOM LOI and SOM WB.Coefficients of determination (R2) of the equations for individual plains were higher than that of the overall equation.Coefficients of determination and line slopes decreased and root mean square error (RMSE) increased with increasing ignition temperature,which may be due to the mineral structural water loss and destruction of carbonates at higher temperatures.A temperature around 360 ℃ was identified as optimum as it burnt most organic carbon,destroyed less inorganic carbon,caused less clay structural water loss,and used less electrical energy.Although the trends of SOM in the kriged maps by the two procedures accorded well,low overall accuracy was observed for the maps obtained by the two methods.While not suitable for determination where high accuracy is required,determination of organic carbon through LOI is likely suitable for exploratory soil surveys where rough estimation of organic matter is required.     

The oxidation of soil organic matter by KBrO for particle size determination

Abstract

The oxidation of soil humus by alkaline KBrO solution at boiling temperature has been shown to be successful even with samples as carbonaceous underwater soils. With these soils treatment with H₂O₂ produces a cohesive foam which prevents further oxidation.     

A high sample volume procedure for the colorimetric determination of soil organic matter

Abstract

A modified procedure for routine determination of soil organic matter is described. The procedure employs a wet combustion method of reducing the carbon in soil organic matter with dichromate in an acid media. The modification will permit 700–800 organic matter determinations per day with samples containing less than 8% 0M without undue difficulty.     

Photodissolution of soil organic matter

Sunlight has been shown to enhance loss of organic matter from aquatic sediments and terrestrial plant litter, so we tested for similar reactions in mineral soil horizons. Losses of up to a third of particulate organic carbon occurred after continuous exposure to full-strength sunlight for dozens of hours, with similar amounts appearing as photodissolved organic carbon. Nitrogen dissolved similarly, appearing partly as ammonium. Modified experiments with interruption of irradiation to include extended dark incubation periods increased loss of total organic carbon, implying remineralization by some combination of light and microbes. These photodissolution reactions respond strongly to water content, with reaction extent under air-dry to fully wet conditions increasing by a factor of 3–4 fold. Light limitation was explored using lamp intensity and soil depth experiments. Reaction extent varied linearly with lamp intensity. Depth experiments indicate that attenuation of reaction occurs within the top tens to hundreds of micrometers of soil depth. Our data allow only order-of-magnitude extrapolations to field conditions, but suggest that this type of reaction could induce loss of 10–20% of soil organic carbon in the top 10 cm horizon over a century. It may therefore have contributed to historical losses of soil carbon via agriculture, and should be considered in soil management on similar time scales.     

Managing soil organic matter – implications for soil structure on organic farms

Abstract. This paper reviews current understanding of soil structure, the role of soil organic matter (SOM) in soil structure and evidence for or against better soil physical condition under organic farming. It also includes new data from farm case studies in the UK. Young SOM is especially important for soil structural development, improving ephemeral stability through fungal hyphae, extracellular polysaccharides, etc. Thus, to achieve aggregate stability and the advantages that this conveys, frequent input of fresh organic matter is required. Practices that add organic material are routinely a feature of organically farmed soils and the literature generally shows that, comparing like with like, organic farms had at least as good and sometimes better soil structure than conventionally managed farms. Our case studies confirmed this. In the reviewed papers, SOM was generally larger on the biodynamic/organic farms because of the organic additions and/or leys in the rotation. We can therefore hypothesize that, because it is especially the light fraction of SOM that is involved in soil structural development, soil structure will improve in a soil to which fresh organic residues are added regularly. Thus, we argue it is not the farming system per se that is important in promoting better physical condition, but the amount and quality of organic matter returned to a soil.     

Modelling refractory soil organic matter

Most models for the turnover of soil organic matter (SOM) include a compartment that is either considered inert, or has a very slow turnover time (refractory SOM; RSOM). The RSOM content of soils varies markedly between sites, and knowledge of its size and variability are essential for determining whether soils behave as sources or sinks of atmospheric CO₂. It has also been suggested that the accurate specification of RSOM pools is essential to modelling studies, and that uncertainty in estimates of the size of RSOM pool could be a major source of error in modelling soil organic C. In this paper, current SOM models are reviewed, and approaches to modelling RSOM and its significance are discussed. Simulations of SOM turnover for the Rothamsted Broadbalk winter wheat experiment using the Rothamsted C model and CENTURY are presented as examples. Received: 13 July 1999     

A method for estimating coefficients of soil organic matter dynamics based on long-term experiments

The one-compartment C model $C_t=C_0{\text{e}}^{-k_{2}t}+k_{1}A/k_2(1-{\text{e}}^{-k_{2}t})$ is being long used to simulate soil organic C (SOC) stocks. C_t is the SOC stock at the time t; C₀, the initial SOC stock; k₂, the annual rate of SOC loss (mainly mineralization and erosion); k₁, the annual rate to which the added C is incorporated into SOC; and A, the annual C addition. The component $C_0{\text{e}}^{-k_{2}t}$ expresses the decay of C₀ and, for a time t, corresponds to the remains of C₀ (C_0 remains). The component $k_{1}A/k_2(1-{\text{e}}^{-k_{2}t})$ refers, at time t, to the stock of SOC derived from C crops (C_crop). We herein propose a simple method to estimate k₁ and k₂ coefficients for tillage systems conducted in long-term experiments under several cropping systems with a wide range of annual C additions (A) and SOC stocks. We estimated k₁ and k₂ for conventional tillage (CT) and no-till (NT), which has been conducted under three cropping systems (oat/maize −O/M, vetch/maize −V/M and oat + vetch/maize + cowpea −OV/MC) and two N-urea rates (0 kg N ha⁻¹ −0 N and 180 kg N ha⁻¹ −180 N) in a long-term experiment established in a subtropical Acrisol with C₀ = 32.55 Mg C ha⁻¹ in the 0–17.5 cm layer. A linear equation (C_t = a + bA) between the SOC stocks measured at the 13th year (0–17.5 cm) and the mean annual C additions was fitted for CT and NT. This equation is equivalent to the equation of the model $C_t=C_0{\text{e}}^{-k_{2}t}+k_{1}A/k_2(1-{\text{e}}^{-k_{2}t})$, so that $a=C_0{\text{e}}^{-k_{2}t}$ and $bA=k_{1}A/k_2(1-{\text{e}}^{-k_{2}t})$. Such equivalences thus allow the calculation of k₁ and k₂. NT soil had a lower rate of C loss (k₂ = 0.019 year⁻¹) than CT soil (k₂ = 0.040 year⁻¹), while k₁ was not affected by tillage (0.148 year⁻¹ under CT and 0.146 year⁻¹ under NT). Despite that only three treatments had lack of fit (LOFIT) value lower than the critical 5% F value, all treatments showed root mean square error (RMSE) lower than RMSE 95% indicating that simulated values fall within 95% confidence interval of the measurements. The estimated SOC stocks at steady state (C_e) in the 0–17.5 cm layer ranged from 15.65 Mg ha⁻¹ in CT O/M 0 N to 60.17 Mg ha⁻¹ in NT OV/MC 180 N. The SOC half-life (t_1/2 = ln 2/k₂) was 36 years in NT and 17 years in CT, reflecting the slower C turnover in NT. The effects of NT on the SOC stocks relates to the maintenance of the initial C stocks (higher C_0 remais), while increments in C_crop are imparted mainly by crop additions.