Factors Affecting the Use of Conservation Tillage in the United States

Conservation tillage was used on nearly 36% of planted hectares in 1996 in the U.S. This level has remained relatively unchanged since 1991. The use of conservation tillage varies by crop and is dependent on site-specific factors including soil sype, topsoil depth, and local climate conditions. A number of economic, demographic, geographic, and policy factors have affected the adsorption of conservation tillage. While it is not possible to quantify exactly the impact of these factors, it is clear that management complexities and profitability are key factors impeding the further adsorption of conservation tillage.     

Determining the Critical Bulking Agent Requirement For Municipal Biosolids Composting

Air space within municipal biosolids composting feedstock is an important design and operating consideration. Bulking agents, such as woodchips, are required to ensure adequate air space levels are maintained. The purpose of the study was to report on the use of bench-scale air space tests to identify the critical bulking agent requirement (CBAR). CBAR was defined as the minimum amount of bulking agent required to maintain adequate pore space oxygen levels. Bench-scale air space tests were correlated to full-scale windrow composting performance, particularly pore space oxygen levels. Four volumetric ratios of municipal biosolids and woodchips were tested ranging from 1:1 to 1:4 (biosolids:wood-chips). The traditional soil physics methodology was used to determine total air space (TAS). A new step was added to the method which allowed one to also determine the free air space (FAS) within the sample. In addition, the effect of compaction on TAS and FAS was also investigated. Windrows were monitored for pile temperature and pore space oxygen concentration. At the end of the run, maturity, fecal coliform density, and the presence of salmonella were determined. The heavy metal content of the feedstock material, finished compost, and recycled woodchips were also determined. For the materials tested, biosolids and woodchips, the CBARs, to achieve a FAS of ≥20% and a minimum pore space oxygen content of ≥5%, were estimated as 1:2.5 and 1:2.8 (biosolids:woodchips; vol:vol), respectively. Assuming a target pore space oxygen level of > 5%, the recommended air space value depended on the test method used, and ranged from 26 to 61%. Bench-scale air space values were found to correlate to windrow pore space oxygen levels and operating temperature. A significant thermophilic period was not observed in any of the recipes tested. It was speculated this was caused by the coarse particle size of the woodchips. Based on the observations of the metal contents of the materials used in this investigation, the metal content of recycled material should be considered when evaluating the advantages and disadvantages of using recycled woodchips as a bulking agent.     

Factors Affecting the Alkaline Cooking Performance of Selected Corn and Sorghum Hybrids

Dent corn (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) sample sets representative of commonly grown hybrids and diverse physical attributes were analyzed for alkaline cooking performance. The influence of kernel characteristics including hardness, density, starch properties (thermal, pasting, and crystallinity), starch content, protein content, and prolamin content on alkaline cooking performance was also determined. Corn nixtamal moisture content was lower for hard, dense kernels with high protein contents; sorghum nixtamal moisture content was lower for kernels with low moisture contents and low starch relative crystallinities. Statistically significant (P < 0.05) regression equations showed that corn nixtamal moisture content was influenced by TADD (tangential abrasive dehulling device) index, kernel moisture content, starch content, and protein content; sorghum nixtamal moisture content was influenced by starch relative crystallinity, kernel moisture content, and abrasive hardness index. Pericarp removal was not strongly correlated with kernel characterization tests. Location (environmental) and hybrid (genetic) factors influenced most kernel characteristics and nixtamalization processing variables.     

Soil Evaporation and its Affecting Factors under Crop Canopy

Abstract

Based on field experiments, changing patterns and affecting factors of soil evaporation and energy balance under crop canopy were studied. Soil evaporation under crop canopy was measured directly using the microlysimetry technique. The main factors affecting soil evaporation under crop canopy including surface net radiation, leaf area index, soil water content, and crop growth period were analyzed to give scientific proof for the soil evaporation control. The results showed that no soil evaporation occurred under the crop canopy when net radiation was reduced to a threshold of 230.57 w/m². Under crop cover conditions, evaporation/evapotranspiration (E/ET) reduced with increases of crop leaf area index, followed by an exponential function to a leaf area index (LAI) threshold of 4. The cumulative evapotranspiration, transpiration, and evaporation under crop canopy conditions during the winter wheat growing season were 443.9 mm, 272.2 mm, and 171.7 mm, respectively, with E/ET having a relatively high value of 38.7%.     

Laboratory Investigation Into Factors Affecting Performance of Capillary Barrier System in Unsaturated Soil

Covers of the nuclear waste repository are of great significance to the long-term safe storage and disposal of nuclear wastes. Capillary barriers have proven to be effective to resist the downward water seeping into the underlying nuclear wastes, especially in dry climate, and have been widely used worldwide. Infiltrating water is removed from the fine layer by evaporation or transpiration or through percolation into the coarse layer, which plays a critical role in preventing the water from further infiltration in the bulk wastes. In this paper, laboratory infiltration tests were conducted with an organic glass box, filled with fine-grained quartz sand in which a layer of coarse-grained quartz sand was emplaced horizontally or at various slopes (10° and 20°), and the capillary barrier effect under various conditions (different thickness, slop of coarse-grained quartz sand layer, and sprinkling intensity) was investigated in detail. The results show that the thickness of the underlying coarse layer plays a critical role in governing the performance of the capillary barrier. The efficiency of capillary barrier increases with increasing thickness and/or slope of the coarse layer, but decreases with increasing sprinkling intensity. For a sprinkling intensity of 20 mm/day, a 30-mm-thick coarse layer even emplaced horizontally can achieve 100% water diversion. In addition, a visible tracer test was performed with an inert red dyestuff to trace the streamlines; the results indicate that even with a 7-mm-thick coarse layer, the capillary barrier can offer marked ability to prevent water from percolating into the coarse layer. The findings could be useful for improving engineered uses of capillary barriers at waste repository sites.     

Changes in the Apolar Organic Fraction Through The Composting Process

The organic fraction soluble in different organic solvents with increasing polarity was studied during the composting process, following its transformation from raw material until the stable final product with the aim to establish new quality indices of compost maturity. All apolar fractions during the composting process had a reduction higher than 50%. Part of the compounds have been utilized by the microflora as energetic material and to perform the biotransformations, and part has been transformed in molecule like the humic molecules. However, in our conditions a relevant part (36%) of apolar material is recovered at the end of the biotransformation. The spectroscopic analysis indicates in the final product an increase of lipidic compounds, as esters or acids as well as hydrocarbons with longer linear aliphatic chain.     

土壤吸附重金属的影响因素研究现状及展望

重金属元素在土壤中的吸附特征是重金属污染研究的重点之一。重金属元素在土壤中的吸附反应极为复杂,受多方面因素的影响。土壤对重金属的吸持依赖于土壤的类型、物理化学性质,如土壤的矿物特性,有机组成,土壤溶液的组成和pH,也与重金属离子本身的特征,外加阴阳离子、人工有机和无机络合剂有关。在今后的土壤吸附研究中应该结合形态分析和放射性同位素示踪的方法,并加强对根际土壤这一新领域的研究。     

A Kinetic Model of the Yard Waste Composting Process

A new kinetic concept was applied to the yard waste composting process. Yard waste mixtures with different fractions of grass clippings were composted in pilot-scale vessels. Ammonia emissions were highest with high fractions of grass clippings. Calculation of reaction rate constants was based on heat and materials balances. Although the compost mass ratios (a dimensionless number that describes how far the process has advanced) of the mixtures after composting were similar, their chemical and biological analyses reveal differences. A first order reaction model is presented that can be used for plant design. The effects of temperature and particle size on process kinetics need to be investigated further.     

稻田甲烷排放影响因素及其研究进展

CH4是大气中仅次于CO2的最重要的温室气体之一,其温室效应贡献已达15～20%。中国稻田是CH4的重要排放源,对全球大气的CH4排放起着重要的作用。本文较为详细地介绍了近几十年来国内外关于稻田CH4排放的研究进展。对稻田CH4的排放机理、CH4的排放规律及影响稻田CH4排放的各种因素作了详细分析,并相应地提出了控制稻田CH4排放的各种措施,最后提出了今后我国稻田CH4排放研究应加强的几个方面内容。     

Factors Affecting Nitrification in Soils

Abstract

Nitrification in soil converts relatively immobile ammonium‐nitrogen (N) to highly mobile nitrate‐N (via nitrite), and this has implications for N‐use efficiency by agricultural systems as well as for environmental quality, especially in situations where the potential for loss of soil or added N is high following nitrate formation. The literature on various physical, environmental, and chemical factors and their interactions on nitrification in soil is reviewed and discussed with examples from natural and agro‐ecosystems. Among the various factors, soil matrix, water status, aeration, temperature, and pH have strong influence on nitrification. The information on factors that influence nitrification is useful when developing strategies for regulating nitrification in soils by employing chemical or biological nitrification inhibitors.     

影响PCR-SSCP的因素分析

ＰＣＲ－ＳＳＣＰ是一种基于ＰＣＲ的单链构象多态性（ｓｉｎｇｌｅ－ｓｔｒａｎｄｅｄ ｃｏｎｆｏｒｍａｔｉｏｎ ｐｏｌｙｍｏｒｐｈｉｓｍ）分析技术,是ＤＮＡ已知突变的检测或未知变异分析中十分常用和实用的技术之一,本研究从非变性聚丙烯酰胺凝胶的配制、样品的变性处理、电泳条件,显色方法和结果分析等方面对影响ＰＣＲ－ＳＳＣＰ实验室操作的因素进行了分析,并结合作者的经验给出了大小在１００～２００ｂｐ范围以内的     

影响盐碱土持续利用主要环境因子演变

根据在山东禹城市多年土壤肥、水、盐定位监测资料，分析了引黄灌区影响土壤次生盐碱化的主要环境因子演变，认为主要环境因子演变经历二个阶段：第一阶段，１９８５年以前，以水利工程排水抗涝、改良盐碱土为主，配合土壤培肥和耕作措施，工程措施是改良土壤盐碱化的主要环境因子；第二阶段，１９８５年以来，主要问题是防御土壤返盐，巩固改良盐碱土壤的效果，土壤耕作是防止土壤次生盐碱化的主要环境因子，是抑制土壤次生盐碱化的有效措施，持续利用盐碱土的关键是加强土壤培肥和种植。     

东亚森林、草地碳利用效率及碳通量空间变化的影响因素分析

森林和草地是陆地生态系统的重要组成部分,研究整合基于涡度相关法观测碳通量的已发表文献,共选取东亚地区40个拥有1年以上数据的通量站(森林26个,草地14个),分析碳利用效率(CUE)以及净生态系统生产力(NEP)、总生态系统生产力(GEP)、生态系统呼吸(RE)的空间变异特征及其影响因素。东亚地区的森林和草地为碳汇,且森林的碳汇显著高于草地(p0.001),其NEP分别为328.64±256.46gC/(m~2·a),63.43±42.99gC/(m~2·a)。森林和草地的CUE分别为0.21,0.20,影响森林CUE变化的因素主要是林龄,呈线性负相关关系(p0.001)。影响草地CUE的因素主要是年均降水量(MAP),呈线性负相关关系(p0.05)。森林和草地的GEP,RE均是随纬度的升高而线性降低,NEP与纬度呈现二次函数关系,随纬度升高而先升高后降低。森林和草地的GEP,RE都与MAP呈线性正相关关系,且NEP与MAP呈先升高后降低的二次函数关系,其中森林和草地的饱和降水量大约为1 300mm和390mm。森林的GEP,RE与年均温(MAT)呈现线性正相关关系。森林和草地的GEP,RE与增强型植被指数(EVI)呈线性正相关关系。     

西南喀斯特石漠化过程对土壤水分特性的影响

通过对西南喀斯特不同石漠化过程中典型土壤水力特征的分析,研究了土壤水分参数与土壤水分库容特征及其影响因素。结果表明:(1)喀斯特地区土壤水分特征曲线呈先陡后缓的趋势,当土壤水吸力S<300 KPa时,土壤含水量θm下降很快,且陡直,土壤水分释放快,释放量大;当水吸力S超过300 KPa,直至1.5 MPa吸力段时,θm变化平直,土壤水分释放慢,释放量小。(2)未石漠化的荔波森林黑色石灰土表层土壤田间持水量达587.8 g/kg,有效水含量达435.8 g/kg,明显高于其它受到石漠化影响的土壤。土壤容重、孔隙度和有机质含量是影响土壤水分特征参数的主要因素。(3)喀斯特地区土壤较薄,土壤总库容和有效库容较低,是石灰岩地区土壤易发生侵蚀性退化和干旱的重要原因。通透库容占总库容的比例为:未石漠化的荔波原始森林黑色石灰土>潜在石漠化的普定灌丛黑色石灰土、玉米地棕色石灰土>轻度石漠化的荔波玉米地黄红壤,石漠化的发展减弱了土壤抗侵蚀能力。土层厚度、土壤有机质含量、土壤颗粒组成及0.3~0.03 mm孔隙度是影响土壤水分库容的主要因素。     

Simulation of the Mathematical Model of Composting Process of Sewage Sludge

An integrated model was developed to simulate the temporal change and spatial variation of temperature and spatial distribution of TM (total mass) and MC (moisture content) of the final compost for composting process of sewage sludge. The model included biodegradation kinetics of organic matter and balance equations of energy and mass. First-order assumption was applied to describe the biodegradation process with correction functions of temperature, oxygen, MC, and FAS (free air space). The transfer process was considered in balance equations of energy and mass. A finite difference method was used to solve the model. Two trials of 0.21 m³ were run to estimate parameters and evaluate the simulation. The model could predict TM and VS (volatile solid) of the final compost well, temporal trend of oxygen concentration and water removal, and also a good fitting of the temporal and spatial change of temperature. H_rx (reaction enthalpy of biodegradable volatile solid) and η_BVS (mass fraction of biodegradable volatile solid) were considered the most sensitive parameters based on the sensitivity analysis. Future research was suggested to focus on reasonable humidity assumption, measuring accurate value of thermodynamics and kinetics parameters of sewage sludge, and simulating the composting process with different aeration modes and turning of the pile.     

保护地土壤质量障碍因素研究

随着种植年限的增加,与露地和大田相比,保护地土壤在温度、湿度、空气、水分等环境条件,土壤有机质、全氮、速效氮、磷、钾、钙镁、酸碱度及生物活性等理化和生物性质、土壤盐分累积等均发生了巨大的变化会给土壤质量、作物生长及人类健康带来危害。为了保证高产、优质、高效的蔬菜生产,研究保护地土壤理化性状及障碍因素具有重要的理论和实践意义。     

Factors Affecting Diffusion of Ions in Soils

In this work the diffusion coefficients of Na+, K+, Ca2+, NO3- and Cl- ions were estimated in terms of measuring apparent direct current (DC) conductivities of latosol, red soil and yellow-brown earth containing, respectively, NaNO3, KCI, and CaCl2 of different concentrations (0.005, 0.05, 0.10, and 0.15 mol/L) in the case of moisture contents ranging from wet to water saturation. The results showed that when bulk density, moisture content, and electrolyte concentration were constant, the diffusion coefficients of cations were in the order Na+> K+> Ca2+ except for Na+ and K+ in latosol, while the order for anions was NO3- > Cl-. The diffusion coefficients (Di) of cations and anions were linearly proportional to volumetric moisture content (θ) as electrolyte concentration and bulk density were unchanged. When moisture content and bulk density were constant, the diffusion coefficients of cations decreased, to varying extents, with the increase of electrolyte concentration, and the decrement in differen     

恶唑菌酮在土壤中淋溶迁移影响因子研究

采用土柱淋溶方法研究了恶唑菌酮在土壤中的淋溶迁移影响因子。结果表明:恶唑菌酮在土柱中的垂直分布随着施药量、降雨量和降雨强度的改变而变化。当施药量从175μg增加到700μg或降雨量从50mm增至200mm时恶唑菌酮的最大淋溶深度随着农药施用量和降雨量的加大而加深;而随着降雨强度的增大,恶唑菌酮的最大淋溶深度减小。不同表面活性剂污染对恶唑菌酮在土壤中的淋溶迁移有显著影响,但作用结果不同。在实验浓度下阴离子和非离子表面活性剂污染对恶唑菌酮的淋溶迁移有促进作用,而阳离子表面活性剂污染则会阻滞恶唑菌酮的淋溶迁移。     

重庆市主要土壤类型硝态氮淋失及其影响因素

采用SRC(Soil-Resin-Core)装置,研究了重庆市主要土壤类型硝态氮淋失的差异以及硝态氮淋失与硝态氮含量、有效氮含量、降雨和气温等4个方面的关系。结果表明:酸性紫色土的硝态氮淋失量最大,而黄壤与碱性紫色土的硝态氮淋失量较小。酸性紫色土硝态氮含量、有效氮含量与硝态氮淋失量之间显著相关,而黄壤和碱性紫色土的硝态氮含量、有效氮含量与硝态氮淋失量之间没有显著的相关性。降雨量、气温也是引起硝态氮淋失的原因。农田施肥对地下水的污染受施肥量、施肥次数、降雨量和气温等综合作用的影响,可采取控制氮肥用量,减少施用人粪尿,避免在降雨量大的时期追肥的措施。     

模拟降雨条件下南方典型粘土坡面土壤侵蚀过程及其影响因素

采用人工模拟降雨的方法,研究了南方典型粘土坡面土壤侵蚀过程及降雨强度、降雨量、坡度对坡面产流产沙量的影响,建立了试验条件下坡面土壤侵蚀模型。结果表明:(1)试验条件下初始产流时间与降雨强度和坡度呈线性关系,随着降雨强度和坡度的增加,初始产流时间变小;(2)随着降雨时间的增加,坡面产流率先逐渐增加后达到稳定,产沙率呈先迅速增加后降低再逐渐达到稳定,产流率和产沙率随降雨强度的增加而相应增加,但随坡度变化不明显;(3)径流含沙量、总产流量、产沙量均随降雨强度和坡度的增加而增加,其中降雨强度为90mm/h、坡度为20°时总产流量为93 335ml,产沙量为636.10g,达到最大值;(4)降雨强度、降雨量、坡度都与产流量和产沙量呈极显著正相关关系,其中降雨量和降雨强度分别是产流量和产沙量最主要的影响因子,坡度对产流产沙量影响最小;(5)得出试验条件下土壤侵蚀量与降雨强度、坡度、时间的回归方程,经过验证,预测值和实测值相关性良好,说明该方程可用于试验条件下的土壤侵蚀量预测。