Predicting soil workability and fragmentation in tillage: a review

Soil workability and friability are required parameters to consider when creating suitable seedbeds for crop establishment and growth. Knowledge of soil workability is important for scheduling tillage operations and for reducing the risk of tillage‐induced structural degradation of soils. A reliable evaluation of soil workability implies a distinctive definition of the critical water content (wet and dry limits) for tillage. In this review, we provide a comprehensive assessment of the methods for determining soil workability, and the effects of soil properties and tillage systems on soil workability and fragmentation. The strengths and limitations of the different methods for evaluating the water content for soil workability, such as the plastic limit, soil water retention curve (SWRC), standard Proctor compaction test, field assessment, moisture‐pressure‐volume diagram, air permeability and drop‐shatter tests are discussed. Our review reveals that there is limited information on the dry limit and the range of water content for soil workability for different textured soils. We identify the need for further research to evaluate soil workability on undisturbed soils using a combination of SWRC and the drop‐shatter tests or tensile strength; (i) to quantify the effects of soil texture, organic matter and compaction on soil workability; and (ii) to compare soil water content for workability in the field with theoretical soil workability, thereby improving the prediction of soil workability as part of a decision support system for tillage operations.     

Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions – a review

Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe‐, Al‐, Mn‐oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo‐mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research.     

Prediction of trafficability and workability from soil moisture deficit

The relationship between the strength of field soils, under grass ley and winter wheat, and soil moisture deficit has been monitored over an 18 month period. The soil types selected represent a range of agricultural soils commonly found in Europe. Strong correlations were found to exist between moisture deficit and penetration resistance. This relationship has been used to develop a technique for predicting the average number of days on which land at a given site can be trafficked or worked during a year.     

土壤裂隙及其优先流研究进展

土壤在干燥脱水的过程中易收缩产生裂隙。裂隙的产生是土壤性质与外界条件等多种因素综合作用的结果,其形态结构也非常复杂,难以准确描述。裂隙能够作为优先流的路径,增加农田水分和养分的流失以及地下水污染的风险。本文总结和归纳了裂隙产生的影响因素、裂隙的表征指标与测定方法、裂隙导致的优先流的研究方法、裂隙对优先流的影响和模拟等方面的研究进展。今后应进一步加强裂隙产生机理的全面深入的研究;构建和完善裂隙三维指标体系及其测定方法;推进裂隙导致的优先流的定量化和数学模拟研究;加大田间原位裂隙及其优先流的研究。     

Conservation and the control of biting flies in temperate regions

In temperate regions biting flies such as members of the Culicidae, Ceratopogonidae, and Simuliidae, are normally controlled by anti-larval methods, and these can conveniently be divided into three major categories—mechanical, biological, and chemical. In methods of the first category, larval habitats are ecologically altered or eradicated and control is usually permanent. Although biological control appears attractive it has had very limited success with biting flies: it necessitates a good knowledge of the ecology and interrelationships of the pest species and their associated fauna. Most control measures consequently rely on the repetitive use of insecticides. Organochlorines (chlorinated hydrocarbons) are still commonly used, despite the danger of their accumulation in food-chains. Owing to their rapid degradation, the organophosphates are more acceptable to most conservationists, and their replacement of the more persistent insecticides is welcomed. Because it is recognized that insecticidal measures will for some time remain the principal method of controlling biting flies, the use of chemicals that appear to present few hazards to wildlife, such as Paris Green and Abate, should be encouraged. The indiscriminate routine application of insecticides, however, is condemned.     

Chemical and microbiological soil quality indicators and their potential to differentiate fertilization regimes in temperate agroecosystems

The study examined the interrelationships between chemical and microbiological quality indicators of soil and their ability to differentiate plots under contrasting fertilization regimes. The study was based on a long-term field experiment established on an Udic Ustocrepts in 1966. The soil was cropped with maize (Zea mays L.) and winter wheat (Triticum aestivum L.) and received no organic fertilization (control), wheat straw and maize stalk (crop residue) or cattle manure (manure) in combination with increasing levels of mineral N (N₀ and N₂₀₀). To asses whether seasonal fluctuations of measured properties might mask the effects of fertilization, soil samples were collected four times within a growing season. Manure amendment increased soil TOC and TN, while crop residue amendment had no significant effects. Mineral N increased TN only in April, while in September it decreased water extractable organic C (WEOC). Data of diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) gave evidence for a higher relative contribution of the aliphatic peak at 2930 cm⁻¹ and a lower relative contribution of the aromatic peaks at 1620 cm⁻¹ and 1520 cm⁻¹ under manure. Manure amendment stimulated enzymatic activities, increased microbial biomass carbon (C_mic) and total phospholipids (PLFAs), and reduced the metabolic quotient (qCO₂). Patterns of PLFAs indicated that manure amendment increased the ratio of Gram-positive to Gram-negative bacteria. Crop residue amendment had no significant effects, while in September mineral N inhibited protease activity and reduced the Gram-positive to Gram-negative ratio. Microbial-related parameters fluctuated over time but their seasonality did not hamper the identification of fertilization-induced effects. The selected properties proved to be valuable indicators of long-term changes of soil quality and were strongly interrelated: changes in soil organic matter content and composition induced by manure amendment were accompanied by changes in abundance and function of the soil microbial community. Partial least square analysis obtained relating DRIFTS spectra to measured soil properties produced accurate predictive models for TOC and PLFAs, and moderately accurate models for C_mic, showing the potential of DRIFTS to be used as a rapid soil testing technique for soil quality monitoring.     

Temporal dynamics and variation with forest type of phospholipid fatty acids in litter and soil of temperate forests across regions

Microorganisms form the basis of soil food webs and represent key control points of carbon cycling and sequestration. Virtually all central European forests are managed and land-use regimes likely impact microbial abundance and community composition. Consequently, knowledge on how land-use intensity and abiotic variables, such as pH, C-to-N ratios, moisture regimes and concomitantly different stress levels, affect microbial communities is needed. We investigated phospholipid fatty acid (PLFA) profiles of leaf litter and soil from four forest types differing in foliage, age and management intensity, replicated in three regions across Germany. To account for temporal variation, samples were taken twice in the same season, but with an interval of three years. Total microbial biomass and microbial community composition differed between years, presumably due to between year variations in weather conditions. The litter layer was more prone to effects of drying, with a reduction of almost 30% of total PLFAs in the drier year. In soil effects of weather conditions depended on soil type and therefore differed between regions, with microorganisms in the sandy soils of the Schorfheide being more susceptible to water-stress, as evidenced by a ten-fold increase of the stress indicator cy/pre ratio in the drier year. Despite temporal variations in microbial biomass and community composition, the balance between the fungal and bacterial energy channel, as measured by fungal-to-bacterial ratios, remained rather constant in particular in soil. While total microbial biomass did not differ between forest types, microbial community composition differed significantly between beech and coniferous forests. Despite more acidic conditions, the fungal energy channel was less pronounced in leaf litter of coniferous forests than in broad-leaved forests, whereas the proportion of bacterial fatty acids was the highest in coniferous forests. Increasing management intensity presumably fosters the bacterial energy channel in the exposed litter layer. Supporting this assumption coniferous forests featured significantly higher values of the stress indicators cy/pre and SAT/MONO ratio. Bacterial community structure and biomass closely correlated with pH, with particular PLFAs dominating at high and low pH, respectively, indicating pH-specific microbial communities. In contrast, fungal abundance in leaf litter was correlated with C-to-N ratio. The results suggest that leaf litter and soil need to be considered separately when investigating changes in microbial community composition, since susceptibility of microorganisms to environmental stressors differs markedly between these layers. This, and repeated sampling events, may be particularly important when investigating subtle effects such as those related to climate change.     

A comparison of soil liming requirement methodologies in temperate,Northern European pedo-climates

Background

Liming agricultural land is essential to optimise crop yield and soil nutrients. Despite the importance of pH management in agricultural soils, liming applications have been decreasing in the United Kingdom for decades. There is no comparison of contemporary and historical liming requirement (LR) methods for Northern European, temperate climate mineral soils high in organic matter (OM).

Aims

The aims of this research were to thoroughly comparatively analyse current methodologies and to ascertain which soil characteristics contribute to LR reactions.

Methods

Analysis compared methods for determining liming values common in the United Kingdom (Scottish Agricultural College [SAC] look-up chart, RothLime model), Europe and the United States (Shoemaker–McLean–Pratt, Sikora, Modified Mehlich buffers), and the 30-min calcium hydroxide titration developed by the University of Georgia.

Results

RothLime and SAC highly underestimated the LR value in acidic soils. The buffers highly over or underestimated LRs. The UGA titration method is a cheap, easy and accurate method which could be utilised for high OM soils but requires further calculation development. The characteristics most associated with soil–lime reactions in this experiment were measures of exchangeability (cation exchange capacity and loss on ignition, and by proxy, lime buffering capacity).

Conclusions

There is an opportunity to create buffer calculators and titration equations adapted to high OM soils. These are suggested for further development, through a larger diversity of UK soil types grouped by buffering capacity ranges. Including soil exchangeability factors in lime management calculations may contribute to more accurate values and therefore better resource management. Increasing LR accuracy for site-specific soil pH management, used in precision agriculture technologies, is a necessary tool for the conservation of natural resources like limestone, managing resource use efficiency, and for optimising yields.     

综述：土壤甲烷生成及其营养的研究进展

Global warming,as a result of an increase in the mean temperature of the planet,might lead to catastrophic events for humanity.This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases(GHG)concentration.Water vapor,carbon dioxide(CO2),methane(CH4)and nitrous oxide(N2O)are the most important GHG,and human activities,such as industry,livestock and agriculture,contribute to the production of these gases.Methane,at an atmospheric concentration of 1.7μmol mol-1currently,is responsible for 16%of the global warming due to its relatively high global warming potential.Soils play an important role in the CH4cycle as methanotrophy(oxidation of CH4)and methanogenesis(production of CH4)take place in them.Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG.The current knowledge of methanogenesis and methanotrophy in soils,anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.     

Improved and sustainable agroecosystem,food security and environmental resilience through zero tillage with emphasis on soils of temperate and subtropical climate regions: A review

Tillage is one of the agricultural management practices that significantly impacts agroecosystems, crop production, and the environment. Conventional tillage (CT) practices alter the soil environment and induce organic constituents’ decomposition and the emission of greenhouse gases (GHGs), which contribute to the greenhouse effect and global warming. Low organic matter, biological diversity, aggregate stability, high erosion and degradation of the soil environment, and sequestration strength are additional factors associated with CT, which negatively affect food security and environmental sustainability. As a result, CT is no more beneficial in the long run; consequently, zero tillage (ZT) could be a viable candidate for sustainable agriculture. The review to establish this systematically compared and summarized the effect of tillage systems (i.e. CT and ZT) by synthesizing and interpreting published data (>150 peer-reviewed articles) with >200 observations on soil ecosystem services and properties/agroecosystem, crop yield/food security, GHG emission, and carbon sequestration/environmental resilience. The review established that ZT improves soil structure, aggregate stability, biological diversity, organic matter and nutrients, water and water use efficiency, and reduces soil degradation, erosion, tillage machinery impacts, and GHG emissions. It allows timely seeding and better crop growth, increases yield and food security, improves carbon sequestration, strengthens soil storage potential, and helps to mitigate the adverse effects of climate change on environmental resilience. Based on various latent direct and indirect benefits, resource-saving ability, and broad adoption scope of ZT, it is corroborated that ZT is a practical and potential approach for improved and sustainable agroecosystem, food security, and environmental resilience.     

温带森林磷沉降-水系统输出-迁移动态特征及对土壤磷影响

采用对比和分析的方法,研究了黑龙江省带岭凉水国家级自然保护区温带森林生态系统磷沉降、溪流、河流和渗透水输出磷含量动态特征,以及磷沉降和水系统磷输出对红松人工林、落叶松人工林、椴树红松混交林、枫桦红松混交林和白桦次生林5种林型土壤全磷和有效磷的影响。结果表明,研究区域通过降雨产生的年磷沉降量约为0.888 kg hm-2,7月除红松人工林外,其他4个林型穿透雨磷浓度均高于大气降雨的磷浓度。7月枫桦红松林、8月白桦次生林和红松人工林A层土壤渗透水磷浓度低于林内雨磷浓度,表层土壤对穿透雨中磷有固定作用。在凉水自然保护区森林生态系统内,森林系统内小溪流、凉水河和凉水森林系统外永翠河水磷浓度均较林外降雨及穿透降雨磷浓度高,表现为永翠河水>土壤A层渗透水>凉水河>小溪>穿透雨>大气降雨。表明土壤中部分磷素通过地表径流和壤中流流出森林生态系统,并汇集于林中小溪,最后进入河流,造成磷在小溪和河流中的富集。大气磷沉降、森林水系统磷输出均与椴树红松林A0层土壤全磷含量呈显著负相关,与红松人工林B层土壤全磷含量呈极显著正相关,与落叶松人工林A0层土壤有效磷含量呈极显著正相关。     

A critique of models for freshwater and soil acidification

Four types of models quantifying effects of acid deposition on freshwaters are reviewed. These include Henriksen's empirical model, an adsorption isotherm model, soil-oriented charge balance models (Reuss-Johnson, Birkenes, MAGIC, ILWAS), and the Trickle Down model. Emphasis is on an assessment of critical assumptions; no attempt has been made to run the various models and compare results. The models range from simple to very complex and from empirical to highly process oriented. The various types have all proven useful and there has been a significant convergence concerning key processes. The importance of anion mobility, sulfate adsorption, ion exchange, dissolution of Al bearing minerals and weathering seems to be accepted by most workers. Future model improvement, however, relies to a large extent on further checking against observations.     

Origin of cristobalite in soils derived from volcanic ash in temperate and tropical regions

Cristobalite was isolated from four Ando soils and a Podzolic soil developed on volcanic ashes in French West Indies, Indonesia and Japan by selective chemical dissolution with 6 M HCl, 0.5 M NaOH and H₂SiF₆ treatments followed by specific gravity separation. All the cristobalite isolates give X-ray diffractograms with a strong and sharp peak at 4.10–4.11 Å and associated peaks at 2.8 and 2.5 Å, which are characteristic for cristobalite of high-temperature origin. Four out of five isolates show a peak at 4.06–4.07 Å ascribed to low-temperature cristobalite. The oxygen isotopic ratios (δ¹⁸O_SMOW) of cristobalite isolates show a range of +5.3 to +11.0%. which suggests a high-temperature igneous origin. These X-ray diffraction and oxygen isotopic data indicate that the cristobalite was inherited from primary volcanic ash rather than formed during pedogenesis.     

Variability in topsoil texture and carbon content within soil map units and its implications in predicting soil water content for optimum workability

The ability to predict the timing of optimum soil workability depends on knowledge of the extent and structure of variability in main physical characteristics of the soil. Our objectives were to quantify the variability in texture and carbon content within soil map units in a small agriculture-dominated catchment in South-east Norway and to assess implications of variability in texture and carbon content on land management operations, using the predicted maximum water content for optimum workability as an example. Information from three different sources were used: a soil map (1:5000), a large sample grid (100 m spacing, 270 ha extent), and a small sample grid (10 m spacing, 2.25 ha extent). Readily available information on texture and organic matter content from the soil map was found to be of limited use for soil management due to broad textural classes together with deviations from the mapped main textural classes. There were significant differences in clay, silt and sand content between the different soil textural classes on the soil map. Statistical distributions within soil map units were generally either positively or negatively skewed and the coefficient of variation was intermediate, 15–50%. Most of the variation in both grids was spatially correlated. The large grid was dominated by a patchy structure, whilst the small grid showed a systematic trend with a gradual transition indicating fuzzy boundaries between map units in this catchment. The effective range for texture was 16 times larger in the large grid. Implications of variability in texture and carbon content on land management operations were assessed for the maximum water content for optimum workability (Wopt), predicted using pedotransfer functions. Wopt was usually in the same range as the water content at–100 kPa matric potential, indicating that considerable evaporation in addition to drainage is required for obtaining workable conditions in the field. The time required for obtaining the water content was estimated to about 5 days, which is longer than an average length of periods without precipitation in the area, median 3.7 days. Wopt predicted from the soil map deviated strongly from Wopt predicted from the sample grids. Comparing estimates of Wopt from the large grid with measurements in the small grid showed differences corresponding to ±2–3 days of evaporation.     

Proteolytic activity in soil: A review

The aim of this work is to review current knowledge on inputs, sources and regulation of protease activities in soils from different ecosystems, while exploring limitations to proteolysis and N mineralisation. Extracellular proteases enter the soil via microbial production and other sources, including plant root exudates, animal excrements, decomposition processes and leaching from agro-industrial fertilisers. The synthesis and activities of proteases in soil are regulated by many factors, including climate, soil properties and the presence of organic compounds of plant and microbial origin. Two particularly important areas for future research are the regulation of proteolysis by low-molecular-weight organic compounds, including amino acids, sugars, flavonoids, plant hormones and siderophores, as well as the identification and characterisation of proteinaceous protease inhibitors of plant and microbial origin in the soil. Despite all the work that has been performed on soil proteases, our understanding of the roles of extracellular plant root proteases in N nutrition is weak. Furthermore, the regulation of soil proteolytic activities of different ecosystems, especially in terms of pollutant inputs and the impact of climate change, requires investigation. Other areas that pose important questions for the future include assessments of protease inhibitor inputs to the soil, regulation of these inhibitors via naturally occurring soil organic compounds and the interactions between soil organisms.     

土壤环境中微塑料的研究进展

微塑料是一类广泛存在于环境中的塑料颗粒,近年来,微塑料对环境的污染引起了国内外学者的广泛关注。关于微塑料对水环境造成的负面影响有较多报道,但微塑料在陆地环境特别是土壤中的存在和影响的系统性研究鲜有报道。本文从土壤微塑料的来源和分布、分析方法、对生态系统的影响、生态环境效应及管控措施等方面进行了系统综述,并针对今后土壤微塑料的研究提出了相关对策。主要包括以下几个方面:1)土壤微塑料的主要来源包括农用塑料薄膜残留、污泥的土地利用、有机肥施用、地表径流、污水灌溉和大气沉降; 2)总结了土壤中微塑料的分离、提取、鉴定及分析方法的优缺点,但目前仍没有标准化的检测和定量技术; 3)微塑料会影响土壤的结构和理化性质,对植物和动物的生长造成威胁,并改变微生物群落的多样性;4)微塑料表面可附着污染物,对环境造成物理和化学污染,可释放内源性有毒物质,并导致复合污染效应;5)微塑料污染的防控措施主要包括3个方面:研发生物降解塑料产品、从源头控制微塑料的输入以及加强世界各国合作。提出今后微塑料的研究应建立统一的定量分析标准方法,发展更准确的可追溯分析技术,加强对土壤中微塑料污染的科学研究。本研究不仅有助于了解微塑料在土壤中的环境行为,为进一步探索土壤微塑料提供思路,而且可为土壤中微塑料的生态风险评估及污染防治提供理论依据和参考。     

Microalgal bioinoculants for sustainable agriculture and their interactions with soil biotic and abiotic components: A review

Modern agricultural practices have posed a detrimental impact on the environment due to their intensive use to meet the food demands of an ever-increasing population. In this context, microalgal bioinoculants, specifically cyanobacteria and green microalgae, have emerged as sustainable options for agricultural practices to improve soil organic carbon, nutrient availability, microbial quality, and plant productivity. An overview of current and future perspectives on the use of microalgal bioinoculants in agriculture practices is presented in this review, along with a discussion of their interactions with soil biotic and abiotic factors that affect soil fertility, plant health, and crop productivity. The benefits of microalgal bioinoculants include releasing agronomically important metabolites (exopolymers and phytohormones) as well as solubilizing soil nutrients. Furthermore, they function as biocontrol agents against soil-borne pathogens and facilitate the establishment of rhizosphere communities of agricultural importance. So far, very few studies have explored the basic mechanisms by which microalgal bioinoculants interact with soil biotic and abiotic factors. In recent years, advanced molecular techniques have contributed to a better understanding of these interactions.