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It is known that soil texture does not change easily, but the effect of soil tillage, soil fragmentation and the passage of agricultural machinery over it, will it affect the soil texture over hundreds of years?
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@ Layth, to change soil texture is very difficult and it involves considerable mechanical and financial input. If your soil is mucky clay, you can improve its texture and structure by adding sand and compost. Sand will quickly improve the texture by separating some of the smaller mineral particles and allowing more openings for air and water circulation.
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I have estimated some parameters of soil (physical and chemical both). I have also used three different depth of soil. Now I am looking to interpret those data and analysis them. What are the ways to analyze the significance and combine those data?
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You can use any standard manual to compare and test you soil's physical and chemical characteristics
Soil Survey Field and Laboratory Methods Manual Soil Survey Investigations
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Do you consider that the availability of soil moisture to crops is solely a function of soil physical properties?
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Of course not.. Soil moisture affects all the activities that take place in the soil, including its effect on the chemical properties of the soil, the transfer of clays and colloids, and the interactions that take place in the soil solution, in addition to its impact on the activity of living organisms in the soil and the vitality of the roots and other vital activities, and all these effects share with the physical properties of the soil influencing the growth and productivity of crops
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Lee's disc apparatus is designed to finsd thermal conductivity of bad conductors. But I am having a doubt that, since soil having the following properties:
1. consists of irregular shaped aggregates
2. Non uniform distribution of particles
3. Presence of voids
Can we use Lee's disc method find thermal conductivity of soil???
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Replace the glass plate in the original Lee kit with a new plate made up of test soil. Run your experiment and have your readings accordingly. It should give accurate results.
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Surfactants in soils and substrates reduce surface tension and increase capillary rise.
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By adding surfactants surface tension of water molecule is lowers due to decrement in cohesive forces acting between water molecule. Due to this loss of water from plant canopy surface reduces which turns reduces in transpiration rate.
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Hi,
I am interested about how quickly SOM can deplete over time, and would like to start a discussion on the topic. Please pardon me if my question is broad.
In temperate systems, it is common to find annual decomposition coefficients around 1-3% (i.e., 1-3% of the SOM stock is lost after a year). However, I wonder how quickly can SOM mineralization occur.
While reading the literature on SOM changes after deforestation in the tropics, I found values suggesting that SOM stocks can decline by 10-50% in a few years (5-10 years) after a forest is cleared for cultivation.
Also, while looking at the AMG soil organic matter model, I noticed that the potential (maximum) SOM mineralization rate (k0) was set to 29%!
Have you ever asked yourself this question?
Related to this topic, I was thinking of a simple experiment that could shed some light on this question. Let's imagine pots with freshly collected soil or a plot of land, which is outside, and for which any plant development is precluded (removing seed, young seedlings manually). I would be curious to see how quickly SOM changes over time (considering that we would regularly monitor it or regularly SOM contents), given that no plant can inject organic matter. Of course, this soil would be exposed to environmental changes (such as regular water inputs from rain or manual watering, not to let it dry).
Any thoughts about this?
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Oxidation and microbial proliferation leads to SOM loss. So as long as it is safe from oxidation and microbes there will be no loss of SOM. But still if tillage is done in soil and exposure of surface soil to sunlight is happen then it will take very less time for SOM to loss.
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A lysimeter decreased in weight by 120 kg over a period when irrigation and rain was 30 mm. What was the evapotranspiration (in mm) if the area of the lysimeter was 1 m2 an the height 0.8 m ?
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In this case ET will 150 {120 +30 (irrigation and rainwater)} mm only. increase or decrease in weight in lysimeter by one kg will be equal to one mm in depth.
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It is exciting to see that this year’s Nobel Prize for physics goes to complex system studies. Fingering flow (wetting front instability) in unsaturated soils is a typical complex-system problem. The complex system is partially characterized by emergence and adaptation. For highly non-linear unsaturated flow, the emergent pattern is the fingering, and the corresponding adaptation principle is the optimality, such as the minimization of global flow resistance. Based on these ideas, I have mathematically demonstrated that the relatively permeability is a function of both saturation and water flux, while the traditional theory considers the relative permeability as a function of saturation only. The work was supported by experimental results and documented in a recent book
One key issue in applying the complex-system framework to unsaturated flow is to find a physical principle to describe the adaptation. To do that, does anyone have a more general principle than the minimization of the global flow resistance?
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Please find the attached files. Regards.
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how we can find poisson's ratio using resonant coulmn (detail procedure )..??
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This is a good question.
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Any conventional and precise way to measure hydraulic conductivity and the permeability of the soil?
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That is a good question.
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Two major flow mechanisms for preferential flow in unsaturated zone are the existence of macro pores or structures and wetting front stability (fingering flow). Do you have any field evidence or theoretical arguments to tell which of the two mechanisms is more important?
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The occurrence and development of figuring flow (wetting front instability) in unsaturated zone are very much like those of turbulence flow in pipes. The environment disturbance may determine transition from laminar flow to turbulent flow. However, once fully developed, the turbulent flow is not significantly impacted by the disturbance any longer. Along the same line, the heterogeneity may impact the initial stage of fingering flow, but not the fully developed fingering flow that is mainly determined by the nonlinear nature of the unsaturated flow.
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Can total porosity be deduced from the water holding at saturation? That is when soil is at saturation does that mean all pore spaces are filled with water? If this is true can one assume that the total water at saturation is equal to total porosity?
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Nice discussion already taken place . I am bit late in joining the discussion . Very good question tossed up by Portia.
Soil porosity refers to the space between soil particles, which consists of various amounts of water and air. Porosity depends on both soil texture and structure. For example, a fine soil has smaller but more numerous pores than a coarse soil. A coarse soil has bigger particles than a fine soil, but it has less porosity, or overall pore space. Water can be held tighter in small pores than in large ones, so fine soils can hold more water than coarse soils.
Soils with smaller particles (silt and clay) have a larger surface area than those with larger sand particles, and a large surface area allows a soil to hold more water. In other words, a soil with a high percentage of silt and clay particles, which describes fine soil, has a higher water-holding capacity.
Source: Enclosed as below
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Many literatures pointed out that soil sand content has a greater contribution to soil thermal conductivity. However, I couldn't find any models that can quantify soil thermal conductivity using the results of soil particle size distribution. In frozen soils, things seems more complicated considering the phase change of soil water. I want to find a model to express the soil thermal conductivity. I just want to find a soil thermal conductivity model that takes into account both the soil phase change process and the soil mechanical composition
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Acturally, I want to find the relationship or model on the effect of soil texture on thermal conductivity in frozen soil. Thank you all the same.
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In my research on soil algae I found that over a period of 3 months the soil pH dropped by 0.6-0.8 units and the algae grew very well. However I did a correlation between the abundance of algae and the respective soil pH and found a positive correlation between, i.e. the more algae there were, the higher the soil pH. I just don't understand why the overall soil pH is dropped from start of the test?
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In my opinion and as other RG colleagues mentioned in comments here, this is not a big change to worry about, but should be controlled time to time continuously and this observed decrease in pH is the consequence of the growing circumstances of that soil algae and I think it totally depends on photosynthesis process and soil respiration. In my opinion there is a compatible range of soil pH which is tolerable for soil algae, which may differ in different genera.
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I have found controversy:
Soil water salinity can affect soil physical properties by causing fine particles to bind together into aggregates. This process is beneficial in terms of soil aeration, root penetration, and root growth. Increasing soil solution salinity has a positive effect on soil aggregation and stabilization.
Sodium has the opposite effect of salinity on soils. The primary physical processes associated with high sodium concentrations are soil dispersion and clay platelet and aggregate swelling. The forces that bind clay particles together are disrupted when too many large sodium ions come between them. When this separation occurs, the clay particles expand, causing swelling and soil dispersion. Soil dispersion causes clay particles to plug soil pores, resulting in reduced soil permeability.
So, could you please anyone clarify about this issue with mechanism.
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  1. Sodium has the opposite effect of salinity on soils. The primary physical processes associated with high sodium concentrations are soil dispersion and clay platelet and aggregate swelling. The forces that bind clay particles together are disrupted when too many large sodium ions come between them. When this separation occurs, the clay particles expand, causing swelling and soil dispersion.
  2. Soil water salinity can affect soil physical properties by causing fine particles to bind together into aggregates. This process is known as flocculation and is beneficial in terms of soil aeration, root penetration, and root growth. Although increasing soil solution salinity has a positive effect on soil aggregation and stabilization, at high levels salinity can have negative and potentially lethal effects on plants. As a result, salinity cannot be increased to maintain soil structure without considering potential impacts on plant health. 
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I have known some physical-based models and emperical models, i.e., the original Stefan model (mainly used in permafrost regions) and its modified modes. However, I consider there would be some better methods to quantify the dynamics of frost depth in seasonal frozen soil region.
Due to the characteristics of two-way melting of the soil during the thawing period in seasonal frozen soil regions, the prediction of the frost depth during the thawing period becomes more complicated and difficult. Are there any good methods to quantify the dynamics of frost depth during thawing period?
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Thank you for sharing your latest related research, I will read it carefully!@Yijian Zeng
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Do you know the methods to estimate soil evaporation reliably in cold and arid region (especially with shallow groundwater level) other than in-situ experiments during freezing-thawing period? Some researchers used the Penman-Monteith equation to estimate the evapotranspiration during freezing-thawing period. Since there were not any crops in the freezing-thawing period in farmland, things were then concentrated on figuring out how much soil evaporation released. Things would be more complex if there were some land covers (straw, snow, or residues et al) on the farmland. I don't know whether the ET0 calculated by Penman-Monteith equation can represent the soil evaporation scientificly. If not, are there any other recommanded methods ?
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Thank you! Well, based on our observation in Inner Mongolia, soil evaporation can be considered as zero in freezing periods. However, it shouldn't be zero in the thawing periods, the ET0 calculated in thawing periods increases to a relatively high level. There is no crops in the farmland at all at that time. Thus, there is no transpiration in the thawing periods. Thus, the soil evaporation can not be neglect in thawing periods. Bayan Hussien
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Do any temperature changes that occur on upper soil layers affect the rise of groundwater or sub-surface water through temperature gradient?
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Well,
In the case of shallow groundwater and close to the land surface, the effect of soil temperature falls within the influence of capillary behavior(action) and the height of capillary water, which in turn depends on the density of the water that is affected by the temperature.
Regards
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pH is the negative logarithm of hydrogen ion concentration which describes about concentration of hydrogen and hydroxyl ion present in the system..pH is an important chemical parameters which can directly or indirectly influence soil physical, chemical and biological properties resulting in interfering crop yield and productivity in question...
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pH is commonly a concept applied to water, and the activity of protons and OH minus ions, but a similar concept might be defined for other systems. In practice, liquid is required to complete 'the electric circuit' between the measuring and reference electrodes.
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Hi all,
I am looking for studies that compared soil texture results obtained from field tests (ribbon test, jar test, throw-the-ball test, sausage test, etc.) with results obtained from laboratory.
Have you heard of such studies and, more generally, which field method would you recommend as the most accurate?
Thank you immensely,
Xavier
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On the field, simply fill method you can use for determination of soil textures and most critically by international pipette method in the laboratory.
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I am in need of knowing the general threshold values (optimal ranges) for mangrove growth and rehabilitation, for the following water/sediment parameters?
  • Bio-chemical Oxygen Demand (BOD)
  • Chemical Oxygen Demand (COB)
  • Colour
  • pH
  • Temperature
  • Total Suspended Solids (TSS)
  • Organic Matter Content (OM)
  • Electric Conductivity (EC)
  • Cation Exchange Capacity
  • Sediment Texture (Particle Size)
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These, parmameters already for a ideal to sustain good ecosystem charcters and that has to be mainatin by with an ideal managment of all practices adoptd for mangrooves conservation. Need to refer the protocl for water use and their properties by FAO .
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Also interested in what people use the data for and what software they use for fitting data.
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We measure the retention function at the Hydrology Lab (University of Napoli). Soil water content values are measured at prescribed soil water matric head values from near-saturation up to -200 cm using suction tables (Romano et al., 2002). Other additional soil water retention points are determined with the pressure chamber method at prescribed low matric head values (let's say from -3000 cm till wilting point for example)
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In this case, I have a study where soil properties were characterized for 100+ pastures and we are trying to link diverse pasture management activities to changes in soil characteristics. During a recent review we were asked to use a multivariate approach (PCA or regression trees). As a plant ecologist I am very familiar with multivariate analyses for plant communities, where all values in a matrix (e.g. diversity or cover) are of similar units/scale. However, a multivariate approach for soil was never explored previously due to differences in the scale of soil characteristics (e.g. pH, electrical conductivity, to percent C, N, OM, texture, etc.). Could someone offer some advice on how the matrix of soil variables would be prepared for a multivariate test like PCA? Do you adjust the scale of variables with a transformation or run the test with original values?
Thank you.
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Thank you. I found a description of this transformation and sample code in Numerical Ecology with R (Borcard et al. 2011).
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Particle size distribution (PSD) aka soil texture is a major feature to understand soils.
Sand, silt and clay classes of mineral particles are so commonly used that they become part of the everyday landscape of agronomists, farmers and others.
However,
Why such size limits have been placed between these categories?
Is there a reason?
In addition, different countries may have different PSD classes (eg., 50 µm or 63 µm between silts and sands).
On which scientific basis has this been made?
To follow up on that,
Don't you think that a more modern approach to soil texture characterisation would be more helpful by measuring soil PSd on a continuous scale? rather than splitting between sand, silt and clays.
Indeed, two soil with the same PSD (lets say 30% sand, 30% silt and 40% clay) could be very different.
Within sands, particles could all be towards th coarse side, or conversely towards the fine side.
Same reasoning for the other classes.
Without solid reasons (physical perhaps?) to set the boundaries between sands, silts and clays, that system seems a bit arbitrary and old-fashioned, isn't it?
Shouldn't it be more useful to represent the frequency distribution of particles on a continuous scale to give a more precise picture of the actual texture of a soil.
New techniques such as laser diffraction seem to be useful to this end, and could give a more representative image of the distribution of the size of soil's mineral particles.
Futhermore, current method to determine soil PSD using sieving and sedimentation is extremely long and prone to errors in measurements.
Any thoughts on this?
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The % of sand, silt and clay in the soil established the nature or texture of soil. Hence, first we have to determine the % of these components of soil.
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I am looking for large datasets including information on soils (texture, depths, carbon , etc.) and their location (GPS coordinates or climates data).
Any suggestions?
Any large studies which would have left their data available for free in repositories?
My objective is to help people find time series on soil carbon on this thread (easily find this discussion with a google search). Thus it could a great reference and link list.
Thanks!
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Dear Dr Fungenzi
You may have seen my response to your first question. One of the attached papers (the first one) was based on a publicly available time series of samplings. We used 41 years and by now there should be data for another 10 years available. The samplings and storage of data takes place at the Swedish University of Agricultural Sciences, Uppsala, Sweden. In case you want a contact I will be happy to support you.
Best regards
Björn Berg
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I am performing some tests with pressure plate apparatus on clayey to loamy soils. I need to compare results. However not able to find a reference paper with reported values of moisture content at 0.33 bar and 15 bar pressure.
Kindly help with some studies in which pressure plate apparatus is used and values are reported.
Thanking you in anticipation
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Dear Mr. Oak,
I published some years ago some papers with collaborators in which you can find soil water content measurements at -33 and -1,500 kPa for soils from Brazil and Venezuela. Some of these measurements were carried out in clay soils. Perhaps, these articles can be useful to you:
1- Gamma ray computed tomography to evaluate wetting/drying soil structure changes. Nuclear Instruments and Methods in Physics Research B 229 (2005) 443–456.
2- Predicting soil water content at − 33 kPa by pedotransfer functions in stoniness soils in northeast Venezuela. Environ Monit Assess (2018) 190: 161.
3- Soil physico-hydrical properties changes induced by weed control methods in coffee plantation. Agriculture, Ecosystems and Environment 246 (2017) 261-268.
Best regards.
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Hello,
My current job is to study soil aggregates and soil microorganisms. I want to extract DNA from individual aggregates and measure some soil physical and chemical properties, such as soil carbon and nitrogen. Our aggregates range in mass from 100 to 300 mg, but DNA extraction takes up a large part of its quality. I want to know what methods can be used to measure soil carbon and nitrogen with small-mass soil samples in individual aggregates.
Thank you in advance.
Mengying
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Thank you for all answers to this question, I will seriously consider it! Thank you all.
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I have studied an area of rain forest which presents a strong gradient of variation in soil moisture and nutrient. The florestal inventory was conducted in 42 plots of 5-25 meters, distributed in seven lines going through three compartments, in order: 1) A floodable plain forest in a organic soil; 2) Intermediary assembly located in a soil with a steep slope; and 3) a dry forest located in the highest place, with poor white sand soil.
For now, i intend to evaluate the water table variation, but i´m not sure how deep and how many piezometers should be needed to perform multivariate analyses involving plant community and soil water content. Initially, would be interesting install 42 piezometers, 1 per plot, but this would be very difficult to perform. Besides, i am not sure if piezometers of 1,5 meters would be deep the enough to access predictive informations about the influence of soil water content in plant community composition.
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Hi everyone anyone have the complete answer for those questions?
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Microalgae are a group of lower plants with the capacity of photosynthesis, widely distributed in marine, freshwater, soil and other environments. As we known, Microalgae are grazed by the other soil organisms which can affect nutrient cycling in terrestrial ecosystems significantly through modifying soil physical, chemical and biological properties, especially the soil macrofauna. But the knowledge of the influence of nitrogen deposition on the diversity of forest soil microalgae and Seasonal succession in a soil algal community associated with biogeochemical cycles is not well known.so how to measure the diversity of forest soil microalgae is important. Who can tell me? or who did it ever? Please send me a message, thank you!
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I am working on precision agriculture and needs to determine the soil properties on a large scale using remote sensing and GIS.
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If your area has been mapped by soil series, by competent soil scientist, someone needs to input into GIS, the delineation boundaries and soil property attributes associated with each soil series. In many instances you might find an agency such as USDA NRCS accomplishing this task. However, in the past, the US Forest Service in USA has different or additional soil mapping criteria and boundaries from NRCS soil series maps, so this data was entered by our agency with soils and GIS experts. If you have old soils maps you want to use, not in GIS, sometimes these can be georeferenced and scanned, with soil boundaries entered as a coverage to reference. ArcMap software has a number of automated routines that makes interrogating GIS spatial data relative easy with basic to moderate training. If using old GIS software, it takes more expertise to accomplish the automated methods in the ArcMap updates.
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Hi everyone,
The quantification of water-dispersible clay in soils is known to be method-dependent. In this sense, I would like to know the specific steps used by you or your laboratory.
The steps commonly used by me are detailed below:
Laboratory: Lab. of soils. Londrina, Brazil.
1) Mechanical dispersion? Yes.
1.1) Shaking intensity: 200 RPM for 1 to 16 hours.
1.2) Shaking direction: orbital horizontal
1.3) Soil:water ratio during shaking: 20 g to 100 ml.
2) Sedimentation performed in the shaking container? No.
2.1) Sieving before sedimentation? No
2.2) Soil:water ratio during sedimentation: 20 g to 1000 ml.
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The method of Carter and Gregorich (2007) as described by Marcos is appropriate
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I conducted CBR tests on unbounded aggregates. As you can see the CBR test results in the attachment, the curves concave up and there is a relatively enormous shift between two test results. Considering that two curves are parallel, it, somehow, can be concluded that two samples has comparable properties, but the presence of the shift make the interpretation of the results difficult.
Based on New Zealand and British standard these curves should not be corrected, however some references in the literature recommended correction of these type of curves (I attached the PDF file).
Question A- If I correct the curves (as explained in the PDF file) or shift the sample-2 the results for two replicated samples are comparable. Under this conditions, do I need to correct the CBR test results?
Question B- If I correct the curve and the resultant curve does not meet 2.5 mm penetration how can I interpret the CBR test results?
Question C- If I should not correct the curves what would be the CBR test results in my case?
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As per AASHTO T-193 if the curves start concave upwards they should be corrected by extending the linear portion of the curve until it intersects the x-axis (penetration) and use the intersection as the new origin of the axis.
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I lecture in Soil Physics, one of the issues I face is that we teach a very knowledge based curriculum, in which critical thinking and applied thinking and knowledge to problem solving is rare and difficult to assess. I have been trying to emphasis critical thinking skills by having student review journal papers with poor or misleading science. The difficulty i face is finding these papers in the field of soil physics. please if you know of any papers which present poor soil physics and understanding of scientific concepts could you please let me know.
Thanks marcus
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I think I get your feeling. It bothered me the last 45 years. Attached perhaps some comfort.
Best wishes
Peter
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Good day RG family
I have been using the Keen-Rackzowski method for determining water holding capacity. I have been getting really good results with this method and it's correlating very well with other know soil indicators that improve water holding capacity of soils. The problem is with one set of soils that I am working with. These soils do not absorb water, instead the water stays on top of the soil sample and forms a bubble or runs to the sides instead of infiltrating. What can I do to overcome this problem in the lab? And what causes soil to repel water?
Thank you in advance for your responses.
Kind regards,
Portia
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Soil infertility, soil chemistry, physical chemistry, Soil physics
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Mr. Phogat,
Via MS.
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(see the attachment)
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Sarem, FYI it is also possible to post your question in the Hydrus forum. You'll find the answer by Jirka and Hydrus team. here is the address:
Cheers,
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with or without considering additional means such as irrigation:
...
could manipulating soil texture (addition/exchange of soil particles) improve physical soil conditions towards higher yields?
It's a basic question, but of applied interest, still not that straightforward to answer as it involves many disciplines and an integrative problem solving approach
lucky to hear your opinion and suggestions
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Lets look at the role of microbial inoculation , cropping sequence , organic manuring , integrated nutrient management , conservation agriculture , and so on...These are possibilities which have been able improve soil aggregation , hydaulic conductivity or water transmission properties of soil , ...
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The basic assumption of the function is that the soil was saturated and it's in drying process. This function should take in consideration texture properties and preferably SOM.
If you know a function like this, please add the relevant paper name.
Thanks a lot!!
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What is the best protocole to measuring phytase enzyme in soil with high organic matter?
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Dear Mostafa
This paper is having information required by you.I hope it might be helpful for your work.
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Dear RG Members,
I'd to know is inferences about soil physical properties (water +granulometry) using RGB +NIR spectrometry is possible?
Thanks in advanced,
ASANTOS
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Yes , surely you can draw better conclusions ...
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Hi everybody,
Is there an available protocol to perform physical fractionation of soil organomineral fractions using an ultrasonic cleaner instead of ultrasonic probe? If so, I would be very glad if you could share it with me.
Thank you!
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Yes it's very much a possibility with certain defined application to  soil physical properties  
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Soil physics
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By soluble soil with water and making Shaker and take 20 ml from solution and add 20 ml from acetone, after that put in centerfuge and calculate electrical conductivity…  reference icarda 2016
Is there any methodology to estimate the gypsum content in gypsiferous soil?. Available from: https://www.researchgate.net/post/Is_there_any_methodology_to_estimate_the_gypsum_content_in_gypsiferous_soil2 [accessed May 31, 2017].
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Thank you for your valuable explanations.
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It is well known that Mg is believed to cause dispersion of soil colloids and enhance surface sealing (Curtin et al. 1994). What is the mechanism? Which character of Mg is responsible for dispersing soil colloid? 
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Dear Habel, thank you so much for mentioning several references. However, I think reference is not matter. We should explain the mechanism/reasons. Now, I am trying to give some explanation.
Clays particles are small in size (less than 0.002 mm) but have a very large surface area. The surface area of all clays is negatively charged. This is because of the complex arrangement of elements (e.g. aluminium, oxygen, silicon) that make up the clay structure. Positive ions (cations such as Ca2+, Mg2+) present in the soil are electrostatically attracted to the negative clay surface and neutralise the charge in the clay. As all the negative charges on the clay are neutralised, a layer of positive charge surrounds the clay particle. This layer of positive charge is also known as a 'shell'.
The width of the shell depends on whether the cations are single (Na+, K+), double (Ca2+, Mg2+) or triple (aluminium, Al3+) charged. That is, one Na+ will neutralise one negative charge on the clay, whereas one Al3+ will neutralise three negative charges on the clay.
Cations floating around in the soil solution as salts, also affect the width of the shell. Cations 'attached' to the clay particle diffuse away from the surface of the clay until the concentration of cations is equal to the concentration of cations in the soil solution. Thus, the saltier the soil solution, the thinner the layer of positive charge surrounding the clay particle.
Like charges repel one another, however, this can be overcome by close distance nuclear attraction, called Van der Waal's forces. If the shell is thick, the clay particles are going to have trouble coming close enough together for the Van der Waals' forces to act and for the particles to flocculate. They will tend to remain as separate (colloidal) entities – and the clay will be dispersed.
Highly charged cations tend to be held more tightly than cations with less charge and secondly, cations with a small hydrated radius are bound more tightly and are less likely to be removed from the exchange complex.
Hydrated magnesium ion is larger (8A) than that of calcium (6A), the magnesium ion is held more weakly and behaves in some instances in soil (i.e. when calcium is low) like sodium. Due to larger hydrated radius of Mg2+ than Ca2+, Mg2+ creates thicker layer than that of Ca2+. As a result, Mg2+ reduces the Van der Waals' forces among the particles which is the reason for clay dispersion. 
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I have latitude and longitude of hundreds of locations and I need to extract soil physical and chemical properties from SSURGO. I know there is manual way to extract those information visiting SSURGO website, but it is very inefficient and trouble some when needs for large site. Thus, it would be great if someone can point me the direction. Thank you.
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Hey buddy  :)
If you are using R for your coding, I would recommend you to use FedData package (https://cran.r-project.org/web/packages/FedData/index.html). 
Very reliable and easy to use set of functions.
Good luck
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I'm looking for an existing tool (maybe a matlab code or a spreadsheet) to have as an output theoretical models of P-wave velocity variation vs hydrate saturation, in order to compare these models (pore-filling, load-bearing, cementing, patchy) with some real data...
Thanks in advance :)
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RPH tools List of Matlab files The Rock Physics Handbook, 2nd Edition,Mavko,Mukerji, and Dvorkin, also QSItools another Matlab list with rock physics templates.
You can try using Pimpedance vs Vp/Vs and color code with Gas hydrate saturation I  think these files can help you.
I hope that it will help you.
best regards
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i want to assess the hydraulic conductivity ( saturated and unsaturated)  in the field through diffrent horizon in the vertical and the horizontal direction. how can i proceed to compute   an average mean of the hydraulic conductivity of my field ?.
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First of all, if your soil is "conventional" with clay, lemon and sand, the assessment of hydraulic conductivity is based on Darcy's law. If your soil is stony or karstic, there are other experimental methods to apply.
In "Darcian soils", the well and piezometers method of Guyon or the auger method are practical to obtain the saturated hydraulic conductivity. If your soil is drained, there is an indirect method for the estimation of the horizontal saturated hydraulic conductivity involving Darcy's law.
The assessment of the unsaturated hydraulic conductivity is more complex because you may include wet and dry stages of the soil. The methodology is rather based on laboratory measurement of the state variables samples: water content, head pressure and unsaturated hydraulic conductivity. Anyway, the Darcy's law application is also the key to assess the unsaturated hydraulic conductivity.
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I am currently working on effect of different tillage methods on soil physical properties, growth and yield of Corn in some selected Provence of China. However, l want integrate modelling or simulation into the work. 
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Look at this doc it may be hlepful for your topic. Good luck.
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Dear colleagues,
basically we intend to correlate lab measurements of soil stability (for details see below) with in situ measurements of soil stability. As in situ measurements we already have:
  1. soil moisture (FDR probe)
  2. depth of the skid trail (laser)
  3. shear strength (shear vane tester)
  4. penetration resistance (hand penetrometer)
  5. oxygen diffusion rate (ODR meter)
  6. saturated hydraulic conductivity, ks (hood-infiltrometer)
These methods are not all really simple and fast. So that's the point where I need your creative ideas.
My question to YOU: What other simple field measurements could possibly be correlated to soil stability and/or function?
It could also be something weird, or crazy, something I would not think of in first instance (e.g. sth related to electricity)
Thanks a lot for your feedback,
Malte
Background of the question:
Lab measurements, undertaken with samples from the field: pre-consolidation stress and cyclic compressibility, shear parameters, Atterberg limits, saturated hydraulic conductivity, air permeability, texture, water retention curve.
Explanation of the project:
My collegues an me want to assess the impact of heavy forestry machines (29t forwarder) on the stability and function of a loess soil (stagnosol). The trafficking experiments will be conducted on already existing skid trails in a spruce forrest. Different machine configurations (tyres, different kind of belts) will be compared with each other. For each machine configuration different trafficking frequencies and slope inclinations will be simulated.
Laboratory experiments are, as the name already says, very laborous and expensive. Therefore we want to try to correlate the results from the lab to results from the field measurements. WIth the resulting pedotransfer functions it might be possible to derive the parameters from the lab measurements just from simple field measurements, so that in future the laboratory measurements could be skipped. With these field measurements large areas of forest soils could be covered rather easily and hence could be used to create maps of loess soil stability. These maps could serve the rangers as a decision guidance for a soil conserving wood harvest.
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Maybe with a dynamic plate load test (acc. to TP BF-StB Teil B 8.3) if you find a way for the description of the correlation of the dynamic drop weight and the weight of the simulated machinery (scaling issue).
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Hi all, I've got 100 realizations for 100 years of a climate model data (daily values) which I intend to use for water risk assessment and want to draw some logical conclusions. Could anyone suggest which statistical tools are the most suited to analyse such huge data set?
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It is a bit confusing, indeed...maybe what you are trying to find out is about the best and the most suitable variables (either dependent and independent) to be used in the data analysis so as to prove really significant correlations and eventually, the true impact of climate change in the area....and this is not that easy, agree.
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Hi,
I am currently undertaking a laboratory investigation on the relationships between soil physical/geotechnical properties and electrical resistivity as part of my PhD. Equipment that I use operates in the frequency range 10Hz to 1kHz. It provides me with a modulus of resistance readings at certain frequency and real and imaginary part of impedance. I would like to know how to, based on these results, determine whether my measurements have been affected by electrode polarization? The literature that I have come across so far does not provide a clear answer. Some papers suggest that below 3kHz there is no effect of electrode polarization whilst others say that 60-100Hz frequency has been chosen to avoid electrode polarization.
Some authors referenced the articles below to justify their choice:
Mitchell, J. K., and Arulanandan, K. (1968). "Electrical dispersion in relation to soil structure." J. Soil. Mech. and Found. Engrg. Div., ASCE, 94(2), 447-470.
Arulanandan, K., and Smith, S. (1973). "Electrical dispersion in relation to soil structure." J. Soil Mech. and Found. Div., ASCE, 99(12), 1113-1132.
Does anyone have an electronic copy of either or both of them that can be shared?
Would be grateful for a response. 
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If I understand correctly your main concern is to obtain good resistivity measurements so that you can correlate them with other soil soil properties rather than to study the effect of frequency of the injected electric current. Whenever we insert the electrode into the soil, even before injecting the current of any frequency, they can be polarized due to different reactions, and between the electrodes there is always a voltage known as self-potenial or natural potential. Therefore, all the professional resistivimeters used in exploration geophysics should be able to compensate (kill off) this natural potential before taking the measurements of voltage. I am not sure the equipment used in environmental engineering or agricultural engineering etc. have this function. Before, people may need to use so-called non-polarizable for some geoelectric methods such as SP or IP, but nowadays with the modern equipment one can use the metallic electrode as usual for a common resistivity survey. Sycal, for example, is a good resistivimeter with excellent natural potential compensation capability.
Coming back to your concern: if your equipment does not have the ability to compensate the natural potential before or during the injection your resistivity measurements will definitely affected no matter what frequency you use. If it has do not worry too much and you can compare the measurements for different frequency to compare by yourself.
A small suggestion: if you measure the resistivity on the soil sample you should be careful at correction of measurements for their finite size/shape effect as  waht you measure is apparent resitivity but not a true one.
The question was very good as we should not take resistivity measurements of soils/rocks for granted.
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Foliar nutrition is becoming popular in the last decade, various products are available in the market (even customized foliar nutrition products), which have been reported to increase yields as well heled in bio-fortification. If we apply micronutrients in the soil, it is most of the time overdose as well the uptake efficiency is very low, the question comes that can foliar micro-nutrition completely substitute for basal (or soil) application?
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Big No Dr Kalra....
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My understanding of porosity is that it gives you the percentage amount of pore spaces within a given volume of soil. I have worked with a range of soils that vary in their bulk density ranging from 0.89 g/cm3 to 1.69 g/cm3. Literature tells us that soils with high carbon should have low soil density because of the organic matter impact. Based on this my questions are as follows: 
1) What is the ideal soil porosity? ( I have read some publications that say land managers should aim for 50%)
2) Is soil porosity of greater than 60% bad for the soil? (My understanding would be that the soil aggregation would be poor when there is very high porosity in a soil?, I stand corrected though)
3) Is there such a thing as too high organic matter in soil? i.e >15%
I hope that my questions are clear, any advice will be appreciated!
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Porosity φ is the fraction of the total soil volume that is taken up by the pore space. Thus it is a single-value quantification of the amount of space available to fluid within a specific body of soil. Being simply a fraction of total volume, φ can range between 0 and 1, typically falling between 0.3 and 0.7 for soils. With the assumption that soil is a continuum, adopted here as in much of soil science litera-ture, porosity can be considered a function of position. Porosity or pore space refers to the volume of soil voids that can be filled by water and/or air. It is inversely related to bulk density. Porosity is calculated as a percentage of the soil volume:
Percentage Solid space =100 X Bulk density/Particle density.
Loose, porous soils have lower bulk densities and greater porosities than tightly packed soils. Porosity varies depending on particle size and aggregation. It is greater in clayey and organic soils than in sandy soils. A large number of small particles in a volume of soil produces a large number of soil pores. Fewer large particles can occupy the same volume of soil so there are fewer pores and less porosity.
Compaction decreases porosity as bulk density increases. If compaction increases bulk density from 1.3 to 1.5 g/cm3, porosity decreases from 50 percent to 43 percent. Aggregation also decreases porosity because more large pores are present as compared to single clay and silt particles that are associated with smaller pores.
Pores of all sizes and shapes combine to make up the total porosity of a soil. Porosity, however, does not tell us anything about the size of pores
The characterization of pore space is a vital and fruitful aspect of soil investigation. Liquid, solid and gas constituents of the soil govern the form and development of pores, whose character in turn profoundly influences the na-ture and behavior of the soil. Soil porosity is fairly well standardized in definition and measurement techniques. Pore size, however, is not obvious how to define, much less to measure. Yet it is central to topics like macropores, aggregation, fractures, soil matrix, and solute mobility. Pore size plays a key role in various proposed means of quanti-fying soil structure. It also has a major practi-cal role in the prediction of hydraulic proper-ties. New pore size concepts, measurement techniques, and relations to transport phenom-ena are likely to remain a major emphasis in the study of soil.
The air in the soil is similar in composition to that in the atmosphere with the exception of oxygen, carbon dioxide, and water vapor. In soil air as in the atmosphere, nitrogen gas (dinitrogen) comprises about 78%. In the atmosphere, oxygen comprises about 21% and carbon dioxide comprises about 0.36%. However, in the soil air, oxygen usually is replaced by carbon dioxide, so both range from about 0.4% to 21%.Oxygen is used by plant roots and soil microbes during respiration, and carbon dioxide is released. Thus, in the soil, the oxygen levels are generally less than atmospheric levels and the carbon dioxide levels are generally greater than atmospheric levels. Some factors that determine the extent of the difference between atmospheric and soil air constituents include depth in the soil profile, soil pore size distribution, and soil water content.]
Depth: Oxygen levels generally decrease with depth in the soil profile due to slow diffusion rates of oxygen from the surface through the soil.
Pore size distribution: Soils with large pores promote more rapid oxygen diffusion into and through the soil, and carbon dioxide movement out of the soil. Soils with small pores have slower oxygen diffusion into the soil and carbon dioxide diffusion out of the soil. Sandy soils generally have low total porosity but large individual pores. Clay soils generally have high total porosity but small individual pores.
Aeration and drainage: Soils with large pores generally have good drainage (less water) and aeration, while soils with small pores generally have poor drainage and aeration. Thus, sands generally have good drainage, while clays have poor drainage and are more likely to become anaerobic (deprived of oxygen) as microbes use oxygen more rapidly than it is replenished through diffusion.
• Soils with more pores filled with water have less space available for air, thus become anaerobic more rapidly than drier soils.
Water vapor: Soil air has a relative humidity very close to 100%. (Relative humidity is the amount of water vapor actually in the air relative to the amount the air could hold at that temperature.) This is much different than atmospheric air, which may vary in relative humidity between 5% and 100%, sometimes within 24 hours in semi-arid and arid regions. A Boy Scout Survival Kit applies this concept by providing a shovel, piece of plastic, and a cup. Dig a hole in the morning, place the cup in the bottom of the hole. Anchor the plastic with soil around the rim of the hole. Place a rock on the plastic above the cup. During the day, the plastic allows the soil to heat, evaporating water. At night, the plastic allows radiational cooling. As the air cools, water vapor condenses on the plastic and drips into the cup. This provides enough water for subsistence. If cacti or other succulents are available, place some of their vegetation in the hole to enhance the water provision.
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I mean soil aggregates are porous materials per se, thus have some cavities on the surface. Depends on the presence of water they may partly or fully saturate with water.  I want to determine the volume of these cavities that are open for water to enter.
Thanks in advance.
Ebrahim
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A method of choice to determine soil porosity is X-ray microtomography (XMT) coupled with software to construct 3D images of the porosity network and to calculate for example pores volumes, pore surfaces and pores connectivity.
Then if you want to determine the water/gas flow through aggregates you can use some modelling flow.
I think the main question when you want to determine soil porosity with XMT is the resolution you want to go, because higher is the resolution, longer the scan will take, higher the price will be, and more difficult the data analysis will be (each run will be many GB).
These methods have already been used on soil aggregates. If you want to scan single aggregates, you will not be able to scan "huge" aggregates (e.g. 10 cm or 20 cm), or tiny (e.g. 1 mm) as the machine present a higher limitation to the maximum size you can put in the scan, and lower limitation to the smallest resolution you can go, This is also true is you want to scan a soil core. Also, to get repeatability of your data (e.g. the porosity of a certain size of aggregates), you will have to scan several single aggregates (e.g. 8 to 10).
I paste below a link to one of my article that looked at soil porosity of soil aggregates before and after soil compaction. We used XMT and flow modelling.
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I know that under the chemical weathering Ferrous (Fe 2+) solve in the water and the because of Oxygen oxidized to the Ferric (Fe 3+) form.
The formation of the crystalline hematite, or any other consequence of the redox reaction, may affect the permeability of the soil or change the mechanical characteristics of it?
I can find the primary minerals that have Fe2+ on their structure, what secondary mineral may result from the redox reaction?
Thank you for your time.
Ebrahim 
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Hi Ebrahim, Chlorites and vermiculites, and mixed-clays may form in soils, for example from weathering of montmorillonite under some circumstances. Try to write the reaction to see what happens. More generally, see the work of N. Van Bremen on the effects of redox processes involving iron on the chemistry and mineralogy of reduced soils. All the best, Anicet
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Ascribing doubting as respects making use of the CY Model in FLAC3D so as to mimic the behavior of clayey soil in the seismic analysis to being utilized the friction hardening in the aforesaid soil constitutive model based on the UBCSAND model subsequent to perusing the paper entitled “NON-ASSOCIATED PLASTICITY FOR SOILS, CONCRETE AND ROCK”. In short, are we allowed to exploit the friction hardening for clay? Additionally, is it rational to have the friction hardening and the cohesion hardening instantaneously?
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Dear Nesterina,
I am going to conduct the seismic analysis associated with saturated undrained cohesive soils. 
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Dear Sir, I would like to monitor soil moisture dynamic at a watershed scale at long time scales. The depth of soil moisture is five meters. Could you please introduce me which instrument is better? Thanks
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Thanks, William. On my study area, taking plant water tension into account is really a good idea, which may highly affect the regime of deep soil moisture. I often use the neutron probe to monitor soil moisture after intalling the aluminum pipes (the current maximum depth is 21 meters), although this method has some shortages.
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Soil as earths living skin provides support to both natural and human systems. In good olden days , we use to define the role of soil in terms of sustaining the crop response over a period of time , without incurring any distinguishable depletion of nutrient stock of the soil , either quantity or intensity factor. Of late , we started looking the role of soil beyond soil fertility and plant nutrition , especially with the realisation of  negative consequences of global warming . My present set of questions revolve in and around this central theme. These are as follows:  
* Is it not true that increasing menace of land degradation ( Irrespective of causal factors) , has opened  another role of soil as  ecosystem service provider?
* What are the  possible ecosystem service , we expect through  soil physical , chemical and biological properties , either in isolation or in combination ?.
* What is the carrying capacity of soil , and how does it relate to ecosystem service ?
* How would you define soil health to differentiate with soil quality in terms of ecosystem service ?
* Do you feel , ecosystem service out of a soil narrates the soil health better than defined set of soil properties or they  simply go hand-in-hand?
* Can we define  ecosystem service of a given soil  in spatial and temporal  scales?
Your precious responses are always appreciated . My regards  
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Dear Anoop! Firstly, thank you. Thank you for your attention to an issue that is long overdue. The soil is vulnerable. Soil is difficult to resist the pressure of modern technologies, the possibility of depleting the soil, accumulated for centuries. We need to consider soil cultivation technology, preservation of fertility. In fact, it is a harmony between man and the soil.
Vladimir
PS. Please have a look an Attachment
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One of the main factor that contribute to soil aggregation is calcium carbonate. How is that even whith high calcium carbonate in sodic soil, we still have poor physical quality ?  
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Hi Dear colleague, 
Ilyass , it's good to mention that calcium with its floculation power and it's abundance in these salt affected soil is found in other mineral, we should also study their relative solubility to assess their contribution in soil structure formation for example. 
Anoop, we have discussed  an inquiry about the relation between CaCO3 and  Chlorosis, but here, my perspective behind my question is that floculation is not sufficient in the improvement of soil structure as stated very well in one paper of J.P.Quirk " Aggregation is floculation Plus" and the plus can be organic matter, type of clay,  sesquioxydes of iron and AL and of course calcium carbonate. and i want to find out in what extend the calcium carbonate in a sodic soil assist the soil in a reclamation process? 
I said that because  we have some experimental result about soil hydraulic conductivity change when the exchange between Na-Ca takes places. and the theory said that when Na is flush out from the soil system and we have only Calcium , There will be an improvement in physical properties (i measue Soil hydraulic conductivity to assess this improvement). and in our case , we didn"t found full recovery of soil hydraulic conductivity. So this is why may be the Plus in the statement of J.P.Quirk is the key to understand the Aggregation process in sodic soil reclamation. 
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Understanding the long-term implications of decreased soil quality will require new information based on advances and breakthroughs in soil science research. A challenge for soil science is the need for interdisciplinary research involving classical soil science subdisciplines—soil chemistry, soil physics, soil biology, soil mineralogy, and pedology.While basic research provides an understanding of fundamental soil processes, increasing trends in land transformations, environmental challenges, and policy issues require interdisciplinary approaches.
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 I appreciate the good question of Mr. Mishra .Doing basic research work in soils is different from receiving the interest,attention  and appreciation of people and public .Solving the soil related problems  based on good basic work on soils and finding easy to follow/adopt solutions is important for farmers in particular and people at large. Dr.Hart has attached a very pertinent report of Soils Research-Evidence Review pertinent to UK but relevant to the whole world.All the five areas covered in the report ,1.soil quality indicators and Ecosystem services,2.soil degradation,3.sustainable soils,4.soil management practices, and 5.economic evaluation of ecosystem services are important.Reclamation/amelioration of problem soils-degraded soils and polluted soils need utmost attention.Soil health/quality assessment, management and monitoring need continuous attention for sustainable agriculture,food and nutritional security , for safeguarding  environment and obtaining ecosystem services to farmers and community as a whole.Dr.Hansen  very rightly narrated in a practical way how to use basic soils knowledge to solve agricultural  environmental and health problems.If such work is done, soil scientists' reputation will increase and also get the attention of public.
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Is there any specific time for saturation of the pressure plate with given pressure (eg: 0.5 bar). 
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In addition, an internet search may help understand there imay be specifics with any analysis to address to get to the data quality you want to present.
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For laterally loaded piled raft, is there any relationship between soil reaction and the magnitude of axial force. Or, does axial force affect soil pressure measured along the pile length?
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Dear Dr Nabil, thank you for this answer. practically that is true. But some analytical methods are depending on the second derivative of moment curves to get the soil reaction distribution. And since the moment depends on the axial force as well as the lateral force, soil reaction changes as axial loads change. Anyway, practically you are right.
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Pls give me your valuable suggestions. Thanks in advance.
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Dear Meshram:
I am interested in your question but you need to be more explicit as it involves two mechanics: physical/mineralogical (swelling) and chemical (soil OMC). 
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radiation use efficiency (expressed in terms of solar radiation, intercepted solar radiation, PAR, intercepted PAR) for potentially grown condition, as well under various biotic/abiotic stress is very important, which could be used for growth and yield assessment, inputs management options and climate change studies.
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 Thanks Abhishek, the radiation use efficiency in terms of total, total incepted, PAR, intercepted PAR for crops is very useful information for evaluating the biomass gains and most of the times used in developing crop models, the values are variant for crops, and also changes appreciably under various biotic nd abiotic stresses, need to be quantified for generating the transfer functions to be employed for developing the decision support systems
regards
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I found this interesting paper that reports the relative water content (RWC) in the leaves of 13 woody species (between 77 and 91% of water).
But what about the rest of the tree. Of course I am not expecting an absolute answer as this would vary with species, age, season, health etc. But is there any study that has measured water content in whole trees? 
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Thanks Tim, 
This paper does look interesting, I will see if I can find more on their website. Thanks also for explaining the turgor loss point, makes more sense to me now.
Cheers,
Stephane.
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Are there any papers or any scientific review about PSMD (Potential Soil Moisture Deficit)?
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There is an article was puplished in the nature copyright that can illustrating and defining that term to you in easy way . The article is:
Nature 176, 1276 (31 December 1955); doi:10.1038/1761276a0
An Instrument for measuring Soil-Moisture Deficit
G. STANHILL & E. J. WINTER
National Vegetable Research Station, Wellesbourne, Warwick. Aug. 17.
THE estimation of residual available soil moisture should be an essential part of irrigation practice. Penman's method1, based on meteorological observations, gives excellent results; but in its present form it is somewhat cumbersome for use by commercial growers. Various alternative methods are available; for example, measured evaporation from an open water surface may be expressed as potential evapo-transpiration by means of a suitable conversion factor1. Garnier has measured evapo-transpiration directly using a standard grass surface2. There is, however, a need for a simple device which will integrate rainfall and evaporation measurements and give a reading expressed as soil-moisture deficit.
Penman, H. L. , Proc. Roy. Soc., A, 193, 120 (1948). | ISI |
Garnier, B. J. , Nature, 170, 286 (1952). | PubMed | ISI | ChemPort |
© 1955 Nature Publishing Group
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Dear fellow scientists,
In the field of wave propagation in elastic half-space, I am trying to model a problem in ABAQUS.
The problem details is:
A harmonic load is applied at the axis of symmetry of a 2D elastic half space and the response of surface nodes at different distances (going as far as 12 meters) are needed.
The problem I have encountered is that for frequencies lower than approximately 50 Hz, the response (e.g. particle velocity, or displacements) is also harmonic at different distances. But for frequencies higher than the mentioned value, the response is neither harmonic nor oscillating with the input frequency, and it more seems like an impulse response. The graphs can be seen in Figures 1 through 4. Figure 1 shows vertical velocity at the location of the input force of 20 Hz, and Figure 2 shows vertical velocity of a surface node 10m far from the source.
Figure 3 shows the same output for 160 Hz input force, and Figure 4 shows the problem.
Figure 5 shows the model geometry.
Material properties:
1.       Density=18 kN/m3
2.       Elastic modulus=180 MPa
3.       Poisson’s ratio=0.25
4.       Rayleigh damping parameters: alpha=1.7 beta=5.5e-4
Input force properties:
1.       Magnitude=267 N
2.       Frequency=20 ~ 160 Hz
3.       Applied as either a point load on a node, or pressure load on element face, the results are roughly the same
Model properties:
1.       Element dimension and time increment are selected according to published literature and ABAQUS manual, since the shear wave velocity for this material is around 200 m/s, and the highest input frequency is 160 Hz, the Rayleigh wavelength is 0.8 m, the maximum element size is chosen 0.25 m and maximum time increment 0.0005 sec.
NOTE: I have tried smaller mesh (e.g. 0.01 m), and smaller time increment (e.g. 1e-6 sec), but the problem still persisted.
2.       Analysis type: Dynamic Explicit, linear bulk viscosity parameter: 0.06 (changed it to 0 but the problem persisted) and Quadratic bulk viscosity parameter: 1.2 (changed it to 0 but the problem persisted)
3.       The result types are History output request at different nodes and with time increment equal to analysis time increment.
4.       The analysis time is 1~2 sec, no different results.
I know that the FEM analysis cannot cover this range of frequency, but what can we do to make it work for high frequencies?
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Hi,
If you look on current literature regarding guided wave propagation in the context of Structural Health Monitoring you will see that it is also possible to simulate elastic waves in a frequency range of up to 1MHz. Therefore, another problem must be present in your modelling approach.
Your initial discretization using 4 linear finite elements per wave length is much too coarse. Generally at least 20 elements per wavelength are recommended. In an explicit analysis you should use the automatic time step control as the time step is set according to the CFL condition by Abaqus.
What you could try is to compute the same model in Abaqus/Implicit using quadratic finite elements that are much more accurate than linear ones.
You should also check if the nonlinear geometry option is switched on or off. This also changes the expected behavior. Furthermore it is advisable to use the enhanced hourglass control in the element type settings. This provides more accurate results for wave propagation analysis.
A last suggestion could be to compute an undamped system and see what happens. The mass proportinal damping (alpha) should damp lower frequencies more effectively and stiffness proportional damping (beta) is related to higher frequencies.
As you want to model an elastic half space, how do you account for the infinite boundaries? This can also be an error source.
Otherwise it would be helpful if you could upload your model.
Hope this helps a bit.
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With increasing population in several countries in Asia and Africa,they have to double their crop yields in coming decades.However crop yields have been stagnating in different parts of the world . Several possible reasons could be  limiting yield potential crops,in sufficient or imbalanced nutrition,limiting soil physical and biological conditions etc. Then how to improve the crop yield in future and meet the food and nutritional needs of  growing population?
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Dear Doctor Rao
In terms of the Phosphorus questions the synergism of legumes through Rhizobia stimulate the mycorrhizal system the stimulated to mycorrhizal fungi  promote Rhizosphere communities of fungi and bacteria that have Phosphorus mobilizing capacity the plant, bacteria and fungi work together synergistically when the system is optimized for them.
These synergistic symbiotic approach required distinctive nutritional support  aimed at supporting the symbionts for the synergism to be most effective. They are especially dependent of micronutrients such as Mo Co and Zn to be most effective and need to evaluated much more thorough.
Symbiotic synergistic is a way of getting more for less and changing negative environmental and energy footprints into positive ones. These solution are systematic in their nature and need interdisciplinary collaborative focus and coordination.
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We are looking for a soil scientist who has worked on volcanic soils, in order to collaborate on research projects, proposals, etc.
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Dear José:
Answer to your question is yes. Which is the next question ?.  Embraces from Colombia.
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Dear Soil physicist and colleagues. 
We are planning can use the 3D scanner to evaluate soil bulk density. If you have done this kind of measurements and can recommend or alter us about limitations.
Can recommend or make comments about the feasibility to use this kind of equipment in the field ?
I thanks in advance
Regards 
Wenceslau
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This works fine for me:
Stewart, R. D., Najm, M. R. A., Rupp, D. E., Selker, J. S. (2012): An image-based method for determining bulk density and the soil shrinkage curve. Soil Sci. Soc. Am. J. 76, 1217–1221.
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The importance of soil testing in fertilizer recommendation is now beyond any doubt, especially with the intervention of geo-spatial tools-aided soil fertility variograms. These developments added another dimension of soil test interpretation.On the other hand, in conventional soil testing research or advisory  laboratories, the  soil samples are stored for different periods. In this regard, i request our learned colleagues to express their views on the following related issues:
* How long , a soil after sampling  , can be stored without experiencing any change in physico-chemical properties?.
* How frequently , different soil properties undergo chnges /.
* Has any study been made to see the changes in soil properties in long term storage ?.
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As Zacharie wrote it depends. I think not only on the type of sampling and storage conditions, but also on soil property. Actually, we can suppose many things, but it is impossible to verify. It can be supposed, that in air dry samples stored in proper conditions (not too hot, low humidity?) majority of properties will not change greatly for many years, although we cannot exclude slow mineralization of organic matter (so - small changes of organic carbon and total N contents). We can also suppose that such properties as mineral N will volatilize.More or less in 1999 I was analysing soil samples from 1974, but I don't know the results obtained in 1974.
I know about one study concerning the time of soil sampling and storage period of soil samples (up to 7 months only) - it is in Polish, with Russian and English abstract:
They did not  observed any changes of pH, P and K contents.
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