Soil Characterization - Science topic

Dear Mukhtar,

According to what you have said regarding soil fertility, I did a search in Google scholar with keywords: soil fertility+Nigeria, and I found many interesting papers; some are linked below:

Soil fertility enrichment potential of Jatropha curcas for sustainable agricultural production: A case study of Birnin Kebbi, Nigeria:

Delineation of Soil Fertility Management Zones for Site-specific Nutrient Management in the Maize Belt Region of Nigeria:

Influence of compost supplemented with jatropha cake on soil fertility, growth, and yield of maize (zea mays L.) in a degraded soil of Ilorin, Nigeria:

Dear Layth Saleem Salman Al-Shihmani ,

You asked an interesting question on the relationship between soil physical appearance and soil fertility. Allow me to proceed as follows:

For a soil to be said to be fertile, it must have a sustainable supply of the right quality and quantities of soil ameliorates which translate to nutrients. There are a number of physical parameters that might indicate fertility status of a soil cohort. However, these factors are not a guarantee that the soil is fertile.

Generally, black -dark colored soils are a positive indicator of the soil fertility status of the soil. They are good absorbers of heat which activates microbial activity hence soil biomass recirculation. This is a common case in 2:1 and 2:2 clay minerals which are generally good nutrient suppliers.

On the other hand,light-bright colored soils such as 1:1 Montmorillonites are generally poor nutrient holders due to poor heat absorption capacity, greater reflection thus poor nutrient churning capacity.

We shall all agree that this can be established by the naked eye.That,large grained soils are generally considered as poor nutrient suppliers as compared to middle grained soil such as Ferrasols,assuming all other factors remain constant. Average soil is directly proportional to water holding capacity, soil Rhizosphere aeration which in turn affects Biota Respiration.

Large grained soils such as sandy soils are loosely attached, prone to erosion. They are also poor water reservoirs due to increased percolation.

Related to point number 1 is vegetative cover. Material cover is directly proportional to soil nutrient fertility status. Such soils might have deeper top layer, zone A and B.A good covered soil shall harbor more soil microbes which accelerates decomposition.Humus,a product of decompostion,makes such soils appear much darker.

Whereas soil physical factors might an indicator of soil fertility status, farmers and researchers should be encouraged to do a completed soil laboratory tests. Some of the physical factors mentioned above could be as a results of other underlying causes such as parent material, soil pollution, environmental degradation etc. Instead of dealing with symptoms which might result to wrong diagnosis/prescription, I recommend soil laboratory analysis.

As you know bulk density is mass of solid divided by total volume of soil. So in Sandy soil total volume is high as volume of solid + volume of pores are there. So as a result bulk density of sandy soils reduces.

we have worked on this point in the following manuscript:

This is a good question.

Video link for determination of Point of zero charge (PZC)

You can separate silt from clay by centrifuge method after removing organic matter, calcium carbonate, and iron oxide, as described by Dekimpe 1976.

Dear Nguyen,

Among the variables analyzed, the compatibility with normal distribution of all variables analyzed can be evaluated using the Kolmogorov–Smirnov test.

Differences between groups can be established by Student’s t -test for normally distributed values and by Mann-Whitney U-test for nonparametric values.

Pearson's correlation coefficient can be searched to examine the relation between normally distributed variables.

Spearman’s correlation coefficient can be used for nonnormally distributed values. Statistical significance was defined as P <0.05 or <0.01 etc...

Best regards...

In expansive soils, swelling increases with increasing dry density and decreasing moisture content. Therefore, standard compaction is better to be used for expansive soils to reduce swelling problem.

The components for soil quality index from the measured soil properties of the mineral soil cores, may include sample weight, bulk density, water content, coarse fragment content, water and salt pH, carbon (total, organic, and inorganic C), total nitrogen (N), 1 M NH4Cl exchangeable cations (sodium [Na], potassium [K], magnesium [Mg], calcium [Ca], aluminum [Al]), 1 M NH4Cl extractable trace elements (manganese [Mn], iron [Fe], nickel [Ni], copper [Cu], zinc [Zn], cadmium [Cd], lead [Pb]), 1 M NH4Cl extractable sulfur (S), and Bray 1 or Olsen extractable phosphorus (P). e SQI

Thank you Hermes Pérez-Hernández

I think the suggested paper is interesting but it focuses on hydrology.

The diagram showed four characteristic regions:

The first region (< 100 ˚C) showed that mass loss which is mainly due to water volatilization.

The second region (170-300˚C), the mass loss is mainly due to decomposition of organic matter, mainly carboxylic and phenolic functional groups of the humic acids, fulvic acids and hydrocarbon compounds.

In the third region (360-460˚C) the mass loss could be due to carbon oxidation of the organic matter (RCH+O2 ® CO2 + H2O).

In the forth region (460-560˚C),the mass loss could be due to dehydroxilation of metallic hydroxides (M-OH ® MO + H2O, were M = Al, Fe, Mn and other metals).

I have attached some articles about preparing soil extract media.

Solid wastes are used as one of the stabilization methods (non-traditional methods) to improve the engineering characteristics of expansive soils and to make these soils suitable in construction. From the geotechnical engineering perspective, fly ash, quarry waste, silica fume, cement kiln dust, tire rubber, rice husk, etc. represent the waste materials having effectual features required by excellent soil admixtures. Different stabilization methods reviewed and discussed in the attached paper.

Dear Marcelo Llano

You can consider the data result shown in the following paper for Quaternary soils. The liquid limit for the soils has been determined using different methods including the fall-cone method.

I have also observed this. At elevated temperatures, some elements will dissolve into the solid solution of the crucible. Look into the ceramics literature on vitrification. I would not worry about the color change, nor would I be concerned about contamination unless you are ashing a sample for subsequent digestion and quantification of elements in the ash. If you're simply looking at soil carbon, the altered crucibles will continue to be fine. Disregard the etching and color change. Keep in mind though that some elements like potassium volatilize at high temperatures (> 500 C).

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.

Dear Marlon

Andisol with a high content of humic compounds, the majority of the proportion of Al-amorphous will be complexed to Al-humic, so it makes sense that in Andisol with high organic content, Al-humic> Al-amorphous. Conversely, at andisol with low OM content, only a small portion of Al-amorphous complexed to Al-humic so that Alo> Alp content

can you send me you cae file?

Hi Nitish,

A soil sample is extracted with an excess of 1 M ammonium acetate solution. The amounts of exchangeable sodium, potassium, calcium and magnesium in the extract are determined by flame photometry (Na and k) and by atomic absorption spectrophometry (ca and Mg). lanthanum or strotium is added as a releasing agent to prevent formation of refractory compounds which may interfere with determinations (e.g. phosphate),

Mohammed JARULLAH Farhan .

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.

Check out the following links:

Note that the last links provide significant information regrading the optimum moisture content and dry density for granular materials.

In order to understand how soil buffer capacity works, you need to learn about permanent charges (caused by soil minerals) and variable charges (caused by organic matter) and how the above charges respond to acidic (e.g. elemental-S, FeSO₄) or alkaline (lime) soil conditioners. A typical laboratory work to assess soil buffer capacity could explain the above phenomenon ( ).

Organic matter does play a significant role in controlling buffer capacity of soils hence it is important to learn the basics of organic matter and soil pH (

http://landresources.montana.edu/nm/documents/NM8.pdf).

I have worked on soil buffer capacity in the context of assessing the effect of urea hydrolysis in soil (which is a reverse process to adding FeSO₄, since it causes soil pH to rise substantially), however, could not find any specific experimental work involving FeSO₄ reaction with soil with wide ranging concentrations.

I am not sure within which context you are working on FeSO₄. Are you assessing FeSO₄ as a soil conditioner?

You can refer to AASHTO T 193.

The level of detail for a particular region will vary significantly and in all cases it is likely to be a lower level of detail than a site specific survey. I'm note sure from your question if you have a particular part of the world in mind. However, here is a link to data relevant to the UK continental shelf;

- Dry a quantity of soil in an oven at 60 ° C until a constant weight ;

- Weigh a quantity p1 (1 kg for example) of dry soil in a pot (the pot must be perforated below);

- Water the pot to saturation and place it in the dark to avoid evaporation;

- After 48 hours, weigh the pot again (p2);

FC = p2-p1

ex: if p2 = 1.2 kg ie FC = 200 g (100% FC)

you must add 200 g of water to your dry soil to have 100% FC and therefore 160 g to have the soil at 80% FC.

NB: Make at least 3 repetitions

If you do not want to dry all of your soil, once the FC determined. Calculate the amount of water present in your soil by making the difference between the weight of the soil and the weight of the dry soil. You will have the amount of water already present in your soil. Complete this quantity to achieve the desired FC.

Dear Colleagues

Nowadays, risk of fire due to climate change and its consequences like drought is becoming and increasing problem in natural landscape etc.

Therefore, fire occur during summer occasionally for different reasons which affect the plantation etc.

I was wondering if the focus of your project is on special species or different species and aspects?

Kind Regards

Alireza

This article can be useful:

OM is most important of all...

Please have a look at enclosed PDF..

 this article is good but  1: I cant download it and 2:it is for qatar sub grade soils that have more than 40% up 10mm grading but is helpfull and I asked from author p.df file.

I think the SPT N Values show wide variation in Clayey soils with a slight change in moisture content . We performed SPT Tests for a clay formation in dry season (June 2015) and got SPT N values in the range of 20-25

for the same site (formation ) the SPT N values were recorded in the Range of 02-05 only in December 2015 (It was after a rain spell)

The relation between ECe and EC 1:2.5 for South Gujarat coastal alluvial plain (Aquepts Ochrepts) is ECe = EC1:2.5 x 3.429+0..606. For getting this relationship we have analysed 500 soil samples 25 years back.

Please get the  0-100 cm weighted mean value of the saturated hydraulic conductivity data  of the soil profile first and get the same data after adding gypsum. The difference may suggest you which method to apply. Moreover  be sure about the presence of  soluble carbonate and bicarbonate salts  vis a vis  chloride and sulphate. In case  former two are more than the latter then surface application of gypsum will be appropriate  before transplanting rice crop. Please get some information on the similar lines from ICAR-CSSRI, Karnal, India website.

Use Surfer GIS software. You can assign a numerical value for each soil class Eg 1, 2,3 .... and create conture map (Use soil class value as Z value. Of-course it is a kind of a iso height map too. It is vary easy. Be careful when editing the legends, as we use soil class numerical value for categorizing it. You can give a name at the legend editing. 

I endorse the comments from Dr Tapas, the best quality fruits like banana, citrus, mango, citrus ..all are produced despite subsoil acidity , which i emphasized in my  responses to almost similar question  flagged off by Dr Pal sir...stating that can we call acid soils chemically degraded..?

I do not think so if you are trying to extract dna from a soil material.

I would recommend:

De Vries, W. 1994; or Van Breemen, N. 1994 ... I did not read all of their research but I came a cross them often in this kind of studies.

Dear Younes- yes, such relation exits. Please find attached a relevant paper. With best wishes-

Dear Jerome,

Please note to the example on page 69 of World reference base

for soil resources 2014 (Update 2015).

The best,

ISA

Interesting discussion . Sensitivity of soil organic matter fraction is largely guided by ease of extraction , active fraction  ( For example humic acid , fulvic acid as part  POM of SOM ) is more labile in nature , and hence contributes towards soil structural stability . Any reduction /depletion in these fractions would indicate loss of soil stability or potential degradation..Loss of organic matter binding soil particles means  soil is fast approaching towards degradation

There are a number of articles on this in the literature - several published over the years in Soil Use and Management. Links attached.

Regards

Andrew

Dear Dr. Kumar,

The oven drying of soil mass at 105 degree centrigrade temperature for 48 hour is often sufficient to remove water contained in micropores and also hygroscopic water retained by soil colloids. The removal of structural water which is a part of mineral structure is achieved at much higher temperature and it is recorded by Thermal Gravimetric Analysis (TGA) or also in Differential Thermal analysis (DTA). These techniques are used in identification and characterization of soil minerals in conjunction to x-ray diffraction.

I agree with the answer of Dr. Beauvais. The structural water imparts specific properties  to soil colloids. High temperature drying of clay minerals for example like that  of vermiculite will collapse the c-axis and reduce it to that of illite. Such drying will affect the entry of other molecules in the interlayer space of 2:1 type  clay minerals. This would also change the specific surface area of the mineral. Similar changes in the reactivity of  hydroxides and oxyhydroxides would occur.

Even in the case of soil organic matter oven drying even at much lower temperatures (around 100-105 centigrade) would induce the internal pairing of  proton donor and proton acceptor  groups making re-hydration of organic colloids difficult.

Dear Hepsiba,

You do not need DSC for soil analysis. TGA alone is sufficient to measure the loss of organic materials although you will need a high temperature (approx 1000 oc) so you will need to use ceramic pans.

I also find it useful to perform PXRD before and after TGA analysis to show that I am not burning or changing any of the mineral content in the sample.

In general 5-15 cm or sometimes 30 cm soil is considered as surface soil. After collection of soil samples from the entire area covering the fields in Zig-Zag way you have to mix the soil samples throughly removing debris and root materials to prepare for analysis in the laboratory. Then you can go for mechanical analysis either by Pipette method or Hydrometer method . After that to air dry samples you may analyse for Hydrogen ion concentration (pH)  by pH meter and Electrical conductivity using EC meter  to measure the water soluble salts. Then you go for measuring Water holding capacity, moisture equivalent, Field Capacity, Permanent Wilting Point, Sticky point etc. Beside this you must determine the soil color after using Munsell color disc or Cardboard Disc. Then you may go for the measuring the exchangeable iions i.e. C.E. C or A. E. C. After completing the physical analysis you may start for Chemical Analysis or Physico-Chemical Analysis like Organic Matter content,, N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, Mo, Zn etc. You may also separate the Clay fraction may be by sodium chloride methods. If you want to do biological parameters then you have to do with the fresh soils and go for microbial count using dilution plate technique, microbial activity by FDA and dehydrogenase measurements, microbial biomass and different beneficial enzyme activities. Lot of Practical Analysis Book are available in the market. Most popular soil analysis books are: Methods of Soil Analysis written by M. L. Jackson and books written by C. A. Black. You may also consult other books like Soil and Plant Analysis written by C. S. Piper

You need to provide more information about your soil to help to determine what can go wrong in your extraction, as well as what improvement did you try:

- the actual pH value (until 5 it should not be a problem to extract DNA).

- soil type/soil texture

- size and type of beads used for bead beating

- bead beating time and speed

- type of improvement you tried

I think if you have difficulties to extract DNA it is because of the biochar which is a common problem. Have a look on the attached paper that test different protocols to extract DNA from biochar enriched soil, although they do not use the Fast DNA Spin kit. You might have to use a different kit, have you thought about it or you do not have the possibility?

Dear Mahmoud,

I recommend the following book for you:

Singh R.A. (1980) Soil physical analysis. New Delhi Kalyani Publishers, New Delhi, India. Accession No. 153484.

Dear Parham,

Why not spend some time in the library there is a wealth of knowledge on soil mechanics and mechanical properties of soil.  The simplest for what you would require are the Attenberg limits and simple compaction models based around these and consolidation density.

You might even find it useful to read (Topp GC, Reynolds WD, Cook FJ, Kirby JM and Carter MR (1997). Chapter 2. Physical Attributes of Soil Quality.  In Soil Quality for Crop Production. (Eds E.G. Gregorich and M.R. Carter), Developments in Soil Science, 25 Elsevier, Amsterdam, 21-58.) which will get you started.

Regards,

Freeman Cook

More than over-use of fertilizers , i feel , the very basis of such over-use of fertilizers , why does it happen ..?. Is it the non-availability of soil test- based fertilizer recommendation , unable to interpret the situation in right perspective in the context of changing yield performance ..? 

THanks a lot! 

The only way is to go trough the WRB soil classes and extract from the qualifier list the textural classe. Indeed in WRB, you will have the Reference Soil Group like Cambisol, Podzol. The latter are followed by qualifier expressing special features like the soil texture (clayic, siltic, arenic qualifiers).

Convert the limit textural class of your Hydrological Soil Group with the soil textural calculator (see attached)  and try to find those limits according to WRB qualifier to build a conversion table.

A rough conversion (I guess, to be verified  )will be :

Group A ->Arenic qualifier

Group B-> Loamic qualifier

Group C -> Siltic qualifer

Group D -> Clayic qualifier

Thank you Dr. Anoop Kumar,

You have raised questions which are highly relevant to present situation because significant area of the world, especially in arid and semi arid zones is going out of cultivation consistently. Thus, the limited resource of land is shrinking slowly and slowly while there is constant rise in the population with ever increasing demand for food, feed and shelter. This situation is expected to worsen with happening of climate change that will raise temperature and decrease water availability in areas already with short supplies. Both these factors of climate favor salination and sodication with the result of converting highly fertile lands into saline, sodic and saline sodic. Increased use of saline groundwater will aggravate the situation. Ultimately, world food security, already shaking, will be coming at stake. It was demand of the day that this situation should be discussed by scientists and researchers of the Researchgate and workable solutions be recommended. Your effort is highly appreciable to open this discussion.  I request to world scientists community to actively take part in this discussion.  

Now I answer sub-questions put forward by Dr. Kumar to keep discussion on the track.

*Why do not we consider calcareous soils as a part of salt affected soils  ?

-Because by definition (EC> 4 dS/m or SAR> 13 or both parameters more than this criteria)  these do not come under these soils. However, these are more prone to be converted into saline, sodic or saline sodeic soils under a little bit negligence of agronomic practices because factors favoring salination or sidication are already operative in these soils.

* Why salts do not accumulate in grains or edible parts of plants ?. What are the mechanistic insights for such physiological events? 

- Up to certain limits all plants and salt tolerant plants in particular, segregate salts into cell vacuoles or there is salt shredding mechanism developed in certain plants (Diplecna chloea, salt grass or Kallar grass). However, in acute cases or in certain plants (like sugarcane- you can taste salts in its juice) salts can accumulate in eating parts.  

* Do we have sensors to  directly measure the salinity and sodicity in field? Or , alternatively , Is there any field diagnostic kit available for appraisal of salinity or sodicity right in the field?

*Which type of reclamation is more sustainable from environment point of view?

-That type of reclamation which disturbs the ecosystem to the minimum extent. However, you have to get rid of accumulated salts at least once and definitely it will distrb the environment once. However, if the natural drainage of soils is good or you are using tile drainage, the salts will be taken away safely.

* How do you see the role(s) of salt tolerant microbes in reclamation and post-reclamation scenario of salt affected soils?  

-Like other favorable soil characters, microbial population is also affected badly due to salt accumulation. It may be finished totally in ultra salt affected soils. That is why, after completion of chemical, hydro-chemical and/or physical reclamation, inoculations are highly recommended. 

* What is the best method of artificial recharge of ground water?

- Keeping a balance between total rainfall of the year and pumping of water for irrigation and domestic purposes will not disturb the ecosystem but if you are disturbing it, the water table will go deep and deep. Artificial recharge dams are made in upstream and this water is allowed to move into affected areas which are to be recharged. However, these practices have not paid much practically and no area have gained its original water table despite all recharging efforts. Al-Batinah area of Sultanate of Oman can be quotes just as an example, though there are many in the world.  

* What is the system of rice intensification , and what magnitude of success, it holds in salt affected soils?

-Rice is included among the crops with highest delta of water. This may be bitter but its a hard fact that rice intensification is increasing salinity problem. Pumping of saline water to irrigate rice is bringing salts into soil surface and sub-surface, thus increasing total salt load into ecosystem. Even good quality river water when kept standing in rice fields concentrates due to evaporation and leave these salts in the sub-surface because the soil is already puddled to save irrigation water. too much can be said in this regard. But I will conclude with the words that salt balance studies must be undertaken to understand the facts.

* How do you see the success of bio-saline agriculture ? Is saline aquaponics  potentially promising ?

- Bio-Saline agriculture is a good practice but still did not contributed much that was required. You can grow salt tolerant plants. But our immediate need is food security in which contribution of this practice is not significant. Actually, it is secondary agriculture and useful to put salty lands to other uses and prevent further degradation. It must be adopted where appropriate but not replacement of reclamation where it is possible. 

*How do you see the emerging issues on salinity and sodicity getting vitiated by consequences of climate change? How shall we reorient our objectives in this context?

- We will be facing worst situation with regard to salinity in areas hit too much by climate change because the problem will highly increase there. We have to revisit of planning of agriculture in these areas, especially where there no supplies of canal/terrestrial water like Qatar. Green house/ aquaculture may be good selection for these areas 

Why do salt affected soils continue to pose potential threats to food security? - 

-As I explained earlier that land resource is shrinking due to salinity and other allied problems. Crop yields decrease significantly when grown in salt affected soils. This all contribute to threats to food security.

Typical region of air-entry value have been reported from 0.05 cm (0.005 bar) for coarse texture soils to 100 cm (0.1 bar) for fine-textured soils in different studies.

Dear Ebrahim

The quality of water or in general the water type is not so important in CBR tests. However, it is the best practice to use river or well water located in the area of study.

All the best

Dear Nesterina,

I am going to conduct the seismic analysis associated with saturated undrained cohesive soils. 

Standard soils are used especially for permission studies according to GLP (Good Laboratory Practice) investigating leaching, degradation and metabolism, influence on soil microflora and fauna, adsorption/desorption characteristics of pesticides in soils as well as for pot experiments and other investigations in the laboratory and in the field. In guidelines of the German JKI (Julis-Kühn-Institut) and other relating guidelines (OECD) soils with certain characteristics are recommended. Standard soils are also used in very different experiments not concerning pesticides.

For these purposes LUFA Speyer offers Standard soil types differing especially in their organic matter content, particle size distribution and pH-value.

Analyses Data Sheet for Standard Soils according to GLP:http://www.lufa-speyer.de/images/stories/2016-STB-Bo-data_sheet.pdf

Micronized sulphur,S in water dispersible microgranular form,can be applied to crops in sulphur deficient soils in small application rates,may be 8-10 kg/ha.To my knowledge it it not intended for sodic soil reclamation as it is a costly material and can not be applied in tonnes as amendment.Can you give the cost of 50 or 100 kg  micronized S?

discuss this with Matthew Taylor, he is an expert on Flouride

: matthew.taylor@waikatoregion.govt.nz

The key problem is that we cannot say with any certainty what value of, e.g. DTPA Zn, is critical without doing the experiment with the soil in question.  That is, it is a big leap of faith to regard a chemical extraction to be a measure of bioavailability.

contact Dr. Utermann at the German Environmental Agency : jens.utermann@uba.de!

see the attachment

Soil quality is how well soil does what we want it to do. More specifically, soil quality is the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. Soil Organic Matter and Soil Biology play a major role in soil Quality.

Soil health is a state of a soil meeting its range of ecosystem functions as appropriate to its environment. Soil Health Testing is an assessment of this status.

Actually these both terms are used interchangeably in literature. The new term referred above "Soil Security" may be accepted over time as well.

Dear Abdullah,

Perhaps the attached paper might help you figure this out. I also saw on the Decagon website that salinity can vary your readings by up to 10%, so that might be a contributing factor.

Regards,

Steve

thanks you so much, Ariadne Tsambani

...

Hi.  Is this the handbook you need?

Also, in the www.id.energy.gov website, I have seen other links to MAPEP Series that might help you too. 

Cheers!

Agricultural practices interfere heavily in the quality of agro-ecosystems. The main changes in the structure and physical ground are through intensive mechanization, native vegetation removal, lack of conservation practices, while soil fertility is affected by the export of nutrients (through harvesting of crops), soil acidification, lixiação nutrients, pesticides (these interfere in the macro, meso, and micro fauna of soil that are responsible for global cycling of nutrients).

Dear Seyed,

you may found the following paper useful

Article · January 1996 with 4 Reads

DOI: 10.3208/sandf.36.3_123

you may request full-text from the author "Takaharu Shogaki" on research gate

best wishes

Hallo Tiago,

According to your question I can give you the following reply: 

Suitable parameters to assess the soil compaction are i)  saturated water conductivity, ii) effective bulk density (= bulk density + (0.009 * clay content [%]  ) by pF 1.8 and 2.5, iii) the macroporosity by pF 1.8, iv) penetration resistance (dynamic - Panda sonde) by pF 2.2 - 2.7. The penetration resistance alone is not enough to assess quantitavely the degree of soil compaction.

Basically, the penetrometer is an excellent and an appropriate intrument to measure the hardness of the soil or wearing capacity of the soil (different from degree of soil compaction). Only with one parameter (penetration resistance) you take into consideration at the same time soil texture, soil sturcture, soil moisture,  ground cover, root density to evaluate the soil  trafficability.  We have observed that in special cases a wet soil (permanent meadow) can be harder than an arable dry soil...

Penetration resistance is an imortant parameter to describe stress propagation in the soil. Penetrometers are not predestinate to assess directly the degree of soil compaction.   

With my best regards,

Etienne

As Stuart Harris indicates, lacustrine sediments are very variable, although mostly fine grained.  Many lacustrine deposits are metres or dekametres deep ,and any tendency towards thixotropic 'quick clay' instability is particularly hazardous for structures that impose high loadings, e.g. high rise blocks in the Mexico City earthquake

Soil test reports generally express TN and TC as a percent (%) of dry mass.  As an example, if the report says soil contains 1.23% of TN, this means that there is 1.23 grams of TN in 100 grams of dry soil.

To convert TN or TC expressed in % to g/kg dry soil:

1.23% TN = (1.23/100) x 1000 = 12.3 g/kg dry soil

 I am supplementing through one very good studies covering the subject , you have raised Dr Ghafoor. Remediating saline–sodic soils with organic amendments is increasingly seen as a cheaper and sustainable alternative to inorganic materials. The reclamation potential of biochar, biosolids and greenwaste composts applied to a saline–sodic soil was evaluated in a laboratory leaching experiment using moderate SAR reclaimed water. Treatments included biochar, biosolids co-compost, greenwaste compost (all applied at a 75 t ha−1 rate), gypsum (50% soil gypsum requirement), biochar + gypsum, biosolids + gypsum, greenwaste + gypsum and a non-amended control ( Chaganti et a. 2015, Agricultural Water Management  158: 255-265).l  All treatments were subjected to a one month incubation after which, soils were filled in columns and leached using reclaimed water until 7 PV of water had passed. Cumulative leachate losses of Na+, Ca2+, and Mg2+ were evaluated in addition to soil properties after leaching. Results show that leaching with moderate SAR water was effective in reducing the soil salinity and sodicity of all soils, irrespective of amendment application. However, incorporating biochar and composts significantly enhanced this effect. Salt leaching was higher in soils treated with organic amendments. Cumulative leachate losses of cations were significantly higher from biochar and compost treated soils compared to gypsum and unamended controls. 

Enclosed below two very interesting PDFs highlighting the role of biochars in remediation of sodic soils.

one of the best indicators (at least under our clima conditions) is the number of earthworms per area unit.

I think, you still need other source of SM to compare with your result. If you have point measurement of SM, you just get the SM of the corresponding pixel. Because the field measurement of SM might be more accurate, you could adjust the SMA SM to match well with the observed one.

Hope that it could help!