According to Saxton method, if you have the percents of sand and clay, you can calculate the PWP and the FC as well as the Ks, Porosity, BD, and AW.

the equations in MS-Excel format are:

a_coef=EXP(-4.396-0.0715*Clay-0.000488*SandSQ-0.00004285*SandSQ*Clay)

b_coef=-3.14-0.00222*ClaySQ-0.00003484*SandSQ*Clay

Porosity=0.332-0.0007251*Sand+0.1276*LOG10(Clay)

PWP=(15/a_coef)^(1/b_coef)

FC=(0.33333/a_coef)^(1/b_coef)

Ks=EXP((12.012-0.0755*Sand)+(-3.895+0.03671*Sand-0.1103*Clay+0.00087546*ClaySQ)/Porosity)

BD=(1-SAT)*2.65

You can write them in Excel and use Solver addon to find possible values of Sand and Clay percents, then you will find the values of PWP and FC (By fixing the values of the Porosity and Ks.)

I attached an excel file that can help you..

Determining the field capacity is quite complex. Usually the field capacity is considered to be at pF=2.5 and the wilting point at 4.2. This requires a little equipment to be able measure the soil moisture while imposing a given water tension. This equipent exists and is used to determine the water retention curve (http://en.wikipedia.org/wiki/Water_retention_curve).

Also see this page:

http://www4.paca.inra.fr/emmah_eng/Facilities/Laboratories/Laboratory-Hydro

There are many different free pieces of software that can estimate the hydrological parameters of your soil samples from various input values from soil texture all the way to water retention curves. Of course such models we only give you rough estimates:

Rosetta model:

http://www.ars.usda.gov/services/docs.htm?docid=8953

SoilPar model:

http://www.sipeaa.it/ASP/ASP2/SOILPAR.asp

RETC:

http://www.pc-progress.com/en/Default.aspx?retc

According to Saxton method, if you have the percents of sand and clay, you can calculate the PWP and the FC as well as the Ks, Porosity, BD, and AW.

the equations in MS-Excel format are:

a_coef=EXP(-4.396-0.0715*Clay-0.000488*SandSQ-0.00004285*SandSQ*Clay)

b_coef=-3.14-0.00222*ClaySQ-0.00003484*SandSQ*Clay

Porosity=0.332-0.0007251*Sand+0.1276*LOG10(Clay)

PWP=(15/a_coef)^(1/b_coef)

FC=(0.33333/a_coef)^(1/b_coef)

Ks=EXP((12.012-0.0755*Sand)+(-3.895+0.03671*Sand-0.1103*Clay+0.00087546*ClaySQ)/Porosity)

BD=(1-SAT)*2.65

You can write them in Excel and use Solver addon to find possible values of Sand and Clay percents, then you will find the values of PWP and FC (By fixing the values of the Porosity and Ks.)

I attached an excel file that can help you..

Very good stuff Mohammad. Thanks

There also exist lots of empirical data for typical soil textures * bulk densities * humus content. The following link is entirely in german, but contains data from several thousends of samples:

http://www.bgr.bund.de/DE/Themen/Boden/Netzwerke/Adhocag/Downloads/KA5_bodenspezKennwerte.pdf?__blob=publicationFile&v=2

You might be interested in table 17.1 (with FK=field capacity and TOT= remaining volumetric water content at pF=4.2) Soil texture classification is explained in table 18.1. Soil desity classes are 0.8-1.4 (rho-t 1+2), 1.4-1.6 (rho-t 3) and 1.6-2.0 rho-t 4+5) and soil humus classes are listed in table 6.1.

You can use a "Pressure Plate" apparatus if there is one available at your laboratory or if you know some lab that have one (it is a experimental way to obtain these data and it could be a laborious way); Other experimental way it is by centrifugation of the soil samples (then you have to know the soil texture and to calculate the "rpm" and time you needed for your soil sample) . Finally, FC and PWP could be estimated by means of standard equations that take into account physical-chemical soil properties

See:

http://www.fao.org/nr/water/docs/AquaCropV40Chapter3.pdf.

http://vro.dpi.vic.gov.au/dpi/vro/gbbregn.nsf/pages/soil_hydraulic_pdf/$FILE/TechReportch02.pdf

Pressure plate apparatus will help u most

You may want to give a look at the following chapter:

Romano, N. and A. Santini, 2002. Water retention and storage: Field. In “Methods of Soil Analysis, Part 4, Physical Methods” (J.H. Dane and G.C. Topp, eds.), pp. 721-738, SSSA Book Series N.5, Madison, WI, USA, ISBN 0-89118-841-X.

Well, if bulk density and textural components are not available, estimating soil-water content at field capacity can be a rather difficult exercise. Overall, you can give a look at the following papers (available in ResearchGate):

1) Romano, N., M. Palladino and G.B. Chirico, 2011. Parameterization of a bucket model for soil-vegetation-atmosphere modeling under seasonal climatic regimes. Hydrol. Earth Syst. Sci. 15:3877-3893, ISSN: 1027-5606.

2) Romano, N. and A. Santini, 2002. Water retention and storage: Field. In “Methods of Soil Analysis, Part 4, Physical Methods” (J.H. Dane and G.C. Topp, eds.), pp. 721-738, SSSA Book Series N.5, Madison, WI, USA, ISBN 0-89118-841-X.

According to Saxton method, if you have the percents of sand and clay, you can calculate the PWP and the FC as well as the Ks, Porosity, BD, and AW.

Very good stuff Mohammad. Thanks 

thanks

If you only have total porosity (i.e. close to saturated water content value) and saturated hydraulic conductivity values I think you cannot do much with reasonable accuracy. You can try using some pedotransfer functions, but with large uncertainty allowing for your (poor) inputs. You should also ask yourself to what spatial scale your study is dealing with. You can find more details in my paper: Romano, N., M. Palladino and G.B. Chirico, 2011. Parameterization of a bucket model for soil-vegetation-atmosphere modeling under seasonal climatic regimes. Hydrol. Earth Syst. Sci. 15:3877-3893, ISSN: 1027-5606.

 pedo-transfer functions (deriving moisture retention / release / transmission and avalable N) on the basis of easily determinable parameters (texture and OC), the approach is used in most of the crop growth models 

but in some cases, it provides greater percent deviation in values from the actuals (validation)

regards

Read the FAO 56 Guide:  http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf

Also, here is a good resource: http://www.fao.org/docrep/r4082e/r4082e03.htm

http://nrcca.cals.cornell.edu/soil/CA2/CA0212.1-3.php

You need to know the bulk density, calculate soil moisture fraction, etc. read the sources provided

thanks Jenkins excellent information provided by you to all of us

regards

Extracted from my work in Laos

Dry Soil Moisture Fraction at Bulk Density Determination

Equation 8 was used to estimate the dry weight soil moisture fraction for each treatment stage adopted from Walker (1989):

• 𝑾=𝑾𝑾 (𝒈)−𝑫𝑾 (𝒈) ÷𝑫𝑾 (𝒈) [8]

Where W is the dry weight soil moisture fraction, WW is wet weight of the sample soil and DW is the dry weight of the soil after being oven-dried for 12 hours (Walker 1989).

Volumetric Soil Moisture Content at Dry Bulk Density Determination

In this study, the volumetric soil moisture content of the soil cores were computed by using equation 9:

• 𝖖=𝖌𝒃 ×𝑾𝖌𝒘 [𝟗]

Where 𝖖 is the volumetric soil moisture content (g/cm3), 𝖌𝒃 is the calculated dry bulk density, W is the dimensionless dry weight soil moisture fraction, and 𝖌𝒘 is the specific weight of water at 5° C is (9.807 kN/m3) (NCEES 2005). Using equation 9, 𝖖 was calculated for each soil core sample collected during dry bulk density determination and the results are presented in Figure 73.

Field Water Balance Estimations

𝑺𝑾𝒄=(𝑷+𝑰+𝑮𝒄+𝑴𝟏)−(𝑬𝑻𝒄+𝑫𝒅+𝑹𝒐+ 𝑴𝟐)

Where P is precipitation, I includes the calculated recharged from ETc minus precipitation plus the adjusted daily irrigation rate, Gc is groundwater charge, M1 is the previous soil water storage (PSWS), ETC is evapotranspiration, Dd is deep drainage, RO is surface runoff, and M2 is the current soil water storage (CSWS).

The total available water (TAW) is the water that is found between the field capacity (FC) and the permanent wilting point (PWP) (Andales et al. 2011). FC and PWP were estimated by using the soil texture classification approach, which suggests that silty clay soils have the total estimated volume (0.41) water at FC and (0.27) moisture at PWP (Dane and Toppe 2002, Saxton and Rawls 2006, Andales et al. 2011). The TAW at the field was estimated using equation 11 adopted from Walker (1989).

• 𝑻𝑨𝑾=(𝖖𝖋𝖈− 𝖖𝖕𝖜𝖕)× 𝑹𝑫 [𝟏𝟏]

Where TAW denotes total available water, 𝖖𝖋𝖈 represents volumetric soil moisture content at field capacity, 𝖖𝖕𝖜𝖕 is the volumetric soil moisture content at the permanent wilting point and RD denotes the potential root depth of water spinach (30cm or 300mm). Using equation 11, the TAW at the experimental units was estimated to be 42mm of water per mm of soil depth (or 4.2cm of water per cm of soil depth).

References

Allen, R. G., L. S. Pereira, D. Raes, and M. Smith. 1998. Crop Evapotranspiration- Guidelines for Computing Crop Water Requirements: FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization of the United Nations, Rome, Italy.

Andales, A. A., J. L. Chavez, and T. A. Bauder. 2011. Irrigation Scheduling: The Water Balance Approach. Pages 1-6 in C. S. U. Extension, editor

Walker, W. R. 1989. Guidelines for Designing and Evaluating Surface Irrigation Systems. Food and Agriculture Organization of the United Nations.

Dane, J. H. and G. C. Toppe. 2002. Methods of Soil Analysis Part 4 Physical Methods. Soil Science Society of America, Inc., Madison, WI.

Saxton, K. E. and W. J. Rawls. 2006. Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions. Soil Science Society of America Journal 70:1569-1678.

As an addendum to my previous answer, I suggest reading my recent work just published as early-view in WRR:

Nasta, P., and N. Romano, 2016. Use of a flux-based field capacity criterion to identify effective hydraulic parameters of layered soil profiles subjected to synthetic drainage experiments. Water Resour. Res., 52, doi:10.1002/2015WR016979.

Hi Dr.Nunzio Romano , could you please post a link or the actual paper here, if possible? It seems interesting.

good work, jenkins as well Nunzio reference also you pl look

there is a need to use pedo-transfer for indian conditions where mosly data is available on sand, sily, clay and oc

regards

Here is the link:

http://onlinelibrary.wiley.com/doi/10.1002/2015WR016979/full

Since the soil can vary in physical properties over short distances, a practical way of measuring field capacity is to use 3 m square plots on flat areas.  Build a low embankment around the plot, then either flood the enclosure or wait until precipitation has made the soil wet to the depth you are studying.  You then cover the plot with polyethylene to prevent evpotranspiration and allow the plot to drain naturally for about 2 days.  Remove the protective cover and sample the soil in depth increments at a number of points to the depth in which you are interested in  At least five sample points are needed for gravimetric determination of moisture content. 

The bulk density should also be measured concurrently to convert the water percentage of oven dry water to unit /volume basis.  The formula is:

Pv = Pw(Bulk density)(1/ water density)

Where Pv = water % by unit Volume

Pw = water % by unit weight

Inches of water in a given depth will be:

Inches of water = Pv x depth

Using pressure plate apparatus, you need similar samples collected in the field.  Each one is treated separately by adding excess distilled water to the sample on a porous plate and then subjecting the bottom of the plate to i/3rd bar pressure.  When the sample stops draining water, measure the amount of water remaining in the sample.  However, the one-third bar is a standard value but will probably not entirely match the field measurements due variation in soil properties.

Stuart.

What is the FC and PWP of sandy soil?

You may want to give a look at the following papers (included in ResearchGate):

Nasta, P., and N. Romano, 2016. Use of a flux-based field capacity criterion to identify effective hydraulic parameters of layered soil profiles subjected to synthetic drainage experiments. Water Resour. Res. 52:566-584.

Romano, N., M. Palladino and G.B. Chirico, 2011. Parameterization of a bucket model for soil-vegetation-atmosphere modeling under seasonal climatic regimes. Hydrol. Earth Syst. Sci. 15:3877-3893, ISSN: 1027-5606.

Romano, N. and A. Santini, 2002. Water retention and storage: Field. In “Methods of Soil Analysis, Part 4, Physical Methods” (J.H. Dane and G.C. Topp, eds.), pp. 721-738, SSSA Book Series N.5, Madison, WI, USA.

how to interpret field capacity in terms of soil

Unfortunately, field capacity and wilting points vary over very short distances in many situations. You certainly cannot come up with values that apply to the soils everywhere in Germany. If the distribution of soils is simple with minimal variation in physical properties, then you can make a number of measurements (perhaps 10) across the area and obtain a reasonable measure of the variation present in each soil horizon. Remember that any layer that is not as porous as the others will tend to cause a perched water table. The measurements are affected by the method of tillage and variations in the number and distribution of the roots of the crops that are grown on the land. Thus potatoes tend to leave friable soils compared to most other crops.

Stuart.

Please suggest the differences between the four soil types with respect to the four properties derived from the field.File is attached.

The field capacity of the soil (FC) and permanent wilting point (PWP) are @determined by pressure cooker method at –100 and –15,000 hPa retention, respectively (Richards 1948).

Regarding Abhkieet's question, B4 would by suitable for hydroponics but too droughty and lacking in water holding capacity to be fertile except or crops needing excellent drainage but having a plentiful water supply. B3 would be better due to its better water holding capacity. Thus carrots could do well on it if supplied regularly with waster., or if if had a high water table. B16 would be the best for most crops since it has relatively good water holding capacity, while B12 would have poor drainage due to poor permeability. However it would retain water well, but some plants may experience difficulty in obtaining a sufficient water supply due to its permeability.