Have a look to the soil moisture model we have made freely available on ResearchGate (see attached link).

Good luck with your research,

Luca

Data Soil Moisture Model (Matlab code)

Hey Luca,

Thanks! I did not know that was available. Downloaded and will look into it.

Best

You can also try Thronthwaite and Mather model

Read research paper mentioned below. I used BUDGET software that is based on soil water balance to compute for each soil types and various crops.

Suresh Kumar, Patel, N.R., Sarkar, A. and Dadhwal, V.K. (2013) Geospatial Approach in Assessing Agro-Climatic Suitability of Soybean in Rainfed Agro-Ecosystem. Indian 

Soc. of Remote Sensing. 41(3):609–618

Read the following research article (p176)

Article: Effect of tillage and water table control on evapotranspiration, surface runoff, tile drainage and soil water content under maize on a clay loam soil C. S. Tan, C. F. Drury, J. D. Gaynor, T. W. Welacky, W. D. Reynolds

Agricultural Water Management 02/2002; 54(3):173-188. · 2.33 Impact Factor

Change in Soil water = (P + I + C) - (ET + D + RO)

I would neglect C (if water table is not very close to root zone),  and RO

The equation becomes

Change in Soil water = (P + I) - (ET + D )

Then you would be able to calculate D if you determine ET using Penmann's equation

Yeah Abdur, we assumed C and RO were zero. You are 100% right. Actually, we used a simplest method to determine ET. We installed an evaporation pan from which we determined daily evaporation rate (ETp) and with the crop coefficient for spinach  for late season (0.95) and we computed the daily ETc.

Yes, you are using correct method, I was going to suggest that ET calculated using 0.95 of E (pan evaporation). If you have time, climatic data you could esality calculate ETpenmann using Penmann-Monteith equation then calculate ETspinach using 0.95 x ETpenmann and compare with your method.

Dear Jenkins,

Few years ago our group conducted a 3-yr field experiment to estimate the soil water budget for maize grown under two tillage systems. We measured all most all environmental variables you have mentioned. Please see the attached paper. I hope it will be of interest to you.

Susantha

Hi,

I used and implemented FAO-56 bucket models based on the resolution of the root zone water balance equation. 

Original model is implemented in a spreadsheet that you can find in:  http://extension.uidaho.edu/kimberly/2013/04/spreadsheets-supporting-fao-56-example-calculations/

If soil water deficit conditions are considered, the following amendment can be used:

- Rallo et al., Comparison of SWAP and FAO Agro-Hydrological Models to Schedule Irrigation of Wine Grape.  Journal of Irrigation and Drainage Engineering 01/2011.

- Rallo et al., Improvement of FAO-56 Model to Estimate Transpiration Fluxes of Drought Tolerant Crops under Soil Water Deficit: Application for Olive Groves. Journal of Irrigation and Drainage Engineering. 01/2014; 140(8).

Dear Jenkins,

You probably find useful information about FAO-56 in http://www.fao.org/docrep/x0490e/x0490e00.htm

(Allen, R.G.; Pereira, L.S.; Raes, D. und Smith, M. (1998): Crop evapotranspiration - Guidelines for computing crop water requirements. FAO Irrigation and Drainage Papers. Paper No 56, FAO, Rome, 326 S.)

I implemented the soil water balance model with single crop coefficient described there in GIS and was quite happy about the detailed instructions in this FAO paper.

Best regards, Andreas

Howdy Dear Mr Macedo

The reference cited below are from some of my work on the use of water balance to quantify some of the major water balance components at the daily basis.  They have detailed information on how to use it with different data sets. Go through them and if you want a copy of any of them let me know. The water balance equation is the most basic equation in hydrology and in science in general because it is based on the principle of conservation of mass; however, it's very helpful in answering many practical water management questions.

Fares A., Dogan A., L. R. Parsons, T. Obreza, and K.T. Morgan. 2008. Effects of Citrus Canopy Interception on Effective rainfall Calculations Using Water Budget Analysis and TR-21 Method. Soil Sci. Soc. of Amer. Journal. 72:578-585.

Fares, A., A.K. Alva. 1999. Field determination of citrus evapotranspiration using the mass balance method based on a continuous monitoring of the soil moisture content. Soil Sci. 164:302 310.

Fares, A., A.K. Alva. 2000. Soil water Balance components based on real-time multisensor capacitance probes in a sandy. Soil Sci. Soc. Am. J. 64:311-318.

Fares, A. and S. Fares. 2012. Irrigation Management System, IMANSYS, a User-Friendly Computer Based Water Management Software Package. Proceedings of the Irrigation Show and Education Conference, Orlando FL, Nov. 2 – 6 2012.

Fares, A. and V.O. Polyakov. 2006. Advances in Crop Water Management Using Capacitive Water Sensors. In D. Sparks (ed.) pp. 43-77. Advances in Agronomy. Vol.90, Academic Press, Amsterdam, The Netherlands.

Dear Jenkins,

I implemented the soil water balance model with single crop coefficient as described in FAO-56 on experimental fields where irrigation is not a treatment and the dual coefficient approach when soil surface wetting and evaporation is a basic concern, i.e. drip (mostly subsurface) irrigation experiments.

Best regards,

Panagiotis

You can use Palmer Water balance. Palmer Method separate soil into 2 different layers. You can find all in : https://www.ncdc.noaa.gov/temp-and-precip/drought/docs/palmer.pdf

This method is widely used for drought monitoring (Palmer Drought Index and Self Calibrated Palmer Dought Index). Finally, I made easy excel sheet for multiple Years calculation (in attachment).

Data Palmer (1965) Z-index and Water Balance - Multiple Years Worksheet

I found this very practical software for Thornthwaite monthly water-balance:

http://pubs.usgs.gov/of/2007/1088/pdf/of07-1088_508.pdf

http://wwwbrr.cr.usgs.gov/projects/SW_MoWS/Thornthwaite.html