Nice question Dr Shirgure . What are the basic principles of computing water requirement . What kind of paradigm shifts while computing the water requirement , have taken place , I am more willing to see.  The methods which look into the intrinsic soil properties to dictate the water requirement of crop like citrus, probably hold more promise in years to come.    

Parameshwar, nice question, FAO has done lot of work for crops and trees, you can refer them, as well our interest could be ET computation, irrigation schedules, water use-yield relationships

i provide you a link for your kind reference

http://www.fao.org/nr/water/cropinfo_citrus.html

regards

Thanks Dr Kalra, your link can solve my few doubts. The situation at Central India is very adverse and climate change is the problem now a days. Any way I will try the solutions also.

Thanks again for your reply.

Dr Shirgure  I appreciate your concern . I am more willing to know from our colleagues , what are developments that have taken place in computing the water requirement ?

Estimation of the crop water requirement for trees may be calculated from

WR = Ep x Kp x Kc x S x WA

Where

  WR  = Water requirement in litres / plant /day

  Ep   = USDA Class A pan evaporation value in mm/day

  Kp   = Pan co-efficient

  Kc   = Crop co-efficient

  S   = Space/Area occupied by each plant/ tree ( m2 )

  = Row to row spacing (m) x plant to plant spacing (m)

  WA   = percentage of “S” to be wetted with irrigation water   (0.3 – 1.0 )

Pan co-efficient and crop co-efficient need to be assessed from past experiments/ experience.

Thanks Dr Kumarswami

  This method is being followed for the extension work. But for any advanced development has been taken place or not it is the question?

We need to develop the ready reckoners 

Hello Dr Shirgure

As many respondents above have provided you some options for estimating water requirement for citrus and of course FAO 56 (http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf) gives a common procedure for crop water requirement estimation. There are two approaches depending on the type of crop grown. For citrus which has partially covered soil surface condition and partially wetted surface, you should follow the dual crop coefficient approach (DCC). It depends on a number of soil, crop and climate related parameters. The most important are ET0, Kcb, Ke, TAW, RAW, TEW, REW and number of fractions which depends on soil surface condition, crop condition and irrigation system followed. The main draw back of this procedure is that this model is bucket type and doesn't consider the water movement which is very important process for estimating water requirements. So we sometimes unable to estimate the deep drainage and fluxes correctly and usually overestimate the ETc. To overcome this problem we tested this approach following a numerical  (HYDRUS) modelling approach which needs to be calibrated and validated under the field conditions. Once a model is calibrated under specified conditions then you can prediction anything such as impact of climate change, low rainfall conditions, less water allocations, water stress options etc. You can also evaluate the salinity and nitrate build up and leaching respectively. We have tested this methodology in Australian conditions for mandrin and orange. Have a look on the attached papers. 

Dear Vinodji

 I am highly thankful for the reply as well some idea especially about modeling. Thanks for the attachments also. I will study as such work is not available under central India.

Simulation model can be further useful under changing weather conditions as well as soil health worsening. 

Personally thanks. and be in touch with me on email : [email protected]  

I have noted that you replied "This method is being followed for the extension work". Any thing proved correct in research only can be adopted in extension. Further you are in a central institute working on a particular crop. please devise any method and send it for others opinion to refine. your interest to prepare a ready reckoner is appreciated. Again its applicability is location/ region specific and need to be adjusted for local weather conditions in other areas.

Dear Kumarswamiji 

You are correct. It will be for the same purpose. and will be extension also.

Depending on the local weather situations the tables needs to be preapred.

This in process. Thanks.