Dear Dr. Rao:

I am assuming that in your question you are talking about the Ky factor in
the Kassam's equation displayed in FAO 33 which relates relative yield to
the quotient real evapotranspiration / potential crop evapotranspiration.
It's true that in FAO 33 there is no millet nor vigna or paddy. But it
doesn't means that there is no such data at FAO now, maybe there is.

For anyone to have such coefficients he would have had to use that approach
to derive it. To find such a coincidence may not be easy. That kind of data
is the hardest to find in the crop modeling field.

I call your attention to the book "Bilan hydrique agricole et secheresse en
Afrique Tropicale" (1994) John Libbey Eurotext, 415 pp. There we have at
least 6 papers on water balance and millet yields with a lot of Tables and
Figures. I think that a a careful analysis of that data could allows you to
derive such Ky values by yourself. As some of those papers are from very
well recognized specialists as G. Maracchi, G. Popov and others, maybe they
could assist you in the reanalysis process of their own experiments.

Additionally, if you take some crop models as Generic CERES from DSSAT or
WOFOST 7.1.2, which give at the output potential yield, real water stressed
yield, and total evapotranspiration during different phenological phases and
for the whole crop cycle, you could also obtain a set of "model derived" Ky
coefficients for every crop that have a biophysical model available.

Then you could substitute that in the equation,

  (1 - (yield/potential yield)) = Ky (1 - (Real evapot./Max. pot. crop.
evap))

Of course, to calculate Max. pot. crop. evap you'll have to use the
Doorenbos and Pruitt Kc coefficients available in the literature or obtain
that data from biophysical potential yields crop model simulations.

Sincerely yours,

Roger E. Rivero Vega


----- Original Message -----
From: "Dr. Srinivasa Rao Gattineni" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, March 19, 2005 12:46 AM
Subject: Request for Ky values


> Dear List,
>
> Sorry for repeated mail.
>
> Can some body provide me "YIELD RESPONSE FACTOR (Ky)" values for paddy,
> pearl millet and green gram (VIGNA RADIATA), please.
>
> Thanks in advance.
>
> Srinivasa Rao Gattineni
> Research Associate
> Databank
> Central Research Institute for Dryland Agriculture (CRIDA)
> Santoshnagar, Hyderabad
> India.
>
>
>
> Dr. Srinivasa Rao Gattineni
> (040) 55791128 / 9848127159
>
>