Dear friends,
In the literature and FAO56, the single crop coefficient (Kc) or dual crop coefficient (Kcb) is reported for many field crops. However, we know that crop coefficient (Kc or Kcb) is very dependent on crop type, cultivar, and climatic condition and it does not generally get beyond 1.2-1.3. Except few evidences in the literature that Kc may reach about 1.6 or 1.8 for maize and wheat in arid areas, or 1.9 for biofuel crops in the Mediterranean area, I am not aware of any other reports or articles that might have reported Kc under non-stressed conditions even beyond 2 in arid and semi arid areas where potential crop evapotranspiration (ETc) is very high (no energy limitation for transpiration). In such cases, crop should have a high ability to take up and transpire a large volume of water under pretty well irrigated conditions, which means two time the reference evapotranspiration (ETo). I would like to know if anyone is aware of studies or crops that report Kc or Kcb higher than 2 in the arid or semi-arid areas? Anyway, this may seem unexpected compared to the current knowledge and literature on crop coefficient but may happen. I expect that such crop should be a super crop with a distinguished transpiration mechanism and physiology that allow high transpiration much more than the ETo. I appreciate any hint! Thank you.
Please find enclosed a paper in which the Kc max reached up to 1.6 and 1.9 for miscanthus and giant reed. There is a possibility of higher Kc under very specific conditions, & crop species
a) The contribution of heat stored in dry soil prior to wetting events , caused by microadvection of heat from dry surface areas to wet surface areas
b) Wind speed , Most of the Kc values given by FAO is as per specific conditions including wind speed
c) As you suggested some super crop species
But in general it will be less , If I come across some specific studies, I will let you know.
in ecuador, in our arid zone, we do not have a very high kc. the irrigation management in bananas, like example, is with kc 1.2 or maximum 1.3
Surendran Udayar Pillai and Carlos Rovello Gando
I appreciate your feed back on my question. I think we may need to revise our old fashion thinking on low Kc or Kcb of all crops in arid and hot zones. As Surendran Udayar Pillai mentioned, in the Mediterranean areas some crops have shown Kc of 1.9, which may indicate it is likely for higher Kc in other crops that are not identified yet! Having an accurate knowledge of real Kc or Kcb of specific crops in the hot regions helps in efficient irrigation planning, indeed. More filed trials are required, I expect.
Yes I agree @ Seyed Hamid Ahmadi, For efficient planning and under the conditions of climate variability, it is worthwhile to have such experiments. I too also interested for having a collaborative study, if interested we can think about planning some experiments.
I appreciate your persistance and quriosity on specific Kc values worldwide. We have never had validated such large Kc values for any crop even using long term (up to 16 years) field observation experimental/ET crop/climate data in Bulgaria. So it is interesting. Good Luck!
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