Ayman Suleiman1, Cecilia Tojo Soler2, and Gerrit Hoogenboom2. (1) Univ. of Jordan, Dept. of Land, Water and Environment, Faculty of Agriculture, Amman, Jordan, (2) Univ. of GA, 1109 Experiment St., Dept. Bio & Ag. Eng., Griffin, GA 30223-1797
The use of FAO-56 reference
evapotranspiration (ETo)
for irrigation scheduling has been recommended worldwide because it provides
the best results under a wide range of climatic conditions. Crop ET (ETc) is calculated from ETo using a stage-dependent crop
coefficient (Kc) which depends on canopy
height, crop-soil surface resistance and albedo.
There is lack of information on Kc for
cotton grown under deficit irrigation in humid regions in the southeastern USA. The
objective of this study was to evaluate the Kc
FAO-56 procedure under different deficit drip irrigation treatments for cotton
grown in a humid climate. An experiment was conducted in 2005 with cotton grown
in three automated rainout shelters located in Georgia. When the actual soil water
content in the effective root zone dropped below a specific threshold of the
available water content (AWC),
irrigation was applied until the soil water reached 100% of AWC. The irrigation treatments were 40%, 60% and
90% irrigation thresholds (IT). Observed daily ETc
was estimated from daily soil moisture readings. The length of the initial,
development and mid stages was the same between the different treatments.
However, the length of late-stage for the 60% and 40% IT was 3 and 5 days less
than that for the 90% IT, respectively. The initial and end Kc
for the 90% IT was greater than for the 60% IT, which in turn was greater than
the 40% IT. For the mid stage, the 60% and 90% IT had a similar value for Kc, which was higher than the 40% IT. The FAO-56
proved to be an accurate method for estimating cotton ETc
under deficit irrigation. The values for the mid and end Kc
and the length of the different developmental stages of the 90% IT may be used
in the humid southeastern USA
for fully irrigated cotton.
Handout (.ppt format, 13400.0 kb)