poster - International Conference of Agricultural Engineering

of 75% FC (T1). Statistical analysis showed significant differences among treatments in the
onion fresh bulb yield. Onion bulb yield for the treatment with lower soil water irrigation
threshold of 55% FC (T3) in 2008 was lower than that in 2009. This might be due to the
difference of climatic conditions with higher solar radiation and lower rainfall in 2008 than
those in 2009. On an average, the yield of treatment T1 was about 33% and 64% higher than
those of treatment T2 and T3, respectively.
3.4. Water productivity
The results of IWP and WP in both seasons are presented in Table 3. The WP ranged from
8.0 to 19.3 kg m -3 in 2008 and from 13.7 to 15.6 kg m -3 in 2009, respectively. Treatment T1
had the highest WP while treatment T3 had the lowest WP in both seasons. The differences in
WP among treatments were statistically significant in 2008, but no significant differences were
found in 2009.
In 2008, the highest value of IWP was 22.0 kg m -3 for treatment T2, while T3 had the
lowest IWP value of 11.8 kg m -3 . The values of IWP in 2009 were in a range of 17.2 to 25.2 kg
m -3 , which decreased with the increase in irrigation depth. No significant differences in IWP
were found among treatments in both seasons.
4. Conclusion
The effect of different irrigation depths on onion ET a , bulb yield, WP and IWP of onion crop
were investigated with weighing lysimeters in an arid climatic region for two consecutive
growing seasons of 2008 and 2009, and finally the site specific crop coefficient was estimated
for onion in this region. Main conclusions draw from the research are:
(1) Irrigation depths significantly influenced ET a , bulb yield, and WP of onion. With
irrigation depths increasing, the seasonal ET a , bulb yield, and WP increased.
(2) The maximum average yield (62.1 t ha -1 ) and the highest average WP (17.5 kg m -3 )
were obtained by the treatment with soil water irrigation threshold of 75% FC with the most
irrigation water (331 mm) and ET a (357 mm) in both seasons. The highest IWP was gained for
treatment with soil water irrigation threshold of 65% FC (22.0 kg m -3 ) in 2008 and the
treatment with soil water irrigation threshold of 55% FC (20.5 kg m -3 ) in 2009. There were no
significant differences in IWP among treatments.
(3) The estimated values of K c during the initial, mid-season, and late season were 0.73,
1.28 and 0.70, respectively. It is 4% and 22% higher during the initial and mid-season, and 6%
lower during the late season than the values suggested by FAO 56. K c can be well predicted
by the fitted third-order polynomial functions expressed as DAT and GDD. The estimated K c
values in this paper can be used to manage irrigation scheduling for onion crop under the
similar agro-climatic conditions.
Acknowledgements
We are grateful to the research grants from the Program 2007BAD88B07-3 supported by the
Ministry of Science and Technology of China and the Program 200801104 supported by the
Ministry of Water Resources of China.