poster - International Conference of Agricultural Engineering

Evapotranspiration and Crop Coefficient of Onion (Allium cepa L.)
under the Mulch of Plastic Film in an Arid Region, Northwest China
Jianhua Zheng 1, 2 , Guanhua Huang 1, 2 *, Jun Wang 1, 2 , Quanzhong Huang 1, 2
1 Center for Agricultural Water Research, China Agricultural University, Beijing, 100083, P. R.
China
2 Chinese-Israeli International Center for Research and Training in Agriculture, China
Abstract
Agricultural University, Beijing, 100083, P. R. China
*Corresponding author. E-mail: ghuang@cau.edu.cn
Field studies were carried out in 2008 and 2009 using nine weighing lysimeters to determine
actual evapotranspiration (ET a ) of onion under surface irrigation with plastic mulch. Three soil
water contents (SWCs) expressed as the percentage of field capacity (FC) were considered
as thresholds for initiating irrigations at mid-season stage, i.e., 75%, 65% and 55% FC. ET a ,
crop coefficient (K c ), yield, irrigation water productivity (IWP) and water productivity (WP) were
determined. The average seasonal ET a of 75% FC was 357 mm, 263 and 200 mm
consequently for 65% and 55% FC, respectively. Results indicated that onion bulb yield was
significantly affected by the irrigation depth. The highest average yield of 62.1 t ha -1 was
obtained with irrigation threshold of 75% FC, and it was reduced by 33% and 65% for the 65%
and 55% FC treatment, respectively. The WP increased as the increase of the irrigation
thresholds. The estimated value of Kc during the initial, mid-season and late season was 0.73,
1.28, and 0.70, respectively. Third-order polynomials were used to well predict K c as functions
of days after transplanting (DAT) and cumulative growing degree-days (GDD), respectively.
The estimated K c values of the present work can be used for irrigation scheduling of onion
crop with similar agro-climatic conditions.
Keywords: evapotranspiration, crop coefficient, onion, lysimeter
1. Introduction
Water scarcity became a bottleneck for the expansion and development of irrigated
agriculture in the Shiyang River basin, an arid inland river basin in Northwest China. The
groundwater is over exploited due to a dramatic reduction of surface water, which causes
serious deterioration of ecological system (Kang et al., 2004). Thus, it is essential to develop
agricultural water-saving strategies for promoting the sustainable utilization of water
resources in the region and the development of the social economy.
Onion (Allium cepa L.) is among the most important horticultural and cash crops in the arid
Northwest China, due to its favoured long sunshine duration and the large day and night
temperature differences. Although plastic mulch is widely applied for reducing soil evaporation,
the water productivity for onion is still low. Therefore, to support precise irrigation scheduling,
it is advisable to adapt the crop coefficient (K c ) values to local agronomic practices.
Weighing lysimeter can provide dependable estimates of actual evapotranspiration (ET a ),
but only if fundamental requirements concerning representativeness of vegetation and