Document Type : Research Paper
Authors
1
Assistant professor in water Engineering Dep., School of Agriculture, Shiraz University Drought Research Center, Shiraz University, Iran
2
Water Engineering Department, School of Agriculture, Shiraz University, Shiraz, Iran
3
Water Engineering Department, School of Agriculture, Shiraz University, Shiraz, Iran Drought Research Center, Shiraz University, Iran
Abstract
To better plan and manage water resources, especially in arid and semi-arid regions, accurate estimation of evapotranspiration of various agricultural products is very important. One of these widely used plants in the household food basket is onion, which has a high water requirement due to frequent irrigation, and if there is a lack of water in the early stages of growth, its yield will decrease significantly. Therefore, this research was conducted to determine crop coefficients of single, double, and standard evapotranspiration of onion in three water balance lysimeters . The reference crop evapotranspiration was calculated using meteorological data and the modified FAO-Pentemann-Monteith equation. Standard onion evapotranspiration rate (ETc) was determined using the soil water balance equation and then the values of single crop coefficients were calculated in different growth stages . According to placing the microlysimeter in three lysimeters, the amount of evaporation coefficient (K_e) and base transpiration coefficients (K_cb) were also calculated in different stages of growth. The average onion tuber yield was 24 tons per hectare. The amount of ETc and transpiration in the entire growing season was calculated as 651.2 mm and 296 mm, respectively. The length of initial, middle and final growth stages was 56, 25, and 21 days, respectively. The average value of single crop coefficient in the initial, middle, and final growth stages of was determined as 0.50, 1.04, and 0.7 respectively. The value of K_e coefficient in the initial, middle and final growth stages was 0.42, 0.26, and 0.47, respectively. The value of K_cb coefficient in the initial, middle, and final growth stage was determined as 0.08, 0.78, and 0.22 respectively. Finally, by using crop coefficients determined by lysimeter, it is possible to determine the exact water requirement of onion plants in areas with similar climates and for different stages of growth.
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