Abstract
Crop coefficients (Kc) are important for the development of irrigation schedules, but few studies on Kc focus on saline soils. To propose the growth-stage-specific Kc values for sunflowers in saline soils, a two-year micro-plot experiment was conducted in Yichang Experimental Station, Hetao Irrigation District. Four salinity levels including non-salinized (ECe = 3.4–4.1 dS·m–1), low (ECe = 5.5–8.2 dS·m–1), moderate (ECe = 12.1–14.5 dS·m–1), and high (ECe = 18.3–18.5 dS·m–1) levels were arranged in 12 micro-plots. Based on the soil moisture observations, Vensim software was used to establish and develop a physically-based water flow in the soil-plant system (WFSP) model. Observations in 2012 were used to calibrate the WFSP model and acceptable accuracy was obtained, especially for soil moisture simulation below 5 cm (R2 > 0.6). The locally-based Kc values (LKc) of sunflowers in saline soils were presented according to the WFSP calibration results. To be specific, LKc for initial stages (Kc1) could be expressed as a function of soil salinity (R2 = 0.86), while R2 of LKc for rapid growth (Kc2), middle (Kc3), and mature (Kc4) stages were 0.659, 1.156, and 0.324, respectively. The proposed LKc values were also evaluated by observations in 2013 and the R2 for initial, rapid growth, middle, and mature stages were 0.66, 0.68, 0.56 and 0.58, respectively. It is expected that the LKc would be of great value in irrigation management and provide precise water application values for salt-affected regions.
Highlights
Sunflower (Helianthus annuus L.) is one of the four most important oil crops in the world [1]
With irrigation as compared to the treatment without irrigation at three growth stages of sunflowers in Turkey; Ertek and Kara [5] conducted a series of deficit irrigation experiments, and concluded that maize fresh ear yield was affected by water stress
The daily precipitation measured by the field meteorological station of the experiment station from April to October in 2012 and 2013 varied from 0–67.2 mm·d−1 to 0–20.8 mm·d−1, respectively, with an accumulated precipitation of 254 mm for 2012 and 64.8 mm for 2013 (Figure 3), which indicated that the year 2012 was much wetter than 2013
Summary
Sunflower (Helianthus annuus L.) is one of the four most important oil crops in the world [1]. The Hetao Irrigation District, which is located in northern China, is the largest sunflower-growing region in China, and sunflower seeds are the main source of income for local farmers [2]. Because of the limited knowledge of crop water use in this region, flood irrigation without scheduling is still the main irrigation practice, which is a non-efficient use of water resources and has the possibility for increasing the risk of groundwater contamination because a large number of solutes could be leached below the root zone using this irrigation practice [11]. It is necessary to determine an efficient and representative irrigation scheduler to improve the crop productivity and water resource management for the region
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