Variations of crop coefficient and its influencing factors in an arid advective cropland of northwest China

Abstract

Understanding the variation and magnitude of crop coefficient (Kc) is important for accurate determination of crop evapotranspiration and water use. In this study, we calculated Kc in an irrigated maize field with ground mulching by eddy covariance evapotranspiration measurements during the whole growing periods in 2009 and 2010 in an arid region of northwest China. A semi‐empirical practical approach for estimating Kc was proposed by introducing the dynamic fraction of canopy cover and incorporating the effect of leaf senescence as a function of days after sowing. The contribution of arid advection of sensible heat resulting from irrigation to Kc and the response of Kc to canopy conductance (Gc) were investigated. The averaged values of daily Kc were lower than typical values obtained previously without mulching due to decreasing effect of mulching on Kc, with 0.82 and 0.80 for the 2 years, respectively. The maximum average Kc occurred at the heading stage, with 1.21 and 1.04 for the 2 years, respectively. The difference of Kc was attributed to the difference of leaf area index. The semi‐empirical practical approach could well estimate the variations of Kc, thus could be a robust and useful tool for the practical users and water managers. The contributions to daily Kc from the arid advection were 4.4–28.0% of the measured Kc. The Gc had stronger control on daily Kc at the early and later stages than at the middle stage. When Gc, leaf area index and relative soil extractable water were lower than the respective threshold values of 20 mm s−1, 3.0 m2 m−2 and 0.5, the daily Kc increased significantly with the increase of the three factors, and almost remained constant when the three factors were beyond the threshold values. These results are helpful for quantifying contributions of individual factors to Kc, and subsequently improving water management practices according to Kc. Copyright © 2014 John Wiley & Sons, Ltd.

Characteristics and influencing factors of crop coefficient for drip-irrigated cotton under plastic-mulched condition in arid environment

“…It was noted in this study, however, that both LAI and extractable soil water were the main driving factors of K c . And the critical values of 3.0 in LAI and 0.5 for extractable soil water were detected, which was similar to the results of Ding et al 2015 . The above-mentioned equations could be useful in analyze or estimating cotton K c independently on LAI or ESW alone.…”

“…3 of gradual increase to maximum LAI is generally lower than 3.0 and nearly stable condition at flowering and boll setting stage LAI is generally higher than 3.0 , suggesting that LAI of about 3.0 is a critical value for evaluating its influences on K c . A possible reason is that canopy interception of radiation, the primary source of evaporative energy, is relative stable at LAI larger than 3.0 and further increase in LAI did not Allen et al,1998;Ding et al, 2015 . Soil water content is an important factor influencing K c . In the present study, a linear and significant P < 0.05 correlation was found between K c and extractable soil water ESW in the root zone 0 -100 cm , expressed as K c =2.39ESW 0.30 for ESW < 0.5 Fig.…”

“…A possible reason is that the crop would be under water stress condition and K c would therefore increase with the increase of ESW when ESW is less than 0.5. Ding et al, 2015. Zhang et al 2012b pointed on soil water content at 10 cm soil depth, rather than biological factors such as LAI, as the driving factor of K c in desert steppe conditions.…”

Environmental controls on seasonal ecosystem evapotranspiration/potential evapotranspiration ratio as determined by the global eddy flux measurements

“…The K c is termed a single-crop coefficient (Allen et al, 2006;Tabari et al, 2013) which is affected by growing periods, crop species, canopy conductance, and soil evaporation in the field scale (Shukla et al, 2014b;Ding et al, 2015). Moreover, K c can be influenced by soil characteristics, vegetative soil cover, height, plant species distribution, and leaf area index in a larger spatial scale (Descheemaeker et al, 2011;Anda et al, 2014;Consoli and Vanella, 2014).…”

“…However, as discussed earlier, ecologists and hydrologists have started to use K c to quantify ecosystem stress and have considered K c as a variable rather than a constant. Past studies found that K c was influenced by the growing stages and leaf area index for maize (Kang et al, 2003;Ding et al, 2015), winter wheat (Allen et al, 1998;Kang et al, 2003), watermelon (Shukla et al, 2014b), and fruit trees (Marsal et al, 2014b;Taylor et al, 2015). The K c values are tabulated for each and every growth stage for many more crops all over the world (Allen et al, 1998).…”