Suying Chen

Application of a new method to evaluate crop water stress index

Optimum water management and irrigation require timely detection of crop water condition. Usually crop water condition can be indicated by crop water stress index (CWSI), which can be estimated based on the measurements of either soil water or plant status. Estimation of CWSI by canopy temperature is one of them and has the potential to be widely applied because of its quick response and remotely measurable features. To calculate CWSI, the conventional canopy-temperature-based model (Jackson’s model) requires the measurement or estimation of the canopy temperature, the maximum canopy temperature (Tcu), and the minimum canopy temperature (Tcl). Because extensive measurements are necessary to estimate Tcu and Tcl, its application is limited. In this study, by introducing the temperature of an imitation leaf (a leaf without transpiration, Tp) and based on the principles of energy balance, we studied the possibility to replace Tcu by Tp and reduce the included parameters for CWSI calculation. Field experiments were carried out in a winter wheat (Triticum aestivum L.) field in Luancheng area, Hebei Province, the main production area of winter wheat in China. Six irrigation treatments were established and soil water content, leaf water potential, soil evaporation rate, plant transpiration rate, biomass, yield, and regular meteorological variables of each treatment were measured. Results indicate that the values of Tcu agree with the values of Tp with a regression coefficient r=0.988. While the values of CWSI estimated by the use of Tp are in agreement with CWSI by Jackson’s method, with a regression coefficient r=0.999. Furthermore, CWSI estimated by the use of Tp has good relations with soil water content and leaf water potential, showing that the estimated CWSI by Tp is a good indicator of soil water and plant status. Therefore, it is concluded that Tcu can be replaced by Tp and the included parameters for CWSI calculation can be significantly reduced by this replacement.

Effects of saline irrigation on soil salt accumulation and grain yield in the winter wheat-summer maize double cropping system in the low plain of North China

Abstract In the dominant winter wheat (WW)-summer maize (SM) double cropping system in the low plain located in the North China, limited access to fresh water, especially during dry season, constitutes a major obstacle to realize high crop productivity. Using the vast water resources of the saline upper aquifer for irrigation during WW jointing stage, may help to bridge the peak of dry season and relieve the tight water situation in the region. A field experiment was conducted during 2009–2012 to investigate the effects of saline irrigation during WW jointing stage on soil salt accumulation and productivity of WW and SM. The experiment treatments comprised no irrigation (T1), fresh water irrigation (T2), slightly saline water irrigation (T3: 2.8 dS m−1), and strongly saline water irrigation (T4: 8.2 dS m−1) at WW jointing stage. With regard to WW yields and aggregated annual WW-SM yields, clear benefits of saline water irrigation (T3 & T4) compared to no irrigation (T1), as well as insignificant yield losses compared to fresh water irrigation (T2) occurred in all three experiment years. However, the increased soil salinity in early SM season in consequence of saline irrigation exerted a negative effect on SM photosynthesis and final yield in two of three experiment years. To avoid the negative aftereffects of saline irrigation, sufficient fresh water irrigation during SM sowing phase (i.e., increase from 60 to 90 mm) is recommended to guarantee good growth conditions during the sensitive early growing period of SM. The risk of long-term accumulation of salts as a result of saline irrigation during the peak of dry season is considered low, due to deep leaching of salts during regularly occurring wet years, as demonstrated in the 2012 experiment year. Thus, applying saline water irrigation at jointing stage of WW and fresh water at sowing of SM is most promising to realize high yield and fresh irrigation water saving.

Assessing the Impact of Air Pollution on Grain Yield of Winter Wheat - A Case Study in the North China Plain

The major wheat production region of China the North China Plain (NCP) is seriously affected by air pollution. In this study, yield of winter wheat (Triticum aestivum L.) was analyzed with respect to the potential impact of air pollution index under conditions of optimal crop management in the NCP from 2001 to 2012. Results showed that air pollution was especially serious at the early phase of winter wheat growth significantly influencing various weather factors. However, no significant correlations were found between final grain yield and the weather factors during the early growth phase. In contrast, significant correlations were found between grain yield and total solar radiation gap, sunshine hour gap, diurnal temperature range and relative humidity during the late growing phase. To disentangle the confounding effects of various weather factors, and test the isolated effect of air pollution induced changes in incoming global solar radiation on yield under ceteris paribus conditions, crop model based scenario-analysis was conducted. The simulation results of the calibrated Agricultural Production Systems Simulator (APSIM) model indicated that a reduction in radiation by 10% might cause a yield reduction by more than 10%. Increasing incident radiation by 10% would lead to yield increases of (only) 7%, with the effects being much stronger during the late growing phase compared to the early growing phase. However, there is evidence that APSIM overestimates the effect of air pollution induced changes on radiation, as it does not consider the changes in radiative properties of solar insulation, i.e. the relative increase of diffuse over direct radiation, which may partly alleviate the negative effects of reduced total radiation by air pollution. Concluding, the present study could not detect a significantly negative effect of air pollution on wheat yields in the NCP.

Simulation of soil evaporation under different ground coverage with semi-empirical models

Minimizing soil evaporation is a key element in improving water use efficiency in dry areas. Experiments were conducted in the winter wheat field during 2004-2005 to compare effects of different row spacing on soil evaporation. A model to estimate soil evaporation was developed based on the experimental data. The reference crop evapotranspiration (ET0) was estimated by the Penman-Montieth equation, and the factors affecting evaporation under crop canopy were divided into both the radiation item (ETs1) and the aerodynamics item (ETs2) according to the degree of crop canopy coverage (fc). The simulation equation for actual evaporation, combining with soil moisture parameter, was established in this paper. In this study, a light meter was utilized to measure fc, which replaced leaf are index (LAI) in evaporation estimation. In comparison with the measured evaporation by micro-lysimeters (ML) in four row spacing: 7.5 cm, 15 cm, 22.5 cm and 30 cm, tested in a randomized block design, the simulated daily evaporation had root mean square errors (RMSE) of 0.22 mm, 0.24 mm, 0.25 mm 0.26 mm and a bias of 0.01 mm, 0.02 mm, -0.08 mm, -0.03 mm respectively. Results showed that using canopy coverage factor to replace leaf area index could effectively estimate soil evaporation.