Xiying Zhang

Determination of daily evaporation and evapotranspiration of winter wheat and maize by large-scale weighing lysimeter and micro-lysimeter

Daily evapotranspiration of irrigated winter wheat (Triticum aestivum L.) and maize (Zea mays L.) were determined for five seasons between 1995 and 2000 using a large-scale weighing lysimeter, and soil evaporation for each crop was measured for one season using two micro-lysimeters at Luancheng Station in the North China Plain. The results showed that total water consumption averaged 453 and 423 mm for winter wheat and maize grown without water deficit. The water consumption of winter wheat during its growth period greatly exceeds the precipitation, which ranges from 50 mm in dry years to 150 mm in wet years. Consequently, supplemental irrigation is very important to winter wheat production in the region. The average crop coefficient during the whole growth period was 0.93 for winter wheat and 1.1 for maize. Evaporation from the soil surface took up 29.7 and 30.3% of the total evapotranspiration for winter wheat and maize, respectively, equaling an annual loss of more than 250 mm water. Thus, reducing soil evaporation could be one of the most important water-saving measures in this serious water deficit region. Leaf area index (LAI) and moisture in the surface soil greatly affect the ratio of soil evaporation to total evapotranspiration. The relationship between this ratio and surface soil moisture and leaf area index was established, and can help to improve field water utilization efficiency.

Estimation of winter wheat evapotranspiration under water stress with two semiempirical approaches

based on ET estimations would allow limited groundwater supplies to be used more efficiently for wheat proWinter wheat (Triticum aestivum L.) is one of most important duction. crops in the North China Plain. However, soil water deficit (SWD) often occurs due to lack of precipitation in its growing season. In this To calculate crop ET over seasonal time, it is essential study, we introduce two semiempirical approaches, a recharge model to simplify ET-estimated methods in the NCP due to and the crop coefficient (Kc)–reference evapotranspiration (ET0) aplack of enough weather, soil, and crop physiological proach, to estimate wheat actual evapotranspiration (ETa) under no data. Thus, it is convenient and suitable to use empirical SWD and slight and severe SWD conditions. The recharge model approaches to estimate crop ETa. These methods are allocated ET0 to reference evaporation and reference transpiration mainly based on the Kc–ET0 approach and on soil water as a function of leaf area index. In the model, ETa is limited by soil balance (SWB) calculation (Rana and Katerji, 2000). water content, and crop water extraction for ETa is distributed through When limited by soil water content, water uptake for the soil profile as exponential functions of soil and root depth. The crop transpiration from a point in a soil profile is an exKc–ET0 approach regarded ETa under the SWD condition as a logarithponential function of soil and root depth (Novak, 1987). mic function of soil water availability. Under no SWD condition, the recharge model simulated 10-d ETa with a root mean square error The Kc–ET0 approach estimates crop ETa as a fraction (RMSE) of 5.58 mm and a bias of 0.95 mm compared with measureof the ET0 (Allen et al., 1998). The Kc–ET0 approach ments from a large-scale weighing lysimeter. The two approaches is simple because the method calculates ETa only by both estimated seasonal evapotranspiration (ET) well compared with estimating ET0 and Kc as well as Ks (Doorenbos and the adjusted ET (from the soil water balance and the recharge model– Pruitt, 1977, p. 144; Kerr et al., 1993; Kang et al., 2000). simulated deep drainage). The recharge model, which simulated the Reference evapotranspiration can be estimated from seasonal ET with the RMSE of 27.8 mm and the bias of 8.0 mm, pan evaporation data (Doorenbos and Pruitt, 1977, was better than the Kc–ET0 approach (RMSE 31.7 mm and bias p. 144). It is also estimated with more data-intensive 33.1 mm). The seasonal pattern of soil water stress coefficient (Ks) methods, e.g., the modified Penman equation and the showed that there were faster water losses at grain-filling stage than modified Penman–Monteith formula (Doorenbos and at other stages. Pruitt, 1977, p. 144; Allen et al., 1989; Allen, 2000). The crop coefficient, Kc, can be determined by the ratio of crop ETa under no SWD condition to ET0. The soil T North China Plain (NCP), one of the most water stress coefficient, Ks, is mainly estimated by a important centers of agricultural production in relationship to the average soil moisture contents or China, contains about 22% of the cultivated land in the matric potential in a soil layer. And, it can usually be country but less than 4% of the water resources (Jin et estimated by an empirical formula based on soil water al., 1999). Winter wheat is one of the most important contents or relative soil available water contents (Jensen crops in the NCP. Serious water shortage problems exist et al., 1970). Poulovassilis et al. (2001) assumed that Ks in the winter wheat season, and the situation has been is an exponential function of the soil water content. aggravated by an increase in agricultural and industrial Kang et al. (2000) found that Ks is highly related to soil demand for groundwater over the last 20 yr (Zhang water availability (Aw) in a logarithmic function. The et al., 2001). Another reason the groundwater table is Kc–ET0 approach has been successfully applied at many persistently declining is that NCP farmers irrigate exceslocations (Kang et al., 2000; Abdelhadi et al., 2000; Alsively by pumping groundwater, which unnecessarily len, 2000; Poulovassilis et al., 2001; Sepaskhah and Anmaximizes crop transpiration and soil evaporation and dam, 2001; De Medeiros et al., 2001; Liu et al., 2002). increases the proportion of nonbeneficial soil water conActual evapotranspiration can also be estimated from sumption (Zhang et al., 2002). Irrigation management ET0, soil water content, and leaf area index (LAI) (Campbell and Norman, 1998; Kendy et al., 2003). ReferYongqiang Zhang, Qiang Yu, and Changming Liu, Luancheng Agroecosyst. Stn., Inst. of Geogr. Sci. and Nat. Resour. Res., Chinese Acad. ence evapotranspiration is partitioned into reference of Sci., Bldg. 917, Datun Rd., Beijing 100101, China; Yongqiang Zhang evaporation from soil and reference transpiration from and Xiying Zhang, Shijiazhuang Inst. of Agric. Modernization, Chiplants, and the ratio of reference evaporation to refernese Acad. of Sci., 286 Huaizhong Rd., Shijiazhuang 050021, P.R. China; and Jie Jiang, Inst. of Environ. Sci., Beijing Normal Univ., Beijing 100875, P.R. China. Received 31 Oct. 2002. *Corresponding Abbreviations: Aw, soil water availability; ET, evapotranspiration; author (zhangyq@igsnrr.ac.cn). ETa, actual evapotranspiration; ET0, reference evapotranspiration; Kc, crop coefficient; Ks, soil water stress coefficient; LAI, leaf area index; Published in Agron. J. 96:159–168 (2004).  American Society of Agronomy NCP, North China Plain; RMSE, root mean square error; SWB, soil water balance; SWD, soil water deficit; SWS, soil water storage. 677 S. Segoe Rd., Madison, WI 53711 USA

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.

Harvesting more grain zinc of wheat for human health

Increasing grain zinc (Zn) concentration of cereals for minimizing Zn malnutrition in two billion people represents an important global humanitarian challenge. Grain Zn in field-grown wheat at the global scale ranges from 20.4 to 30.5 mg kg−1, showing a solid gap to the biofortification target for human health (40 mg kg−1). Through a group of field experiments, we found that the low grain Zn was not closely linked to historical replacements of varieties during the Green Revolution, but greatly aggravated by phosphorus (P) overuse or insufficient nitrogen (N) application. We also conducted a total of 320-pair plots field experiments and found an average increase of 10.5 mg kg−1 by foliar Zn application. We conclude that an integrated strategy, including not only Zn-responsive genotypes, but of a similar importance, Zn application and field N and P management, are required to harvest more grain Zn and meanwhile ensure better yield in wheat-dominant areas.

Effects of defoliation on grain yield and water use of winter wheat

Field and pot experiments were conducted to investigate the effects of defoliation on crop performance and the possibility of using defoliation as a method for conserving soil moisture. The study was conducted during 2006-2008, over two growing seasons of winter wheat (Triticum aestivum L.) in the North China Plain. Three levels of defoliation (mild, moderate and severe) were imposed on winter wheat in the field during the following crop phases and conditions: at heading, at anthesis under water deficit conditions and at anthesis under two or three levels of irrigation. Additional pot experiments with three levels of defoliation under two water regimes were arranged. The results showed that both the intensity of defoliation and the timing of defoliation significantly reduced grain production. Under wet conditions the reduction was over 20 %, while under dry conditions the reduction was c. 12 %. Yield reduction was greater for defoliation at heading than at anthesis and it was mainly caused by a reduction in kernel weight. Mild defoliation (top three leaves retained) did not affect grain yield. Moderate defoliation (top two leaves retained) slightly reduced grain production. Root length density in the topsoil profile was significantly reduced by severe defoliation at anthesis under wet conditions, but it increased under dry conditions. Dry matter remobilization to grains under moderate and mild defoliation was increased and resulted in a relatively higher harvest index (HI). The photosynthetic rate of the leaves remaining after defoliation was enhanced under all soil moisture conditions. Although defoliation reduced the seasonal water use (ET), the yield reduction was much greater than the reduction in ET under severe defoliation, resulting in lower water use efficiency (WUE). The results show that conserving soil moisture by removing leaves might not be an economic choice. Under the conditions of the present study, the WUE of winter wheat was not improved by defoliation; however, in very dry conditions the reduction in ET by defoliation might help the crop survive.

Effects of Different Cultivation Practices on Soil Temperature and Wheat Spike Differentiation

Field cultivation practices affected soil temperature that influenced the crop development of winter crops. This study was undertaken to determine the effects of different mulch materials, tillage depths and planting methods on spike differentiation of winter wheat (Triticum aestivum L.). The field experiment was consisted of three tests: (i) polythene mulch, straw mulch and no mulch; (ii) ridge planting and furrow planting; (iii) conventional tillage and shallow tillage. The results showed that soil temperature was affected by different practices. The higher soil temperature under polythene mulch resulted in the earlier initiation of spike differentiation, while straw mulch decreased soil temperature in spring that delayed the initiation compared with the non-mulch treatment. The spike initiation under ridge planting started earlier than that of furrow planting. Reduced tillage delayed the initiation compared with the conventional tillage. Duration of spike differentiation lasted longer under earlier starting of initiation that increased the grain numbers per spike. Other yield component characters were not affected by soil temperature. It was concluded that in the North China Plain where grain-filling duration of winter wheat was limited, agricultural practices that increased soil temperature in spring were favorable for grain production.

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.

Improving water use efficiency in grain production of winter wheat and summer maize in the North China Plain: a review

Reducing irrigation water use by improving water use efficiency (WUE) in grain production is critical for the development of sustainable agriculture in the North China Plain (NCP). This article summarizes the research progresses in WUE improvement carried out at the Luancheng station located in the Northern part of NCP for the past three decades. Progresses in four aspects of yield and WUE improvement are presented, including yield and WUE improvement associated with cultivar selection, irrigation management for improving yield and WUE under limited water supply, managing root system for efficient soil water use and reducing soil evaporation by straw mulch. The results showed that annual average increase of 0.014 kg

Rainfall and Vegetation Coupling Index for soil erosion risk mapping

m -3 for winter wheat and 0.02 kg