Grain zinc (Zn) and iron (Fe) concentrations and their responses to foliar application of micronutrients in 28 Chinese wheat landraces and 63 cultivars were investigated in a two-year field experiment.  The average grain Zn and Fe concentrations were 41.8 mg kg^–1 (29.0−63.3 mg kg^–1) and 39.7 mg kg^–1 (27.9−67.0 mg kg^–1), respectively.  Compared with cultivars, landraces had greater grain Zn (11.0%) and Fe (4.8%) concentrations but lower harvest index (HI), grain weight per spike (GWS), grain number per spike (GNS) and thousand grain weight (TGW).  Both Zn and Fe concentrations were negatively and significantly correlated with HI, GWS, and GNS, while showed a poor association with TGW, suggesting that lower HI, GWS, and GNS, but not TGW, accounted for higher Zn and Fe concentrations for landraces than for cultivars.  Grain Zn concentrations of both cultivars and landraces significantly increased after foliar Zn spray and the increase was two-fold greater for landraces (12.6 mg kg^–1) than for cultivars (6.4 mg kg^–1).  Foliar Fe spray increased grain Fe concentrations of landraces (3.4 mg kg^–1) and cultivars (1.2 mg kg^–1), but these increases were not statistically significant.  This study showed that Chinese wheat landraces had higher grain Zn and Fe concentrations than cultivars, and greater increases occurred in grain Zn concentration than in grain Fe concentration in response to fertilization, suggesting that Chinese wheat landraces could serve as a potential genetic source for enhancing grain mineral levels in modern wheat cultivars.

Available irrigation resources are becoming increasingly scarce in the North China Plain (NCP), and nitrogen-use efficiency of crop production is also relatively low. Thus, it is imperative to improve the water-use efficiency (WUE) and nitrogen fertilizer productivity on the NCP. Here, we conducted a two-year field experiment to explore the effects of different irrigation amounts (S60, 60 mm; S90, 90 mm; S120, 120 mm; S150, 150 mm) and nitrogen application rates (150, 195 and 240 kg ha^–1; denoted as N1, N2 and N3, respectively) under micro-sprinkling with water and nitrogen combined on the grain yield (GY), yield components, leaf area index (LAI), flag leaf chlorophyll content, dry matter accumulation (DM), WUE, and nitrogen partial factor productivity (NPFP). The results indicated that the GY and NPFP increased significantly with increasing irrigation amount, but there was no significant difference between S120 and S150; WUE significantly increased first but then decreased with increasing irrigation and S120 achieved the highest WUE. The increase in nitrogen was beneficial to improving the GY and WUE in S60 and S90, while the excessive nitrogen application (N3) significantly reduced the GY and WUE in S120 and S150 compared with those in the N2 treatment. The NPFP significantly decreased with increasing nitrogen rate under the same irrigation treatments. The synchronous increase in spike number (SN) and 1 000-grain weight (TWG) was the main reason for the large increase in GY by micro-sprinkling with increasing irrigation, and the differences in SN and TGW between S120 and S150 were small. Under S60 and S90, the TGW increased with increasing nitrogen application, which enhanced the GY, while N2 achieved the highest TWG in S120 and S150. At the filling stage, the LAI increased with increasing irrigation, and greater amounts of irrigation significantly increased the chlorophyll content in the flag leaf, which was instrumental in increasing DM after anthesis and increasing the TGW. Micro-sprinkling with increased amounts of irrigation or excessive nitrogen application decreased the WUE mainly due to the increase in total water consumption (ET) and the small increase or decrease in GY. Moreover, the increase in irrigation increased the total nitrogen accumulation or contents (TNC) of plants at maturity and reduced the residual nitrate-nitrogen in the soil (SNC), which was conducive to the increase in NPFP, but there was no significant difference in TNC between S120 and S150. Under the same irrigation treatments, an increase in nitrogen application significantly increased the residual SNC and decreased the NPFP. Overall, micro-sprinkling with 120 mm of irrigation and a total nitrogen application of 195 kg ha–1 can lead to increases in GY, WUE and NPFP on the NCP.

In past 30 years, the wheat yield per unit area of China has increased by 79%. The super-high-yield (SH) cultivation played an important role in improving the wheat photosynthesis and yield. In order to find the ecophysiological mechanism underneath the high photosynthesis of SH cultivation, in situ diurnal changes in the photosynthetic gas exchange and chlorophyll (Chl) a fluorescence of field-grown wheat plants during the grain-filling stage and environmental factors were investigated. During the late grain-filling stage at 24 days after anthesis (DAA), the diurnal changes in net CO₂ assimilation rate were higher under SH treatment than under high-yield (H) treatment. From 8 to 24 DAA, the actual quantum yield of photosystem II (PSII) electron transport in the light-adapted state (ΦPSII) in the flag leaves at noon under SH treatment were significantly higher than those under H treatment. The leaf temperature, soil temperature and soil moisture were better suited for higher rates of leaf photosynthesis under SH treatment than those under H treatment at noon. Such diurnal changes in environmental factors in wheat fields could be one of the mechanisms for the higher biomass and yield under SH cultivation than those under H cultivation. ΦPSII and CO₂ exchange rate in wheat flag leaves under SH and H treatments had a linear correlation which could provide new insight to evaluate the wheat photosynthesis performance under different conditions.

To improve efficiency in the use of water resources in water-limited environments such as the North China Plain (NCP), where winter wheat is a major and groundwater-consuming crop, the application of water-saving irrigation strategies must be considered as a method for the sustainable development of water resources.  The initial objective of this study was to evaluate and validate the ability of the CERES-Wheat model simulation to predict the winter wheat grain yield, biomass yield and water use efficiency (WUE) responses to different irrigation management methods in the NCP.  The results from evaluation and validation analyses were compared to observed data from 8 field experiments, and the results indicated that the model can accurately predict these parameters.  The modified CERES-Wheat model was then used to simulate the development and growth of winter wheat under different irrigation treatments ranging from rainfed to four irrigation applications (full irrigation) using historical weather data from crop seasons over 33 years (1981–2014).  The data were classified into three types according to seasonal precipitation: <100 mm, 100–140 mm, and >140 mm.  Our results showed that the grain and biomass yield, harvest index (HI) and WUE responses to irrigation management were influenced by precipitation among years, whereby yield increased with higher precipitation.  Scenario simulation analysis also showed that two irrigation applications of 75 mm each at the jointing stage and anthesis stage (T3) resulted in the highest grain yield and WUE among the irrigation treatments.  Meanwhile, productivity in this treatment remained stable through different precipitation levels among years.  One irrigation at the jointing stage (T1) improved grain yield compared to the rainfed treatment and resulted in yield values near those of T3, especially when precipitation was higher.  These results indicate that T3 is the most suitable irrigation strategy under variable precipitation regimes for stable yield of winter wheat with maximum water savings in the NCP.  The application of one irrigation at the jointing stage may also serve as an alternative irrigation strategy for further reducing irrigation for sustainable water resources management in this area.

    To understand the contribution of ear photosynthesis to grain yield and its response to water supply in the improvement of winter wheat, 15 cultivars released from 1980 to 2012 in North China Plain (NCP) were planted under rainfed and irrigated conditions from 2011 to 2013, and the ear photosynthesis was tested by ear shading. During the past 30 years, grain yield significantly increased, the flag leaf area slightly increased under irrigated condition but decreased significantly under rainfed condition, the ratio of grain weight:leaf area significantly increased, and the contribution of ear photosynthesis to grain yield changed from 33.6 to 64.5% and from 32.2 to 57.2% under rainfed and irrigated conditions, respectively. Grain yield, yield components, and ratio of grain weight:leaf area were positively related with contribution of ear photosynthesis. The increase in grain yield in winter wheat was related with improvement in ear photosynthesis contribution in NCP, especially under rainfed condition.

The photosynthetic characteristics of flag leaf and the accumulation and remobilization of pre-anthesis dry mass (DM) and nitrogen (N) in vegetable organs in nine wheat cultivars under different source-sink manipulation treatments including defoliation (DF), spike shading (SS) and half spikelets removal (SR) were investigated. Results showed that the SS treatment increased the photosynthetic rate (Pn) of flag leaf in source limited cultivar, but had no significant effect on sink limited cultivar. The SR treatment decreased the Pn of flag leaf. Grain DM accumulation was limited by source in some cultivars, in other cultivars, it was limited by sink. Grain N accumulation was mainly limited by source supply. The contribution of pre-anthesis dry mass to grain yield from high to low was stem, leaf and chaff, while the contribution of pre-anthesis N to grain N from high to low was leaf, stem and chaff. Cultivars S7221 and TA9818 can increase the contribution of remobilization of DM and N to grain at the maximum ratio under reducing source treatments, which may be the major reason for these cultivars having lower decrease in grain yield and N content under reducing source treatments.