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.

Received  2 August, 2017    Accepted  31 October, 2017
 © 2018, CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
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Groundwater is a key component for water resources in Sanjiang and Songnen Plain, an important agriculture basement in China.  The quality and the renewability of irrigation groundwater are essential for the stock raising and agricultural production.  Shallow groundwater was sampled and analyzed for various variables.  The salinity sodium concentration and bicarbonate hazard, were examined with regard to the United States Department of Agriculture (USDA) irrigation water standards.  The concentration of chlorofluorocarbons (CFCs) was determined to analyze the age of groundwater.  Most groundwater samples labeled as excellent to good for irrigation with low salinity hazard or medium salinity hazard.  Four groundwater samples were good and suspected for irrigation with high salinity hazard.  Generally groundwater in Sanjiang Plain was younger than the groundwater in Songnen Plain.  Meanwhile, groundwater nearby river is younger than the groundwater further away inside the watershed.  The mean age of groundwater in Sanjiang Plain is in average of 44.1, 47.9 and 32.8 years by CFC-11 (CCl₃F), CFC-12 (CCl₂F₂) and CFC-113 (C₂Cl₃F₃),  respectively.  The mean ages of groundwater in Songnen Plain is in average of 46.1, 53.4, and 40.7 years by CFC-11, CFC-12 and CFC-113, respectively.  Thus, groundwater nearby rivers could be directly exploited as irrigation water.  Partial groundwater has to be processed to lower the salt concentration rather than directly utilized as irrigation water in Songnen Plain.  Both water quality and renewability should be put in mind for sustainable agricultural development and water resources management.

    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.