Applying mathematic models to evaluate absorbed-N effects on dry matter production at different developmental stages would help determine proper nitrogen management according to crop demands and yield target. Two field trials were carried out for establishing absorbed-N effects on dry matter production (ANEDr) model, using uniform design in 2010–2011 and 2012–2013 winter wheat growing seasons in Hebei Province, China. Another field trial was carried out in 2010–2011 for model validation. Dry matter and N concentration in leaf and non-leaf organs were measured at setting, jointing, anthesis, and maturity. Theory of best linear unbiased prediction (BLUP) was applied to analyse the N effects of leaf and non-leaf organs on dry matter production. Within ANEDr model, four N-affected phases at each stage were concerned, leaf absorbed-N effect before this stage, non-leaf organ absorbed-N effect before this stage, leaf absorbed-N effect at this stage, and non-leaf organ absorbed-N effect at this stage. In addition, developmental processes, genotype characters and temperature were three factors that determine each N effect. It was demonstrated that ANEDr model can precisely quantify absorbed-N effects on dry matter production with high correlation coefficient (r=0.95). Comparing with other models, ANEDr model considered both leaf and non-leaf organs according to developmental processes of winter wheat, showed higher flexibility and simplicity, thus could be applied to different environments, cultivars and crops after parameter adjustment.

The solar radiation intensity and duration are continuously decreasing in the major wheat planting area of China. As a consequence, leaf senescence, photosynthesis, grain filling and thus wheat yield shall be affected by light deficiency. Therefore, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Ji’nan 17 (a multiple-spike cultivar), were subjected to shading during anthesis and maturity under field condition in 2010–2011 and 2011–2012. Under the slight shading treatment (S1, 88% of full sunshine), leaf senescence was delayed, net photosynthesis rate (Pn) and canopy apparent photosynthesis rate (CAP) were improved, and thus thousand-kernel weight (TKW) and grain yield were higher as compared with the control. However, mid and severe shading (S2 and S3, 67 and 35% of full sunshine, respectively) led to negative effects on these traits substantially. Moreover, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in flag leaf were significantly greater under slight shading than those in other treatments, while the malondialdehyde (MDA) content was less than that under other treatments. In addition, the multiple-spike cultivar is more tolerant to shading than large-spike cultivar. In conclusion, slight shading after anthesis delayed leaf senescence, enhanced photosynthesis and grain filling, and thus resulted in higher grain yield.

The calculation method of potential evapotranspiration (PET) was improved by adopting a more reliable PET estimate based on the Penman-Monteith equation into the standardized precipitation evapotranspiration index (SPEI) in this study (SPEIPM). This improvement increased the applicability of SPEI in North China Plain (NCP). The historic meteorological data during 1962–2011 were used to calculate SPEIPM. The detrended yields of maize from Hebei, Henan, Shandong, Beijing, and Tianjin provinces/cities of NCP were obtained by linear sliding average method. Then regression analysis was made to study the relationships between detrended yields and SPEI values. Different time scales were applied, and thus SPEIPM was mentioned as SPEIPMk-j (k=time scale, 1, 2, 3, 4,…, 24 mon; j=month, 1, 2, 3,..., 12), among which SPEIPM3-8 reflected the water condition from June to August, a period of heavy precipitation and vigorous growth of maize in NCP. SPEIPM3-8 was highly correlated with detrended yield in this region, which can effectively evaluate the effect of drought on maize yield. Additionally, this relationship becomes more significant in recent 20 yr. The regression model based on the SPEI series explained 64.8% of the variability of the annual detrended yield in Beijing, 45.2% in Henan, 58.6% in Shandong, and 54.6% in Hebei. Moreover, when SPEIPM3-8 is in the range of –0.6 to 1.1, –0.9 to 0.8 and –0.8 to 2.3, the detrended yield increases in Shandong, Henan and Beijing. The yield increasing range was during normal water condition in Shandong and Henan, where precipitation was abundant. It indicated that the field management matched well with local water condition and thus allowed stable and high yield. Maize yield increase in these two provinces in the future can be realized by further improving water use efficiency and enhancing the stress resistance as well as yield stability. In Hebei and Beijing, the precipitation is less and thus the normal water condition cannot meet the high yield target. Increasing of water input and improving water use efficiency are both strategies for future yield increase. As global climate change became stronger and yield demands increased, the relationship between drought and maize yield became much closer in NCP too. The research of drought monitoring method and strategies for yield increase should be enhanced in the future, so as to provide strong supports for food security and agricultural sustainable development in China. Received 12